Bunsen Reaction Research Articles

Continuous multiphase Bunsen reactor of iodine-sulfur thermochemical water splitting cycles for hydrogen production: Experimental, Modelling and Design Insights

Thermochemical water splitting cycles (TWSCs) hold promise for sustainable H2 production in future energy systems, with Iodine-Sulfur (IS) and Nickel-Iodine-Sulfur (NIS) processes standing out as efficient options. The core of both these processes lies in the Bunsen reaction, underscoring the need to identify optimal operational conditions and plant solutions for this crucial reaction section. Thus, in this study, a continuous counter-current flow Bunsen reactor fed with 5 NL h−1 of SO2 was constructed and tested. An inventive aspect was the introduction of solid I2 pellets from the top to enhance saturation at the liquid-liquid interface between sulfuric and hydriodic product phases, promoting segregation. This ingenious design achieved nearly complete SO2 conversion and optimal H2SO4 and HI concentrations in the respective product phases, while avoiding undesirable byproduct formation. The study further advanced the modelling of the experimental reactor by employing innovative kinetic and liquid-liquid equilibrium description approaches, and demonstrating exceptional validation accuracy of R2 = 0.9988. Additionally, with the aim of obtaining design charts as a potential tool for Bunsen reactor design, a microscopic model describing the gas phase trend along bubble or packed Bunsen-type reactors was developed. The model’s dimensionless analysis revealed a characteristic times ratio (Bu) comprehensively describing all the phenomena occurring to the gas phase within the Bunsen reaction section, and identified an optimal Bu value of 0.4 for pure SO2 gas inlet. Overall, the study's innovative strategies and models contribute significantly to the advancement of Bunsen reactor engineering.

Electrocatalytic Performance of Carbon Layer and Spherical Carbon/Carbon Cloth Composites Towards Hydrogen Evolution from the Direct Electrolysis of Bunsen Reaction Product

Electrocatalytic Performance of Carbon Layer and Spherical Carbon/Carbon Cloth Composites Towards Hydrogen Evolution from the Direct Electrolysis of Bunsen Reaction Product

Process modelling and assessment of thermochemical sulfur-iodine cycle for hydrogen production considering Bunsen reaction kinetics

Thermochemical sulfur-iodine (SI) cycle is one of the large-scale, clean, and efficient hydrogen production routes. The Bunsen reaction process is always simulated by a stoichiometric reaction, without considering the realistic Bunsen reaction kinetic process. Herein, a user-defined Fortran module concerning Bunsen reaction kinetics was developed and embedded into a continuous stirred tank reactor (RCSTR), and then a SI flowsheet with 100 L/h hydrogen production was modeled. The key parameter optimization, mass and energy balance were analyzed, the internal heat exchange network was created using the pinch point temperature difference analysis and the principle of energy cascade utilization, along with thermal efficiency evaluation. Bunsen reaction process reaches equilibrium after a period, which is consistent with experiments. The increase of H2SO4 decomposition ratio is beneficial to reduce the energy consumption of system. Increase in temperature has less effect on increasing the equilibrium decomposition ratio of HI. The theoretical thermal efficiency of system reaches 14.0–57.4 % considering the recovery of exothermic heat. This work provides a theoretical basis for the optimization of SI cycle.

Design and evaluation of a novel process for green hydrogen production in the iodine–sulfur cycle via pressure-swing distillation of HIx (HI-I2-H2O)

In striving for carbon neutrality, hydrogen energy serves as a sustainable solution, and the iodine–sulfur (IS) cycle stands out as the most promising method for hydrogen production. The separation and purification of HI from the HIx (HI-I2-H2O) mixture holds significant research value, as they constitute the crucial aspect of the iodine–sulfur cycle in hydrogen production. Due to the azeotropic behavior of HI and H2O, the HIx system poses a considerable challenge. In this research, a technique for purifying HI via pressure-swing distillation was developed, exploiting the changes in azeotropic points under varying pressure conditions. The most effective method for HI purification was determined to be a three-column pressure-swing distillation configuration, as revealed by Aspen Plus phase diagrams and process topology mapping. It yielded H2O and I2 at the top of the first column, I2 at the bottom of the second column, and HI at the top of the third column with an HI recovery rate of 97 %. By analyzing the Bunsen reaction kinetics of the core reaction in the IS system, a comprehensive method for evaluating the separation and reaction coupling quality network of HIx cycle system using Bunsen-factor (B-factor) was proposed. The B-factor elucidates the correlation between the Bunsen reaction rate and the concentrations of [H+], [I-], [I3-], as well as the pH level. A comprehensive analysis of the B-factor was conducted for the pressure-swing distillation topologies of the HIx system, and the results were contrasted with those of alternative separation processes. The findings indicated that the three-column pressure-swing distallation is the most suitable option for both separation and reaction quality in a recycled network. The total energy consumption of the newly designed HIx three-column process is 352 MJ/kmol, rendering it more economical and beneficial than other processes. This study presents a pressure-swing distillation method for HI separation and purification, which is broadly applicable in IS cycles and aids in achieving large-scale production of green H2. This method enables the achievement of the dual-carbon objective, which seeks to mitigate carbon emissions while safeguarding the environment.

Decoupling the anodic and cathodic behavior in asymmetric electrochemical hydroiodic acid decomposition cell for hydrogen production in the iodine-sulfur thermochemical cycle.

The HI section of the iodine-sulfur (I-S) thermochemical cycle for hydrogen production is one of the most energy-intensive sections and with significant material handling challenges, primarily due to the azeotrope formation and the corrosive nature of the hydroiodic acid-iodine-water mixture (HIx). As an alternative, the single-step direct electrochemical decomposition of the hydroiodic acid (HI) to generate hydrogen can circumvent the challenges associated with the conventional multistep HI section in the I-S cycle. In this work, we present new insights into the electrochemical HI decomposition process by deconvoluting the contributions from the anodic and the cathodic sections in the electrochemical cell system, specifically, the redox reactions involved and the overpotential contribution of the individual sections (anolyte and catholyte) in the overall performance. The studies on the redox reactions indicate that the HIx solution output from the Bunsen reaction section should be used as the anolyte. In contrast, aqueous HI without any iodine (I2) should be used as the catholyte. In the anodic section, the oxidation proceeds with I2 as the final oxidized species at low bias potentials. Higher positive potentials result in iodate formation along with oxygen evolution. For the catholyte section, I2 and tri-iodide ion reduction precede the hydrogen evolution reaction when I2 is present along with HI. Furthermore, the potential required for hydrogen production becomes more negative with an increasing I2/HI ratio in the catholyte. Polarization studies were conducted with simultaneous deconvolution of the anodic and cathodic behavior in a two-compartment cell. Model fitting of the polarization data revealed that the anolyte section's activation overpotential is negligibly low. In contrast, the activation overpotential requirement of the catholyte section is higher and dictates the onset of hydrogen production in the cell. Furthermore, the catholyte section dominates the total overpotential losses in the cell system. Operation in the ohmic resistance-dominated zone resulted in close to 90% current efficiency for the electrochemical HI decomposition. The results highlight that the potential for process improvement lies in reducing the ohmic resistance of the anolyte section and in lowering the activation overpotential of hydrogen evolution in the catholyte section.

An Interference-Free Voltammetric Method for the Detection of Sulfur Dioxide in Wine Based on a Boron-Doped Diamond Electrode and Reaction Electrochemistry.

This paper describes a new, simple, and highly selective analytical technique for the detection of sulfur dioxide in wine, as a real sample with a relatively complicated matrix. The detection of the above analyte was based on the electrogeneration of iodine from iodide on a boron-doped diamond electrode, without modifications, in the presence of 0.1 mol dm-3 HClO4 as a supporting electrolyte. The electrogenerated iodine reacted with sulfur dioxide, forming iodide ions and sulfuric acid (i.e., a Bunsen reaction). The product of this reaction, the iodide ion, diffused back to the surface of the boron-doped diamond electrode and oxidized itself again. This chemical redox cycling enhanced the voltammetric response of the boron-doped diamond electrode. The selectivity of the determination was assured using NaOH and formaldehyde during sample preparation, and a blank was also measured and taken into account. The detection limit was estimated to be 10-6-10-7 mol dm-3. However, the content of sulfur dioxide in wine is significantly higher, which can lead to more accurate and reliable results.

A comprehensive evaluation integrating thermodynamics and mechanism kinetics for the Bunsen reaction in a sustainable iodine–sulfur cycle

Carbon neutrality makes hydrogen a promising alternative source of energy. Iodine-sulfur cycle shows the greatest potential among hydrogen production methods. Bunsen reaction holds significant research value as the core reaction of the iodine-sulfur cycle. This paper presents an innovative method for evaluating Bunsen reactions, integrating equilibrium thermodynamics and kinetics to explore the influence of temperature, pressure, and reactant concentration on the Bunsen reaction. The thermodynamic results show that the influence of pressure on reaction balance is weak; with the gradual excess of I2, the amount of H2O required for Bunsen reaction decreases; the optimal operation ratio of H2O:I2:SO2 is 16:4:1 at 360K; the Bunsen reaction system should be carried out in an acidic system, while H2O promotes the spontaneous exothermic reaction of Bunsen. Additionally, we propose 8 reactions as Bunsen reaction mechanisms, and derive the rate equation. Bunsen reaction rates are promoted by [I2], [I3−], and [SO2] concentrations, inhibited by [I−] and [H+] concentrations, and the reaction rate of the whole solution system is sensitive to pH, [I−] and [H+] concentration changes. Added H2O improves pH, whereas acidic systems benefit from higher pH. Lastly, the interconnection of thermodynamic and kinetic results is discussed and compared with other literature. The method proposed in this study has universal application value for Bunsen reaction. It contributes to system process optimization and Bunsen reactor amplification, and facilitating carbon neutralization and hydrogen energy.

Simulation and optimization of an innovative thermochemical water splitting cycle for the production of greenhydrogen

Highly efficient and cost-effective green Hydrogen production is a crucial challenge in a future sustainable economy. The innovative Nickel–Iodine-Sulphur (NIS) thermochemical cycle is a potential candidate for this purpose. For the first time in literature, this paper provides a complete Aspen Plus V10 simulation of the closed NIS cycle. Whitin the cycle, the Bunsen reactor was simulated as a PFR with a kinetic constant k = 1.38 m3/mol·s, while the other four reactors were considered at the thermodynamic equilibrium. A simulation of the conventional IS cycle was used as a benchmark for the NIS cycle, whose process parameters were optimized through a sensitivity study. Finally, the thermal efficiency without heat recovery of both cycles was calculated through an energy balance. The simulation results shows that the NIS cycle simulation achieves the same stoichiometric hydrogen yield as the IS cycle and a 17% higher thermal efficiency than the latter.

Performance evaluation of oscillatory baffle Bunsen reactor in iodine sulfur thermochemical process for hydrogen production

<abstract> <p>Hydrogen is an environmentally attractive transportation fuel that can replace fossil fuels. The iodine-sulfur (I-S) thermo-chemical process involves three reaction steps. The Bunsen reaction is one of the main reaction steps of I-S process and plays an important role in defining overall process efficiency. Different types of reactors are being studied, including the oscillatory baffle Bunsen reactor. The reactor selection is based on process intensification and process integration, i.e., reaction and separation in the single equipment. Simulations are performed for two-dimensional cases by solving incompressible Navier-Stokes equations along with continuity equation, the geometry chosen is of single section in the column and diameter of 50 mm and baffle spacing of 50, 75,100 mm i.e. 1, 1.5 and 2 times the diameter of column and baffle free area 22%. The residence time distribution experiments are carried out in a metallic reactor with NaCl as a tracer operated at different frequencies, amplitudes and flow rates. D/uL is evaluated from experimental curves. The power per unit mass is compared for oscillatory baffled column and stirred tank for a semi-batch process. From the numerical simulations, good eddy interactions are present at higher frequencies and amplitudes and at a baffle spacing of 1.5 times the diameter of the column. Residence time distribution analysis gives a lower dispersion number at medium frequencies and higher amplitudes with constant flow rate. If the flow rates are high, then it is better to operate at higher frequencies and amplitudes to achieve plug flow behavior. Power per unit mass is less for oscillatory baffle column compared to the stirred tank of given configuration. With better mixing performance and less power per unit volume, the oscillatory baffle column is a good alternative to other columns.</p> </abstract>

Introduction and preliminary testing of a 5 m3/h hydrogen production facility by Iodine–Sulfur thermochemical process

The Iodine–Sulfur (IS) or Sulfur–Iodine (SI) thermochemical water-splitting cycle is considered as one of the most promising hydrogen production methods through thermal chemical cycle process with heat. This paper introduces the new built hydrogen production testing facility of IS process made by industrial structural material (IS-5m3 facility). The TC4, Hastelloy C276 and SiC materials were chosen in this pilot-scale testing facility for different modules. The new designed structure of Bunsen reactor, HI decomposer and H2SO4 decomposer are described particularly, and the corresponding individual tests are successfully executed to verify the function of each section. Based on testing, a preliminary continuous experimental run was carried out in September of 2021 for about 4 h with the hydrogen production capacity of 80 L/h. The problems such as slight corrosion, lower hydrogen gas yield and shorter operation time faced in this experiment will be modified in the near future. A longer time operation and higher H2 production rate test will be carried out soon.

Direct electrolysis of bunsen reaction product for hydrogen production: The continuous-flow operation

Hydrogen sulfide (H2S) emitted from oil industry's hydrotreating processes can be converted into hydrogen and used back to the same processes through a H2S splitting cycle, where the Bunsen reaction and HI decomposition are two participating reactions. To overcome the difficulties and complications posted in the scaling up of the cycle, direct electrolysis of the Bunsen reaction product solution was proposed and has been studied in a batch electrolysis cell in our earlier work. This paper studies the direct electrolysis using a customer-made, continuous-flow electrolysis cell. The effects of the operating parameters including the current density, the entering HI concentration and flow rate of the anolyte, the toluene to aqueous phase ratio and stirring speed in anolyte cell, the H2SO4 concentration and circulation rate of the catholyte on the performing parameters such as the conversion of iodide ions, the yield of iodine transferred to toluene, and the anodic and cathodic current efficiencies for iodide conversion and hydrogen production were carefully investigated. The results show that the cathodic current efficiency for hydrogen production is nearly 100% for all the runs and that the anodic current efficiency for iodide ion conversion to iodine is relatively low (20%–70%) and varies with the changes in operating parameters. Running at high levels of the current density, the volumetric ratio of toluene to aqueous phase in anolyte, or the stirring speed in anolyte, and low levels of the entering concentration of I− in anolyte or the flow rate of anolyte in electrolysis operation are in favor of having a high iodide conversion and high I2-toluene yield. Iodide anions at a few mmol L−1 level (a few thousandths of the entering concentration) are found in the cathodic chamber caused by its diffuse against the electric field and the proton exchange membrane. The continuous, direct electrolysis of the Bunsen product solution can be considered being adapted in the sulfur-iodine (S–I) water splitting cycle for hydrogen production.

Heat, economic and multi-path safety (HEMPS) management on co-generation of hydrogen and sulfuric acid through modified sulfur-iodine cycle

This research suggests a novel framework for heat, safety, and economic management based on the leverage relationship among those analyses on polygeneration system of hydrogen and sulfuric co-production from flue gas and water using modified sulfur-iodine cycle. The exergy assessment is conducted to identify the useful energy available in the section. Following that, the heat integration and economic assessment are performed simultaneously to investigate the minimum cost corresponding minimum temperature difference. The novel leverage assessment between risk- costs, heating cost –cost, heating – risk were conducted to suggest optimal parameters. The results show that the minimum temperature difference is 25 °C for heat integration, indicating the capital + operating cost was expected to be reduced by 3%. The HI decomposition section reveals the low exergy efficiency and high exergy destruction. The expected accident probabilities of Bunsen reaction section and HI decomposition section are contributed to be 46% and 54%, respectively. The novel thermal risk coefficient method suggests 160 °C to be the minimal risk temperature. The total 23 safety pipes were optimal considering the cure cost for accident and pipe installation cost indicating a 35% total cost reduction.

Process optimization and safety assessment on a pilot-scale Bunsen process in sulfur–iodine cycle

This study investigates Bunsen reaction in the sulfur-iodine (SI) cycle for optimal conditions and specification of equipment in terms of the maximum HI yield and the least impurities in HIx (mixture of HI, I2 and H2O), the reaction safety, and dispersion of SO2 gas and HIX solution for leakage accident. The pilot-scale Bunsen process was simulated and validated. The optimization of the Bunsen reactor, 3-phase separator, and HIX purifier have been investigated in order to parameterize the operating conditions and equipment specification for three cases: (1) Maximize the HI yield for the final product (2) Minimize the H2SO4 impurities (3) Multi-objective case of both maximum HI production and minimum impurities. The gas reactivity safety was investigated on HI, H2SO4, I2, SO2, H2O, and O2. Also, the SO2 gas dispersion distance for 30 ppm, 0.75 ppm, and 0.2 ppm and HI dispersion distance for 120 ppm, 25 ppm, and 1 ppm was investigated for targeted unit operators at each optimization scenario. The deviation between pilot-scale experiment and simulation case falls within 1–3% for Bunsen reactor, 6~8% for 3-phase separator, and 2~4% for HIX purifier. The maximized HI production was increased by 17% for the maximum HI yield case from the designed case. The size and temperature of the Bunsen reactor was increased to enhance the reaction. However, the HIX purifier size was reduced since reverse Bunsen reaction causes loss in HI product. The H2SO4 impurities in the minimize H2SO4 impurities case were reduced by 71% from the designed case. The size of the Bunsen reactor remained the same as design case, but the HIX purifier size was increased to enhance the reverse Bunsen reaction. For multi-objective case, the HI productivity was increased by 16% and the H2SO4 impurities were reduced by 67% simultaneously. According Chemical Reactivity Worksheet (CRW) result, O2 should therefore not be stored with any components except iodine. For SO2 and HIX dispersion assessment, the maximum HI yield case reveals the maximum dispersion of SO2 gas and HIX solution from the Bunsen reactor. The dispersion from 3-phase separator was almost the same for all the cases. For HIX purifier, the minimum H2SO4 case exhibited the longest distance of SO2 gas and HI solution dispersion. At 3 bar and 140 °C, the maximum SO2 and HIX dispersion distance were occurred.

Review of researches on H2S splitting cycle for hydrogen production via low-temperature route

This paper presents an overview of the research and development of the H2S splitting cycle for hydrogen and sulfuric acid production via the low-temperature route of using iodine-toluene solution for Bunsen reaction and direct electrolysis of the mixed hydroiodic acid and sulfuric acid for hydrogen production. The use of I2-toluene solution makes low-temperature Bunsen reaction possible such that many drawbacks including side reactions, iodine vapor deposition, and corrosion have been eliminated or eased. The use of the Corning® Advanced-FlowTM Reactors to carry out multiphase Bunsen reaction allows not only the corrosion-free operation but also enhances mass transfer rate. The direct electrolysis of the product solution from the Bunsen reaction enables the production of hydrogen and separation of sulfuric acid from hydroiodic acid to occur in a single step. A customer-made continuous electrolysis cell was used for the direct electrolysis of Bunsen reaction products, which makes the scale up possible.

Hydrogen production using thermochemical water-splitting Iodine–Sulfur process test facility made of industrial structural materials: Engineering solutions to prevent iodine precipitation

A thermochemical water-splitting iodine–sulfur process offers the potential for mass-producing hydrogen at high-efficiency levels, and it uses high-temperature heat sources, including high-temperature gas-cooled reactors, solar heat, and waste heat of industries. The raw material (H2O) is split into H2 and O2 by combining three chemical reactions using sulfur and iodine. Currently, R&D tasks are essential to confirm the integrity of the components that are made of practical structural materials and the stability of hydrogen production in harsh working conditions. A test facility for producing hydrogen was constructed from corrosion-resistant components that are developed using industrial materials. In addition, for stable hydrogen production, technical issues for instrumental improvements (i.e., stable pumping of the hydrogen iodide (HI)–I2–H2O solution without locking the shaft seal, prevention of leakage by improving the quality control of glass-lined steel, prevention of I2 precipitation using a water removal technique in a Bunsen reactor) were solved. The entire process was successfully operated for 150 h at the rate of ca. 30 L/h. The integrity of components made of practical structural materials and the operational stability of the hydrogen production facility in harsh working conditions were demonstrated.

Development of a membrane reactor with a closed-end silica membrane for nuclear-heated hydrogen production

Hydrogen production from nuclear energy has attracted considerable interest as a clean energy solution to address the challenges of climate change and environmental sustainability. With respect to the large-scale and economical production of hydrogen using nuclear energy, the thermochemical water-splitting iodine-sulfur (IS) process is a promising method. The IS process uses sulfur and iodine compounds to decompose water into its elemental constituents, hydrogen and oxygen, by using three coupled chemical reactions: the Bunsen reaction; sulfuric acid decomposition; and hydrogen iodide (HI) decomposition. The decomposition of HI is the efficiency-determining step of the process. In this work, a membrane reactor with a silica membrane closed on one end was designed, and its potential for hydrogen production from HI decomposition was explored. In the reactor-module design, only one end of the membrane tube was fixed, while the closed-end of the tube was freely suspended to avoid thermal expansion effects. The closed-end silica membranes were prepared for the first time by a counter-diffusion chemical vapor deposition of hexyltrimethoxysilane. In application, HI conversion of greater than 0.60 was achieved at a decomposition temperature of 400 °C, which is three times greater than the equilibrium conversion (0.20). Thus, the membrane reactor with closed-end silica membrane was shown to produce a successful equilibrium shift in the production of hydrogen via HI decomposition in the thermochemical IS process.

Energy and exergy analyses of a novel sulfur–iodine cycle assembled with HI–I2–H2O electrolysis for hydrogen production

A novel sulfur–iodine (SI or IS) cycle integrated with HI–I2–H2O electrolysis for hydrogen production was developed and thermodynamically analyzed in this work. HI–I2–H2O electrolysis was used to replace the conventional concentration, distillation, and decomposition processes of HI, so as to simplify the flowsheet of SI cycle. And then the new cycle was divided into Bunsen reaction, H2SO4 decomposition and HI–I2–H2O electrolysis sections. Through incorporating the user-defined module of HI–I2–H2O electrolysis with Aspen Plus, the cycle was simulated and 0.448 mol/h (10 L/h) of H2 was produced. The overall energy and exergy efficiencies of the novel SI system were estimated to be 15.3–31.0% and 32.8%, respectively. Most exergy destruction occurred in the H2SO4 decomposer and condenser for H2SO4 decomposition and Bunsen reaction sections, which accounted for 93.0% and 63.4%, respectively. A high exergy efficiency of 92.4% for HI–I2–H2O electrolysis section with less exergy destruction was determined, mostly due to the transformation of the overall electricity in electrolytic cell to exergy. Appropriate internal heat exchange and waste heat recovery will favor improving the energy and exergy efficiencies.

Sulphonated (PVDF-co-HFP)-graphene oxide composite polymer electrolyte membrane for HI decomposition by electrolysis in thermochemical iodine-sulphur cycle for hydrogen production

In overall iodine-sulphur (I-S) cycle (Bunsen reaction), HI decomposition is a serious challenge for improvement in H2 production efficiency. Herein, we are reporting an electrochemical process for HI decomposition and simultaneous H2 and I2 production. Commercial Nafion 117 membrane has been generally utilized as a separator, which also showed huge water transport (electro-osmosis), and deterioration in conductivity due to dehydration. We report sulphonated poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP) (SCP) and sulphonated graphene oxide (SGO) composite stable and efficient polymer electrolyte membrane (PEM) for HI electrolysis and H2 production. Different SCP/SGO composite PEMs were prepared and extensively characterized for water content, ion-exchange capacity (IEC), conductivity, and stabilities (mechanical, chemical, and thermal) in comparison with commercial Nafion117 membrane. Most suitable optimized SCP/SGO-30 composite PEM exhibited 6.78 × 10−2 S cm−1 conductivity in comparison with 9.60 × 10−2 S cm−1 for Nafion® 117. The electro-osmotic flux ofSCP/SGO-30 composite PEM (2.53 × 10−4 cm s−1) was also comparatively lower than Nafion® 117 membrane (2.75 × 10−4 cm s−1). For HI electrolysis experiments, SCP/SGO-30 composite PEM showed good performance such as 93.4% current efficiency (η), and 0.043 kWh/mol-H2 power consumption (Ψ). Further, intelligent architecture of SCP/SGO composite PEM, in which hydrophilic SGO was introduced between fluorinated polymer by strong hydrogen bonding, high efficiency and performance make them suitable candidate for electrochemical HI decomposition, and other diversified electrochemical processes.

Overvoltage reduction in membrane Bunsen reaction for hydrogen production by using a radiation-grafted cation exchange membrane and porous Au anode

An electrochemical membrane Bunsen reaction using a cation exchange membrane (CEM) is a key to achieving iodine-sulfur (IS) thermochemical water splitting for the mass-production of hydrogen. In this study, we prepared a radiation-grafted CEM with a high ion exchange capacity (IEC) and a highly-porous Au-electroplated anode, and then used them for the membrane Bunsen reaction to reduce cell overvoltage. The high ionic content of our CEM led to low resistivity for proton transport, while the high porosity of the electrode led to a large effective surface area for anodic SO2 oxidation. The cell overvoltage for the membrane Bunsen reaction was significantly reduced to 0.21 V at 200 mA/cm2, one-third of that achieved using a commercial CEM and non-porous anode. From the analysis of the current-voltage characteristics, the grafted CEM was demonstrated to play a dominant role in the overvoltage reduction compared to the porous Au anode.

High-Performance Pt Catalyst with Graphene/Carbon Black as a Hybrid Support for SO2 Electrocatalytic Oxidation.

In the electrochemical Bunsen reaction, which is the key reaction of the sulfur-iodide cycle, the main overpotential corresponds to the oxidation of SO2. The catalysts currently used for the liquid phase electrocatalytic oxidation of SO2 are mainly based on noble metals, which have excellent corrosion resistance and catalytic activity in an acidic environment. To improve the performance of the commercial Pt catalyst, a Pt catalyst with reduced graphene oxide (RGO) and carbon black as a hybrid support was synthesized by the microwave-assisted polyol reduction process. The large two-dimensional planar structure of RGO was a better anchor for Pt nanoparticles, and a catalyst with fine and uniform distribution of Pt particles was obtained. The carbon black interior prevented the agglomeration of RGO, forming a stereoscopic catalyst structure. The electrochemical test results showed that the RGO/carbon black hybrid support catalyst possessed a higher electrocatalytic activity than the single support catalysts and could be used as an efficient and stable catalyst for the SO2 electrolyzer.