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DOI: 10.1039/D1QM00914A (Review Article) Mater. Chem. Front., 2021, 5, 7403-7418

Mini-review: progress on micro/nanoscale MnMoO4 as an electrode material for advanced supercapacitor applications

Zhu Zhu† a, Yan Sun *a, Chunsheng Li *ac, Chen Yang† a, Lin Li b, Jiahao Zhu a, Shulei Chou *b, Miaomiao Wang a, Didi Wang a and Yuanliang Li d
aSchool of Chemistry and Life Sciences, Suzhou University of Science and Technology, Suzhou City, Jiangsu Province 215009, P. R. China. E-mail: juzi147@163.com; lichsheng@163.com
bInstitute for Carbon Neutralization, College of Chemistry and Materials Engineering, Wenzhou University, Wenzhou, Zhejiang 325035, P. R. China. E-mail: chou@wzu.edu.cn
cXi’an Key Laboratory of Advanced Photo-electronics Materials and Energy Conversion Device, School of Science, Xijing University, Xi’an, 710123, P. R. China
dHebei Provincial Key Laboratory of Inorganic Nonmetallic Materials, Key Laboratory of Environment Functional Materials of Tangshan City, College of Materials Science and Engineering, North China University of Science and Technology, Tangshan City, Hebei Province 063210, P. R. China

Received 24th June 2021 , Accepted 17th August 2021

First published on 18th August 2021

Abstract

Manganese molybdate (MnMoO4) has attracted extensive attention as the electrode material for supercapacitors, owing to its high theoretical specific capacity, excellent redox activity, good structural stability, abundant reserves and low cost. However, its low actual specific capacity and poor electronic conductivity limit the industrial development and practical applications. In this mini-review, the microstructure, preparation strategies, plausible reaction mechanisms, drawbacks and corresponding improvement technologies of micro/nanoscale MnMoO4 materials are systematically summarized. In addition, the challenges and prospects of MnMoO4 for supercapacitors in future applications are discussed.

image file: d1qm00914a-p1.tif

Yan Sun

Yan Sun obtained her BS degree from the Liaoning Normal University in 2004, MS degree from Wenzhou University in 2007, and PhD degree from Nankai University (China) in 2010. She was promoted to a full Professor in North China University of Science and Technology in 2017. She has been teaching at Suzhou University of Science and Technology since 2019 and is leading a research team investigating functional micro/nanomaterials and their clean energy storage and conversion in supercapacitors, lithium-ion batteries, metal–air batteries, and sodium-ion batteries.

image file: d1qm00914a-p2.tif

Chunsheng Li

Chunsheng Li received his MS and PhD degree from the Institute of New Energy Materials Chemistry in Nankai University (Tianjin, China) in 2007 and 2010, respectively. He is a Professor at the North China University of Science and Technology, Hebei Province, since 2017. He works at Suzhou University of Science and Technology, and is mainly engaged in nanostructured materials for advanced applications in supercapacitors, lithium-ion batteries and metal–air batteries (Mg-air batteries, Zn–air batteries and Al-air batteries).

image file: d1qm00914a-p3.tif

Shulei Chou

Shulei Chou is a professor at the College of Chemistry and Materials Engineering, Wenzhou University. He obtained his BS (2003) and MS degree (2007) in Nankai University, China. He received his PhD degree from the University of Wollongong in 2010. His research has been focused on energy storage materials for battery applications, especially on novel composite materials, new binders, and new electrolytes for Li/Na batteries.

image file: d1qm00914a-p4.tif

Yuanliang Li

Yuanliang Li received his PhD degree in materials science from Tianjin University. Currently, he is a full associate professor at College of Materials Science and Engineering, North China University of Science and Technology. His current research interests include in situ measurement technologies, especially in electrode mechanisms.

1. Introduction

Based on the growing resources crisis and environmental pollution issues, the exploration of efficient conversion technologies and advanced energy storage devices is as important as the rational utilization of various renewable energies to promote the sustainable development of society.1–5 At present, electrochemical capacitors with fast charge/discharge rate, wide operating voltage range, long cycle-life and economical maintenance cost, have been considered as one of the most popular and practical means for storing and delivering electrical energy.6–10Fig. 1 shows the plot of the power density versus energy density for different electrochemical energy storage technologies.6 Supercapacitors with considerable power delivery performance bridge the gap between traditional capacitors and batteries, but their energy density is much lower than that of secondary lithium-ion and sodium-ion batteries.11–14 It is necessary to improve the electrochemical performances of supercapacitors to meet the higher requirements of future life and production, ranging from wearable electronic devices to electric vehicles and industrial equipment, by deepening our understanding of the nano-scale electrochemical interface.15–18
image file: d1qm00914a-f1.tif
Fig. 1 The power density versus energy density of various energy storage devices.6 Copyright 2020, Elsevier.

Compared with the electric double layer capacitor (EDLC), the pseudocapacitor exhibits higher specific capacitance, which is the consequence of its electrode materials’ surface possessing rapid redox reaction.19–22Fig. 2a and b illustrate the schematic diagrams of EDLC and pseudocapacitor.7 For the pseudocapacitor, transition metal oxides are recognized as ideal functional materials by virtue of their special structure and physical/chemical properties,23–25 including MnMoO4,26 CoMoO4,27,28 NiMoO4,29,30 ZnMoO4,31 Co3O4,32 Mn2O3,33 NiCo2O4,34,35 and MnCo2O4,36etc.


image file: d1qm00914a-f2.tif
Fig. 2 The schematic diagrams: (a) EDLC, and (b) pseudocapacitor.6 Copyright 2020, Multidisciplinary Digital Publishing Institute. (c) The number of published papers, and (d) the SCI citation times with the topics on “MnMoO4” and “Supercapacitor”. Data were derived from the Web of Science on March 30, 2021.

Among these transition metal oxides, MnMoO4, showing superior structural stability, good redox activity, cost-effective and environmental friendliness, has been investigated to expand the practical applications.37–39 Currently, MnMoO4 as an electrode has received extensive attention, which can be proved by the number of published articles and SCI citation times on the topic increasing significantly between the years of 2012–2020 (Fig. 2c and d). The material mainly possesses the following advantages: (1) α-MnMoO4 belongs to a monoclinic structure in the space group of C2/m with the lattice parameters of a = 10.469 Å, b = 9.516 Å, c = 7.143 Å, α = 90.0°, β = 106.28° and γ = 90.0°.40–42 MnMoO4 exhibits a good structural stability (compared with Co-based molybdates and Ni-based molybdates) by calculation, which is attributed to its special structure and lower cohesive energy.26,43 (2) MnMoO4 possesses a high theoretical capacity, originating from the synergistic effect of Mn and Mo (manganese ions contribute redox activity, and molybdenum ions offer electronic conductivity).44 (3) It is of strategic and practical significance to develop and utilize molybdenum resources, because 56% molybdenum mines of the world are in China under the survey data in 2016.45

Herein, this mini-review provides a systematic overview of the latest advances in the microstructures in favor of the outstanding electronic conductivity, superior interface reaction kinetics and the excellent diffusion kinetics to improve the electrochemical performance of MnMoO4 for supercapacitor, especially for the specific capacitance, rate capability and cycling stability. Furthermore, the morphology modification, heterostructure fabrication, electrochemical properties and plausible reaction mechanisms of MnMoO4 in recent years have been summarized. Finally, the remaining challenges and the future optimization direction of MnMoO4 materials are put forward, which furnishes guidance that serves the commercialization of novel MnMoO4-based electrodes.

2. The structure and synthesis of MnMoO4 materials

2.1 Crystal structure of MnMoO4

In general, anhydrous MnMoO4 has three polymorphs: the first phase is α-MnMoO4, the second phase is ω-MnMoO4, and the third phase is isostructural with α-CoMoO4.42,46–49 Among these, α-MnMoO4 is stable under normal temperature and pressure, and ω-MnMoO4 can be converted into α-MnMoO4 upon heating overnight in the air at 600 °C.50 Meanwhile, the α-MnMoO4 lattice is composed of corner-shared MnO6 octahedra and MoO4 tetrahedra.42 Mn and Mo occupy the centers of octahedral MnO6 and tetrahedral MoO4, respectively, as shown in Fig. 3.43 In particular, the synergistic distortion in α-MnMoO4 results in the generation of extra channels for the kinetic processes, and thus paves a good way for promoting adequate reactions between the electrode material and electrolyte.
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Fig. 3 The crystal structure of α-MnMoO4.43 Copyright 2017, American Chemical Society.

2.2 Fabrication methods for MnMoO4

It is well known that the synthesis route greatly affects the electrochemical behaviors of energy storage, because the morphology and surface area of the electrode materials are highly dependent on the fabrication conditions.41,50 Up to now, the common preparation methods for micro/nanoscale MnMoO4 include solid-phase method,51,52 combustion synthesis,53 sonochemical route,16 sol–gel,54–56 co-precipitation,31,57,58 hydrothermal/solvothermal reaction,59–61 and microwave irradiation-assisted technique.62,63 Among the above available technologies in preparing nanomaterials, the hydrothermal/solvothermal reaction is regarded as one of the most efficient processes of soft chemistry. The closed reaction system facilitates the reduction of distractions from external factors, and promotes the interaction of Mn and Mo raw materials in super-critical status with high pressure.64–66 For the precipitation strategy, it is difficult to avoid the agglomeration of nano-product particles resulting from relatively high deviations of the local concentration and temperature in the reactant solutions. To solve these issues, the microwave irradiation-assisted method has been widely applied to prepare MnMoO4 micro/nanoparticles, owing to its obvious advantages, such as high penetration depth, low thermal gradient effect and fast synthesis speed.67,68 For example, Muralidharan and his colleagues synthesized α-MnMoO4 nanorods through co-precipitation (Cp-MnMoO4) and microwave hydrothermal route (MH-MnMoO4), respectively.69 The Cp-MnMoO4 nanorods with a diameter of ∼200 nm and a length of ∼1.6 μm deliver a specific capacitance of 143 F g−1 at a current density of 1.0 A g−1. Meanwhile, the tube-like MH-MnMoO4 (diameter: ∼600 nm and length: ∼1.6 μm) composed of 5–6 pieces of nanorods (diameter: 100–200 nm) achieves a specific capacitance of 551 F g−1 at 1.0 A g−1 using 2 M NaOH as the electrolyte. As the above data show, the MH-MnMoO4 exhibits higher specific capacitance than that of Cp-MnMoO4. This is due to the tube-like morphology possessing a larger surface area and richer electroactive sites.69,70 Moreover, our group obtained several MnMoO4 nanomaterials with different morphologies via the microwave irradiation method: (1) MnMoO4 microrods, which were self-assembled from tens of MnMoO4 nanosheets with a thickness of 30–60 nm and a length of 4–10 μm.71 (2) MnMoO4 nanospheres with a diameter of 50–80 nm.72 (3) Three-dimensional (3D) MnMoO4 nanoflowers/graphene composites,73 as presented in Fig. 4a–c. (4) MnMoO4 nanowires/graphene composites, as depicted in Fig. 4d–f.74 The synthesis routes and experimental condition factors (fabricating temperature, reaction time and concentration) affect the shape and size of the products, and the morphologies and dimensions of the MnMoO4 particles can be effectively controlled by further optimizing these parameters.
image file: d1qm00914a-f4.tif
Fig. 4 (a–c) Scanning electron microscopy (SEM) images of the MnMoO4 nanoflowers/graphene composites.73 Copyright 2021, CN 112875756 A. (d–f) SEM images of the MnMoO4 nanowires/graphene composites.74 Copyright 2021, CN 112875757 A.

3. Research status of MnMoO4

3.1 Key parameters affecting the electrochemical performances of MnMoO4 materials

3.1.1 The electronic conductivity. The actual low specific capacitance of MnMoO4 hinders its wide applications, which is associated with its poor electronic conductivity and slow reaction kinetics. α-MnMoO4 is a n-type semiconducting material with a band gap of 1.96 eV.75 The narrow band gap allows electrons in the valence band to be more easily excited to the conduction band under an applied external voltage. Although Mo atoms with a smaller electron contribution do not participate in the redox reactions of the MnMoO4 electrochemical activity under alkaline condition, Mo atoms mainly offer electrical conductivity to improve the electrochemical properties of MnMoO4.43,76 In addition, the unsatisfactory electronic conductivity of MnMoO4 as an electrode material restricts the current response over a wide voltage range,77,78 mainly through the form of compounds with special microstructure to make up for this deficiency.
3.1.2 The interface reaction kinetics. The transfer rate of the electrons/ions and the redox ability of the active material largely determine the storage capacity of the Faradaic supercapacitors, especially for the high-rate cycling and low-temperature properties (Fig. 5).23,79,80 MnMoO4 particles with more regular morphologies are assembled from smaller ones with large surface areas, which is advantageous for the acceleration of reaction kinetics and the increase in the charge storage.41,81,82 Many feasible means are facilitated to improve the reaction kinetics of MnMoO4, such as reducing the size of active materials, adjusting the morphology and designing the novel microstructures.50,83
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Fig. 5 (a) Principles of the MnMoO4 nanowires/graphene electrodes in the supercapacitor. (b) The transfer of electrons/ions at the MnMoO4 nanowires/graphene electrodes during charge and discharge.
3.1.3 The diffusion kinetics. The particle size of MnMoO4 is one of the significant parameters for influencing the ion diffusion kinetics of the supercapacitor, which is a crucial direction to regulate the diffusion and transport of the ion/electron, leading to high specific capacity and excellent rate capability electrode materials.84–86 In general, owing to the reducing particle size, the internal active space of the MnMoO4 electrode can be adequately occupied, and the rapid ion diffusion improves the reaction kinetics.87–89 In addition, ion diffusion within the MnMoO4 host material depends on the diffusion distance and ion diffusion coefficient (τ = L2/D, where τ, D and L are the ion diffusion time, ion diffusion coefficient and diffusion length, respectively), suggesting that the particle size minimization can directly shorten the diffusion distance and therefore enhance the rate capability.90,91 For instance, Minakshi et al. fabricated bulk-like α-MnMoO4 with the size of 10–20 μm using a precipitation technique that displayed a specific capacitance of 200 F g−1 at 1.6 A g−1.92 In addition, Ramaraj and co-workers prepared MnMoO4 nanorods with a diameter of ∼160 nm and length of 2.3 μm through a co-precipitation method, showing a high discharge capacity of 424 F g−1 at 1.0 A g−1.93 Another example includes the α-MnMoO4 nanorod electrodes with a diameter of ∼30 nm and length of 75 nm, which were synthesized via a microwave-assisted method by Harichandran et al. and yielded a higher specific capacitance of 733 F g−1 at 1.0 A g−1.63 In all, these results distinctly reveal that the effective decreasing particle size is beneficial for the ion diffusion kinetics of MnMoO4 electrodes, thus enabling a good specific capacitance and rate capability.

3.2 Strategies to improve the performances of the MnMoO4 electrodes

3.2.1 Morphology modification. Morphology modification has been regarded as an effective approach to enhance the specific capacity and cycling performance of MnMoO4 electrodes for supercapacitors, owing to the larger specific surface area and greater pore size caused by various structures.94 In this mini-review, the electrodes assembled by MnMoO4-based materials will be systematically divided into the following three categories with different dimensionalities:95

(1) One-dimensional (1D) structures. The advantages of 1D structures for a stable structure and effortless strain relaxation are providing fast axial electron transport and shortening ion diffusion pathways.96,97 For instance, Mai and co-workers synthesized hierarchical MnMoO4/CoMoO4 heterostructured nanowires via a simple refluxing method, and the 1D MnMoO4 nanowires and 1D CoMoO4 nanorods were used as the backbone material and shell material, respectively. The hierarchical structure is beneficial to give sufficient active sites for the redox reactions. Consequently, the specific capacitance of the 3D composite nanowires can reach 187 F g−1 at 1.0 A g−1, which is higher than that of pure MnMoO4 (9.7 F g−1), CoMoO4 (62.8 F g−1) and MnMoO4/CoMoO4 composite with a non-three-dimensional structure (69.2 F g−1). Surprisingly, the as-prepared 3D MnMoO4/CoMoO4 nanocomposite displays an exceptional reversibility with 98% of the initial capacitance retained after 1000 cycles.98 In addition, Lu et al. fabricated 1D porous MnMoO4 nanotubes via a single-spinneret electrospinning technique with an annealing process in air. The tube-like microstructure of MnMoO4 aims to improve the contact between the electrolyte and electrode to optimize the electrochemical properties. Therefore, the aforementioned MnMoO4 nanotubes electrode exhibits a specific capacitance of 620 F g−1 at 1.0 A g−1, and retains 91% of the specific capacitance after 10[thin space (1/6-em)]000 cycles.26

(2) Two-dimensional (2D) structures. By supplying more active sites on the larger surfaces and higher utilization of the whole active planar materials to result in fast charge-transfer processes, the specific capacitance and cycling stability are promoted to some extent.99–102 Mu et al. produced ultrathin 2D manganese molybdate (MnMoO4·nH2O) nanosheets that anchored on nickel foam (NF) surfaces through a one-step hydrothermal reaction. These nanosheets present a specific capacitance of 1271 F g−1 at a scan rate of 5 mV s−1, and retained 84.5% of its initial specific capacitance after 2000 cycles at a current density of 10.0 A g−1.101

(3) 3D structures. Remarkably, on the basis of the previous research works, the 3D structures combine the merits of functional 1D and 2D structures, and possess their unique features of the sturdy structure, synergistic effects between different elements, preeminent permeabilities and many channels for Faraday reactions, which has attracted intense attention.103–105 For example, Feng and co-workers developed 3D hierarchical MnMoO4/NiWO4 microspheres (self-assembled by MnMoO4 nanoflakes and NiWO4 nanoparticles) using a hydrothermal method, which delivered a capacitance of 598 F g−1 at 1.0 A g−1 and the capacitance retention of 82% after 5000 cycles. It is because the 3D microspheres afford vast open space and electroactive sites for Faradaic reactions to heighten the specific capacity and cycle stability.103 Furthermore, Gu and co-workers reported a facile hydrothermal and calcination method to obtain 3D NiCo2O4@MnMoO4 core/shell nano-flowers that demonstrate a specific capacitance of 1118 F g−1 at 1.0 A g−1, and a long-term cycling stability of 87.85% after 5000 cycles.104

In summary, these valuable consequences reveal that the sequence of the specific capacity and cycle property from better to average is 3D > 2D > 1D by only considering the influence of the microstructures of the MnMoO4-based materials, while neglecting the difference of the diverse sorts of electrolytes. As a consequence, MnMoO4-based materials with 3D structures overcome the restrictions of materials with single or two dimensionalities, which offer functional properties of excellent surface area for effective ion/charge transport pathways, minimized electrode polarization and alleviated the volume expansion/shrinkage, leading to high specific capacitance and superior cycle stability to show significant potential in supercapacitor applications.106–111 Finally, the morphology adjustment of the electrode materials suggests a future direction for more research studies in further enhancing the electrochemical performances.

3.2.2 In situ growth of MnMoO4 on the conductive metal substrate. The conductive metal substrate with a 3D porous structure is generally considered a good deposition material because of its stable structure and good electronic conductivity.83 For instance, the 3D fan-like α-MnMoO4 nanostructures with an average radius of 5 μm were in situ grown on a Cu coil prepared by Wang and his colleagues via a precipitation process.112 The 3D fan-like α-MnMoO4 displays a specific capacitance of 562 F g−1 at 1.0 A g−1 and a long-term cycling stability with 99.8% of the initial capacitance retained after 1000 cycles using 2 M KOH as the electrolyte. The commendable electrochemical behaviors of the as-prepared nanoribbon-based α-MnMoO4 electrode result from the novel 3D hierarchical nanostructures. Based on the above study, Xu et al. reported a hydrothermal route to prepare the MnMoO4 ultrathin nanosheets on nickel foam (NF@MnMoO4).113 The vertically ordered MnMoO4 nanosheets, grown on NF, generate a large amount of 3D network channels, as illustrated in Fig. 6a–f. The cavities of the as-gained MnMoO4 nanostructures are convenient for the OH− insertion and the electron diffusion. Additionally, the interconnected porous structure of the MnMoO4 nanosheets can store part of the electrolyte, which contributes to the improvement in the possibility of charge transfer at the electrode–electrolyte interfaces. The NF@MnMoO4 electrode has a specific capacitance of 4609 F g−1 at 1.0 A g−1 and retained 92.4% capacitance over 20[thin space (1/6-em)]000 cycles in 3 M KOH electrolyte (Fig. 6g–j). The electrochemical properties of the α-MnMoO4 materials in situ grown on the conductive substrates are revealed to be much better compared with the materials without substrates. This is because the conductive metal substrates can effectively avoid the agglomeration of MnMoO4 micro/nanoscale particles, and prevent “dead volume” caused by the polymer binder in electrode sheets.
image file: d1qm00914a-f6.tif
Fig. 6 (a–c) SEM images of the NF@MnMoO4 nanosheet arrays at different magnifications. (d–e) Transmission electron microscopy (TEM) images of the NF@MnMoO4 nanosheet arrays. (f) High-resolution transmission electron microscopy (HRTEM) image of a single MnMoO4 nanosheet. (g) Cyclic voltametric (CV) curves of the NF@MnMoO4 nanosheet electrode at different scan rates. (h) Galvanostatic charge–discharge (GCD) curves of the NF@MnMoO4 nanosheet electrode. (i) Specific capacitances of the NF@MnMoO4 electrodes for various reaction conditions at different current densities. (j) Cycling retention of the NF@MnMoO4 electrode at a constant scan rate of 100 mV s−1.113 Copyright 2020, American Chemical Society.
3.2.3 Designing composites with transition-metal oxides. Recently, the 3D multi-component core–shell arrays with large specific surface areas, high porosity and numerous active sites have been extensively researched for supercapacitors.114 The core part can afford an efficient transfer path to ions or electrons, and maintains sufficient stability during the electrochemical reactions. Meanwhile, the shell part possesses a larger specific surface area and furnishes more active sites in electrochemical reactions. The combination of MnMoO4 and transition-metal oxide to form 3D heterostructures is beneficial to improve the specific capacitance and redox reversibility of composites. To date, 3D core–shell nanocomposites have been demonstrated to significantly improve the low specific capacity of MnMoO4.115 For example, Yuan et al. prepared a 3D NiCo2O4@MnMoO4 core–shell nanocolumn via a two-step hydrothermal route.116 The NiCo2O4@MnMoO4 hybrid electrode has a high specific capacitance of 1169 F g−1 at 2.5 mA cm−2, as well as a good reversibility with cycling efficiency of 92.58% after 5000 cycles at 30 mA cm−2. Lv et al. created the MnCo2O4@MnMoO4 core–shell nanoarrays through a facile hydrothermal reaction,117 and the MnCo2O4 nanosheets were grown on nickel foam to serve as the core, while MnMoO4 nanosheets served as the shell. The MnCo2O4@MnMoO4 electrode delivers a specific capacity of 885 C g−1 at a current density of 3.0 A g−1 and remarkable reversible capacity with 95% retention over 5000 cycles at 10.0 A g−1. More recently, Arvind Singh et al. synthesized porous NiCo2O4@MnMoO4 heterostructures via a simple hydrothermal route (Fig. 7a and b).118 The as-obtained NiCo2O4@MnMoO4 electrode exhibits superior electrochemical performance, specifically a high specific capacitance of 1821 F g−1 at 5.0 A g−1, and an outstanding cycling stability of ∼94% retained after 5000 cycles at 70.0 A g−1 (Fig. 7c–e). Furthermore, the NiCo2O4@MnMoO4 electrode shows better specific capacitance compared to those of pure NiCo2O4 and pure MnMoO4 at various current densities (Fig. 7f). The choice of two-phase particles plays a decisive role in the construction of innovative 3D MnMoO4 multi-component heterostructures electrode materials.
image file: d1qm00914a-f7.tif
Fig. 7 (a and b) Field emission scanning electron microscopy (FE-SEM) images of the NiCo2O4@MnMoO4 heterostructures. (c) CV curves of the NiCo2O4@MnMoO4 electrode at various scan rates. (d) GCD curves of the NiCo2O4@MnMoO4 heterostructures at different current densities. (e) The stability profile of the NiCo2O4@MnMoO4 electrodes at 70.0 A g−1. (f) Specific capacitances of MnMoO4, NiCo2O4 and NiCo2O4@MnMoO4 electrodes at typical current densities.118 Copyright 2020, Elsevier.
3.2.4 Forming composites with other conductive materials. Apart from the transition-metal oxides, diverse conductive materials were applied to modify the microstructures of MnMoO4 to enhance the ion transparent properties, such as sulfides,115,119 graphene120–122 and conducting polymers.123,124 Wei et al. fabricated hierarchical NiCo2S4@MnMoO4 core–shell composites via a three-steps hydrothermal route.115 The MnMoO4 nanosheets with a thickness of 0.5 μm controllably attached to the NiCo2S4 nanotubes with a diameter of ∼100 nm. The specific capacitance of this NiCo2S4@MnMoO4 hybrid electrode is calculated to be 1186.44 F g−1 at 1.0 A g−1, and maintains 90.1% of the initial capacitance after 5000 cycles at 10.0 A g−1. Furthermore, Li et al. developed a novel core–shell CoS/MnMoO4/rGO/NF nanocomposite with a complicated network structure through hydrothermal treatment, followed by electrodeposition routes, as shown in Fig. 8a.119 When the loading amount of CoS is 0.4 mg cm−2, the corresponding CoS-0.4/MnMoO4/rGO/NF electrode with the thickness of 30 nm shows that CoS-0.4/MnMoO4 is tightly bound to rGO/NF. In particular, the CoS shell is evenly wrapped on the MnMoO4 core (Fig. 8b–d). As illustrated in Fig. 8e–h, the as-prepared CoS-0.4/MnMoO4/rGO/NF electrode displays a significant specific capacitance of 3074.5 F g−1 at 1.0 A g−1 and the capacitance retention of 87% over 5000 cycles at a constant current density of 10.0 A g−1. These nice electrochemical properties can be ascribed to the appropriate proportion of active substance, as well as the orderly unique microstructure.
image file: d1qm00914a-f8.tif
Fig. 8 The characterizations of the CoS-0.4/MnMoO4/rGO/NF nanocomposites: (a) The schematic illustration of the synthesis approach for the composite. (b and c) SEM images. (d) TEM images. (e) CV curves at different scan rates. (f) GCD curves. (g) The real capacitance and specific capacitance at various current densities. (h) Cycle performances of parallel samples at 10 A g−1.119 Copyright 2019, Elsevier.

3.3 Reaction mechanisms for MnMoO4 in the supercapacitor

The charge storage mechanisms of the MnMoO4 electrodes in different electrolytes have a vital influence on the pseudo-capacitive properties.125–127 The Faradaic redox reactions and electron transference numbers of MnMoO4 in aqueous electrolytes, including alkaline, neutral, and acidic solutions, are described in Table 1. In alkaline electrolytes, a plausible mechanism is the fully reversible redox reactions on the surface of the MnMoO4 electrodes corresponding to the pseudocapacitive capability and the adsorption/desorption of OH− in the electrochemical double layer.98,128 At the beginning, Mn2+ undergoes an oxidation process (losing one electron) to form Mn3+ (Mn2O3), which matches eqn (1).92,119,129 Later, Mn2O3 further reacts with OH− to generate MnO2 with increasing electrode potentials, manifesting the occurrence of the electron transfer of Mn3+/Mn4+ (eqn (2)).113,115 Meanwhile, the presence of Mo can raise the electronic conductivity of the MnMoO4 electrodes (MnMoO4: 4.27 × 10−3 S cm−1vs. MnO2: 10−5–10−6 S cm−1),110,130,131 and then furnish the fundamental of decreasing the internal resistances to enhance the rate capability and cycling stability of MnMoO4. During the charge and discharge, the molybdate species exist as MoO42− in alkaline solution,132,133 in which every Mo atom in the tetrahedral MoO42− is surrounded by four O atoms. Each Mo–O bond processes a high binding energy of 540 kJ mol−1;134,135 thus, the Mo element does not take part directly in the redox reaction. For instance, the electrochemical processes of the MnMoO4@MWCNT electrode, reported by Jai Bhagwan et al., equal the following eqn (1) and (2) having the charge transfer kinetics of Mn2+/Mn3+ and Mn3+/Mn4+, achieving a specific capacitance of 1017 F g−1 at 1.0 A g−1 and an energy density of 18.1 W h kg−1 at a power density of 362.4 W kg−1 using 1 M KOH electrolyte.128
Table 1 The reaction mechanisms of MnMoO4 electrodes in three typical aqueous electrolytes
Type of electrolytes Faradaic redox reactions Ref.
Alkalinity 2[Mn(OH)3]− ↔ Mn2O3 + 3H2O + 2e− (1) 98, 113, 115 and 128
Mn2O3 + 2OH− ↔ 2MnO2 + H2O + 2e− (2)
Neutrality MnMoO4 + M+ + e− ↔ MMnMoO4 (3) 122
Acidity Mechanism 1: 136–139
Mo(VI)O42− + 2H+ ↔ H2Mo(VI)O4 (4)
H2Mo(VI)O4 + 2e− + 2H+ ↔ H2Mo(IV)O3 + H2O (5)
H2Mo(VI)O4 + e− + H+ ↔ HMo(V)O3 + H2O (6)
Mechanism 2: 44
MnxMo1−xO4 + yH+ + ye− ↔ HyMnxMo1−xO4 (7)

For the neutral electrolyte (e.g., Na2SO4, KCl, etc.), the redox process of the Faradaic reaction at the MnMoO4 electrodes is changed from MnMoO4 to MMnMoO4 (eqn (3)), which is accompanied by the embedding and disembedding of the electrolyte cationic M+ (e.g., Na+, K+, etc.). Debasis Ghosh and his colleagues reported that the Faradaic reactions at the hexahedron-shaped α-MnMoO4 electrodes in 1 M Na2SO4 electrolyte can be expressed as an equation: MnMoO4+ Na+ + e− ↔ NaMnMoO4, which made a high pseudocapacitance contribution (267 F g−1 at 5 mV s−1) since the Na+ was involved in the redox processes.122

Distinct from the alkaline and neutral electrolyte, the effects of the acidic electrolyte for the performances of MnMoO4 have been discussed in a few literature, which entails more systematic research. It was reported that MnMoO4 abides by two possible reaction mechanisms in the acid solutions: (1) The molybdate species (MoO42−) tend to form polymeric ions of H2MoO4 (eqn (4)). H2MoO4 can be further transformed to H2Mo(IV)O3 and HMo(V)O3 through the redox reaction between the redox pairs Mo(VI)/Mo(V) and Mo(VI)/Mo(IV), which is shown in eqn (5) and (6).136–139 (2) The Faradaic reaction gets and releases electrons among MnxMo1−xO4 and HyMnxMo1−xO4, and is directly correlated to the insertion/extraction of H+ ions (eqn (7)). For example, Purushothaman et al. proposed that the possible redox reaction of α-MnMoO4 nanorods in 0.06 M H2SO4, HCl or para toluene sulfonic acid (p-TSA) can be expressed in eqn (7): MnxMo1−xO4 + yH+ + ye− ↔ HyMnxMo1−xO4. They also found that the specific capacitance of α-MnMoO4 nanorods in 0.06 M H2SO4 electrolyte was 998 F g−1 at 5 mV s−1, which displayed a superior capacitive behavior compared to that of p-TSA (784 F g−1) and HCl (530 F g−1) acid solutions.44 In conclusion, the reaction mechanisms of the MnMoO4 electrodes can be strongly determined by the pH of the electrolytes, and the electrochemical properties in these as-mentioned systems are summarized in the following sequence: alkalinity > acidity > neutrality.

According to the above reports on the reaction mechanisms of the MnMoO4 electrodes for a supercapacitor, a deeper understanding of the complex electrochemical behaviors under different acidic and alkaline electrolytes and dynamics attributed by MnMoO4-based materials is the key to a major breakthrough.140–142 Therefore, the introduction of in situ analysis techniques, such as in situ X-ray diffraction (XRD), in situ Raman, in situ X-ray absorption spectroscopy (XAS) and in situ X-ray photoelectron spectroscopy (XPS) can track the redox process in real-time during cycling, and directly reveal the intermediate phase structures and the valence changes of Mn and Mo, resulting in an enhanced specific capacitance.143–145 The combination of in situ TEM and in situ SEM roundly demonstrates the morphological changes of the MnMoO4-based electrodes during the operation of supercapacitors, including volume expansion and crack formation, which suggests that regulating the growth parameters of MnMoO4-based electrodes will be beneficial to improve its cycling stability.146,147 These advanced in situ characterization approaches have an important effect on monitoring the microstructural evolution of the MnMoO4-based materials during the charge and discharge process, providing guidance for the reasonable design of electrode materials and electrolyte, which can accelerate the large-scale practical application of supercapacitors.

For a recent comprehensive comparison, the synthetic routes and corresponding electrochemical performances of MnMoO4-based electrodes are summarized in Table 2. A rationally designed microstructure with specific features is the premise of its superior electrochemical behaviors.148–157 The great specific surface area and the regular morphology of the MnMoO4 micro/nano particles can effectively accelerate the diffusion rate of the ion/electron, and promote the reaction kinetics, thereby improving its electronic conductivity and specific capacitance. Besides, both conductive materials and MnMoO4 materials show enhanced specific capacitance among the conductive material/MnMoO4 composites. MnMoO4 composites are promising electrode materials for supercapacitors.

Table 2 Summary on the electrochemical properties of manganese molybdate and its composites in supercapacitors
Type of electrolyte Material Synthesis method Electrolyte Specific capacitance Rate capability Cyclic stability Energy density Power density Ref.
Alkalinity MnMoO4@MWCNT Hydrothermal reaction 1 M KOH 1017 F g−1 at 1.0 A g−1 — — 18.1 W h kg−1 362.4 W kg−1 128
MnMoO4·0.9H2O nanorods Precipitation 1 M KOH 215 F g−1 at 1 mA cm−2 — — — — 76
MnMoO4 nanorods Microwave-assisted method 1 M KOH 836 F g−1 at 5 mV s−1 100 F g−1 at 15 A g−1 84% after 3000 cycles (100 mV s−1) — — 63
Tube-like MnMoO4 Single-spinneret electrospinning technique 2 M KOH 620 F g−1 at 1.0 A g−1 460 F g−1 at 60 A g−1 91% after 10[thin space (1/6-em)]000 cycles (1.0 A g−1) 31.7 W h kg−1 797 W kg−1 26
α-MnMoO4 nanorods Microwave-assisted method 2 M KOH 446.7 F g−1 at 1 mA cm−2 125.4 F g−1 at 10 mA cm−2 81.12% after 3000 cycles (8 mA cm−2) — — 67
α-MnMoO4 3D fan-like nanostructures Precipitation 2 M KOH 562 F g−1 at 1.0 A g−1 218 F g−1 at 10.0 A g−1 99.8% after 1000 cycles (1.0 A g−1) — — 112
MnMoO4 nanorods Solvothermal method 2 M KOH 697.4 F g−1 at 0.5 A g−1 237.4 F g−1 at 10.0 A g−1 84% after 500 cycles (5.0 A g−1) — — 81
CoS-0.4/MnMoO4/rGO/NF Hydrothermal and electrodeposition methods 2 M KOH 3074.5 F g−1 at 1.0 A g−1 2236.5 F g−1 at 10.0 A g−1 87% after 5000 cycles (10.0 A g−1) 50.3 W h kg−1 415.8 W kg−1 119
Ni3S2@MnMoO4 Hydrothermal reaction 2 M KOH 979.3 C g−1 at 2 mA cm−2 690.0 C g−1 at 30 mA cm−2 88.3% after 7000 cycles (10 mA cm−2) 31.4 W h kg−1 399.9 W kg−1 148
MnMoO4·H2O@MnO2 Hydrothermal reaction 2 M KOH 3560.2 F g−1 at 1.0 A g−1 — 84.1% after 10[thin space (1/6-em)]000 cycles (5.0 A g−1) 45.6 W h kg−1 507.3 W kg−1 149
NiCo2O4@MnMoO4 Hydrothermal reaction 2 M KOH 1705.3 F g−1 at 5 mA cm−2 1252.6 F g−1 at 20 mA cm−2 92.6% after 5000 cycles (5 mA cm−2) — — 150
MnMoO4/NiWO4 Hydrothermal reaction 2 M KOH 598 F g−1 at 1.0 A g−1 422 F g−1 at 20 A g−1 82% after 5000 cycles (1.0 A g−1) — — 103
Rod-like MnMoO4 Precipitation 2 M KOH 112.8 C g−1 at 0.5 A g−1 58.8 C g−1 at 8.0 A g−1 109 C g−1 after 2000 cycles (1.0 A g−1) — — 100
NiCo2O4@MnMoO4 Hydrothermal reaction 3 M KOH 1169 F g−1 at 2.5 mA cm−2 — 92.58% after 5000 cycles (30 mA cm−2) 15 W h kg−1 6734 W kg−1 116
Co3O4@MnMoO4 Hydrothermal reaction 3 M KOH 663.75 F g−1 at 2.5 mA cm−2 399 F g−1 at 15 mA cm−2 95.32% after 3000 cycles (3.0 A g−1) 12.03 W h kg−1 300 W kg−1 39
NiCo2S4@MnMoO4 Hydrothermal reaction 3 M KOH 1186.44 F g−1 at 1.0 A g−1 820 F g−1 at 15 A g−1 90.1% after 5000 cycles (10.0 A g−1) 47.8 W h kg−1 699.9 W kg−1 115
NF@MnMoO4 Hydrothermal reaction 3 M KOH 4609 F g−1 at 1.0 A g−1 2800 F g−1 at 20 A g−1 92.4% after 20[thin space (1/6-em)]000 cycles (100 mV s−1) 107.38 W h kg−1 801.34 W kg−1 113
NiCo2O4@MnMoO4 Hydrothermal reaction 3 M KOH 1118 F g−1 at 1.0 A g−1 746 F g−1 at 10.0 A g−1 87.85% after 5000 cycles (1.0 A g−1) 236.44 W h kg−1 699.99 W kg−1 104
NiCo2O4@MnMoO4 Hydrothermal reaction 6 M KOH 1821 F g−1 at 5.0 A g−1 1265 F g−1 at 60 A g−1 94% after 5000 cycles (70 A g−1) 91.87 W h kg−1 374.15 W kg−1 118
MnCo2O4@MnMoO4 Hydrothermal reaction 6 M KOH 885 C g−1 at 3.0 A g−1 629 C g−1 at 30 A g−1 95% after 5000 cycles (10.0 A g−1) 49.4 W h kg−1 815 W kg−1 117
CuCo2O4@MnMoO4 Hydrothermal reaction 6 M KOH 1327.5 F g−1 at 1.0 A g−1 1055.3 F g−1 at 20 A g−1 92.8% after 6000 cycles (5 A g−1) 58.9 W h kg−1 670 W kg−1 151
NiCo2O4@MnMoO4 Hydrothermal reaction 6 M KOH 2603.9 F g−1 at 5 mA cm−2 — 92.1% after 3000 cycles (5 mA cm−2) 44.16 W h kg−1 800 W kg−1 152
MnMoO4·nH2O Hydrothermal reaction 1 M NaOH 1271 F g−1 at 5 mV s−1 619 F g−1 at 100 mV s−1 84.5% after 2000 cycles (10 A g−1) 31.6 W h kg−1 935 W kg−1 101
MnMoO4·4H2O Hydrothermal reaction 1 M NaOH 2300 F g−1 at 4 mA cm−2 1260 F g−1 at 24 mA cm−2 92% after 3000 cycles (5 mV s−1) — — 105
α-MnMoO4 nanorods Microwave hydrothermal method 2 M NaOH 551 F g−1 at 1.0 A g−1 253 F g−1 at 5.0 A g−1 89% after 1000 cycles (5.0 A g−1) — — 69
MnMoO4/MnCO3 Hydrothermal reaction 2 M NaOH 1311.1 F g−1 at 1.0 A g−1 400 F g−1 at 10.0 A g−1 79% after 5000 cycles (10.0 A g−1) 26.5 W h kg−1 657 W kg−1 153
MnMoO4 nanorods Solid-state chemistry reaction 2 M NaOH 210.2 F g−1 at 1.0 A g−1 — 112.6% after 10[thin space (1/6-em)]000 cycles (5.0 A g−1) 23.5 W h kg−1 187.4 W kg−1 154
MnMoO4/CoMoO4 Simple refluxing method 2 M NaOH 187.1 F g−1 at 1.0 A g−1 134.7 F g−1 at 3.0 A g−1 98% after 1000 cycles (3.0 A g−1) — — 98
CNT/rGO/MnMoO4 Hydrothermal reaction 2 M NaOH 2374.9 F g−1 at 2 mV s−1 703.9 F g−1 at 100 mV s−1 97.1% after 3000 cycles (2 mV s−1) 59.4 W h kg−1 1367.9 W kg−1 121
Rhombohedron-like α-MnMoO4 Precipitation 2 M NaOH 200 F g−1 at 1.6 A g−1 84 F g−1 at 6.4 A g−1 91% after 1000 cycles (1 mA cm−2) 11 W h kg−1 100 W kg−1 92
α-MnMoO4 nanorods Sonochemical method 2 M NaOH 168.32 F g−1 at 0.5 mA cm−2 — 96% after 2000 cycles (100 mV s−1) 9.87 W h kg−1 95.58 W kg−1 155
Neutrality MnMoO4/G Hydrothermal reaction 1 M Na2SO4 142.08 F g−1 at 0.7 A g−1 129.1 F g−1 at 1.0 A g−1 93.7% after 1000 cycles (0.7 A g−1) 41.9 W h kg−1 208 W kg−1 120
α-MnMoO4/PANI Sonochemical method 1 M Na2SO4 396 F g−1 at 5 mV s−1 — 321 F g−1 after 500 cycles (5 mV s−1) — — 124
MnMoO4/graphene Hydrothermal reaction 1 M Na2SO4 364 F g−1 at 2.0 A g−1 287 at 8.0 A g−1 88% after 1000 cycles (8.0 A g−1) 202.2 W h kg−1 2000 W kg−1 122
PEG-MnMoO4 Precipitation 1 M Na2SO4 424 F g−1 at 1.0 A g−1 138 F g−1 at 5.0 A g−1 — — — 93
PPy@MnMoO4 In situ oxidative polymerization 2 M KCl 374.8 F g−1 at 0.2 A g−1 208.5 F g−1 at 5.0 A g−1 80.6% after 1000 cycles (5.0 A g−1) 34.4 W h kg−1 500 W kg−1 123
Acidity PPy@MnMoO4/CFs Double in situ deposition method 0.6 M H2SO4 440.1 F g−1 at 0.2 A g−1 143.4 F g−1 at 4.0 A g−1 83% after 1000 cycles (2.0 A g−1) — — 156
α-MnMoO4 nanorods Sol–gel spin coating method 0.06 M H2SO4 998 F g−1 at 5 mV s−1 449 F g−1 at 15 mV s−1 — — — 44
0.06 M para toluene sulfonic acid 784 at 5 mV s−1 527 F g−1 at 15 mV s−1
0.06 M HCl 530 at 5 mV s−1 294 F g−1 at 15 mV s−1

Conclusions

In summary, MnMoO4 and its composite materials have been widely studied as promising electrodes for advanced supercapacitors. The crystal structure, preparation methods, advantages and energy storage mechanisms of MnMoO4 have been discussed in detail, especially its current progress. Although the development of MnMoO4 electrodes has accessed some progress, several substantive issues about practical applications still pose a great challenge for us, which should be resolved toward its commercialization.

(1) All strategies for synthesizing micro/nanoscale MnMoO4 electrode materials revolve around the improvement of specific capacitance, rate performance and cycling durability, as well as synthetic controllability. Therefore, the key points to be studied are how to integrate the existing methods and obtain an architecture that is well-ordered, porous, ultra-tiny and more stable in high-rate charging/discharging.

(2) The microscopic morphology adjustment of MnMoO4, such as fabricating the 3D core–shell structure, in situ growth on conductive metal substrates, and composite formation with sulfides, graphene and polymers, can enhance the electrochemical properties of MnMoO4. Designing and fabricating novel Mn-based molybdates with high surface area, rich porosity, excellent specific capacitance and outstanding structural stability deserves considerable effort.

(3) During the electrochemical activities, the evolution and deformation of MnMoO4-based electrodes are not clear. Thus, there is a need for an in-depth analysis and profound revelation for the phase transformation and morphological changes of MnMoO4 composites via more accurate theoretical calculations and more detailed experimental data, which favors affording the basis for other related experimental characterization, such as in situ XRD, in situ XAS, in situ XPS, in situ SEM, and in situ TEM. The combination of theoretical calculations and experiments may open some new avenues to boost the characterizations of the MnMoO4 electrode.

(4) The current research studies on MnMoO4 electrodes for supercapacitors are mainly limited to the laboratory. However, the ultimate objective is to achieve the business application of MnMoO4 materials. Thus, more attention should be paid to the development of controllable routes for the large-scale synthesis of MnMoO4 with an optimum performance. It is expected that the MnMoO4-based electrodes will occupy an important position in the field of supercapacitors in the near future.

Author contributions

Zhu Zhu, Yan Sun, and Shulei Chou designed and wrote the review. Jiahao Zhu and Chunsheng Li revised the paper. Chen Yang and Miaomiao Wang drew the figures. Lin Li edited the mini-review. Didi Wang and Yuanliang Li discussed the structure of the paper.

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

The authors gratefully acknowledge financial support from the National Natural Science Foundation of China (No. 51971182, 21203051, 21643005, and 21203135), the “Xingliao Talent Innovation Program” in Science and Technology of Liaoning Province, the Science and Technology Projects of Suzhou City (SYG201938 and SYG202025), and the Science and Technology Projects of Shanxi Province (S2022-JC-YB-0440). The work is also supported by the Australian Research Council through a Linkage Project (LP120200432).

Notes and references

  1. X. Y. Cao, A. Halder, Y. Y. Tang, C. Y. Hou, H. Z. Wang, J. Ø. Duus and Q. J. Chi, Engineering two-dimensional layered nanomaterials for wearable biomedical sensors and power devices, Mater. Chem. Front., 2018, 2, 1944–1986 RSC .
  2. M. Z. Dai, D. P. Zhao and X. Wu, Research progress on transition metal oxide based electrode materials for asymmetric hybrid capacitors, Chin. Chem. Lett., 2020, 31, 2177–2188 CrossRef CAS .
  3. J. M. Gonçalves, M. L. da Silva, H. E. Toma, L. Angnes, P. R. Martins and K. Araki, Trimetallic oxides/hydroxides as hybrid supercapacitors electrode materials: a review, J. Mater. Chem. A, 2020, 8, 10534–10570 RSC .
  4. K. Zhu, Y. Wang, J. A. Tang, S. H. Guo, Z. M. Gao, Y. J. Wei, G. Chen and Y. Gao, A high-performance supercapacitor based on activated carbon fibers with an optimized pore structure and oxygen-containing functional groups, Mater. Chem. Front., 2017, 1, 958–966 RSC .
  5. T. Xue and H. J. Fan, From aqueous Zn-ion battery to Zn–MnO2 flow battery: a brief story, J. Energy Chem., 2021, 54, 194–201 CrossRef .
  6. B. K. Saikia, S. M. Benoy, M. Bora, J. Tamuly, M. Pandey and D. Bhattacharya, A brief review on supercapacitor energy storage devices and utilization of natural carbon resources as their electrode materials, Fuel Cells, 2020, 282, 118796 CrossRef CAS .
  7. P. Forouzandeh, V. Kumaravel and S. C. Pillai, Electrode Materials for Supercapacitors: A Review of Recent Advances, Catalysts, 2020, 10, 969 CrossRef CAS .
  8. L. L. Lyu, K. D. Seong, D. Ko, J. Choi, C. Lee, T. Hwang, Y. Cho, X. Z. Jin, W. Zhang, H. Pang and Y. Z. Piao, Recent development of biomass-derived carbons and composites as electrode materials for supercapacitors, Mater. Chem. Front., 2019, 3, 2543–2570 RSC .
  9. C. Wang, J. Y. Wang, W. P. Hu and D. Wang, Controllable Synthesis of Hollow Multishell Structured Co3O4 with Improved Rate Performance and Cyclic Stability for Supercapacitors, Chem. Res. Chin. Univ., 2020, 36, 68–73 CrossRef CAS .
  10. H. W. Wang, Z. J. Xu, H. Yi, H. G. Wei, Z. H. Guo and X. F. Wang, One-step preparation of single-crystalline Fe2O3 particles/graphene composite hydrogels as high performance anode materials for supercapacitors, Nano Energy, 2014, 7, 86–96 CrossRef CAS .
  11. A. González, E. Goikolea, J. A. Barrena and R. Mysyk, Review on supercapacitors: technologies and materials, Renewable Sustainable Energy Rev., 2016, 58, 1189–1206 CrossRef .
  12. Poonam, K. Sharma, A. Arora and S. K. Tripathi, Review of supercapacitors: materials and devices, J Energy Storage, 2019, 21, 801–825 CrossRef .
  13. S. Ghosh, S. M. Jeong and S. R. Polaki, A review on metal nitrides/oxynitrides as an emerging supercapacitor electrode beyond oxide, Korean J. Chem. Eng., 2018, 35, 1389–1408 CrossRef CAS .
  14. R. X. Fei, H. W. Wang, Q. Wang, R. Y. Qiu, S. S. Tang, R. Wang, B. B. He, Y. S. Gong and H. J. Fan, In Situ Hard-Template Synthesis of Hollow Bowl-Like Carbon: A Potential Versatile Platform for Sodium and Zinc Ion Capacitors, Adv. Energy Mater., 2020, 10, 2002741 CrossRef CAS .
  15. B. Dunn, H. Kamath and J. M. Tarascon, Electrical Energy Storage for the Grid: A Battery of Choices, Science, 2011, 334, 928–935 CrossRef CAS PubMed .
  16. D. P. Dutta, A. Mathur, J. Ramkumar and A. K. Tyagi, Sorption of dyes and Cu(II) ions from wastewater by sonochemically synthesized MnWO4 and MnMoO4 nanostructures, RSC Adv., 2014, 4, 37027–37035 RSC .
  17. G. P. Wang, L. Zhang and J. J. Zhang, A review of electrode materials for electrochemical supercapacitors, Chem. Soc. Rev., 2012, 41, 797–828 RSC .
  18. C. W. Cheng and H. J. Fan, Branched nanowires: synthesis and energy applications, Nano Today, 2012, 7, 327–343 CrossRef CAS .
  19. J. Yang, Y. Liu, S. L. Liu, L. Li, C. Zhang and T. X. Liu, Conducting polymer composites: material synthesis and applications in electrochemical capacitive energy storage, Mater. Chem. Front, 2017, 1, 251–268 RSC .
  20. P. Sharma and T. S. Bhatti, A review on electrochemical double-layer capacitors, Energy Convers. Manage., 2010, 51, 2901–2912 CrossRef CAS .
  21. P. Simon and Y. Gogotsi, Perspectives for electrochemical capacitors and related devices, Nat. Mater., 2020, 19, 1151–1163 CrossRef CAS PubMed .
  22. R. Y. Bi, D. Mao, J. Y. Wang, R. B. Yu and D. Wang, Hollow Nanostructures for Surface/Interface Chemical Energy Storage Application, Acta Chim. Sin., 2020, 78, 1200–1212 CrossRef CAS .
  23. F. Yang, J. Chu, Y. P. Cheng, J. F. Gong, X. Q. Wang and S. X. Xiong, Hydrothermal Synthesis of NiCo-layered Double Hydroxide Nanosheets Decorated on Biomass Carbon Skeleton for High Performance Supercapacitor, Chem. Res. Chin. Univ., 2021, 37, 772–777 CrossRef CAS .
  24. C. Zhong, Y. D. Deng, W. B. Hu, J. L. Qiao, L. Zhang and J. J. Zhang, A review of electrolyte materials and compositions for electrochemical supercapacitors, Chem. Soc. Rev., 2015, 44, 7484–7539 RSC .
  25. P. Simon and Y. Gogotsi, Materials for electrochemical capacitors, Nat. Mater., 2008, 7, 845–854 CrossRef CAS PubMed .
  26. Y. Lu, M. L. Zhao, R. J. Luo, Q. H. Yu, J. R. Lv, W. X. Wang, H. L. Yan, T. Peng, X. M. Liu and Y. S. Luo, Electrospun porous MnMoO4 nanotubes as high-performance electrodes for asymmetric supercapacitors, J. Solid State Electrochem., 2018, 22, 657–666 CrossRef CAS .
  27. Q. Li, Y. L. Li, J. Zhao, S. H. Zhao, J. J. Zhou, C. Chen, K. Tao, R. Liu and L. Han, Ultrathin nanosheet-assembled hollow microplate CoMoO4 array derived from metal-organic framework for supercapacitor with ultrahigh areal capacitance, J. Power Sources, 2019, 430, 51–59 CrossRef CAS .
  28. W. Xiao, J. S. Chen, C. M. Li, R. Xu and X. W. Lou, Synthesis, Characterization, and Lithium Storage Capability of AMoO4 (A = Ni, Co) Nanorods, Chem. Mater., 2010, 22, 746–754 CrossRef CAS .
  29. J. Hong, Y. W. Lee, B. Hou, W. Ko, J. Lee, S. Pak, J. P. Hong, S. M. Morris, S. N. Cha, J. I. Sohn and J. M. Kim, Solubility-dependent NiMoO4 nanoarchitectures: direct correlation between rationally designed structure and electrochemical pseudo-kinetics, ACS Appl. Mater. Interfaces, 2016, 8, 35227–35243 CrossRef CAS PubMed .
  30. C. Qing, C. X. Yang, M. Y. Chen, W. H. Li, S. Y. Wang and Y. W. Tang, Design of oxygen-deficient NiMoO4 nanoflake and nanorod arrays with enhanced supercapacitive performance, Chem. Eng. J., 2018, 354, 182–190 CrossRef CAS .
  31. Q. Y. Ma, X. T. Li, G. Y. Li and Z. C. Shao, Synthesis and electrochemical properties of cubic-like ZnMoO4 anode materials, J. Mater. Sci., 2020, 55, 13905–13915 CrossRef CAS .
  32. N. Venugopal, W. S. Kim and K. Y. Sohn, Room-temperature synthesis of Co3O4 nanoparticles self-assembled into meso/nanoporous microstructures and their application, Korean J. Chem. Eng., 2019, 36, 1536–1542 CrossRef CAS .
  33. Z. Y. Li, M. S. Akhtar, P. T. M. Bui and O. B. Yang, Predominance of two dimensional (2D) Mn2O3 nanowalls thin film for high performance electrochemical supercapacitors, Chem. Eng. J., 2017, 330, 1240–1247 CrossRef CAS .
  34. B. Saravanakumar, T. Priyadharshini, G. Ravi, V. Ganesh, A. Sakunthala and R. Yuvakkumar, Hydrothermal synthesis of spherical NiCO2O4 nanoparticles as a positive electrode for pseudocapacitor applications, J. Sol–Gel Sci. Technol., 2017, 84, 297–305 CrossRef CAS .
  35. H. W. Wang, Z. A. Hu, Y. Q. Chang, Y. L. Chen, H. Y. Wu, Z. Y. Zhang and Y. Y. Yang, Design and synthesis of NiCo2O4-reduced graphene oxide composites for high performance supercapacitors, J. Mater. Chem., 2011, 21, 10504–10511 RSC .
  36. A. Krittayavathananon, T. Pettong, P. Kidkhunthod and M. Sawangphruk, Insight into the charge storage mechanism and capacity retention fading of MnCo2O4 used as supercapacitor electrodes, Electrochim. Acta, 2017, 258, 1008–1015 CrossRef CAS .
  37. B. Q. Guan, W. W. Sun and Y. Wang, Carbon-Coated MnMoO4 Nanorod for High-Performance Lithium-Ion Batteries, Electrochim. Acta, 2016, 190, 354–359 CrossRef CAS .
  38. H. X. Wei, J. Yang, Y. F. Zhang, Y. Qian and H. B. Geng, Rational synthesis of graphene-encapsulated uniform MnMoO4 hollow spheres as long-life and high-rate anodes for lithium-ion batteries, J. Colloid Interface Sci., 2018, 524, 256–262 CrossRef CAS PubMed .
  39. D. F. Cui, Y. F. Li, Y. K. Li, Y. Y. Fan, H. M. Chen, H. Y. Xu and C. Y. Xue, Co3O4@MnMoO4 Nanorod Clusters as an Electrode Material for Superior Supercapacitors, Int. J. Electrochem. Sci., 2020, 15, 2776–2791 CrossRef CAS .
  40. Y. P. Liu, Y. J. Luo, Q. Q. Li, J. Wang and K. Chu, Bimetallic MnMoO4 with dual-active-centers for highly efficient electrochemical N2 fixation, Chem. Commun., 2020, 56, 10227–10230 RSC .
  41. M. Isacfranklin, B. J. Rani, G. Ravi, R. Yuvakkumar, S. I. Hong, D. Velauthapillai and B. Saravanakumar, Hydrothermal Method-Derived MnMoO4 Crystals: Effect of Cationic Surfactant on Microstructures and Electrochemical Properties, ChemistrySelect, 2020, 5, 7728–7733 CrossRef CAS .
  42. A. Clearfield, A. Moini and P. R. Rudolf, Preparation and Structure of Manganese Molybdates, Inorg. Chem., 1985, 24, 4606–4609 CrossRef CAS .
  43. T. Watcharatharapong, M. M. Sundaram, S. Chakraborty, D. Li, G. Shafiullah, R. D. Aughterson and R. Ahuja, Effect of transition metal cations on stability enhancement for molybdate based hybrid supercapacitor, ACS Appl. Mater. Interfaces, 2017, 9, 17977–17991 CrossRef CAS PubMed .
  44. K. K. Purushothaman, M. Cuba and G. Muralidharan, Supercapacitor behavior of α-MnMoO4 nanorods on different electrolytes, Mater. Res. Bull., 2012, 47, 3348–3351 CrossRef CAS .
  45. L. Zhang, H. P. Yang, A. S. Feng and X. M. Tan, Study on General Situation and Analysis of Supply and Demand of Global Molybdenum Resource, Multipurp. Util. Miner. Resour., 2019, 3, 11–16 Search PubMed .
  46. S. J. Lei, K. B. Tang, Q. C. Liu, Z. Fang, Q. Yang and H. G. Zheng, Preparation of manganese molybdate rods and hollow olive-like Spheres, J. Mater. Sci., 2006, 41, 4737–4743 CrossRef CAS .
  47. S. C. Abrahams and J. M. Reddy, Crystal Structure of the Transition-Metal Molybdates. I. Paramagnetic Alpha-MnMoO4, J. Chem. Phys., 1965, 43, 2533–2543 CrossRef CAS .
  48. A. W. Sleight and B. L. Chamberland, Transition Metal Molybdates of the Type AMoO4, Inorg. Chem., 1968, 7, 1672–1675 CrossRef CAS .
  49. M. Jang, T. J. R. Weakley and K. M. Doxsee, Aqueous Crystallization of Manganese(II) Group 6 Metal Oxides, Chem. Mater., 2001, 13, 519–525 CrossRef CAS .
  50. G. M. Martins, P. O. Coelho, K. P. F. Siqueira, R. L. Moreira and A. Dias, Investigation of Polymorphism and Vibrational Properties of MnMoO4 Microcrystals Prepared by Hydrothermal Process, Cryst. Growth Des., 2018, 18, 2474–2485 CrossRef CAS .
  51. M. M. Selim and M. K. El-Aiashy, Solid-solid interaction between manganese carbonate and molybdic acid and the stability of the formed thermal products, ACS Appl. Mater. Lett., 1994, 21, 265–270 CAS .
  52. M. Kassem, Reactivity in the Solid State Between Cobalt and Aluminum Molybdate, ACS Appl. J. Phase Equilib. Diffus., 2010, 31, 433–438 CrossRef CAS .
  53. M. B. Rammal and S. Omanovic, Synthesis and characterization of NiO, MoO3, and NiMoO4 nanostructures through a green, facile method and their potential use as electrocatalysts for water splitting, Mater. Chem. Phys., 2020, 255, 123570 CrossRef CAS .
  54. J. V. Kumar, R. Karthik, S. M. Chen, K. H. Chen, S. Sakthinathan, V. Muthuraj and T. W. Chiu, Design of Novel 3D Flower-like Neodymium Molybdate; An Efficient and Challenging Catalyst for Sensing and Destroying Pulmonary Toxicity Antibiotic Drug Nitrofurantoin, Chem. Eng. J., 2018, 346, 11–23 CrossRef .
  55. V. Umapathy, P. Neeraja, A. Manikandan and P. Ramu, Synthesis of NiMoO4 nanoparticles by sol–gel method and their structural, morphological, optical, magnetic and photocatlytic properties, Trans. Nonferrous Met. Soc. China, 2017, 27, 1785–1793 CrossRef .
  56. V. Umapathy and P. Neeraja, Sol–Gel Synthesis and Characterizations of CoMoO4 Nanoparticles: An Efficient Photocatalytic Degradation of 4-Chlorophenol, J. Nanosci. Nanotechnol., 2016, 16, 2960–2966 CrossRef CAS PubMed .
  57. G. Kianpour, F. Soofivand, M. Badiei, M. Salavati-Niasari and M. Hamadanian, Facile synthesis and characterization of nickel molybdate nanorods as an effective photocatalyst by co-precipitation method, J. Mater. Sci.: Mater. Electron., 2016, 27, 10244–10251 CrossRef CAS .
  58. S. Khademolhoseini and M. Goudarzi, Controllable synthesis of cadmium molybdate nanostructures with different morphologies by novel approach, J. Mater. Sci.: Mater. Electron., 2016, 27, 11593–11598 CrossRef CAS .
  59. W. C. Tan and J. F. Luan, Investigation into the synthesis conditions of CuMoO4 by an in situ method and its photocatalytic properties under visible light irradiation, RSC Adv., 2020, 10, 9745–9759 RSC .
  60. X. Yang, E. S. Han, Y. Z. He, J. B. Liu, Y. H. Tian, C. Y. Du, S. P. Qiao and L. Gao, Influence of template agent on NiMoO4 for high-performance hybrid energy storage devices, Ionics, 2020, 27, 875–887 CrossRef .
  61. M. Kumar, R. Singh, H. Khajuria and H. N. Sheikh, Facile hydrothermal synthesis of nanocomposites of nitrogen doped graphene with metal molybdates (NG-MMoO4) (M = Mn, Co, and Ni) for enhanced photodegradation of methylene blue, J. Mater. Sci.: Mater. Electron., 2017, 28, 9423–9434 CrossRef CAS .
  62. M. Shkir, Z. R. Khan, M. S. Hamdy, H. Algarni and S. AlFaify, A facile microwave-assisted synthesis of PbMoO4 nanoparticles and their key characteristics analysis: a good contender for photocatalytic applications, Mater. Res. Express, 2018, 5, 095032 CrossRef .
  63. G. Harichandran, S. Radha, P. Divya and J. Yesuraj, Facile morphology-controlled synthesis of nanostructured MnMoO4 nanorods as an advance electrode material for supercapacitor application, J. Mater. Sci.: Mater. Electron., 2020, 31, 1646–1653 CrossRef CAS .
  64. K. Namratha and K. Byrappa, Hydrothermal processing and in situ surface modification of metal oxide Nanomaterials, J. Supercrit. Fluids, 2013, 79, 251–260 CrossRef CAS .
  65. K. Byrappa, Novel hydrothermal solution routes of advanced high melting nanomaterials processing, J. Ceram. Soc. Jpn., 2009, 117, 236–244 CrossRef CAS .
  66. K. Namratha and K. Byrappa, Novel solution routes of synthesis of metal oxide and hybrid metal oxide nanocrystals, Prog. Cryst. Growth Charact. Mater., 2012, 58, 14–42 CrossRef CAS .
  67. Y. W. Zhang, Y. F. Teng, Y. D. Li, X. M. Du, L. Y. Liu, Y. P. Wu, Y. N. Meng, Y. J. Hua, X. D. Zhao and X. Y. Liu, Microwave-assisted green synthesis of manganese molybdate nanorods for high-performance supercapacitor, Ionics, 2019, 25, 4361–4370 CrossRef CAS .
  68. S. H. Jhung, T. H. Jin, Y. K. Hwang and J. S. Chang, Microwave Effect in the Fast Synthesis of Microporous Materials: Which Stage Between Nucleation and Crystal Growth is Accelerated by Microwave Irradiation?, Chem. – Eur. J., 2007, 13, 4410–4417 CrossRef CAS PubMed .
  69. S. Jayasubramaniyan, S. Balasundari, P. A. Rayjada, N. Satyanarayana and P. Muralidharan, Microwave hydrothermal synthesis of α-MnMoO4 nanorods for high electrochemical performance supercapacitors, RSC Adv., 2018, 8, 22559–22568 RSC .
  70. C. Y. Zhu, H. W. Wang and C. Guan, Recent Progress on Hollow Array Architectures and Their Applications in Electrochemical Energy Storage, Nanoscale Horiz., 2020, 5, 1188–1199 RSC .
  71. Y. Sun, C. S. Li, Y. Z. Wang, L. N. Wang, X. G. Ma, Z. J. Zhang and P. J. Ma, CN102502846A, 2012.06.20.
  72. Y. Sun, C. S. Li, Y. Z. Wang, L. N. Wang, X. G. Ma, Z. J. Zhang and P. J. Ma, CN102502847A, 2012.06.20.
  73. Y. Sun, C. S. Li, Z. Zhu, Z. W. Mao, G. S. Yin, C. Yang, D. D. Wang, K. Y. Zeng and J. Q. Chen, CN112875756A, 2021.06.01.
  74. Y. Sun, C. S. Li, Z. W. Mao, Z. Zhu, G. S. Yin, C. Yang, D. D. Wang, K. Y. Zeng and J. Q. Chen, CN112875757A, 2021.06.01.
  75. P. D. Kichambare and R. B. Kharat, Photoelectrochemical studies of MnMoO4 electrodes, Sol. Energy Mater., 1991, 22, 63–68 CrossRef CAS .
  76. F. Nti, D. A. Anang and J. I. Han, Facile room temperature synthesis and application of MnMoO4·0.9H2O as supercapacitor electrode material, Mater. Lett., 2018, 217, 146–150 CrossRef CAS .
  77. S. B. Patil, B. Kishore, M. K. Nagaraj, N. Ganganagappa and U. Velu, Mesoporous MnMoO4 Nanorods for Enhanced Electrochemical Performance, ChemistrySelect, 2018, 3, 7490–7495 CrossRef CAS .
  78. J. L. Xie, P. P. Yang, Y. Wang, T. Qi, Y. Lei and C. M. Li, Puzzles and confusions in supercapacitor and battery: theory and solutions, J. Power Sources, 2018, 401, 213–223 CrossRef CAS .
  79. C. Largeot, C. Portet, J. Chmiola, P. L. Taberna, Y. Gogotsi and P. Simon, Relation between the Ion Size and Pore Size for an Electric Double-Layer Capacitor, J. Am. Chem. Soc., 2008, 130, 2730–2731 CrossRef CAS PubMed .
  80. S. G. Kandalkar, D. S. Dhawale, C. K. Kim and C. D. Lokhande, Chemical synthesis of cobalt oxide thin film electrode for supercapacitor application, Synth. Met., 2010, 160, 1299–1302 CrossRef CAS .
  81. B. Saravanakumar, S. P. Ramachandran, G. Ravi, V. Ganesh, A. Sakunthala and R. Yuvakkumar, Transition mixed−metal molybdates (MnMoO4) as an electrode for energy storage applications, Appl. Phys. A: Mater. Sci. Process., 2019, 125, 6 CrossRef .
  82. J. Libich, J. Máca, J. Vondrák, O. Čech and M. Sedlaříková, Supercapacitors: properties and applications, J Energy Storage, 2018, 17, 224–227 CrossRef .
  83. J. Haetge, I. Djerdj and T. Brezesinski, Nanocrystalline NiMoO4 with an ordered mesoporous morphology as potential material for rechargeable thin film lithium batteries, Chem. Commun., 2012, 48, 6726–6728 RSC .
  84. Y. Ko, C. H. Kwon, S. W. Lee and J. H. Cho, Nanoparticle-Based Electrodes with High Charge Transfer Efficiency through Ligand Exchange Layer-by-Layer Assembly, Adv. Mater., 2020, 32, 2001924 CrossRef CAS PubMed .
  85. J. Y. Wang, J. W. Wan, N. L. Yang, Q. Li and D. Wang, Hollow multishell structures exercise temporal-spatial ordering and dynamic smart behaviour, Nat. Rev. Chem., 2020, 4, 159–168 CrossRef .
  86. J. Y. Wang, H. J. Tang, H. Wang, R. B. Yu and D. Wang, Multi-shelled hollow micro-/nanostructures: promising platforms for lithium-ion batteries, Mater. Chem. Front, 2017, 1, 414–430 RSC .
  87. Y. Y. Liu, Y. Y. Zhu and Y. Cui, Challenges and opportunities towards fast-charging battery materials, Nat. Energy, 2019, 4, 540–550 CrossRef .
  88. Y. M. Sun, N. Liu and Y. Cui, Promises and challenges of nanomaterials for lithium-based rechargeable batteries, Nat. Energy, 2016, 1, 16071 CrossRef CAS .
  89. D. C. Lin, Y. Y. Liu and Y. Cui, Reviving the lithium metal anode for high-energy batteries, Nat. Nanotechnol., 2017, 12, 194–206 CrossRef CAS PubMed .
  90. J. Y. Wang, J. W. Wan and D. Wang, Hollow Multishelled Structures for Promising Applications: Understanding the Structure-Performance Correlation, Acc. Chem. Res., 2019, 52, 2169–2178 CrossRef CAS PubMed .
  91. X. Huang, J. Y. Tang, B. Luo, R. Knibbe, T. E. Lin, H. Hu, M. Rana, Y. X. Hu, X. B. Zhu, Q. F. Gu, D. Wang and L. Z. Wang, Sandwich-Like Ultrathin TiS2 Nanosheets Confined within N, S Codoped Porous Carbon as an Effective Polysulfide Promoter in Lithium–Sulfur Batteries, Adv. Energy Mater., 2019, 9, 1901872 CrossRef .
  92. B. Senthilkumar, R. K. Selvan, D. Meyrick and M. Minakshi, Synthesis and Characterization of Manganese Molybdate for Symmetric Capacitor Applications, Int. J. Electrochem. Sci., 2015, 10, 185–193 Search PubMed .
  93. S. M. Babulal, K. Venkatesh, T. W. Chen, S. M. Chen, A. Krishnapandi, S. P. Rwei and S. K. Ramaraj, Synthesis of MnMoO4 Nanorods by a Simple Co-Precipitation Method in Presence of Polyethylene Glycol for Pseudocapacitor Application, Int. J. Electrochem. Sci., 2020, 15, 7053–7063 CrossRef CAS .
  94. S. B. Ni, J. L. Liu, D. L. Chao and L. Q. Mai, Vanadate-Based Materials for Li-Ion Batteries: The Search for Anodes for Practical Applications, Adv. Energy Mater, 2019, 9, 1803324 CrossRef .
  95. C. R. Zhu, P. H. Yang, D. L. Chao, W. J. Mai and H. J. Fan, Heterogeneous Nanostructures for Sodium Ion Batteries and Supercapacitors, ChemNanoMat, 2015, 1, 458–476 CrossRef CAS .
  96. C. W. Shi, K. A. Owusu, X. M. Xu, T. Zhu, G. B. Zhang, W. Yang and L. Q. Mai, 1D Carbon-Based Nanocomposites for Electrochemical Energy Storage, Small, 2019, 15, 1902348 CrossRef CAS PubMed .
  97. Q. L. Wei, F. Y. Xiong, S. S. Tan, L. Huang, E. H. Lan, B. Dunn and L. Q. Mai, Porous One-Dimensional Nanomaterials: Design, Fabrication and Applications in Electrochemical Energy Storage, Adv. Mater., 2017, 29, 1602300 CrossRef PubMed .
  98. L. Q. Mai, F. Yang, Y. L. Zhao, X. Xu, L. Xu and Y. Z. Luo, Hierarchical MnMoO4/CoMoO4 heterostructured nanowires with enhanced supercapacitor performance, Nat. Commun., 2011, 2, 381 CrossRef PubMed .
  99. X. D. Yan, L. H. Tian, J. Murowchick and X. B. Chen, Partially amorphized MnMoO4 for highly efficient energy storage and hydrogen evolution reaction, J. Mater. Chem. A, 2016, 4, 3683–3688 RSC .
  100. H. L. Cao, N. N. Wu, Y. Z. Liu, S. Y. Wang, W. J. Du and J. R. Liu, Facile synthesis of rod-like manganese molybdate crystallines with two-dimensional nanoflakes for supercapacitor application, Electrochim. Acta, 2017, 225, 605–613 CrossRef CAS .
  101. X. M. Mu, Y. X. Zhang, H. Wang, B. Y. Huang, P. B. Sun, T. Chen, J. Y. Zhou, E. Q. Xie and Z. X. Zhang, A high energy density asymmetric supercapacitor from ultrathin manganese molybdate nanosheets, Electrochim. Acta, 2016, 211, 217–224 CrossRef CAS .
  102. Y. L. Chen, Z. A. Hu and H. Y. Wu, Zinc Oxide/Reduced Graphene Oxide Composites and Electrochemical Capacitance Enhanced by Homogeneous Incorporation of Reduced Graphene Oxide Sheets in Zinc Oxide Matrix, J. Phys. Chem. C, 2011, 115, 2563–2571 CrossRef CAS .
  103. X. S. Feng, Y. Huang, M. H. Chen, X. F. Chen, C. Li, S. H. Zhou and X. G. Gao, Self-assembly of 3D hierarchical MnMoO4/NiWO4 microspheres for high-performance supercapacitor, J. Alloys Compd., 2018, 763, 801–807 CrossRef CAS .
  104. Z. X. Gu and X. J. Zhang, NiCo2O4@MnMoO4 Core-shell Flower for High Performance Supercapacitors, J. Mater. Chem. A, 2016, 4, 8249–8254 RSC .
  105. Y. J. Cao, W. Y. Li, K. B. Xu, Y. X. Zhang, T. Ji, R. J. Zou, J. M. Yang, Z. Y. Qin and J. Q. Hu, MnMoO4·4H2O Nanoplates Grown on a Ni Foam Substrate for Excellent Electrochemical Properties, J. Mater. Chem. A, 2014, 2, 20723–20728 RSC .
  106. Q. Q. Ke and J. Wang, Graphene-based materials for supercapacitor electrodes − A review, J Materiomics, 2016, 2, 37–54 CrossRef .
  107. S. Dutta, A. Bhaumik and K. C. W. Wu, Hierarchically Porous Carbon Derived from Polymers and Biomass: Effect of Interconnected Pores on Energy Applications, Energy Environ. Sci., 2014, 7, 3574–3592 RSC .
  108. A. L. M. Reddy, S. R. Gowda, M. M. Shaijumon and P. M. Ajayan, Hybrid Nanostructures for Energy Storage Applications, Adv. Mater., 2012, 24, 5045–5064 CrossRef CAS PubMed .
  109. S. Kumar, G. Saeed, L. Zhu, K. N. Hui, N. H. Kim and J. H. Lee, 0D to 3D carbon-based networks combined with pseudocapacitive electrode material for high energy density supercapacitor: A Review, Chem. Eng. J., 2021, 403, 126352 CrossRef CAS .
  110. L. L. Jiang, L. Z. Sheng and Z. J. Fan, Bimass-derived carbon materials with structural diversities and their applications in energy storage, Sci. China Mater, 2018, 61, 133–158 CrossRef CAS .
  111. Z. F. Mao, H. W. Wang, D. L. Chao, R. Wang, B. B. He, Y. S. Gong and H. J. Fan, Al2O3-Assisted Confinement Synthesis of Oxide/Carbon Hollow Composite Nanofibers and Application in Metal-Ion Capacitors, Small, 2020, 16, 2001950 CrossRef CAS PubMed .
  112. L. Q. Wang, L. F. Yue, X. Zang, H. Z. Zhu, X. P. Hao, Z. Leng, X. L. Liu and S. G. Chen, Synthesis of 3D α-MnMoO4 Hierarchical Architectures for High-Performance Supercapacitor Applications, CrystEngComm, 2013, 18, 9286–9291 RSC .
  113. Z. H. Xu, S. S. Sun, Y. Han, Z. P. Wei, Y. H. Cheng, S. G. Yin and W. Cui, High energy density asymmetric supercapacitor based on durable and stable manganese molybdate nanostructures electrode for energy storage system, ACS Appl. Energy Mater., 2020, 3, 5393–5404 CrossRef CAS .
  114. J. Y. Wang, Y. Cui and D. Wang, Design of Hollow Nanostructures for Energy Storage, Conversion and Production, Adv. Mater., 2018, 31, 1801993 CrossRef PubMed .
  115. X. J. Wei, Y. H. Li, H. R. Peng, C. L. Liu, Y. H. Zhang and P. Xiao, Core-shell NiCo2S4@MnMoO4 as an Advanced Electrode Material for High-performance Electrochemical Energy Storage, ChemElectroChem, 2017, 4, 2634–2642 CrossRef CAS .
  116. Y. L. Yuan, W. C. Wang, J. Yang, H. C. Tang, Z. Z. Ye, Y. J. Zeng and J. G. Lu, Three-dimensional NiCo2O4@MnMoO4 core-shell nanoarrays for high-performance asymmetric supercapacitors, Langmuir, 2017, 33, 10446–10454 CrossRef CAS PubMed .
  117. Y. M. Lv, A. F. Liu, H. W. Che, J. B. Mu, Z. C. Guo, X. L. Zhang, Y. M. Bai, Z. X. Zhang, G. S. Wang and Z. Z. Pei, Three-dimensional interconnected MnCo2O4 nanosheets@MnMoO4 nanosheets core-shell nanoarrays on Ni foam for high-performance supercapacitors, Chem. Eng. J., 2018, 336, 64–73 CrossRef CAS .
  118. A. Singh and A. K. Ojha, Designing Vertically Aligned Porous NiCo2O4@MnMoO4 Core@Shell Nanostructures for High-performance Asymmetric Supercapacitors, J. Colloid Interface Sci., 2020, 580, 720–729 CrossRef CAS PubMed .
  119. H. S. Li, H. C. Xuan, J. H. Gao, T. Liang, X. K. Han, Y. Y. Guan, J. Yang, P. D. Han and Y. W. Du, Construction of core-shell cobalt sulfide/manganese molybdate nanostructure on reduced graphene oxide/Ni foam as an advanced electrode for high-performance asymmetric supercapacitor, Electrochim. Acta, 2019, 312, 213–223 CrossRef CAS .
  120. R. Thangappana, R. D. Kumarb and R. Jayavelc, Synthesis, structural and electrochemical properties of Mn-MoO4/graphene nanocomposite electrode material with improved performance for supercapacitor application, J Energy Storage, 2020, 27, 101069 CrossRef .
  121. X. M. Mu, J. W. Du, Y. X. Zhang, Z. L. Liang, H. Wang, B. Y. Huang, J. Y. Zhou, X. J. Pan, Z. X. Zhang and E. Q. Xie, Construction of hierarchical CNT/rGO supported MnMoO4 nanosheets on Ni foam for high performance aqueous hybrid supercapacitors, ACS Appl. Mater. Interfaces, 2017, 9, 35775–35784 CrossRef CAS PubMed .
  122. D. Ghosh, S. Giri, M. Moniruzzaman, T. Basu, M. Mandala and C. K. Das, α MnMoO4/graphene hybrid composite: high energy density supercapacitor electrode material, Dalton Trans., 2014, 43, 11067–11076 RSC .
  123. H. Wang, Y. H. Song, J. K. Zhou, X. Y. Xu, W. Hong, J. Yan, R. N. Xue, H. L. Zhao, Y. Liu and J. P. Gao, High-performance supercapacitor materials based on polypyrrole composites embedded with core-sheath polypyrrole@MnMoO4 nanorods, Electrochim. Acta, 2016, 212, 775–783 CrossRef CAS .
  124. J. Yesuraj, V. Elumalai, B. Muthuraaman, S. A. Suthanthiraraj, E. Elanthamilan and J. P. Merlin, A facile sonochemical assisted synthesis of α-MnMoO4/PANI nanocomposite electrode for supercapacitor applications, J. Electroanal. Chem., 2017, 797, 78–88 CrossRef .
  125. Y. G. Wang, Y. F. Song and Y. Y. Xia, Electrochemical capacitors: mechanism, materials, systems, characterization and applications, Chem. Soc. Rev., 2016, 45, 5925–5950 RSC .
  126. F. X. Wang, X. W. Wu, X. H. Yuan, Z. C. Liu, Y. Zhang, L. J. Fu, Y. S. Zhu, Q. M. Zhou, Y. P. Wu and W. Huang, Latest advances in supercapacitors: from new electrode materials to novel device designs, Chem. Soc. Rev., 2017, 46, 6816–6854 RSC .
  127. W. Raza, F. Ali, N. Raza, Y. W. Luo, E. E. Kwon, J. H. Yang, S. Kumar, A. Mehmood and K. H. Kim, Recent advancements in supercapacitor technology, Nano Energy, 2018, 52, 441–473 CrossRef CAS .
  128. J. Bhagwan, S. K. Hussain, B. N. V. Krishna and J. S. Yu, Facile synthesis of MnMoO4@MWCNT and their electrochemical performance in aqueous asymmetric supercapacitor, J. Alloys Compd., 2021, 856, 157874 CrossRef CAS .
  129. O. Rabbani, S. Ghasemi and S. R. Hosseini, Sonochemical Assisted Synthesis of Manganese-Nickel Molybdate/Reduced Graphene Oxide Nanohybrid for Energy Storage, J. Alloys Compd., 2020, 840, 155665 CrossRef CAS .
  130. G. H. Yu, L. B. Hu, M. Vosgueritchian, H. L. Wang, X. Xie, J. R. McDonough, X. Cui, Y. Cui and Z. N. Bao, Solution-Processed Graphene/MnO2 Nanostructured Textiles for High-Performance Electrochemical Capacitors, Nano Lett., 2011, 11, 2905–2911 CrossRef CAS PubMed .
  131. Z. N. Yu, B. Duong, D. Abbitt and J. Thomas, Highly ordered MnO2 nanopillars for enhanced supercapacitor performance, Adv. Mater., 2013, 25, 3302–3306 CrossRef CAS PubMed .
  132. C. V. Krishnan, M. Garnett, B. Hsiao and B. Chu, Electrochemical Measurements of Isopolyoxomolybdates:1. pH Dependent Behavior of Sodium Molybdate, Int. J. Electrochem. Sci., 2007, 2, 29–51 CAS .
  133. V. K. Elmes and N. J. Coleman, Interactions of Cd2+, Co2+ and MoO42− Ions with Crushed Concrete Fines, J. Compos. Sci., 2021, 5, 42–57 CrossRef CAS .
  134. A. Y. Neiman, Cooperative transport in oxides: diffusion and migration processes involving Mo(VI), W(VI), V(V) and Nb(V), Solid State Ionics, 1996, 83, 263–273 CrossRef CAS .
  135. L. I. Liu, Y. Yang, Z. H. Yang and S. L. Pan, The enhancement of Birefringence Resulted from Anionic Dimensionality Changes through Adjusting Cationic Density, J. Alloys Compd., 2017, 717, 317–325 CrossRef CAS .
  136. Y. B. Xie and Y. C. Zhang, Electrochemical performance of carbon paper supercapacitor using sodium molybdate gel polymer electrolyte and nickel molybdate electrode, J. Solid State Electrochem., 2019, 23, 1911–1927 CrossRef CAS .
  137. G. K. Veerasubramani, K. Krishnamoorthy, P. Pazhamalai and S. J. Kim, Enhanced electrochemical performances of graphene based solid-state flexible cable type supercapacitor using redox mediated polymer gel electrolyte, Carbon, 2016, 105, 638–648 CrossRef CAS .
  138. E. Cevik, A. Bozkurt, M. Hassan, M. A. Gondal and T. F. Qahtan, Redox-Mediated Poly(2-acrylamido-2-methyl-1-propanesulfonic acid)/Ammonium Molybdate Hydrogels for Highly Effective Flexible Supercapacitors, ChemElectroChem, 2019, 6, 2876–2882 CrossRef CAS .
  139. K. Nasrin, S. Gokulnath, M. Karnan, K. Subramani and M. Sathish, Redox-Additives in Aqueous, Non-Aqueous, and All-Solid-State Electrolytes for Carbon-Based Supercapacitor: A Mini-Review, Energy Fuels, 2021, 35, 6465–6482 CrossRef CAS .
  140. J. Tan, D. N. Liu, X. Xu and L. Q. Mai, In situ/operando characterization techniques for rechargeable lithium–sulfur batteries: a review, Nanoscale, 2017, 9, 19001–19016 RSC .
  141. P. P. R. M. L. Harks, F. M. Mulder and P. H. L. Notten, In situ methods for Li-ion battery research: a review of recent developments, J. Power Sources, 2015, 288, 92–105 CrossRef CAS .
  142. Y. Y. Yan, C. Cheng, L. Zhang, Y. G. Li and J. Lu, Deciphering the Reaction Mechanism of Lithium–Sulfur Batteries by In Situ/Operando Synchrotron-Based Characterization Techniques, Adv. Energy Mater., 2019, 9, 1900148 CrossRef .
  143. X. J. Wei, X. P. Wang, X. Tan, Q. Y. An and L. Q. Mai, Nanostructured Conversion-Type Negative Electrode Materials for Low-Cost and High-Performance Sodium-Ion Batteries, Adv. Funct. Mater., 2018, 28, 1804458 CrossRef .
  144. X. R. Liu, D. Wang and L. J. Wan, Progress of electrode/electrolyte interfacial investigation of Li-ion batteries via in situ scanning probe microscopy, Sci. Bull., 2015, 60, 839–849 CrossRef CAS .
  145. S. Ramdon, B. Bhushan and S. C. Nagpure, In situ electrochemical studies of lithium-ion battery cathodes using atomic force microscopy, J. Power Sources, 2014, 249, 373–384 CrossRef CAS .
  146. D. L. Chao, C. H. Lai, P. Liang, Q. L. Wei, Y. S. Wang, C. R. Zhu, G. Deng, V. V. T. Doan-Nguyen, J. Y. Lin, L. Q. Mai, H. J. Fan, B. Dunn and Z. X. Shen, Sodium Vanadium Fluorophosphates (NVOPF) Array Cathode Designed for High-Rate Full Sodium Ion Storage Device, Adv. Energy Mater., 2018, 8, 1800058 CrossRef .
  147. M. P. Jiang, K. K. Huang, J. H. Liu, D. Wang, Y. Wang, X. Wang, Z. D. Li, X. Y. Wang, Z. B. Geng, X. Y. Hou and S. H. Feng, Magnetic-Field-Regulated TiO2 {100} Facets: A Strategy for C–C Coupling in CO2 Photocatalytic Conversion, Chem, 2020, 6, 2335–2346 CAS .
  148. Z. J. Xie, L. Y. Liu, Y. X. Li, D. Y. Yu, L. H. Wei, L. Y. Han, Y. J. Hua, C. T. Wang, X. D. Zhao and X. Y. Liu, Synthesis of core-shell structured Ni3S2@MnMoO4 nanosheet arrays on Ni foam for asymmetric supercapacitors with superior performance, J. Alloys Compd., 2021, 874, 159860 CrossRef CAS .
  149. J. S. Xu, Y. D. Sun, M. J. Lu, L. Wang, J. Zhang, J. H. Qian and X. Y. Liu, Fabrication of hierarchical MnMoO4·H2O@MnO2 core-shell nanosheet arrays on nickel foam as an advanced electrode for asymmetric supercapacitors, Chem. Eng. J., 2018, 334, 1466–1476 CrossRef CAS .
  150. C. Y. Cui, J. T. Xu, L. Wang, D. Guo, M. L. Mao, J. M. Ma and T. H. Wang, Growth of NiCo2O4@MnMoO4 Nanocolumn Arrays with Superior Pseudocapacitor Properties, ACS Appl. Mater. Interfaces, 2016, 8, 8568–8575 CrossRef CAS PubMed .
  151. S. M. Chen, S. Q. Cui, S. Chandrasekaran, C. Ke, Z. F. Li, P. H. Chen, C. H. Zhang and Y. D. Jiang, Growth of CuCo2O4@MnMoO4 core/shell nanosheet arrays for high energy density asymmetric supercapacitors, Electrochim. Acta, 2020, 341, 135893 CrossRef CAS .
  152. Y. Chen, Y. F. Li, Z. Y. Hai, Y. K. Li, S. H. Kan, J. M. Chen, X. Chen, S. Zhuiykov, D. F. Cui and C. Y. Xue, Facile-synthesized NiCo2O4@MnMoO4 with novel and functional structure for superior performance supercapacitors, Appl. Surf. Sci., 2018, 452, 413–422 CrossRef CAS .
  153. M. R. Pallavolu, A. N. Banerjee, R. R. Nallapureddy and S. W. Joo, Urea-assisted hydrothermal synthesis of MnMoO4/MnCO3 hybrid electrochemical electrode and fabrication of high-performance asymmetric supercapacitor, J. Mater. Sci. Technol., 2022, 96, 332–344 CrossRef .
  154. R. Sheng, J. D. Hu, X. Y. Lu, W. Jia, J. Xie and Y. L. Cao, Solid-state synthesis and superior electrochemical performance of MnMoO4 nanorods for asymmetric supercapacitor, Ceram. Int., 2021, 47, 16316–16323 CrossRef CAS .
  155. G. K. Veerasubramani, K. Krishnamoorthy, R. Sivaprakasam and S. J. Kim, Sonochemical synthesis, characterization, and electrochemical properties of MnMoO4 nanorods for supercapacitor applications, Mater. Chem. Phys., 2014, 147, 836–842 CrossRef CAS .
  156. J. W. Huang, X. R. Qian, X. H. An, X. Li and J. Guan, Double in situ fabrication of PPy@MnMoO4/cellulose fibers flexible electrodes with high electrochemical performance for supercapacitor applications, Cellulose, 2020, 27, 5829–5843 CrossRef CAS .
  157. L. Gao, G. H. Chen, L. L. Zhang, B. Yan and X. L. Yang, Engineering pseudocapacitive MnMoO4@C microrods for high energy sodium ion hybrid capacitors, Electrochim. Acta, 2021, 379, 138185 CrossRef CAS .

Footnote

† Z. Zhu and C. Yang contributed equally to this work.
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