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DOI: 10.1039/D5CP01911G (Paper) Phys. Chem. Chem. Phys., 2025, Advance Article

Efficient capture and conversion of H2S into H2 and sulfur in guanidinium ionic liquid–NaOH aqueous solution

Qianqian Peng† ab, Chengxuan Zhou†a, Shucan Qinab, Jinbiao Liangb, Shengyun Xuab, Jiaming Maobd, Jianming Shic, Yanrong Liu*bde and Yunqian Ma*abc
aCollege of Environmental Science and Engineering, Qilu University of Technology (Shandong Academy of Science), Jinan, 250353, PR China. E-mail: mayq@qlu.edu.cn
bLongzihu New Energy Laboratory, Zhengzhou Institute of Emerging Industrial Technology, Henan University, Zhengzhou, 450000, PR China
cMingshuo Environment Technology Group Co., Ltd, Weifang, 262605, PR China
dCAS Key Laboratory of Green Process and Engineering, State Key Laboratory of Mesoscience and Engineering, Beijing Key Laboratory of Ionic Liquids Clean Process, Institute of Process Engineering, Chinese Academy of Sciences, Beijing, 100190, PR China
eSchool of Chemical Engineering, University of Chinese Academy of Sciences, Beijing, 100049, PR China

Received 21st May 2025 , Accepted 1st August 2025

First published on 22nd August 2025

Abstract

Electrochemistry allows for the simultaneous conversion of hydrogen sulfide (H2S) to hydrogen (H2) and sulfur, achieving atomic economy, and is a sustainable and cost-effective method. At the same time, an electrolyte with high conductivity and H2S absorption that can effectively capture H2S in an electrochemical process is essential. An ionic liquid electrolyte system for the absorption and electrolysis of H2S was constructed using the guanidine salt ionic liquid with amine-based functional groups as the carrier electrolyte, water as the solvent, and NaOH as the H2S absorber. The prepared electrolyte ([TMG][IM]-AE-30) showed a strong absorption of H2S with an equilibrium solubility of 100.82 g L−1. Under constant potential electrolysis at 1.0 V vs. RHE, the maximum hydrogen production rate reaches 2919.97 μmol h−1 and the Faraday efficiency reaches 99%, and the anodic product is α-sulfur with a production of 0.881 g after electrolysis for 8 h; the current density and hydrogen production rate are still higher than those of the AE systems after three cycles. Overall, the system has good hydrogen sulfide absorption and electrolysis performances, and [TMG][IM] can effectively improve the H2S absorption and electrolysis efficiencies.

1. Introduction

Hydrogen sulfide (H2S), an extremely irritating, foul-smelling and toxic chemical, is present as an impurity in many kinds of important fuel gases, contributing to naturally occurring sulfur emissions in the atmosphere, leading to environmental pollution and life-threatening hazards.1,2 To treat H2S, the current industrial technology is mainly based on the Claus process primarily, in which H2S is catalytically converted to the element sulfur, but the hydrogen element in H2S is ultimately wasted as water.3–6 Due to thermodynamic limitations, H2S cannot be completely converted in the Claus process, therefore, additional purification processes, such as absorption by alkanolamine solutions7 and selective catalytic oxidation by metal oxides8 or activated carbons,9 are required to remove residual H2S from the Claus tail gas,10 also without stabilization of hydrogen components. The high calorific value hydrogen resource is a clean fuel and one of the most promising candidates as a sustainable green energy carrier.11–13 Therefore, cost-effective and sustainable methods for simultaneous conversion of H2S into H2 and sulfur with atomic economy are highly desirable.

Extensive research has been conducted over the years to obtain high conversion rates for H2S decomposition through pyrolysis,14,15 photolysis,16,17 electrolysis,18–22 plasma-assisted conversion,23–25 microwave-assisted reactions,26,27 superadiabatic combustion,28 biolysis,29,30 etc. Compared with the other H2S decomposition technologies, H2S electrolysis is more economically viable, which can recover H2 at the cathode and S at the anode, where the sulfion oxidation reaction (SOR: S2− → S + 2e−, E = −0.48 V vs. SHE) is more thermodynamically favorable than the oxygen evolution reaction (OER: 4OH− → O2 + 2H2O + 4e−, E = 0.40 V vs. SHE) for water splitting.31–33 Most researchers pay attention to the SOR using Na2S and NaOH as anolytes,34,35 while the pre-H2S absorption is ignored. Efficient capture of H2S using electrochemical technology is of great importance, due to the concentration of H2S and the form of the reactant, therefore, a kind of electrolyte with high electrical conductivity and high H2S absorption capacity that can switch between absorption and electrolysis is essential.

Ionic liquids (ILs), as a new medium, have shown unique advantages in the field of gas absorption and separation as well as electrochemistry.36–39 The interactions between ILs and H2S have been confirmed, and the performance of H2S absorption and separation can be enhanced through functionalized design.40–49 It has been reported that carboxylate-functionalized ILs,40 dual Lewis base (DLB)-functionalized ILs,46 and azole-derived protic ionic liquids (PILs)42 have high absorption capacities for H2S. ILs with 1,1,3,3-tetramethylguanidine and its derivatives as cations are called guanidinium ILs, and they all have an amine structure (–NH2), and the nitrogen atoms on the amine group possess a strong electronegativity and strong hydrogen bonding, which allow H2S to interact with them and enhance the absorption capacities. Currently, SO2 absorption has been studied by the guanidinium IL, whose amino group in the cation reacts with SO2 for desulfurization.50–52 Wu et al.51 have first used 1,1,3,3-tetramethylguanidine lactate ([TMG]L) for SO2 absorption, and the results showed that 1 mol of [TMG]L could absorb 0.978 mol of SO2 from a mixture of SO2 and N2 at ambient pressure and 40 °C, and the absorbed SO2 could then be reversibly desorbed in a vacuum or by heating. However, these guanidinium ILs are rarely used for H2S absorption. Huang et al.52 have prepared a series of phenolic ILs containing different cations and investigated H2S and CO2 adsorption performance, which showed that [TMGH][PHO] has high H2S solubility and high H2S/CO2 selectivity due to the strong basicity of its anion and the strong ability of its cation to contribute to hydrogen bonding. With a wide electrochemical window and high ionic conductivity, ILs have been used as electrolytes in many electrochemical processes.53 For H2S electrolysis, ILs have been reported as supporting electrolytes to organic electrolytes. These IL based organic electrolytes were composed of TGDE, MEA and [C3OHmim]BF4, and were proved to be dependent on the sulfur solubility at high temperature with absorption effects of MEA in the system, in favor of solving passivation problems.54 However, there is no report on the use of ionic liquids in aqueous electrolytes for H2S electrolysis or the SOR. Since specific functionalized ILs have good absorption capacities for H2S, they help promote the electrocatalytic H2S decomposition reaction and improve the yield of products at both the anode and cathode in IL based aqueous electrolytes. Therefore, the absorption and electrolysis can be further intensified by ILs for highly efficient capture and conversion of H2S, which is superior to the Claus process.

In this study, an ionic liquid–NaOH aqueous solution was used for the first time as both an absorbent and an electrolyte for efficient valorization of H2S in an electrochemical method. A series of guanidinium ILs (Fig. 1) were selected to design advanced desulfurization solutions. H2S absorption capacities by the desulfurization solutions were evaluated, and the electrochemical performances for H2S decomposition on a plain carbon cloth were tested, using the desulfurization solution saturated with H2S as the anode electrolyte, and the product rate and Faraday efficiency of sulfur and H2 were calculated. The anion species and the content of guanidinium ILs were optimized to regulate the absorption and electrolysis of H2S.


image file: d5cp01911g-f1.tif
Fig. 1 Chemical structures of a series of guanidinium ionic liquids.

2. Materials and methods

2.1. Materials

1,1,3,3-Tetramethylguanidine (C5H13N3, TMG), imidazole (C3H4N2, IM), 2,2,2-Trifluoroethanol (C2H3F3O, TE), pyrazole (C3H4N2, Pyr), 1,2,4-Triaz (C2H3N3), suberic acid (C8H14O4, SUB) and succinic acid (C4H6O4, SUC) were purchased from Adamas, and tetrafluoroboric acid (HBF4) was obtained from Aladdin. Sodium hydroxide (NaOH), sulfuric acid (H2SO4), and ethanol (CH3CH2OH) were purchased from Adamas. The H2S standard gas (1%, N2 as the carrier gas) was supplied by Henan Yuanzheng Special Gas Co., LTD.

2.2. Preparation of ILs

The ILs [TMG][IM], [TMG][SUC] and [TMG]BF4 were synthesized according to the established method described in the literature. [TMG][IM] was synthesized via direct neutralization of TMG and imidazole.50,55 Briefly, 11.52 g (0.10 mol) of TMG was placed in a 25 mL round bottom flask, and then an equal molar amount of imidazole was added and the mixture was stirred in a magnetic agitator at room temperature for 12 h, and finally [TMG][IM] was obtained. The synthetic method of [TMG][TE], [TMG][1,2,4-triaz] and [TMG][Pyr] is similar to that of [TMG][IM]. In order to synthesize [TMG][SUC],56 1,1,3,3-tetramethylguanidine (11.52 g, 0.10 mol) was weighed into a 100 mL round bottom flask and dissolved by adding 40 mL of absolute ethanol. Then, succinic acid (5.90 g, 0.05 mol) was added gradually under magnetic stirring, and the reaction was stopped after stirring for 24 h at room temperature. A white solid was obtained after the solvent was removed by rotary evaporation. Finally, the IL [TMG][SUC] was obtained by drying for 24 h under vacuum. The synthesis method of [TMG][SUB] is similar to that of [TMG][SUC]. To prepare [TMG]BF4,57 the concentrated 50% HBF4 (17.60 g, 0.10 mol) was slowly added to the stirred TMG (11.50 g, 0.10 mol) in ethanol solution (100 mL) while cooling in an ice bath. After continuous stirring (298 K, 24 h), the liquid was heated and dried at 343 K under reduced pressure (1 mbar), and finally the colorless and viscous ionic liquid was obtained.

2.3 H2S absorption experiments

The H2S absorbent, described as the IL based aqueous electrolyte or ionic liquid–NaOH aqueous solution, consisted of the synthesized guanidinium IL (from 10 wt% to 50 wt%) and sodium hydroxide aqueous solution (1.0 mol L−1), named as IL-AE-x (x = 10, 20, 30, 40, and 50). Moreover, the 30 mL of IL-AE was treated under ultrasound for 30 min before bubbling with H2S gas. After being saturated with H2S or ventilated with N2 for 30 min without H2S, the expended or pristine absorbents were used as the anolyte.

The H2S absorption capacity was tested by continuously bubbling H2S standard gas (1%, N2 as the carrier gas) at room temperature with a flow rate of 100 mL min−1 through a gas absorbent bottle containing IL-AE until H2S appeared in the outlet gas. The concentration of H2S was detected by a portable hydrogen sulfide gas analyzer (MIC600). The gas flowmeter (D08-1F) from Beijing Seven Star Flow Co., LTD was used to control the quantitative and constant flow rate of the H2S standard gas. The time that it takes for H2S to enter and eventually penetrate the electrolyte is called the breakthrough time. The removal efficiency of H2S is calculated using eqn (1).

 
image file: d5cp01911g-t1.tif(1)
where Cin and Cout represent the inlet concentration (mg m−3) and the outlet concentration of H2S, respectively.

2.4. Electrochemical experiment

In the H2S electrochemical decomposition experiment, a H-type cell and a three-electrode system were used in the electrochemical workstation (CHI660e), and the H-type cell is divided into a cathode chamber and an anode chamber, which were separated by a Nafion 117 proton exchange membrane. In this three-electrode system, a carbon cloth (1 × 1 cm2), Hg/HgO and a platinum sheet (1 × 1 × 0.02 cm3) were used as the working electrode, reference electrode and the counter electrode, respectively. 30 mL of IL-AE with saturated H2S and 30 mL of 0.5 mol L−1 H2SO4 solution were used as the anolyte and catholyte, respectively.21

Firstly, the electrolysis performance of H2S was evaluated by linear sweep voltammetry (LSV). Slow magnetic agitation was applied during the scanning process to make the anodic solution more uniform and stable. The anodic polarization curves were obtained at a scanning rate of 5 mV s−1 and at the scanning potential ranging from 0 V to 1 V (vs. RHE). The products were studied by constant potential electrolysis. During the electrochemical reaction, the gas product at the cathode was collected using gas collection bags, and the qualitative and quantitative analysis was carried out by gas chromatography (8860 GC system, Agilent). The solid products at the anode, obtained through acidification and filtration of the anode electrolyte IL-AE, were analyzed quantitatively and qualitatively.

The hydrogen production rate was calculated using eqn (2).

 
image file: d5cp01911g-t2.tif(2)
where image file: d5cp01911g-t3.tifrepresents the volume fraction of H2 in the tail gas at the nth hour in the process of electrolysis, which can be calculated using the calibration curves of the GC; R = 8.314 J (mol K)−1; P0 = 1.013 bar and T = 298.15 K; and the flow rate is the rate at which gas enters the system.

The Faraday Efficiency of the gas product H2 per hour image file: d5cp01911g-t4.tif was calculated using eqn (3).

 
image file: d5cp01911g-t5.tif(3)
where n is the nth hour of electrolysis, here n = 8; image file: d5cp01911g-t6.tif is the volume fraction of H2 in the tail gas at the nth hour of electrolysis; tn is the time at the nth hour of electrolysis, here t = 1 h; z is the number of electrons required to form one molecule of H2 (here, Z = 2); F is Faraday's constant, F = 96[thin space (1/6-em)]485 C mol−1; and Qn is the value of the Coulomb charge transferred at the nth hour of electrolysis.

3. Results and discussion

3.1. Screening of guanidinium ionic liquids in IL-AEs

3.1.1. H2S absorption capacities of IL-AEs. In order to compare the H2S absorption capacities of different ILs ([TMG][IM], [TMG][TE], [TMG][1,2,4-triaz], [TMG][Pyr], [TMG][SUC], [TMG][SUB] and [TMG]BF4), the H2S removal efficiency and equilibrium solubilities of IL-AEs were measured. Fig. 2(a) shows that the H2S removal efficiencies of [TMG][IM]-AE, [TMG][TE]-AE and [TMG][Pyr]-AE were significantly higher than those of the other four IL-AEs, and [TMG][Pyr]-AE had the highest H2S absorption capacity with a breakthrough time of more than 960 min. In Fig. 2(b), it is further shown that at normal temperature and pressure, the H2S equilibrium solubility of [TMG][Pyr]-AE reached the maximum (50 g L−1), and the H2S equilibrium solubility of [TMG][IM]-AE and [TMG][TE]-AE reached 45 g L−1 approximately. The equilibrium solubilities of the four alkaline IL-AEs were higher than that of the conventional electrolyte AE.
image file: d5cp01911g-f2.tif
Fig. 2 (a) H2S removal efficiency of IL-AE, and (b) H2S breakthrough time and equilibrium solubility of IL-AE.
3.1.2. Electrochemical performance of IL-AEs. Fig. 3(a) shows the linear LSV curves in different H2S-saturated electrolytes based on guanidinium ILs. It can be observed that the current density of the electrolytic H2S system regulated by guanidinium IL is significantly higher than that of the single sodium hydroxide electrolytic system, so the high conductivity of these ionic liquids can promote the H2S electrolytic reaction, and the current density of the electrolytic H2S system with [TMG][IM]-AE is the highest. The Tafel slopes are plotted and analyzed, as shown in Fig. 3(b). Among the IL regulated aqueous electrolytes, the Tafel slope of the anode in [TMG][IM]-AE, 138 mV dec−1, is the smallest one, indicating that [TMG][IM]-AE has favorable catalytic kinetics for the SOR. Fig. 3(c) summarizes the current densities at 0.7, 0.8, and 0.9 V for different ILs-AE. At 0.9 V, the current density of [TMG][IM]-AE can reach up to 97.31 mA cm−2 with the carbon cloth as the anode. Although the [TMG][Pyr]-AE system exhibits a strong alkaline advantage in the absorption stage, the unique conjugated planar structure of the imidazole anion endows the IL with high electrical conductivity and excellent charge transport capacity, promoting the improvement of ion migration and electron transfer efficiency during electrolysis. Consequently, [TMG][IM] was selected as the key ionic liquid to regulate the aqueous electrolyte.
image file: d5cp01911g-f3.tif
Fig. 3 (a) LSV curves of IL-AE, (b) Tafel slope for SOR of IL-AE, and (c) current densities of IL-AE and AE at 0.7 V, 0.8 V and 0.9 V for the SOR.

3.2. Screening of electrolytes with the [TMG][IM] content

3.2.1. H2S absorption capacities of [TMG][IM]-AE-x. It is found that the aqueous electrolyte with the [TMG][IM] ionic liquid has the best effect on the H2S absorption capacities and electrochemical performances. Therefore, the effect of different [TMG][IM] contents (10 wt%, 20 wt%, 30 wt%, 40 wt% and 50 wt%) on the SOR was further investigated. In Fig. 4, it is shown that the breakthrough time became longer as the [TMG][IM] contents increase, and the H2S equilibrium solubility became larger as the [TMG][IM] contents increase. Therefore, 50 wt% is the best [TMG][IM] content, and its breakthrough time and H2S equilibrium solubility reached 1560 min and 100.82 g L−1, respectively (Fig. 4(b)).
image file: d5cp01911g-f4.tif
Fig. 4 (a) H2S absorption capacities of [TMG][IM]-AE-x, and (b) H2S breakthrough times and equilibrium solubilities of [TMG][IM]-AE-x (x = 10–50).
3.2.2. Electrochemical performance evaluation of [TMG][IM]-AE-x. Fig. 5(a) shows the LSV curves of [TMG][IM] aqueous electrolytes with different IL contents. The current density reaches the maximum (181.6 mA cm−2 at 1.2 V) when the addition amount of the IL is 30 wt%. As shown in Fig. 5(b), the aqueous electrolyte with 30 wt% of the ionic liquid has the lowest Tafel slope, which is only 149 mV dec−1. It was suggested that [TMG][IM]-AE-30 has the fastest electron transfer rate at the electrode interface and the best kinetic advantage during the reaction. The increase of the [TMG][IM] content increases the density of imidazole anions in the electrolyte and significantly optimizes the charge transport capacity. Fig. 5(c) summarizes the current densities at 0.7, 0.8, and 0.9 V for [TMG][IM]-AE-x. At 0.9 V, the current density of [TMG][IM]-AE-30 can reach as high as 96.34 mA cm−2. The increase in the IL content and the decrease in current density is due to the fact that more anion pairs form a large number of ion clusters, which do not contribute to the conductivity of the solution.
image file: d5cp01911g-f5.tif
Fig. 5 (a) LSV curves of [TMG][IM]-AE-x (x = 10–50), (b) Tafel slope for the SOR of [TMG][IM]-AE-x, and (c) current densities of [TMG][IM]-AE-x at 0.7 V, 0.8 V, and 0.9 V.

3.3. Product analysis

3.3.1. Anode product. Based on the above analysis of the electrochemical performance in guanidinium IL aqueous electrolytes saturated with H2S, [TMG][IM]-AE, which has the largest activity, is applied to the H2S electrolytic process and the product was studied by potentiostatic electrolysis. In order to analyze the speciation of polysulfides, the anolyte was tested by UV-vis spectroscopy, and it was found to show obvious absorption peaks at 300 nm and 370 nm, attributed to the existence of short-chain polysulfide ions (S22−–S42−) in the electrolyte (Fig. 6(a)).58,59 Polysulfides were formed as the anodic product of sulfur further combining with the sulfide in the electrolyte.60 Through the acid treatment of the spent anolyte, the yellow precipitate could be efficiently obtained,61 and then analyzed by XRD (Fig. 6(b)). It was confirmed to be elemental sulfur (α-sulfur), which is the most stable among the three species (α-sulfur, β-sulfur and γ-sulfur), indicating the successful cycling of sulfur in H2S electrolysis regulated by guanidinium ionic liquids in the anode. As shown in Fig. 6(c), by comparing the FT-IR spectra of [TMG][IM] at different stages, it is found that the electrolyte after absorption and electrolysis of H2S shows a weak peak at 2361 cm−1, belonging to the S–H stretching vibration, and a peak appeared at 1561 cm−1, which is attributed to the N–H deformation vibration, and a chemical complexation between [TMG][IM] and H2S is proved. Fig. 6(d) demonstrates the sulfur production of the [TMG][IM]-AE-x system, and it can be seen that [TMG][IM]-AE-30 produced the most sulfur at 0.881g, the Sulfur Faraday Efficiency is 72%.
image file: d5cp01911g-f6.tif
Fig. 6 (a) UV-vis spectrum of [TMG][IM]-AE-30 at different electrolytic times, (b) XRD pattern of the anodic liquid solid product, (c) FI-IR spectrum of [TMG][IM]-AE-30 before and after electrolysis, and (d) sulphur production in [TMG][IM]-AE.

In order to further elaborate the excellent absorption of H2S by the [TMG][IM]-AE system, DFT calculations were performed. First, a [TMG][IM] structural model was constructed and optimized based on the structures found in the literature (Fig. 7(a)–(c)). Fig. 7(d) shows the adsorption free energies for the three sites on [TMG][IM]. As shown in the figure, [TMG][IM] has excellent adsorption performance for H2S in the adsorption stage, where the adsorption energies are −1.40 eV for site a, −1.28 eV for site b and −1.57 eV for site c, and it can spontaneously bind to H2S at ambient temperature and pressure without the need to provide additional energy.


image file: d5cp01911g-f7.tif
Fig. 7 DFT optimized structures of ionic liquids with (a) adsorption site a, (b) adsorption site b, (c) adsorption site c, and (d) adsorption free energies of H2S with the three adsorption sites of [TMG][IM].
3.3.2. Cathode product. The potential and electrolysis time were set to 1.0 V (vs. RHE) and 8 h, respectively, and slow magnetic stirring was applied to the process. From Fig. 8(a), it can be observed that bubbles are generated on the platinum electrode in the cathode chamber. The cathodic product was qualitatively confirmed to be H2 using a gas chromatograph instrument. As shown in Fig. 8(b) and (c), the H2S electrolysis system regulated by 30 wt% [TMG][IM] had the highest hydrogen production rate, up to 2919.97 μmol h−1, and the H2 Faraday efficiency is 99%, which is consistent with that obtained in the electrochemical test discussed in section 3.2.2, and the current density of the [TMG][IM]-AE-30 system is the maximum. As the H2S electrolysis progressed, the hydrogen production rate of the [TMG][IM]-AE-30 system gradually decreased, which can be attributed to the continuous reduction of the substrate concentration, and this material is not suitable for the reaction at this potential of only 1.0 V (vs. RHE).
image file: d5cp01911g-f8.tif
Fig. 8 (a) Bubbles on the platinum electrode of the cathode chamber, (b) hydrogen production rate (per hour) of [TMG][IM]-AE-x (x = 10–50) in potentiostatic electrolysis at 1.0 V (vs. RHE) for 8 h, and (c) hydrogen production rate and Faraday efficiency (per hour) of [TMG][IM]-AE-30 in potentiostatic electrolysis at 1.0 V (vs. RHE) for 8 h.

3.4. Circulation

From the comparison of the performance considering various aspects, [TMG][IM]-AE-30 is found to be the best electrolyte in this study. Therefore, [TMG][IM]-AE-30 was used as the research object to study the circulation performance for H2S electrolysis. The constant potential electrolysis was carried out at 1.0 V in [TMG][IM]-AE-30 saturated with H2S. In the process of electrolysis, the pH value of the electrolyte changed from 11.03 to 8.74, and the electrolyte volume dropped by around 30%. After 12 h of electrolysis, the pH value was adjusted to 13.96 consistent with that before absorption, and the volume of the electrolyte was also adjusted to 30 mL. Then the next absorption–electrolysis cycle was repeated. The current densities at different potentials and H2 production rates in each circulation are shown in Fig. 9. At 1.0 V (vs. RHE), the current density in the three cycles reached 143.9 mA cm−2, 156.4 mA cm−2 and 116.4 mA cm−2, respectively. With an electrolysis duration of 8 h per cycle, the maximum hydrogen production rate decreased from 2925 μmol h−1 to 1504 μmol h−1 for the first cycle; the maximum hydrogen production rate reduced from 2282 μmol h−1 to 506 μmol h−1 for the second cycle; the maximum hydrogen production rate for the third cycle decreased from 2347 μmol h−1 to 353 μmol h−1. From the FT-IR spectrum (Fig. 6(c)), it can be seen that the IL has changed irreversibly after electrolysis, therefore, the stability of the system is poor, and the electrochemical performance and the production rate of the system decreased, but the measured current densities and hydrogen production rates are still higher than those of conventional AE systems without ILs after three cycles, indicating that the changed IL derivatives still have a promoting effect on the reaction.
image file: d5cp01911g-f9.tif
Fig. 9 (a) LSV curves for three cycles, and (b) H2 production rate for three cycles.

3.5. Prospective analysis of industrialization

This technology can be used in the desulphurisation process of natural gas, coal gasification products and petroleum refinery gas, and is expected to replace the traditional Claus process to achieve high-precision removal of high, medium and low concentrations of hydrogen sulfide, and to obtain high-value products: hydrogen and sulfur chemical products. Compared with the traditional Claus process, according to the H2S treatment capacity of 3000 t per a,62 the amount of hydrogen produced is 56 t, and the amount of sulfur produced is 1296 t. According to the price of H2 of 35 CNY per kg and the price of sulfur of 1600 CNY per t, an additional 0.20 million CNY can be added to the income through the production of green hydrogen, and an additional 2.07 million CNY can be generated by high-value sulfur products (no upfront investment cost).

4. Conclusions

In this study, seven guanidine salt-functionalized ILs were prepared and mixed with NaOH aqueous solution in different ratios, which were applied as absorbents and anode electrolytes in the H2S absorption electrolysis reaction system. Through the screening of different guanidinium salt ILs and the addition amount, [TMG][IM]-AE-30 was found to be the optimal electrolyte system in this study, which was applied as a desulfurizing agent and an anode-loaded electrolyte in the H2S absorption electrolysis reaction system; the electrochemical performances of the system were evaluated, and the electrolyte had a certain degree of stability. In the electrolysis system, a carbon cloth and a platinum sheet were used as the working and counter electrodes, respectively, without any additional designed catalysts at the anode. The current density of the [TMG][IM]-AE-30 system was maximized to 181.6 mA cm−1 and the Tafel slope was minimized to 149 mA dec−1, indicating that it had the fastest reaction rate, which was conducive to electron transfer at the electrode interface. The hydrogen production rate of the [TMG][IM]-AE-30 system reached 2919.97 μmol h−1 after electrolysis at a constant potential of 1.0 V for 8 h. High-purity sulfur was extracted from the anode electrolyte by acidification and characterized as α-sulfur by XRD. The S yield after 8 hours of electrolysis was 0.881 g. After three cycles, the electrochemical performance and hydrogen production rate of the system decreased. Through FT-IR characterization, the reason for the decrease is found to be the changes in the guanidine salt ionic liquid after electrolysis. However, the derivatives of the changed guanidine salt ionic liquid still have a promoting effect on the reaction. Therefore, the current density and hydrogen production rate after three cycles are still higher than those of the AE systems.

Author contributions

Qianqian Peng: methodology, investigation, and writing – original draft. Weizhen Kong: methodology and investigation. Shucan Qin: writing – review and editing. Anshuang Wu: methodology. Longmei Shi: investigation. Shengyun Xu: investigation. Jianming Shi: visualization and funding acquisition. Chongqing Xu: formal analysis and funding acquisition. Yanrong Liu: conceptualization, supervision, and writing – review and editing. Yunqian Ma: conceptualization, data curation, supervision, writing – review and editing, and funding acquisition.

Conflicts of interest

There are no conflicts to declare.

Data availability

Data will be available upon reasonable request.

Acknowledgements

This work is supported by the Longzihu New Energy Laboratory, the major innovation projects of science, education, industry integration of Qilu University of Technology (Shandong Academy of Science) (2022JBZ02-05), the Key R&D Program of Henan Province (No. 231111241800), the National Natural Science Foundation of China (No. 22278402), the Frontier Basic Research Projects of Institute of Process Engineering, CAS (No. QYJC-2023-03), and research fund of State Key Laboratory of Mesoscience and Engineering (No. MESO-23-A08).

References

  1. A. Pudi, M. Rezaei, V. Signorini, M. P. Andersson, M. G. Baschetti and S. S. Mansouri, Sep. Purif. Technol., 2022, 298, 121448 CrossRef CAS .
  2. A. G. De Crisci, A. Moniri and Y. Xu, Int. J. Hydrogen Energy, 2019, 44, 1299–1327 CrossRef CAS .
  3. M. Zhang, J. Guan, Y. Tu, S. Chen, Y. Wang, S. Wang, L. Yu, C. Ma, D. Deng and X. Bao, Energy Environ. Sci., 2020, 13, 119–126 RSC .
  4. M. S. Shah, M. Tsapatsis and J. I. Siepmann, Chem. Rev., 2017, 117, 9755–9803 CrossRef CAS PubMed .
  5. E. L. Reddy, V. M. Biju and C. Subrahmanyam, Int. J. Hydrogen Energy, 2012, 37, 2204–2209 CrossRef CAS .
  6. M. Lou, R. Wang and H. Song, Renewable Sustainable Energy Rev., 2024, 199, 114529 CrossRef CAS .
  7. R. K. Abdulrahman and I. M. Sebastine, J. Nat. Gas Sci. Eng., 2013, 14, 116–120 CrossRef CAS .
  8. F. Dashtestani, M. Nusheh, V. Siriwongrungson, J. Hongrapipat, V. Materic and S. Pang, Fuel, 2021, 295, 120586 CrossRef CAS .
  9. T. J. Bandosz, J. Colloid Interface Sci., 2002, 246, 1–20 CrossRef CAS PubMed .
  10. K. Huang, F. Xi, X.-M. Zhang, Y.-T. Wu and X.-B. Hu, Green Chem., 2016, 18, 1859–1863 RSC .
  11. S. E. Hosseini and M. A. Wahid, Renewable Sustainable Energy Rev., 2016, 57, 850–866 CrossRef CAS .
  12. S. Wang, Z. Geng, S. Bi, Y. Wang, Z. Gao, L. Jin and C. Zhang, Green Energy Environ., 2024, 9, 659–683 CrossRef CAS .
  13. D. Li, J. Tu, Y. Lu and B. Zhang, Green Chem. Eng., 2023, 4, 17–29 CrossRef .
  14. J. Xu, S. Tang, S. Zhong, L. Song, P. Wu, W. Jiang, K. Wu, Q. Hu, C. Liu, H. Yue, B. Liang and Y. Yang, Int. J. Hydrogen Energy, 2023, 48, 8807–8818 CrossRef CAS .
  15. K. M. Kwok, S. W. D. Ong, L. Chen and H. C. Zeng, ACS Catal., 2017, 8, 714–724 CrossRef .
  16. A. Jiang, H. Guo, S. Yu, F. Zhang, T. Shuai, Y. Ke, P. Yang and Y. Zhou, Appl. Catal., B, 2023, 332, 122747 CrossRef CAS .
  17. M. Dan, A. Prakash, Q. Cai, J. Xiang, Y. Ye, Y. Li, S. Yu, Y. Lin and Y. Zhou, Sol. RRL, 2018, 3, 1800237 CrossRef .
  18. M. Kumar and T. C. Nagaiah, J. Mater. Chem. A, 2022, 10, 13031–13041 RSC .
  19. Y. Pei, J. Cheng, H. Zhong, Z. Pi, Y. Zhao and F. Jin, Green Chem., 2021, 23, 6975–6983 RSC .
  20. S. Zhang, Q. Zhou, Z. Shen, X. Jin, Y. Zhang, M. Shi, J. Zhou, J. Liu, Z. Lu, Y. N. Zhou and H. Zhang, Adv. Funct. Mater., 2021, 31, 2101922 CrossRef CAS .
  21. L. Yi, Y. Ji, P. Shao, J. Chen, J. Li, H. Li, K. Chen, X. Peng and Z. Wen, Angew. Chem., Int. Ed., 2021, 60, 21550–21557 CrossRef CAS PubMed .
  22. Y. Li, Y. Duan, K. Zhang and W. Yu, Chem. Eng. J., 2022, 433, 134472 CrossRef CAS .
  23. L. Zhao, Y. Wang, A. Wang, X. Li, C. Song and Y. Hu, Catal. Today, 2019, 337, 83–89 CrossRef CAS .
  24. A. Karapekmez and I. Dincer, Int. J. Hydrogen Energy, 2018, 43, 10569–10579 CrossRef CAS .
  25. K. Gutsol, R. Robinson, A. Rabinovich, A. Gutsol and A. Fridman, Int. J. Hydrogen Energy, 2017, 42, 68–75 CrossRef CAS .
  26. J. Zhu, W. Xu, J. Chen, Z. Gan, X. Wang and J. Zhou, Catal. Sci. Technol., 2020, 10, 6769–6779 RSC .
  27. M. Luo, J. Zhou, W. Xu, J. Chen, M. Xiang and K. Peng, Fuel, 2020, 281, 118729 CrossRef CAS .
  28. M. Abdul Mujeebu, Appl. Energy, 2016, 173, 210–224 CrossRef .
  29. G. Tóth, N. Nemestóthy, K. Bélafi-Bakó, D. Vozik and P. Bakonyi, Int. Biodeterior. Biodegrad., 2015, 105, 185–191 CrossRef .
  30. K. Rana, N. Rana and B. Singh, Physiological and Biotechnological Aspects of Extremophiles, 2020, pp. 131–136 Search PubMed .
  31. W. Wang, Q. Mao, K. Deng, H. Yu, Z. Wang, Y. Xu, X. Li, L. Wang and H. Wang, Small, 2023, 19, 2207852 CrossRef CAS PubMed .
  32. J. Li, S. Wang, J. Chang and L. Feng, Adv Powder Mater, 2022, 1, 100030 CrossRef .
  33. Y. He, Z. Kang, J. Li, Y. Li and X. Tian, Ind. Chem. Mater., 2023, 1, 312–331 RSC .
  34. Z. Mao, A. Anani, R. E. White, S. Srinivasan and A. J. Appleby, J. Electrochem. Soc., 1991, 138, 1299–1303 CrossRef CAS .
  35. A. A. Anani, Z. Mao, R. E. White, S. Srinivasan and A. J. Appleby, J. Electrochem. Soc., 1990, 137, 2703–2709 CrossRef CAS .
  36. J. Feng, H. Gao, L. Zheng, Z. Chen, S. Zeng, C. Jiang, H. Dong, L. Liu, S. Zhang and X. Zhang, Nat. Commun., 2020, 11, 1–8 CrossRef PubMed .
  37. D. Yang, Q. Zhu and B. Han, Innovation, 2020, 1, 1–25 CrossRef .
  38. G. Tian, Green Sustainable Process for Chemical and Environmental Engineering and Science, 2021, pp. 149–201 Search PubMed .
  39. W. Bai, J. Chen, F. Liu, J. Zhang, X. Zhang, Z. Gu and J. Yu, Phys. Chem. Chem. Phys., 2023, 25, 6295–6305 RSC .
  40. T. Zhao, P. Li, X. Feng, X. Hu and Y. Wu, J. Mol. Liq., 2018, 266, 806–813 CrossRef CAS .
  41. X. Zhang, W. Xiong, M. Shi, Y. Wu and X. Hu, Chem. Eng. J., 2021, 408, 127866 CrossRef CAS .
  42. W. Zheng, D. Wu, X. Feng, J. Hu, F. Zhang, Y.-T. Wu and X.-B. Hu, J. Mol. Liq., 2018, 263, 209–217 CrossRef CAS .
  43. X. Zhang, W. Xiong, L. Peng, Y. Wu and X. Hu, AlChE J., 2020, 66, 16936 CrossRef .
  44. K. Huang, Y. T. Wu and X. B. Hu, Chem. Eng. J., 2016, 297, 265–276 CrossRef CAS .
  45. K. Huang, J. Y. Zhang, X. B. Hu and Y. T. Wu, Energy Fuels, 2017, 31, 14060–14069 CrossRef CAS .
  46. K. Huang, D. N. Cai, Y. L. Chen, Y. T. Wu, X. B. Hu and Z. B. Zhang, ChemPlusChem, 2013, 79, 241–249 CrossRef PubMed .
  47. W. Xiong, M. Shi, L. Peng, X. Zhang, X. Hu and Y. Wu, Sep. Purif. Technol., 2021, 263, 118417 CrossRef CAS .
  48. K. Huang, X. M. Zhang, X. B. Hu and Y. T. Wu, AlChE J., 2016, 62, 4480–4490 CrossRef CAS .
  49. K. Huang, X. M. Zhang, Y. Xu, Y. T. Wu, X. B. Hu and Y. Xu, AlChE J., 2014, 60, 4232–4240 CrossRef CAS .
  50. Y. Shang, H. Li, S. Zhang, H. Xu, Z. Wang, L. Zhang and J. Zhang, Chem. Eng. J., 2011, 175, 324–329 CAS .
  51. W. Wu, B. Han, H. Gao, Z. Liu, T. Jiang and J. Huang, Angew.Chem., 2004, 116, 2469–2471 CrossRef .
  52. K. Huang, X.-M. Zhang, L.-S. Zhou, D.-J. Tao and J.-P. Fan, Chem. Eng. Sci., 2017, 173, 253–263 CrossRef CAS .
  53. Y. Liu, J. Cui, H. Wang, K. Wang, Y. Tian, X. Xue, Y. Qiao, X. Ji and S. Zhang, Green Chem., 2023, 25, 4981–4994 RSC .
  54. Y. Ma, X. Jin, Y. Hu, Q. Huang and Z. Wang, Energy Fuels, 2020, 34, 7756–7762 CrossRef CAS .
  55. X. Lei, Y. Xu, L. Zhu and X. Wang, RSC Adv., 2014, 4, 7052–7057 RSC .
  56. X. Meng, J. Wang, H. Jiang, X. Zhang, S. Liu and Y. Hu, J. Chem. Technol. Biotechnol., 2016, 92, 767–774 CrossRef .
  57. J. Huang, A. Riisager, R. W. Berg and R. Fehrmann, J. Mol. Catal. A: Chem., 2008, 279, 170–176 CrossRef CAS .
  58. C. Barchasz, F. Molton, C. Duboc, J.-C. Leprêtre, S. Patoux and F. Alloin, Anal. Chem., 2012, 84, 3973–3980 CrossRef CAS PubMed .
  59. L. Zhang, Z. Wang and J. Qiu, Adv. Mater., 2022, 34, 2109321 CrossRef CAS PubMed .
  60. Y. Wu and N. Liu, Chemistry, 2018, 4, 438–465 CrossRef CAS .
  61. J. P. Fornés and J. M. Bisang, Electrochim. Acta, 2017, 243, 90–97 CrossRef .
  62. C. Duan, C. Tang, M.-N. Wu, S. Yu, T.-J. Yu, H. Guo, J.-J. Li and Y. Zhou, Natural Gas Chemical Industry, 2021, 46, 24–30 CAS .

Footnote

† Q. Peng and C. Zhou authors contributed equally to this work.
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