Sulfur Iodine Thermochemical Cycle Research Articles

Effect of catholyte in a single step electrochemical hydroiodic acid decomposition for hydrogen production using the iodine-sulfur thermochemical cycle.

This study identifies the most suitable catholyte for the electrochemical HI decomposition process, an emerging single-step alternative to the conventional multistep HI section of the I-S thermochemical cycle for hydrogen production. Four catholytes, H2O, H3PO4, H2SO4, and HI, were shortlisted based on compatibility with the I-S cycle and ability to support the hydrogen evolution. Polarization studies in a two-compartment electrochemical cell revealed a similar order of onset potentials for the electrochemical HI decomposition across all four catholyte electrolytes. However, the performance at higher overpotentials following the onset of the electrochemical HI decomposition followed the order H2SO4 > HI > H3PO4 > H2O. The polarization behavior was not found to vary significantly with the catholyte concentration. Model fitting revealed that the invariance in polarization behavior with the catholyte concentration arose from the compensation between the changes in activation overpotentials with the open-circuit voltage. The onset potential was predominantly influenced by the I2/HI ratio in the anolyte, with higher ratios resulting in an increase in the onset potentials for electrochemical HI decomposition. Polarization studies identified H2SO4 and HI as the most promising catholytes for further investigation. Consequently, continuous electrochemical HI decomposition and hydrogen production was demonstrated with H2SO4 and HI as the catholyte for three I2/HI ratios of 0.25, 0.5, and 1 at two different current densities, with an average current efficiency of ∼97%. Among the two acids, H2SO4 showed higher current efficiency and lower energy consumption per mole of hydrogen compared to HI under the similar anolyte configuration and current density.

Unlocking Interfacial Interactions of In Situ Grown Multidimensional Bismuth‐Based Perovskite Heterostructures for Photocatalytic Hydrogen Evolution

AbstractTo combat the energy crisis and environmental pollution, developing renewable energy technology such as hydrogen (H2) production is necessary. The sulfur–iodine thermochemical cycle has high commercial potential in conducting hydrogen iodide (HI) splitting for H2 generation, but it requires high‐temperature conditions. In comparison, photocatalytic HI splitting of halide perovskites is non‐polluted and low‐cost for H2 production at room temperature. Herein, an in situ constructed multidimensional bismuth (Bi)‐based 3D/2D EDABiI5/MA3Bi2I9 perovskite heterojunction is developed first by synergistically integrating dimensionality control with heterostructure engineering. Accordingly, the optimal EDABiI5/MA3Bi2I9 without any co‐catalysts exhibits the H2 evolution rate of 213.63 µmol h−1g−1 under irradiation. Equally importantly, interfacial dynamics of solid/solid and solid/liquid interfaces play a crucial role in photocatalytic performance. Therefore, using temperature‐dependent transient photoluminescence and electrochemical voltammetric techniques, it is confirmed that the exciton transportation of EDABiI5/MA3Bi2I9 is accelerated by stronger electronic coupling arising from an enhanced overlap of electronic wavefunctions. Moreover, the effective diffusion coefficient and electron transfer rate of EDABiI5/MA3Bi2I9 demonstrate efficient heterogeneous electron transfer, resulting in improved photocatalytic hydrogen production. Consequently, the in situ formation of perovskite heterostructures studied by a combination of photophysical and electrochemical techniques provides new insights into green hydrogen evolution and interfacial interaction dynamics for commercial applications of solar‐to‐fuel technology.

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.

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.

Energy and exergy analysis of a novel solar-hydrogen production system with S–I thermochemical cycle

A novel hydrogen production system based on a sulfur-iodine (S–I) thermochemical water-splitting cycle driven by 100% solar energy is proposed in this paper. A solar power tower (SPT) with thermal energy storage (TES) is used to supply heat stably. Considering the large heat recovery potential in the S–I cycle, a supercritical carbon dioxide (S–CO2) Brayton cycle is used to improve the system performance. A complete thermodynamic model and detailed description of the energy and exergy flow from the sun to SPT, TES, S–I cycle, S–CO2 Brayton cycle and hydrogen is obtained. The system performance in the base case and actual weather conditions are obtained. The influence of major parameters on the system performance is investigated. The results show that the hydrogen production rate is 3.52 mol s−1 in the base case. Using the S–CO2 Brayton cycle, the overall energy and exergy efficiency can be increased from 10.6%, 11.1% to 30.5%, 32.4%, respectively. The solar part accounts for 48.2% of the total energy loss and 76.1% of the exergy destruction. In addition, increasing DNI, the maximum reaction temperature, the regeneration ratio of the S–CO2 Brayton cycle (RR) can improve the system performance, and the system efficiency is more sensitive to RR.

Environmental impacts of a standalone solar water splitting system for sustainable hydrogen production: A life cycle assessment

Hydrogen is broadly utilized in various industries. It can also be considered as a future clean energy carrier. Currently, hydrogen is mainly produced from typical fuels such as coal; however, there exist some other clean alternatives which use water decomposition techniques. Water splitting via the copper-chlorine (Cu–Cl) thermochemical cycle is a superb option for producing clean carbon-free fuel. Here, the life cycle assessment (LCA) technique is used to investigate the environmental consequences of an integrated solar Cu–Cl fuel production facility for large-scale hydrogen production. The impact of varying important input parameters including irradiation level, plant lifetime, and solar-to-hydrogen efficiency on various environmental impacts are investigated next. For instance, an improve in the solar-to-hydrogen efficiency from 15% to 30%, results in a reduction in the GWP from 1.25 to 6.27E-01 kg CO2 eq. An uncertainty analysis using Monte Carlo simulation is conducted to deal with the study uncertainties. The results of the LCA show that the potential of acidification and global warming potential (GWP) of the current system are 8.27E-03 kg SO2 eq. and 0.91 kg CO2 eq./kg H2, respectively. According to the sensitivity analysis, the plant lifetime has the highest effect on the total GWP of the plant with a range of 0.63–1.88 kg of CO2 eq./kg H2. Results comparison with past thermochemical-based studies shows that the GWP of the current integrated system is 7% smaller than that of a solar sulfur-iodine thermochemical cycle.

Exergy study of hydrogen cogeneration and seawater desalination coupled to the HTR-PM nuclear reactor

This work presents a novel integration system of the high-temperature gas-cooled reactor-pebble bed module project to a hydrogen production process using the iodine-sulfur cycle in cogeneration with seawater desalination. The current approach includes a Rankine cycle, a sulfur-iodine thermochemical cycle for hydrogen production and a multi-stage flash desalination process. The use of a catalyst that allows the H2SO4 decomposition reaction to being carried out at temperatures compatible with the nuclear reactor project is considered. The residual heat from the acid decomposition reactions is used to desalinate seawater through the multi-stage flash process. A chemical process simulator is used to create a computational model that allows estimates of global and local efficiencies of the proposed flow diagram. Some operating parameters were sized, and their influence on the efficiency is also reported. The proposed model for the sulfur-iodine cycle can produce 0.41 kg/s of hydrogen with partial energy and exergetic efficiency of 37.35% and 38.64%. The desalination process can process 40.70 kg/s with energy and exergy efficiencies of 58.78% and 82.66%, respectively. The higher exergy destruction share is obtained in the heat exchangers (36.55%), chemical reactors (16.56%) and separators (12.80%). The global system showed efficiencies of 40.13% and 52.04%, respectively.

Directional introduction of pyridine nitrogen functional groups in activated carbon catalysts for the catalytic production of hydrogen: An experimental and DFT calculation

With the increase in global energy consumption, it has become difficult for traditional energy (re)sources to meet our basic needs. Hydrogen energy is an important component of a low-carbon or carbon-free energy strategy, and the thermochemical sulfur-iodine cycle is considered to be one of the most promising methods for hydrogen production. Nitrogen-doped activated carbon catalysts (NACCs) can improve the decomposition efficiency of hydrogen iodide (HI). However, the investigation of the active nitrogen-containing functional group (NFG) is still in progress. In this study, results from experiments and density functional theory (DFT) calculations were combined to achieve a pyridine nitrogen targeted modification, with the idea that pyridine nitrogen is the catalytically active center.Using ammonia-carbon dioxide co-activation, the samples contained a maximum of 7.79 % N content, and 77.28 % pyridine nitrogen content. An increase in the pyridine nitrogen content resulted in an increase in the catalytic decomposition efficiency. Bipyridine was used to increase the pyridine nitrogen content to complement the nitrogen-modulation mechanism. The N-6 content reached a maximum when the bipyridine solution concentration was in the range of 0.3–0.35 g/L; this resulted in the highest catalytic efficiency. The transition state and reaction path energies were calculated at the B3LYP/def2-TZVP level and combined with thermodynamic enthalpy correction quantities to improve accuracy. According to the DFT calculations, the models for pyridine nitrogen substitution all reduced the activation energy of HI decomposition reaction compared to the other models.

Integration of neural network-based prediction for enhanced process controllability: application in hydrogen iodide decomposer for hydrogen production via water splitting process

Sulfur-Iodine Thermochemical cycle (SITC) process can be broken down into 3 sections. Based on the literature, there is limited study on the third section which is hydrogen iodide (HI) decomposition. In this work, a study to develop a model and controller of the HI decomposition is carried out. The goal of this work is to address this important gap, and more specifically to focus on the controllability of the HI decomposition section. Before the control and simulation study can be performed, a dynamic model of a HI decomposer is first established to obtain the baseline for the necessary data to be fed into the Artificial Neural Network for training to predict the correct outcome accordingly. The proposed controller is a Multi-Scale Control (MSC) integrated into an Artificial Neural Network (ANN) model (ANN-MSC-based-PID). It is worth highlighting that; the proposed model-based control strategy has proven to effectively control the HI decomposition reactor.

SO3 decomposition over silica-modified β-SiC supported CuFe2O4 catalyst: characterization, performance, and atomistic insights.

The sulfur-iodine (S-I) thermochemical water-splitting cycle is one of the potential ways to produce hydrogen on a large scale. CuFe2O4 was dispersed over modified silica or treated β-SiC and untreated β-SiC using the wet impregnation method for SO3 decomposition, which is the most endothermic reaction of the S-I cycle. Various state-of-the-art techniques such as XRD, FT-IR, BET, XPS, TEM, HR-TEM, FESEM-EDS and elemental mapping were employed to characterize both the synthesized catalysts. CuFe2O4 catalyst supported on silica-modified β-SiC resulted in enhanced catalytic activity and stability due to better metal-support interaction. In order to get a better insight into the reaction mechanism over this bimetallic catalyst, the first principles based simulation under the framework of density functional theory was performed. We have found that the presence of Cu gives rise to an improved charge localization at the O-vacancy site alongside favourable reaction kinetics, which results in an enhanced catalytic activity for the CuFe2O4 nano-cluster compared to that of a single metallic catalyst containing Fe2O3 nano-cluster.

Performance analysis of hydrogen iodide decomposition membrane reactor under different sweep modes

Hydrogen iodide decomposition is the core hydrogen production step in the sulfur-iodine thermochemical cycle, which determines the hydrogen production rate and thermal efficiency of the device. The conventional decomposition reactor is limited by equilibrium conditions, so the hydrogen iodide conversion rate is low at normal reaction temperature, and membrane reactor technology can break the limit of equilibrium condition and greatly improve the conversion rate. Most of the previous hydrogen iodide membrane reactor models were built under isothermal conditions and did not consider the influence of different sweep modes. In this paper, a one-dimensional non-isothermal hydrogen iodide decomposition membrane reactor mathematical model in co-current and countercurrent sweep modes is established, and the effects of reactor parameter on hydrogen iodide conversion and hydrogen recovery rate are analyzed under the two sweep modes. The results show that the countercurrent mode can obtain higher hydrogen iodide conversion rate than the co-current mode under larger sweep flow rate, inlet pressure of reaction and permeation zone, reactor length; the maximum recovery rate of hydrogen in countercurrent mode is close to 100%. A modified membrane reactor structure combining the traditional reactor and membrane reactor is proposed, which could effectively increase the hydrogen permeation flux per unit membrane surface. In engineering application, the reasonable design of the modified membrane reactor can effectively reduce the investment cost of the membrane reactor on the premise of satisfying the hydrogen production rate.

Investigation of hydrogen production by sulfur‐iodine thermochemical water splitting cycle using renewable energy source

In this study, a novel integrated structure for generation of the oxygen, hydrogen, power, and hot water by employing thermochemical reactors and solar dish collectors is proposed. The presented process including solar dish collectors, sulfur-iodine thermochemical cycle, and Organic Rankine Cycle. In this configuration, for 5854 kmol/h of inlet water, 2236 kmol/h of oxygen, and 4432 kmol/h of hydrogen are produced. This system can provide 22 666 kW of power that 22 026 kW is utilized in the sulfur-iodine reaction. So, the net electrical power is found to be 640 kW. A general exergy analysis is carried out on the whole structure and equipment to find its exergy losses and improvement potential to enhance the exergy efficiency of the system. The total exergy efficiency of the process is calculated 56.33% and its exergy destruction is obtained 382 301.31 kW. Heat exchangers and solar collectors have the highest values of destructed exergy, which about 69% of destructed exergy is related to them. These devices have a strong potential for enhancement. The results showed that component P1 (pump) has the lowest exergy efficiency that is 15.58%, while its exergy destruction is not the greatest. Therefore, for having a better examination of this structure, both exergy efficiency and exergy destruction parameters should be evaluated simultaneously. Moreover, a sensitivity analysis is applied to survey the performance of some performance indicators vs different design parameters. It is concluded that by an increase in generated heat by solar collectors, exergy efficiency, energy efficiency, oxygen, and hydrogen production faces increment.

Minimization of Entropy Generation Rate in Hydrogen Iodide Decomposition Reactor Heated by High-Temperature Helium.

The thermochemical sulfur-iodine cycle is a potential method for hydrogen production, and the hydrogen iodide (HI) decomposition is the key step to determine the efficiency of hydrogen production in the cycle. To further reduce the irreversibility of various transmission processes in the HI decomposition reaction, a one-dimensional plug flow model of HI decomposition tubular reactor is established, and performance optimization with entropy generate rate minimization (EGRM) in the decomposition reaction system as an optimization goal based on finite-time thermodynamics is carried out. The reference reactor is heated counter-currently by high-temperature helium gas, the optimal reactor and the modified reactor are designed based on the reference reactor design parameters. With the EGRM as the optimization goal, the optimal control method is used to solve the optimal configuration of the reactor under the condition that both the reactant inlet state and hydrogen production rate are fixed, and the optimal value of total EGR in the reactor is reduced by 13.3% compared with the reference value. The reference reactor is improved on the basis of the total EGR in the optimal reactor, two modified reactors with increased length are designed under the condition of changing the helium inlet state. The total EGR of the two modified reactors are the same as that of the optimal reactor, which are realized by decreasing the helium inlet temperature and helium inlet flow rate, respectively. The results show that the EGR of heat transfer accounts for a large proportion, and the decrease of total EGR is mainly caused by reducing heat transfer irreversibility. The local total EGR of the optimal reactor distribution is more uniform, which approximately confirms the principle of equipartition of entropy production. The EGR distributions of the modified reactors are similar to that of the reference reactor, but the reactor length increases significantly, bringing a relatively large pressure drop. The research results have certain guiding significance to the optimum design of HI decomposition reactors.

Dynamic Simulation of Hydrogen Iodide Decomposition in Catalytic Multi-Tubular Reactor

Sulfur-Iodine thermochemical cycle process has been considered a promising method to generate hydrogen from water. One of the main limitations of this process lies in the hydrogen iodide decomposer section, which requires substantial amount of heat at high temperature. The present study analyses the heat transfer limitation effect on the performance of hydrogen iodide decomposition in a multi-tubular catalytic reactor by means of dynamic simulation. The extensive numerical simulation shows that the inlet temperature heating medium (Helium gas) should be at least 700°C so to enable at least 90% conversion when the inlet molar fraction of hydrogen iodide is 0.6. Lowering the inlet heating medium will require the reduction in the inlet molar fraction of hydrogen iodide in order to keep the conversion at 90% and above.

Design of 24/7 continuous hydrogen production system employing the solar-powered thermochemical S–I cycle

We propose a system design for continuous and emission-free hydrogen production using the thermochemical Sulfur–Iodine cycle. Process heat required for the sulfuric acid decomposition is exclusively generated by a combination of concentrating solar thermal parabolic trough and solar tower systems, which are operated during the daytime only. The proposed design relies on the decoupling of the high temperature section from the rest of the process through material and energy storage for continuous operation. We conceptually design the whole process via steady-state simulation and assess its thermal efficiency and economics. We reveal that the proposed system is comparable to its alternatives in terms of the heat-to-hydrogen efficiency (38.0%) and the levelized cost of hydrogen 10.4$/kgH2. Since the levelized cost is primarily attributed to the capital investment, enlarging the proposed system will lead to significant cost reduction due to economies-of-scale.

Materials resistance to corrosion by I2–HI–H2O mixtures for the realization of a sulfur-iodine plant

The substances involved in the sulfur-iodine (SI) thermochemical cycle to produce H2 by water splitting are very corrosive and may attack reactors, pumps, catalysts supports, and whatever part of the plant. This paper investigates the corrosion exerted by HI solutions in liquid, boiling, and gaseous phase at different temperatures. It shows the broadest overview of the behavior of different materials, ranging from pure metals to metallic alloys, from carbon materials to organic polymers, from ceramic materials to composite ones. Commercial nickel alloys and the effect of a specific element in their composition have here considerable attention. Regarding the composites materials, the impact of the substrate as well as the coating nature and thickness is studied, also through SEM-EDS (Scan Electron Microscope Energy Dispersive Spectroscopy) investigations.Carbon materials performed well, while most of the analyzed materials showed intergranular corrosion, pitting phenomena, and sometimes, carbide precipitation in the higher energy zones.

Experimental Study for HIx Concentration by Electro-Electrodialysis (EED) Cells in the Water Splitting Sulfur-Iodine Thermochemical Cycle

The efficiency of HI concentration/separation from a HIx solution, (mixture of HI/H2O/I2) represents a crucial factor in the sulfur-iodine thermochemical water splitting process for hydrogen production. In this paper, an experimental study on HI cathodic concentration in HIx solution using stacked electro-electrodialysis (EED) cells was carried out under the conditions of 1 atm and at three different temperature (25, 55 and 85 °C) and using a current density of 0.10 A/cm2. Results showed that an increase in HI concentration can be obtained under certain conditions. The apparent transport number (t+) in all the experiments was very close to 1, and the electro-osmosis coefficient (β) changed in a range of 1.08–1.16. The tests showed a detectable, though slow, increase in both the anodic iodine and cathodic hydriodic acid concentrations.

Catalytic performance of semi-coke on hydrogen iodide decomposition in sulfur-iodine thermochemical cycle for carbon dioxide-free hydrogen production

Sulfur-iodine thermochemical water splitting cycle is a promising and carbon dioxide-free method for hydrogen production. Among the reactions in this cycle, hydrogen iodide catalytic decomposition is the rate-determining step. In this study, catalytic reactivity test combined with characterizations of nitrogen physisorption, X-Ray diffraction, and Raman spectroscopy provide evidences that hydrofluoric acid modified semi-coke is a promising catalyst candidate for hydrogen iodide decomposition because of its high active and low cost. The raw semi-coke enhanced the hydrogen iodide conversion rate. After modification of hydrofluoric acid, the catalytic activity of semi-coke increased largely. Semi-coke modified by 40 wt% hydrofluoric acid showed better performance than commercial activated carbon catalyst. Combine the characterization results and catalytic reactivity, the graphitic edge carbon atoms in semi-coke are the active sites for hydrogen iodide decomposition. This finding pointed out the direction of carbon material catalyst design for hydrogen iodide decomposition.

Analyses of the Efficiency of a High-Temperature Gas-Cooled Nuclear Reactor Cogeneration System Generating Heat for the Sulfur–Iodine Cycle

The paper presents the possibilities of the use of a high-temperature gas-cooled nuclear reactor for energy purposes in the hydrogen and electricity production process. The system provides heat for a thermochemical sulfur–iodine cycle producing hydrogen and generates electricity. Its structure and electricity generation capacity are conditioned by the demand for heat and the levels of temperature required at the sulfur–iodine cycle individual stages. In the three structures under analysis, electricity is generated in a gas turbine system and steam systems (steam, low-boiling fluids). The impact of helium parameters in a two-stage compression system with interstage cooling on power efficiency of the analyzed structures of cogeneration systems and on total power efficiency of the systems is investigated assuming that both hydrogen and electricity are produced. Thermodynamic analyses are conducted using the EBSILON Professional program. The aim of the analyses is to determine the optimum structure of the system and parameters of the mediums in terms of power efficiency.

Catalyst Screening and Development for HI Decomposition in Sulfur-iodine Thermochemical Cycle for Hydrogen Production

The intrinsic activities of six important transition metals for HI decomposition were identified by kinetic study. Ru showed high activity and a low apparent activation barrier, indicating a good activity at low temperature. Ru/AC (Ru clusters supported on activated carbon) was designed and proved to be a highly active, cost-effective, and long-term durable catalyst for HI decomposition. The present work could contribute to catalyst development for the industrialization of the sulfur-iodine thermochemical cycle for hydrogen production.