High Temperature Steam Electrolysis Research Articles

Effect of coatings on long term behaviour of a commercial stainless steel for solid oxide electrolyser cell interconnect application in H2/H2O atmosphere

K41X (AISI 441) stainless steel evidenced a high electrical conductivity after 3000 h ageing in H2/H2O side when used as interconnect for solid oxide electrolyser cells (SOEC) working at 800 °C. Perovskite (La1 − xSrxMnO3 − δ) and spinel (Co3O4) oxides coatings were applied on the surface of the ferritic steel for ageing at 800 °C for 3000 h. Both coatings improved the behaviour of the steel and give interesting opportunities to use the K41X steel as interconnect for hydrogen production via high temperature steam electrolysis. Co3O4 reduced into Co leading to a very good Area Specific Resistance (ASR) parameter, 0.038 Ω cm2. Despite a good ASR (0.06 Ω cm2), La1 − xSrxMnO3 − δ was less promising because it partially decomposed into MnO and La2O3 during ageing in H2/H2O atmosphere.

Parametric study of an efficient renewable power-to-substitute-natural-gas process including high-temperature steam electrolysis

Power-to-Substitute Natural Gas processes are investigated to offer solutions for renewable energy storing or transportation. In the present study, an original Power-to-SNG process combining high-temperature steam electrolysis and CO2 methanation is implemented and simulated. A reference process is firstly defined, including a specific modelling approach of the electrolysis and a methanation modelling including a kinetic law. The process also integrates a unit to clean the gas from residual CO2, H2 and H2O for gas network injection. Having set all the units, simulations are performed with ProsimPlus 3™ software for a reference case where the electrolyser and the methanation reactors are designed. The reference case allows to produce 67.5 Nm3/h of SNG with an electrical energy consumption of 14.4 kW h/Nm3. The produced SNG satisfies specifications required for network injection. From this reference process, two sensitivity analyses on electrolysis and methanation working points and on external parameters and constraints are considered. As a main result, we observe that the reference case maximises both process efficiency and SNG production when compared with other studied cases.

Study of the Efficiency of a HT Power-to-Gas Process

Power-to-Gas processes are investigated since they offer solutions for renewable energy storing and transportation. In the present study, an original Power-to-Substitute Natural Gas (SNG) process combining high-temperature steam electrolysis and CO2 methanation is designed and simulated. A specific modelling approach of the electrolysis based on experimental measurements is used, and a methanation modelling involving a kinetic law is also introduced. Both of these modelling are then integrated into the whole process simulation as well as a unit for residual CO2, H2 and H2O gas cleaning. Having set all the process units, simulation is performed for a reference case where the electrolyser and the methanation reactors are designed. This case allows to produce 2.7 Nm 3 SNG/h/m 2 SOEC with an electrical-to-HHV fuel efficiency equalling 74.5 %, whereas current low-electrolysis processes show an HHV efficiency near 60 %. The produced SNG meets the specifications required for network injection. A sensitivity analysis has been made around the working point conditions of the electrolyser and the methanation units. From this study, we observed that no parameter set allows to have higher values of both process efficiency and SNG production than in the reference case.

Effects of Current Collector Positions on Temperature and Reactive Current Distributions in a Micro-Tubular Solid Oxide Electrolysis Cell

A two-dimensional tubular model of a Ni+YSZ electrode supported micro-tubular solid oxide electrolysis cell (SOEC) was developed to clarify its temperature distribution on high temperature steam electrolysis. The entropy change of SOEC is endothermic and the temperature distribution is more complex than that of SOFCs. In addition, in the micro-tubular SOEC, large bias of reaction distributions can be occurred by current collecting position, and it will lead further complicated thermal transport phenomena and big thermal distributions. Therefore, in this model, heat, mass, electric charge transport and electrochemical reaction were calculated simultaneously. The overpotential and the temeprature change were validated by experimental i-V curves and temperature changes of micro-tubular SOEC. The numerical results suggest that effects of current collector position were not small and cannot be ignored in micro-tubular SOEC operation.

Redox-reversible niobium-doped strontium titanate decorated with in situ grown nickel nanocatalyst for high-temperature direct steam electrolysis.

Composite cathodes based on Sr0.94Ti0.9Nb0.1O3 (STNO) can be utilized for direct steam electrolysis; however, the insufficient electrocatalytic activity limits electrode performance and current efficiency. In this work, redox-reversible (Sr0.94)0.9(Ti0.9Nb0.1)0.9Ni0.1O3 (STNNO) with A-site deficiency and B-site excess has been designed as a cathode material in an oxide-ion-conducting solid oxide electrolyzer for direct steam electrolysis. The XRD, TEM, SEM, EDS, TGA and XPS results together confirm that the exsolution or dissolution of Ni nanoparticles anchored on the STNO surface is completely reversible in the redox cycles. The electrical properties of STNO and STNNO are investigated and correlated to electrode performances. The current efficiency with an STNNO cathode is enhanced by about 20% compared to the values with a bare STNO cathode in 5% H2O/H2/Ar or 5% H2O/Ar at 800 °C. The synergetic effect of catalytically active nickel nanoparticles and the redox-stable STNO skeleton contributes to the improved performance and excellent stability of the cathode for steam electrolysis.

Degradation study by 3D reconstruction of a nickel–yttria stabilized zirconia cathode after high temperature steam electrolysis operation

Microstructural evolution of a Solid Oxide Electrolyser Cell (SOEC) Ni–YSZ cermet cathode is investigated using three dimensional electrode characterisations. 3D reconstructions are obtained on a reference and two long-term tested cells, which were maintained at −0.5 and −0.8 A cm−2 for 1000 h at 800 °C. During the long term tests, air was fed at the anode and a mixture of 10% H2–90% H2O was fed at the cathode. In this framework, reconstructions have been obtained from synchrotron X-ray nano-tomography technique. Microstructural properties extracted from the 3D reconstructions exhibit an evolution during the tests. Triple Phase Boundary length is decreasing from 10.49 ± 1.18 μm−2 for the reference cell to 6.18 ± 0.6 μm−2 for the long term tested cell at −0.8 A cm−2. Evolutions of morphological parameters were introduced in an in-house multi-scale model to evaluate their impacts on the electrode degradation, and hence, on the global SOEC performance.

Design and simulation of hybrid solar high-temperature hydrogen production system using both solar photovoltaic and thermal energy

Hydrogen demand should significantly increase in the next few years due to rapid growth of energy demand, the refinery industry’s growing needs and applications such as biofuel production. To meet the demand advanced processes are being developed throughout the world in a sustainability context. Among the most studied ones is high temperature electrolysis of steam using solar photovoltaic and thermal energy. In this work, a large scale hybrid solar hydrogen production system was designed and optimized. The system consists of the solid oxide steam electrolysis system coupled to a Photovoltaic array through a Direct Current converter and coupled to a Parabolic Trough Collector through a heat exchanger network optimized using a Generalized Reduced Gradient algorithm. Under local tropical conditions, the theoretical production rate of hydrogen per second and per day recorded from simulation of interconnected system based on optimum scenario are respectively 0.064kg/s and 1843.2kg/day. The exergy efficiency, land used and water consumption of system component was also performed.

Enhanced Performance of Ag-Doped Oxygen Electrode Based Solid Oxide Electrolyser Cell under High Temperature Electrolysis of Steam

Solid oxide electrolyser (SOE) has been receiving increasing attention due to its potential applications in large-scale hydrogen production and carbon dioxide recycling for fuels. Improving the performance of SOE cell through oxygen electrode development has been of main interest because the major polarization loss of the SOE cell is at the oxygen electrode during high temperature electrolysis (HTE). In the present study, Ag was doped into (La0.75Sr0.25)0.95MnO3+δ(LSM) based oxygen electrode of Ni/YSZ cathode-supported SOE cell through a solid state method enhanced by ball milling. Short stacks were manufactured using doped and undoped cells and tested under HTE of steam at 800°C up to 150h for in situ comparative study of doping effect. The cells with doped oxygen electrodes showed less polarization loss, lower resistance and improved performance by comparison with the undoped cell. Post-mortem examination revealed Ag migrated from the current collecting layer to the electrolyte/anode interface, which may promote the cell performance.

Selection and study of basic layered cobaltites as mixed ionic–electronic conductors for proton conducting fuel cells

Abstract High Temperature Steam Electrolysis using Proton Conducting Cells is a promising method for large-scale hydrogen production, but such system requires the development of new electrode materials ideally presenting Mixed Proton and Electron Conductivity. Different cobaltites were investigated in terms of durability and compatibility with the BaZr0.9Y0.1O3 proton conducting electrolyte. REBaCo2O5+δ (RE = Pr, Nd, Sm, Gd, Y), YBaCo4O7, Ca3Co4O9 and Ca3Co2O6, were considered, among which the vacancy ordered perovskites were found to be the most stable in wet air. Oxygen vacancy formation and hydration properties of REBaCo2O5+δ were studied by iodometry and TGA in dry and wet atmospheres, respectively.

Composite titanate cathode enhanced with in situ grown nickel nanocatalyst for direct steam electrolysis

This paper investigates the reversible exsolution of a Ni nanocatalyst anchored on the surface of La0.3Sr0.7TiO3−δ (LSTO) for enhancing the electrocatalytic activity of the composite cathode. The metallic Ni nanoparticles significantly enhance the electrode performance and elevate the current efficiency of the electrode in high-temperature steam electrolysis. The combination of XRD, SEM, EDS and XPS results confirms that the exsolution and dissolution of the Ni nanoparticles are completely reversible in redox cycles. The electrical conductivities of the Ni-loaded samples accordingly improved as well. The synergetic effects of the Ni nanocatalyst and redox-stable titanate contribute to the excellent stability and improved performance for direct steam electrolysis. The current efficiencies with Ni-anchored LSTO can be accordingly enhanced by 20% in contrast to the bare cathode with or without reducing gas flowing over the cathode under the applied voltage of 2.0 V at 800 °C.

Perovskite titanate cathode decorated by in-situ grown iron nanocatalyst with enhanced electrocatalytic activity for high-temperature steam electrolysis

The use of perovskite titanate as composite cathode for direct steam electrolysis has demonstrated promising performances due to its unique specific redox-stable properties. However, the insufficient electro-catalytic activity of the perovskite titanate remains a major setback that inhibits the electrode performance. This study addresses the drawbacks and reports an investigation of iron doped titanate (La0.2Sr0.8)0.9Ti0.9Fe0.1O3-δ (LSTFO), which can be reduced to in-situ grown iron nano-catalyst on substrate, as a potential composite cathode for steam electrolysis in a solid oxide electrolyser. Results of XRD, SEM, EDS, XPS and TGA analysis together confirm that the exsolution and dissolution of the iron nanoparticles is completely reversible in redox treatment cycles. The electrical properties of the LSTO and LSTFO are investigated and correlated to the performances of the composite electrodes. The presence of exsolved iron nanocatalyst significantly enhanced the polarizations of the symmetrical and electrolysis cells of the LSTFO composite electrode. The synergetic effect of catalytically-active iron and redox-stable LSTO produced excellent short-term stability of the cathode with attendant efficient electrochemical reduction of steam and remarkable enhancement of Faraday efficiency by about 100%.

Reversibly in-situ anchoring copper nanocatalyst in perovskite titanate cathode for direct high-temperature steam electrolysis

This paper investigates a potential cathode material (La0.2Sr0.8)0.9Ti0.9Cu0.1O3−δ (LSTCO) with A-site deficiency and B-site excess which was designed as a parent material for anchoring exsolved copper nanocatalyst on the surface of La0.2Sr0.8TiO3+δ (LSTO) through a high-temperature reduction. Physical characterization of the samples by combined use of X-ray diffraction, scanning electron microscope, energy-dispersive spectroscopy, thermogravimetric analyzer and X-ray photoelectron spectroscopy indicated that the exsolution and dissolution of the Cu nanoparticles in the cathode was completely reversible in the redox cycles. Electrical properties of LSTO and LSTCO were systematically investigated which correlated closely with electrochemical performance of the composite electrodes in symmetrical cells and electrolysis cells. Polarization resistance (Rp) of the symmetrical cells was improved from 3 Ω cm2 of the LSTO to 1.5 Ω cm2 of the LSTCO in hydrogen atmosphere at 800 °C. Current efficiencies of the solid oxide electrolyzer with Cu-anchored LSTO cathode were found to be enhanced by approximately 20% compared to the bare cathode with or without reducing gas flowing over them under the applied voltage of 2.0 V at 800 °C, respectively.

Development of a Cost-Efficient and Performing High Temperature Steam Electrolysis Stack

The main challenges for High Temperature Steam Electrolysis (HTSE) to become competitive towards other hydrogen production technologies are the increase of performance and durability and the decrease of cost. For that purpose, a “low-weight” stack has been designed, including advanced cells and stack components. A performance of -1.9 A.cm-2 at the thermoneutral voltage of 1.3 V has been obtained at 800°C at the scale of a 3-cell stack and its robustness upon thermal cycling has been validated. The upscaling of the technology has been checked with a stack of 10 cells that allowed producing 0.9 Nm3.h-1 of hydrogen. Techno-economical analysis showed that this low-weight design led to a considerable decrease of the stack cost.

Effect of Coatings on a Commercial Stainless Steel for SOEC Interconnect Application in Anode Atmosphere

The high temperature steam electrolysis (HTE) represents one of the most promising technologies for mass hydrogen production. A commercial K41X steel (AISI441) containing 18 wt. % of chromium was tested as interconnect for solid oxide electrolyser cells (SOEC). In a previous paper, it was shown that the uncoated alloy is not suitable for SOEC interconnect application at 800°C in O2-H2O atmosphere. It was also proved that the application of a LaNi0.6Fe0.4O3-δ coating on the surface by physical vapour deposition process improves the alloy electrical behaviour and reduces chromium species evaporation. For this study, the same coating was deposited on the alloy surface by screen-printing process. Moreover, two spinel-type oxides, Co2MnO4 and Co3O4, deposited by physical vapour deposition process, were also tested in O2-H2O atmosphere at 800°C. The electrical conductivity did not present any improvement, but the Cr species volatility was reduced, especially with the LaNi0.6Fe0.4O3-δ coating.

Durability of Solid Oxide Electrolysis Cell and Interconnects for Steam Electrolysis

Durability of a solid oxide electrolysis cell tested at -1.5A/cm2 for high temperature steam electrolysis was investigated in the present work under stack relevant conditions. Detailed electrochemical and microstructural analyses were carried out. The results show that both the hydrogen and the oxygen electrodes degraded during the durability test. The degree of percolation loss in the active Ni-YSZ hydrogen electrode is found to decrease along the steam flow direction whereas the formation of cracks or cavities/pores within the electrolyte shows the opposite trend. The influence of sealing and interconnects on cell degradation under harsh electrolysis conditions is further discussed.

Perovskite Chromates Cathode with Exsolved Iron Nanoparticles for Direct High-Temperature Steam Electrolysis

Recently, composite cathodes based on doped lanthanum chromates have been widely employed for direct steam electrolysis. However, this approach limits the electrode performances and Faraday efficiency due to insufficient electrocatalytic activity. This study addresses the drawbacks and reports an improved electrocatalytic activity and Faraday efficiency of composite cathode with a reversibly exsolved iron nanoparticles anchored on the surface of doped lanthanum chromates. A-site deficient and B-site excess (La0.75Sr0.25)0.85(Cr0.5Fe0.5)0.85Fe0.15O3-δ (LSCrFF) was designed as the parent material to anchor the exsolved iron nanoparticles on the surface of perovskite chromate (La0.75Sr0.25)(Cr0.5Fe0.5)O3-δ (LSCrF) via high-temperature reduction. The electrical properties of LSCrF and Fe/LSCrF were systematically investigated and correlated with electrochemical performance of the composite electrodes in symmetrical cells and electrolysis cells. The iron nanoparticles significantly improve the electrical conductivity of LSCrF from 1.80 to 6.35 S cm(-1) for Fe/LSCrF at 800 °C and Po2 of 10(-15) atm. The polarization resistance, Rp, of the symmetrical cells was accordingly enhanced from 4.26 Ω cm2 with LSCrF to 2.58 Ω cm2 with Fe/LSCrF in hydrogen atmosphere at 800 °C. The Faraday efficiency for the direct steam electrolysis showed a marked increase of 89.3% with LSCrFF cathode at 800 °C and 1.8 V as opposed to 76.7% with the cathodes based on LSCrF. The synergetic effect of catalytic-active iron nanoparticles and redox-stable LSCrF substrate produced improved performances and excellent stability for the direct steam electrolysis without a flow of reducing gas over the composite cathodes.

Perovskite chromates cathode with resolved and anchored nickel nano-particles for direct high-temperature steam electrolysis

Doped lanthanum chromates are now commonly used to prepare composite cathodes for direct steam electrolysis. However, the limitation of electrochemical performances and cell current efficiency by insufficient electro-catalytic activity is a major challenge. This paper reports the use of reversibly exsolved catalytic metallic Ni nano-particles on A-site deficient and B-site excess perovskite (La0.75Sr0.25)0.95(Cr0.8Ni0.2)0.95Ni0.05O3−δ (LSCNNi), in order to achieve an activity-enhanced composite cathode via high-temperature reduction under reducing atmospheres. The electrical properties of the ceramic are investigated methodically and correlated with the performances of the composite electrodes in symmetric and electrolysis cells. XRD, SEM, EDS and XPS results, confirm that the exsolution or dissolution of nano metallic catalyst is reversible in redox treatment cycles. The Faradic efficiency reaches approximately 80% for the LSCNNi cathode with the flow of 5%H2/Ar. Ultimately, the unified effect of metallic catalyst and redox-stable ceramic produce striking redox stability as well as electrochemical performances of the titled composite cathode. The results signify that the composite cathode with exsolved nickel nano-particles, is a good potential fuel electrode for direct steam electrolysis in an oxygen-ion conducting solid oxide electrolyzer.

Composite cathode La0.4Sr0.4TiO3−δ–Ce0.8Sm0.2O2−δ impregnated with Ni for high-temperature steam electrolysis

Composite Ni–SDC (Samaria doped Ceria) cathodes are able to operate in strong reducing atmospheres for steam electrolysis, and composite cathodes based on redox-stable La0.4Sr0.4TiO3 (LSTO) have demonstrated promising performances without the reducing gas flow. However, the electro-catalytic activity of cathodes based on LSTO is insufficient for the efficient electrochemical reduction of steam or carbon oxide. In this work, catalytic-active Ni nanoparticles were loaded on a La0.4Sr0.4TiO3−δ–Ce0.8Sm0.2O2−δ cathode (Ni-loaded LSTO–SDC) via an impregnation method to improve the electrode performances for direct steam electrolysis. The synergetic effect of catalytically-active Ni nanoparticles and the redox-stable LSTO–SDC skeleton contributed to the improved performances and the excellent stability of the cathode for direct steam electrolysis. The current efficiency with a Ni-loaded cathode was enhanced by 3% and 17% compared to the values with a bare LSTO–SDC cathode under 2.0 V of applied voltage at 800 °C with a flow of 3% H2O/5% H2/Ar and 3% H2O/Ar to cathodes, respectively.

Simulation of a syngas from a coal production plant coupled to a high temperature nuclear reactor

In light of the rapid depletion of the world’s oil reserves, concerns about energy security prompted the exploration of alternative sources of liquid fuels for transportation. One such alternative is the production of synthetic fuel using an indirect coal liquefaction process or coal-to-liquids (CTL) process. In this process, coal is gasified in a gasifier in the presence of steam and oxygen to produce a synthesis gas or syngas consisting mainly of hydrogen and carbon monoxide. The syngas is then converted to liquid fuels and a variety of useful chemicals in a Fischer Tropsch-type synthesis reactor. However, the traditional process for syngas production also produces substantial amounts of carbon dioxide. In fact, only about one third of the carbon in the coal feedstock ends up in the liquid fuel product using traditional CTL technology. If more hydrogen was available than the hydrogen produced during the gasification step, the carbon utilisation of the process could be improved significantly. The high temperature reactor (HTR) is a gas cooled Generation IV nuclear reactor ideally suited to provide power and high temperature heat for carbon neutral production of hydrogen via high temperature electrolysis. The integration of an HTR into a CTL process therefore provides an opportunity to improve the thermal and carbon efficiency of the CTL process significantly. This paper presents a possible process flow scheme for a nuclear assisted CTL process. The system is evaluated in terms of its thermal or syngas production efficiency (defined as the ratio of the heating value of the produced syngas to the sum of the heating value of the coal plus the HTR heat input) as well as its carbon utilisation. If the hydrogen production plant is sized to produce only enough associated oxygen to supply the needs of the gasification plant, syngas is produced at about 63% thermal efficiency, while 71.5% of the carbon is utilised in this process. It was found that the optimum HTR outlet temperature to produce hydrogen with a high temperature steam electrolysis process is 850°C. If enough process heat and power are available and process equipment capacities are sufficient, the carbon utilisation of the process could be improved even further to values in excess of 90%.

Enhanced Performance and Durability of a High Temperature Steam Electrolysis Stack

AbstractHigh temperature steam electrolysis (HTSE) is one of the most promising ways for hydrogen mass production. If coupled to a CO2‐free electricity and a low cost heat source, this process is liable to a high efficiency. High levels of performance and durability, in association with cost‐effective stack and system components are the key points. To reach such goals, a low‐weight stack has been designed, keeping the advantages of the high performing and robust stack previously validated in terms of performance, durability, and cyclability [1], but aiming at reducing the cost by the use of thin interconnects. This low‐weight stack has demonstrated at the scale of a 3‐cell stack a good performance of –1.0 A cm–2 at 1.3 V at 800 °C. Before performing the durability test, preliminary studies at the cell level have been carried out to highlight the effect of two major operating parameters that are the current density and the steam conversion (SC) ratio, those studies being carried out at one temperature, 800 °C. Based on these results, optimized operating parameters have been defined to perform the durability test on the stack, that is –0.5 A cm–2 and a SC ratio of 25%. Degradation rates around 3–4% 1,000 h–1 have been measured. The thermal cyclability of this stack has also been demonstrated with one thermal cycle. Therefore it can be concluded that these results make HTSE technology getting closer to the objectives of performance, durability, thermal cyclability, and cost.