Hybrid Thermochemical Hydrogen Production

A novel cryogenic-thermochemical approach for clean hydrogen production from industrial flue gas streams with carbon capture and storage

As part of the Next Generation Nuclear Plant (NGNP) project, an evaluation of a low-temperature heat-pump interface design for a nuclear-driven high-temperature electrolysis (HTE) hydrogen production plant was performed using the UniSim process analysis software. The low-temperature interface design is intended to reduce the interface temperature between the reactor power conversion system and the hydrogen production plant by extracting process heat from the low temperature portion of the power cycle rather than from the high-temperature portion of the cycle as is done with the current Idaho National Laboratory (INL) reference design. The intent of this design change is to mitigate the potential for tritium migration from the reactor core to the hydrogen plant, and reduce the potential for high temperature creep in the interface structures. The UniSim model assumed a 600 MWt Very-High Temperature Reactor (VHTR) operating at a primary system pressure of 7.0 MPa and a reactor outlet temperature of 900°C. The low-temperature heat-pump loop is a water/steam loop that operates between 2.6 MPa and 5.0 MPa. The HTE hydrogen production loop operated at 5 MPa, with plant conditions optimized to maximize plant performance (i.e., 800°C electrolysis operating temperature, area specific resistance (ASR) = 0.4 ohm-cm2, and a current density of 0.25 amps/cm2). An air sweep gas system was used to remove oxygen from the anode side of the electrolyzer. Heat was also recovered from the hydrogen and oxygen product streams to maximize hydrogen production efficiencies. The results of the UniSim analysis showed that the low-temperature interface design was an effective heat-pump concept, transferring 31.5 MWt from the low-temperature leg of the gas turbine power cycle to the HTE process boiler, while consuming 16.0 MWe of compressor power. However, when this concept was compared with the current INL reference direct Brayton cycle design and with a modification of the reference design to simulate an indirect Brayton cycle (both with heat extracted from the high-temperature portion of the power cycle), the latter two concepts had higher overall hydrogen production rates and efficiencies compared to the low-temperature heat-pump concept, but at the expense of higher interface temperatures. Therefore, the ultimate decision on the viability of the low-temperature heat-pump concept involves a tradeoff between the benefits of a lower-temperature interface between the power conversion system and the hydrogen production plant, and the reduced hydrogen production efficiency of the low-temperature heat-pump concept compared to concepts using high-temperature process heat.

Polymer electrolyte membrane (PEM) electrolysis is widely considered a promising technology for energy storage and clean hydrogen production, due to the advantages it has over state-of-the-art alkaline water electrolysis.1 Typically, PEM electrolysers can operate at higher current densities than their alkaline counterparts, have a more robust design, and due to the zero-gap design, exhibit smaller Ohmic losses. Furthermore, PEM electrolysers can yield hydrogen at elevated pressures, eliminating the need for compression. Nevertheless, a series of challenges hinder the large-scale commercial implementation of PEM electrolysers. One of the most critical drawbacks is the need for noble metal electrocatalysts, especially at the anode of the cell, such as iridium or ruthenium, to catalyze the oxygen evolution reaction (OER) (1).2H2O → O2 + 4H+ + 4e- E° = 1.23 V vs NHE (1)These metals are used due to their high catalytic activity and long-term stability in the corrosive acidic environment of the PEM cells and their replacement by more available materials is difficult. Over the years, the main efforts of the scientific community towards solving this challenge were focused on increasing the noble metal dispersion, by using various high surface area catalyst supports, using core-shell catalysts, with the aim to minimize the amount of noble metal, modifying the morphology of the electrode, to improve mass transport limitations and electric contact between components and maximize noble metal utilization.2-4 Antimony-doped tin oxide has been reported as a stable OER catalyst support, offering sufficient electronic conductivity at the same, in order to minimize Ohmic losses.5 Furthermore, recent reports indicate that SnO2 does not only act as a catalyst support but takes part in catalysis.6 Building upon literature reports, we prepared a series of Sn/Ir OER catalysts by a two-step sodium borohydride reduction method, in which Sn nanoparticles were deposited over the surface of iridium black particles, decorating it. Catalysts with varying Sn content were incorporated in membrane electrode assemblies (MEAs) and their cell performance was evaluated in a single cell PEM electrolyser. We found that catalysts with up to 20 wt% tin content exhibited an improved cell performance compared to MEAs with similar iridium black loading. We modeled Ohmic, kinetic and mass transport overpotential contributions to experimentally acquired polarization curves and identified that the better cell performance arises mainly from the higher intrinsic catalytic activity, reflected by a higher apparent exchange current density of Sn/Ir OER catalysts compared to Ir black catalysts. The Sn/Ir MEAs also displayed lower mass transport overpotentials, which indicate improved transport in the catalyst layer. This can be due to a more porous structure and less agglomeration of iridium particles induced by the presence of tin over their surface.Interestingly, this performance improvement was only observed for iridium black catalysts. We prepared a series of IrO2-SnO2 catalysts by solution combustion synthesis method, which is known to yield high surface area disperse oxide materials. Comparing the performance of these catalysts to commercial iridium oxide catalysts in the PEM electrolysis cell, the MEAs with SnO2-containing catalysts displayed worse cell performance than MEAs with commercial iridium oxide. Modelling the overpotential contributions showed a lower apparent exchange current density, indicating a lower intrinsic catalytic activity of IrO2-SnO2 catalysts, as well as a higher Ohmic resistance, due to SnO2 addition. These observations indicate the importance of iridium oxidation state for harnessing the promotion effect of tin addition and give important insights into designing more efficient OER catalysts for PEM electrolysis cells.

Modeling of a direct solar receiver reactor for decomposition of sulfuric acid in thermochemical hydrogen production cycles

Hydrogen production using high temperature nuclear reactors: Efficiency analysis of a combined cycle

Hydrogen is a commercially important element. Basically, there are several methods of hydrogen production that have been commercially used, such as Steam Methane Reforming (SMR), High Temperature Steam Electrolysis (HTSE), and thermochemical cycles, like Sulphur-Iodine (SI). Among these methods, SMR is the most widely used for large-scale hydrogen production, with conversion efficiency between 74–85% and it has commercially used in some fertilizer industries in Indonesia. Steam reforming is a method to convert alkane (natural gas) compounds to hydrogen and carbon dioxide (synthetic gas) by adding moisture at high pressure and temperature (35-40 bar; 800-900°C). These hydrogen production technologies can be coupled with different nuclear reactors based on the heat required in the process. The High Temperature Gas-cooled Reactor (HTGR) using helium as a coolant, has a high outlet temperature (900°C), so it can potentially be used to supply for process heat for hydrogen production, coal liquefaction/gasification or for other industrial processes requiring high temperature heat. Hydrogen production cost from SMR method is influenced by a range of technical and economic factors. The fuel component of natural gas needed in the SMR method can be replaced by nuclear heat from a nuclear power plant (NPP) operating in cogeneration mode (i.e. simultaneous producing electric power and heat), hence contributing to the reduction of carbon dioxide in the process.In the SMR method, fuel costs are the largest cost component, accounting for between 45% and 75% of production costs. Therefore, there is opportune to assess the economics of hydrogen production by using nuclear heat. The economic evaluation is done by using IAEA HEEP-4 Software.The results comprise cost break up for 2 cases, coupling SMR process for hydrogen production with: (1) 2 HTGRs of 170 MWth/unit; and (2) 1 HTGR of 600 MWth/unit. The cost of hydrogen production is highly depend on the scale of the NPP as energy source and results indicated that hydrogen production cost of the 1 HTGR Unit600 MWth (Case 2) has a lower value (1.72 US$/kgH2), than the cost obtained when 2 HTGR units of 170 MWth each (case 1) are considered (2.72 US$/kgH2). For comparison, the hydrogen production cost by using SMR with carbon capture and storage (CCS) with natural gas as fuel is 2.27 US$/kgH2.

Introduction Research and development of polymer electrolyte fuel cells (PEFCs) has been conducted to increase their power density. The gas diffusion layer (GDL) and microporous layer (MPL) used in PEFCs are much thicker than the electrocatalyst layer and electrolyte membrane. Down-thinning GDL and MPL is expected to reduce gas diffusion resistance and increase the power density per volume of the cell stack. However, while the electrocatalyst layer and electrolyte membrane have been thinned to about 10 µm each, the MPL/GDL is still thick at about 150 µm. Thinner layers have been shown to reduce the molecular diffusion resistance of oxygen, resulting in a lower concentration overvoltage1. The application of highly conductive MPL can also reduce ohmic overvoltage by reducing contact resistance and electrical resistance. In addition, MPLs with appropriate hydrophilic and hydrophobic properties can prevent flooding in a high current density range2. Previous studies have investigated the possibilities and technical challenges of using porous metals as GDLs, which can be a thin layer with high strength3. In addition, a composite MPL with both hydrophobic and hydrophilic channels was developed and its effect on molecular diffusion resistance was investigated4. Based on these findings, in this study, we try to reduce contact resistance and electrical resistance by printing MPL layer onto carbon mesh, which is relatively stable and thinner than carbon paper, an existing material, as GDL, and to reduce molecular diffusion resistance by thinning the carbon mesh. We also add polytetrafluoroethylene, a hydrophobic material, and tin oxide, a hydrophilic material, to control hydrophobicity and hydrophilicity of MPLs. The objective of this study is to develop a self-supporting thin-layer MPL/GDL for improved power density. Experimental In this study, the MPL/GDL was fabricated by printing a MPL onto a carbon mesh (50 µm thick, Cosmotech, Japan) as a GDL using a screen-printing method. Cells were fabricated by using these materials. Current-voltage characteristics measurements, microstructure observation, and gas diffusion resistance measurements were conducted. The MPLs were initially composed of carbon black, carbon nanotubes (CNT), polytetrafluoroethylene (PTFE), hydrophilic tin oxide (SnO2), and solvent (a mixture of polyethylene glycol 600, and water). The MPL/GDL preparation was completed by heat treatment at 300°C for 30 min to remove solvent. A standard Pt/C electrocatalyst (TEC10E50E, Tanaka Kikinzoku, Japan) was used for preparing membrane-electrode assemblies (MEAs). As the electrochemical characterization in this study, current-voltage characteristics were evaluated using an electrochemical impedance analyzer (SAS SP-240, Bio-Logic Science Instruments, France), various overvoltages were separated, and molecular resistance of oxygen was measured. Microstructural observations were conducted using a focused ion beam scanning electron microscope (FIB-SEM). Results and discussion Figure 1 (a) shows the current-voltage characteristics of the cell using various MPL/GDLs. The thickness of the MPL/GDLs fabricated was about 80 µm. For comparison, the characteristics of a cell using a standard, commercially-available MPL/GDL (22BB, SGL Carbon, Germany) are also shown. These results show that the use of MPL significantly improves cell performance even with thin GDLs. Using a highly conductive material for the MPL and applying it to carbon-based fibrous materials reduced electrical resistance, and down-thinning MPL/GDLs layers reduced the molecular diffusion resistance of oxygen (Figure 1 (b)). However, the electrical resistance of the GDL substrate is relatively high, and contact resistance is still an issue due to the roughness of the MPL surface in contact with the electrocatalyst layer. If these technical issues can be solved, further improvement in cell performance could be achieved. MPLs with SnO2 showed high performance at a low humidity. This may be due to improved dry-up resistance by the addition of hydrophilic material, whereas flooding was noticeable at high humidity. It is suggested that an appropriate mixture of hydrophobic and hydrophilic channels can enhance the dry-up and flooding resistance of MPLs, resulting in improved cell performance. Acknowledgements This paper is based on results obtained from a project, JPNP20003, commissioned by the New Energy and Industrial Technology Development Organization (NEDO). An educational part for young scientists was supported by the Japan Science and Technology Agency (JST) as a part of Adopting Sustainable Partnerships for Innovative Research Ecosystem (ASPIRE), Grant Number JPMJAP2307. References N. Nonoyama, S. Okazaki, A.Z. Weber, Y. Ikogi, T. Yoshida, J. Electrochem. Soc. 158,B416 (2011).T. Kitahara, T. Konomi, H. Nakajima, and J. Shiraishi, Kikai B, 76 (761), 101 (2010).K. Yamamoto, M. Yasutake, Z. Noda, S. M. Lyth, J. Matsuda, M. Nishihara, A. Hayashi, and K. Sasaki, ECS Trans., 109 (9),265 (2022).P. Wang, H. Nakajima, and T. Kitahara, J. Electrochem, Soc., 171, 014501 (2024). Figure 1

The evidence of the impacts that fossil fuel energy sources have on the environment is inescapable. From poor air quality, warmer temperatures, to contaminated land and water, research thrusts in the use of non-fossil fuel renewable energy sources have greatly increased. There has been a large impact, both economically and environmentally, with the switch to using hydrogen as an energy carrier and reagent for renewable energy. There is still much room for improvement, as the current cost per kilogram of hydrogen produced via renewables is $5-6. The DOE is pushing to decrease that cost to $1 per kilogram in the next decade through its Hydrogen Energy Earth Shots thus, making the process more accessible for wide use of hydrogen [1]. Ionomer-based water electrolysis is a promising avenue to gather hydrogen with little to no carbon emissions. Within water electrolysis there are many moving parts that impact the cost and efficiency of hydrogen production. For our interests, we will be working on the understanding of the ionomer membrane and interfaces in the membrane electrode assembly. Currently, fluoropolymers are widely used as polymer membranes within the energy field, although there is concern about their lifelong byproducts from the production and disposal practices. These byproducts have been found in soil, water, and even blood, as a result of contaminated drinking water [2]. By fully understanding the capabilities of these ionomers, we can move away from the predominant use of fluoropolymers which have dominated other options for polymer membrane materials despite their rising environmental and cost concerns [2].We aim to improve these macromolecules by altering both the material’s morphology and chemistry. The morphology of the polymer refers to the backbone and the configuration of how each chain aligns. We believe by studying how different configurations align, such as lamellar and cylindrical stacking, and how these regions react to water swelling, we can observe the most ideal sequence for ionomer-catalyst interactions. These studies will be conducted by testing different copolymer configurations, as in random and block sequences of the backbone monomers, adjusting ratios of monomers, altering linkages between copolymer segments, the changing of side groups, and varying hydrophilic and hydrophobic blocks. As for the polymers’ chemistry, by testing varying ion-conducting groups we can adjust the characteristics of the ionomer itself and how the ionomer works with the catalyst. To do so, we will begin with synthesizing a known ionomer, Polyisoprene-ran-poly(vinylbenzyl chloride) (Pip-ran-PVBCl), via nitroxide-mediated polymerization followed by hydrogenation and quaternization reactions with different cationic groups. Specifically, we will be adding groups of varying lengths of carbon chains, including triethylamine (TEA) and trimethylammonium (TMA) as the longer the carbon chain the lower the Ion Exchange Conductivity (IEC). This is due to the decreasing reactivity of long carbon chains [3]. We expect these to give us a strong baseline of ionomers which we can further test the solubility of to better understand how the different cationic side groups can change the amount of water at the ionomer-catalyst interface.To further test these interactions with the catalysts, working with our colleagues in the Center of Ionomer-based Water Electrolysis (CIWE), through microelectrodes, small-angle x-ray scattering (SAXS), wide-angle x-ray scattering (WAXS), and calorimetry. Through CIWE, we are working with computer scientists who can develop digital twins of this work and therefore bridge the knowledge gap from researcher to consumer. By gathering more data and through machine learning we can improve the ionomers for use in ionomer-based water electrolysis, so that we can aid in the push to harness efficient hydrogen production materials for future hydrogen production.

Uranium thermochemical cycle used for hydrogen production

Neutronic analyses were performed in a hybrid reactor using 50% TRISO coated CANDU spent nuclear fuel and 50% Th mixture as fuel and natural Li as coolant. The XSDRNPM/SCALE nuclear code program was used for neutronic analyses. Under these conditions, the hybrid reactor operated for 48 months. TBR and M values were calculated from neutronic analyses. At the beginning of the 48-month operation period, the TBR value was approximately 1.176, while at the end of the operation period, this value was approximately 1.196. The M value was calculated as approximately 1.653 and 1.869 at the beginning and end, respectively. In addition, the amount of hydrogen production in the hydrogen production facility integrated into the reactor was examined. The vanadium-chloride (V-Cl) thermochemical cycle was preferred as the hydrogen production method. The approximate hydrogen production amount at the beginning and end of the 48-month operation period of the plant was calculated as 1,659 kg/s and 2,287 kg/s. As a result, it seems that the hybrid reactor and vanadium chloride (V-Cl) thermochemical cycle are preferable for hydrogen production

Hydrogen production by water-splitting thermochemical cycle based on manganese ferrite/sodium carbonate reactive system is reported. Two different preparation procedures for manganese ferrite/sodium carbonate mixture were adopted and compared in terms of material capability to cyclical hydrogen production. According to the first procedure, conventionally synthesized manganese ferrite, i.e., high temperature (1250°C) heating in Ar of carbonate/oxide precursors, was mixed with sodium carbonate. The blend was tested inside a temperature programed desorption reactor using a cyclical hydrogen production/material regeneration scheme. After a few cycles, the mixture resulted rapidly passivated and unable to further produce hydrogen. An innovative method that avoids the high temperature synthesis of manganese ferrite is presented. This procedure consists in a set of consecutive thermal treatments of a manganese carbonate/sodium carbonate/iron oxide mixture in different environments (inert, oxidative, and reducing) at temperatures not exceeding 750°C. Such material, whose observed chemical composition consists of manganese ferrite and sodium carbonate in stoichiometric amounts, is able to evolve hydrogen during 25 consecutive water-splitting cycles, with a small decrease in cyclical production efficiency.

Hydrogen production by water splitting with Mn3-xCoxO4 mixed oxides thermochemical cycles: A thermodynamic analysis

Life cycle assessment of nuclear-based hydrogen and ammonia production options: A comparative evaluation

Advances in fuel-cell technology and an increasing demand for hydrogen are driving the need for the development of more efficient methods to produce hydrogen. Thermochemical cycles, which produce pure hydrogen by splitting water through a series of chemical reactions, are being investigated as avenues for producing hydrogen efficiently on a large scale. Although there are hundreds of possible thermochemical cycles, the hybrid-sulfur process is the only practical, all-fluid, two-step thermochemical cycle. In a solar-driven process, solar radiation is used in a solar receiver/reactor to provide the energy needed to vaporize and decompose sulfuric acid. The resulting sulfur dioxide (SO2) is used in the second step consisting of an SO2-depolarized electrolyzer (SDE) that electrochemically oxidizes SO2 with water to form sulfuric acid at the anode and hydrogen at the cathode. All the sulfur species are internally recycled and the overall reaction is the splitting of water to form hydrogen and oxygen. We report here on our patented gas-fed SDE that was tested over a range of operating conditions (e.g., current, temperature) and design variations (e.g., membrane type and thickness). A key insight from our work is that perfluorinated sulfonic acid membranes like Nafion® dehydrate at high acid concentrations, leading to high membrane resistance. Using acid-doped polybenzimidazole membranes represent an alternative material because they do not rely on water for their proton conductivity, and they can operate at temperatures above 100 °C.

Energy and exergy analyses of magnesium-chlorine (Mg-Cl) thermochemical cycle