Solid Oxide Steam Electrolyzer Research Articles

Exergoeconomic, carbon, and water footprint analyses and optimization of a new solar-driven multigeneration system based on supercritical CO2 cycle and solid oxide steam electrolyzer using various phase change materials

This study presents an innovative multigeneration for power, cooling load, distilled water, and hydrogen production from solar energy. The proposed system is comprised of a supercritical carbon dioxide (sCO2) ejector refrigeration cycle, a solar still desalination unit (SSDU), and a solid oxide steam electrolyzer (SOSE), integrated with parabolic dish collectors (PDCs) field. Exergoeconomic, carbon footprint (CF), and water footprint (WF) analyses are performed to assess the comprehensive performance of the system using seven inorganic and metal high-temperature PCMs, namely MgCl2, NaCl, LiF-MgF2, NaF-CaF2-MgF2, Zn-Cu-Mg, Cu-Si-Mg, and Cu-Si. It is found that Cu-Si delivers superior thermodynamic performance enhancement, and NaF-CaF2-MgF2 leads to the lowest economic, carbon, and water footprint performances among the desired PCMs. Moreover, multi-objective antlion optimization (MOALO) is conducted to ascertain and compare the maximum exergy efficiency and the minimum product cost, CO2 emission, and water consumption rates of Cu-Si and NaF-CaF2-MgF2. Under optimal conditions, Cu-Si gives an exergy efficiency of 31.27% with hydrogen, net power, cooling capacity, and distilled water production of 44.56 kg/h, 1508 kW, 74.03 kW, and 15.48 kg/h, respectively, and NaF-CaF2-MgF2 yields the lowest cost, CO2 emission, and water consumption rates of 73.55 $/h, 86.338 CO2e/h, and 180.73 kg H2O/h, respectively indicating 11.01%, 5.20% and 7.88% improvements with an 8.98% decrement in exergy efficiency compared with Cu-Si.

A Dynamic Multi-Scale Model for Solid Oxide Cells Validated on Local Current Measurements: Impact of Global Cell Operation on the Electrodes Reaction Mechanisms

A dynamic physically based model has been developed to unravel the complex relationships between the overall Solid Oxide Cells (SOCs) response and the reaction mechanisms taking place in the electrodes. This numerical tool combines modules for different length-scales from the electrode microstructure up to the single repeat unit. First, models have been developed to emulate digital twins of electrode microstructures made of the classical SOCs materials [1]. The microstructural properties of the active layers and the current collectors are then computed on the synthetic volumes and used as inputs in the electrochemical models. The microscale models for the active layers take into account the mass and the charge transport phenomena for the solid and gas phases. For each electrode, the proposed reaction mechanism is split in a sequence of elementary steps with different pathways that can be activated depending on the polarization [2, 3]. The electrode models are finally coupled with a macroscopic description including the cell geometry and the design of the gas channels [4]. This model allows computing the cell polarization curves, the overpotentials and the EIS together with the distribution of the local current density and gas composition in the single repeat unit. This multiscale model has been used to study a typical cell made of the classical SOCs materials: the electrolyte was in Yttria Stabilized Zirconia (YSZ) whereas the hydrogen and oxygen electrodes were respectively composed by a cermet of Nickel and YSZ (Ni-YSZ) and a composite of Lanthanum doped Strontium Cobaltite Ferrite and Ceria doped Gadolinium Oxide (LSCF-CGO). For this cell, the representativeness of the electrodes synthetic microstructures have been checked on reconstructions obtained by tomographic techniques. It has been shown that the synthetic electrodes reproduce accurately the real microstructures. Moreover, the models at the electrode level have been carefully validated on polarizations curves and Electrochemical Impedance Spectra (EIS) measured on symmetrical cells using a three-electrode setup. It is worth noting that the electrodes of the tested symmetrical cells were manufactured using the same materials and composition than the complete cell. Finally, a specific attention has been paid in this work to validate the approach with an original experimental setup allowing the measurement of the local current densities on the full cell without electrode segmentation. This setup is composed of nine symmetrical-spaced pins that perform the measurement of local polarization curves from the inlet to the cell outlet. A campaign of tests has been carried out in fuel cell and electrolysis mode with different temperatures and flow rates. A good agreement has been found between the experimental and simulated data. It has been shown that the model is able to reproduce the evolution of the local polarization curves with a higher current density at the cell inlet. Furthermore, the simulated EIS for the cell have been found to be consistent with the experimental ones. The fully validated model has been used to analyze the cell operation in electrolysis and fuel cell mode. The reaction pathways associated to the elementary steps in the active layers have been discussed depending on the position within the electrodes and the polarizations. This model will then be used to implement the degradation laws such as the Ni agglomeration and compute the loss of cell performances and the remaining useful lifetime [5]. Moreover, the model could be applied to interpret the evolution of the EIS upon operation.[1] H. Moussaoui, J. Laurencin, Y. Gavet, G. Delette, M. Hubert, P. Cloetens, T. Le Bihan, J. Debayle, Stochastic geometrical modeling of solid oxide cells electrodes validated on 3D reconstructions, Computational Materials Science. 143 (2018) 262-276.[2] F. Monaco, E. Effori, M. Hubert, E. Siebert, G. Geneste, B. Morel, E. Djurado, D. Montinaro, J. Laurencin, Electrode Kinetics of Porous Ni-3YSZ Cermet Operated in Fuel Cell and Electrolysis Modes for Solid Oxide Cell Application. Under review. [3] E. Effori, J. Laurencin, E. Da Rosa Silva, M. Hubert, T. David, M. Petitjean, L. Dessemond, E. Siebert, An elementary kinetic model for the LSCF and LSCF-CGO electrodes for solid oxide cells: impact of oxygen partial pressure and degradation on the electrode response. Under review. [4] J. Laurencin, D. Kane, G. Delette, J. Deseure, F. Lefebvre-Joud, Modelling of solid oxide steam electrolyser: Impact of the operating conditions on hydrogen production. Journal of Power Sources. 196 (2011) 2080-2093.[5] M. Hubert, J. Laurencin, P. Cloetens, B. Morel, D. Montinaro, F. Lefebvre-Joud, Impact of Nickel agglomeration on Solid Oxide Cell operated in fuel cell and electrolysis modes. Journal of Power Sources. 397 (2018) 240-251. Figure 1

Integrating a gas turbine system and a flameless boiler to make steam for hydrogen production in a solid oxide steam electrolyzer

Solid oxide steam electrolyzer (SOSE) uses both electricity and steam to produce hydrogen in a large scale. Considering losses in the electrical power transmission and significant amounts of fuel for steam making, it is affordable to integrate the gas turbine (GT) system to the SOSE in the power plant to generate hybrid electrical power-hydrogen fuel. In this paper, design and performance of a hybrid electrical power generation-hydrogen production system are analytically analyzed. To make steam, a flameless boiler is coupled to the GT system using the GT extremely hot exhaust gases as the oxidizer. The results revealed that the turbine inlet temperature (TIT) should be kept more than 1314 K to obtain GT exhaust gases at temperatures higher than 870 K (auto-ignition temperature of methane) to maintain flameless combustion mode in the boiler. By increasing the flameless boiler temperature and consequently enhancing the SOSE steam temperature from 950 K to 1350 K, the rate of overall fuel consumption in the flameless boiler slightly increases, however the hydrogen production rate escalates from 2.2 mol/s to 10.2 mol/s. The novelty of this paper lies on the using the GT exhaust gases enthalpy to run a flameless boiler to drastically mitigate fuel consumption in hydrogen production system. The presented model in this paper can be used to perform more thermochemical analyses to attain insightful understanding of the hybrid electrical power-hydrogen production systems.

Design and analysis of renewable hydrogen production from biogas by integrating a gas turbine system and a solid oxide steam electrolyzer

In this paper, design and performance analysis of a biogas (60%CH4 + 40%CO2) fueled gas turbine (GT) power generation system integrated with a flameless boiler for steam generation for hydrogen production in a solid oxide steam electrolyzer (SOSE) is reported. In this design, the exhaust gases from GT is conducted to a flameless boiler where diluted and preheated exhaust gases are employed as an oxidizer in this process. Using a small amount of biogas in the flameless boiler enables the hybrid system to produce required steam for SOSE process and the whole generated electrical power by GT is employed in SOSE as well to produce hydrogen. The effects of biogas blends and flowrate, turbine inlet temperature (TIT), steam temperature and the electrode characteristics on the performance of the hybrid system are evaluated. The results indicate that by purification of biogas and increasing CH4 concentration up to 80%, the generated electrical power and produced hydrogen of the hybrid system augment 24% and 20% respectively. In GT system, the TIT should be set at the temperatures higher than 1300 K to prepare a desirable circumstance for the operation of flameless mode in the boiler. At the constant electrical power, when steam temperature increases, the overall SOSE potential decreases and consequently the current of the SOSE enhances which result in the enhancement of the overall hydrogen production in high steam temperatures. To increase the steam temperature from 850 K to 1450 K, the rate of overall biogas consumption of the system increases 1% while the amount of overall hydrogen production from SOSE system augments from 0.01 to 0.052 mol/s. The presented analysis in this paper can be employed to perform more analyses to achieve insightful understanding of the green hydrogen production using hybrid systems.

Design and thermodynamic assessment of a biomass gasification plant integrated with Brayton cycle and solid oxide steam electrolyzer for compressed hydrogen production

In this paper, a comprehensive thermodynamic evaluation of an integrated plant with biomass is investigated, according to thermodynamic laws. The modeled multi-generation plant works with biogas produced from demolition wood biomass. The plant mainly consists of a biomass gasifier cycle, clean water production system, hydrogen production, hydrogen compression, gas turbine sub-plant, and Rankine cycle. The useful outputs of this plant are hydrogen, electricity, heating and clean water. The hydrogen generation is obtained from high-temperature steam electrolyzer sub-plant. Moreover, the membrane distillation unit is used for freshwater production, and also, the hydrogen compression unit with two compressors is used for compressed hydrogen storage. On the other hand, energy and exergy analyses, as well as irreversibilities, are examined according to various factors for examining the efficiency of the examined integrated plant and sub-plants. The results demonstrate that the total energy and exergy efficiencies of the designed plant are determined as 52.84% and 46.59%. Furthermore, the whole irreversibility rate of the designed cycle is to be 37,743 kW, and the highest irreversibility rate is determined in the biomass gasification unit with 12,685 kW.

Integration of Solid Oxide Steam Electrolyzer System into the UCI Microgrid to Support High Renewable Use

The goal of this study is to evaluate the impacts and capabilities of dynamically dispatching Solid Oxide Steam Electrolysis (SOSE) systems to support high penetration of renewable photovoltaic sources in the UCI microgrid. The UCI microgrid operation has been simulated as a linear programming problem in Matlab® considering all of its operational constraints to analyze the microgrid behavior to the additional PV installed capacity. Simulations cases consist of current 4 MW PV installed capacity and future PV installed capacities up to 35 MW. The integration of modular SOSE systems in the University of California, Irvine (UCI) microgrid, to absorb the excess Photovoltaic (PV) generated power is investigated in this study for different PV installed capacity. Also, the possibility of utilizing the available excess steam produced in the Heat Recovery Steam Generator (HRSG) as a portion of the required steam in SOSE systems is evaluated. Microgrid simulation results prove that for cases with PV installed capacity greater than 10 MW, the otherwise curtailed excess electricity would be a great potential to be used in SOSE for hydrogen production. The produced hydrogen in high installed capacities would be enough to feed the gas turbine with a gas mixture containing 15% volumetric hydrogen together with hydrogen used in the UCI hydrogen fuel stations. Consequently, natural gas consumption and carbon dioxide production are decreased substantially.

Performance assessment of a new solar energy based cogeneration system for dimethyl-ether and electricity production

A novel renewable energy based integrated system for dimethyl-ether (DME) production and electricity generation is proposed, analyzed thermodynamically and evaluated energetically and exergetically. The DME is produced in a unique way through carbon hydrogenation process to produce pure methanol, and then DME is synthesized from methanol through methanol dehydration process. The hydrogen required for the process is produced using solid oxide steam electrolyzer (SOSE) which is powered by the thermal energy provided by solar heliostat field to generate steam and generate electricity through a steam turbine. The carbon dioxide is captured from steel furnace exhaust gas using chemical absorption method. The present system is modeled and simulated using both Aspen plus process simulation software and Engineering Equation Solver (EES), and assessed according to energy and exergy performance evaluations. The overall system energy and exergy efficiencies are then found to be 28.75% and 32.54% respectively.

Proton conducting reversible SOFC integrated in a solar thermal power generation system

This paper proposes a novel solar thermal power generation system that employs a proton conducting reversible solid oxide fuel cell (RSOFC-H) and a hybrid photovoltaic thermal module. The photovoltaic thermal module supplies electrical power to the solid oxide fuel cell (SOFC) while operating in electrolysis mode. The stored fuel (Hydrogen), generated by electrolysis mode is utilised to generate power in fuel cell mode. Electrochemical modelling and analysis of RSOFC-H is presented in this paper. The working condition of the system is: as a solid oxide steam electrolyser (SOSE) mode during the day time and solid oxide fuel cell (SOFC) mode during night time. Performance analysis of RSOFC-H has been conducted under varying operating and design parameters, such as current density and cell temperature. In SOSE mode of operation, efficiency has been observed to be almost constant with the variation of current density and it is obtained to be 78.31%. During SOFC mode of operation, maximum efficiency obtained is to be 64.62% at cell temperature of 873K and current density of 500A/m2.

Energetic and exergetic assessments of a novel solar power tower based multigeneration system with hydrogen production and liquefaction

Abstract In this article, a thermodynamic investigation of solar power tower assisted multigeneration system with hydrogen production and liquefaction is presented for more environmentally-benign multigenerational outputs. The proposed multigeneration system is consisted of mainly eight sub-systems, such as a solar power tower, a high temperature solid oxide steam electrolyzer, a steam Rankine cycle with two turbines, a hydrogen generation and liquefaction cycle, a quadruple effect absorption cooling process, a drying process, a membrane distillation unit and a domestic hot water tank to supply hydrogen, electrical power, heating, cooling, dry products, fresh and hot water generation for a community. The energetic and exergetic efficiencies for the performance of the present multigeneration system are found as 65.17% and 62.35%, respectively. Also, numerous operating conditions and parameters of the systems and their effects on the respective energy and exergy efficiencies are investigated, evaluated and discussed in this study. A parametric study is carried out to analyze the impact of various system design indicators on the sub-systems, exergy destruction rates and exergetic efficiencies and COPs. In addition, the impacts of varying the ambient temperature and solar radiation intensity on the irreversibility and exergetic performance for the present multigeneration system and its components are investigated and evaluated comparatively. According to the modeling results, the solar irradiation intensity is found to be the most influential parameter among other conditions and factors on system performance.

A novel design of solid oxide electrolyser integrated with magnesium hydride bed for hydrogen generation and storage – A dynamic simulation study

This paper proposes a novel solid oxide steam electrolyser with in-situ hydrogen storage by integrating a magnesium hydride (MH) section with proton-conducting solid oxide electrolysis cell (SOEC) section. Dynamic simulation results show that it takes 1950 s to fully charge the MH section with a 56% H2 storage efficiency without any flow recirculation, when the electrolyser is operated at 1.4V and 4atm, yielding a current density of 4956.40 A/m2. The evolution of temperature, H2 partial pressure and reaction of Mg powder through the charging process are analysed. It is found that the exothermic H2 absorption process of MH section can enhance the performance of the electrolysis process of SOEC section. The effects of operating parameters including operating pressure, electrolysis voltage, and cooling air temperature on the performance of the novel design are investigated by sensitivity studies. Results show that it is beneficial to operate the electrolyser at elevated pressure for shorter absorption time and higher H2 storage efficiency. Increasing the operating voltage can shorten the absorption time, but lower H2 storage efficiency. An optimal cooling air temperature is found at 521K when the electrolyser is operated at 1.4V and 4atm.

Redox-reversible perovskite ferrite cathode for high temperature solid oxide steam electrolyser

In this work, perovskite Sr1−xPrxFeO3-δ (SPF) (x=0.02, 0.04, 0.06, 0.08 and 0.10) are investigated and employed as solid oxide steam electrolyser cathode at 800°C. X-ray diffraction (XRD), scanning electron microscope (SEM), and transmission electron microscopy (TEM) analysis together indicate that the Sr1−xPrxFeO3-δ is redox reversible with a phase transition from cubic to orthorhombic structure in redox cycles. The doping of Pr in A site has remarkably enhanced the electronic conduction to 1.0–1.2Scm−1 at intermediate temperatures in reducing atmosphere. Electrochemical measurements demonstrate that the polarization resistance with Sr0.96Pr0.04FeO3-δ electrode shows the lowest values of 0.25Ω cm2 in symmetric cells in reducing atmosphere at 800°C. Direct steam electrolysis with Sr0.96Pr0.04FeO3-δ cathode shows a current density of 1.64Acm−2 at 2.0V when fed with 5%H2O/Ar. The hydrogen production rate reaches 4.73, 6.68, 8.35 and 10.23mLmin−1cm−2 at 1.4, 1.6, 1.8, 2.0V, respectively, while the highest Faraday efficiency is as high as 97.16% at 1.8V.

Design and analysis of a solar tower based integrated system using high temperature electrolyzer for hydrogen production

This paper studies the integration of solar tower technology and thermal energy storage (TES) with a power plant and a high temperature Solid Oxide Steam Electrolyzer (SOSE) to produce hydrogen from solar energy. The different subsystems are integrated and optimized to achieve high overall energy efficiency, maintain continuous operation, and reduce exergy destruction. In this regard, energy and exergy analyses are conducted to investigate the requirements and performance of the SOSE while powered by a solar tower subsystem. Therefore, the SOSE cell performance is modeled and the hydrogen production is measured based on different cell and solar field operating conditions. The SOSE is modeled as an integral part of a concentrated solar power plant where the power produced is used for hydrogen production as a final product. In order to maintain continuous plant operation, a TES subsystem is integrated. Furthermore, a supercritical carbon dioxide (s-CO2) Brayton cycle is adapted for the power plant for high efficiency energy conversion from thermal to electric energy. The overall integrated system solar-to-hydrogen conversion efficiency is found to be about 12.7% while charging the TES, and 39.5% while discharging (TES-to-hydrogen). These high efficiencies rank this technology as competitive with other renewable hydrogen production technologies. The integrated high temperature TES achieved energy and exergy efficiencies of more than 96%. The main implementation challenges are discussed in addition to the comprehensive energy and exergy analyses which provide deeper insight into the performance of the system components, potential improvements and limitations.

A scandium-doped manganate anode for a proton-conducting solid oxide steam electrolyzer

In this work, catalytic active Sc has been doped into perovskite La0.8Sr0.2MnO3−δlattice to enhance electrode activity and promising electrode performance for steam oxidation has been obtained.

Redox-Reversible Iron Orthovanadate Cathode for Solid Oxide Steam Electrolyzer.

A redox-reversible iron orthovanadate cathode is demonstrated for a solid oxide electrolyser with up to 100% current efficiency for steam electrolysis. The iron catalyst is grown on spinel-type electronic conductor FeV2O4 by in situ tailoring the reversible phase change of FeVO4 to Fe+FeV2O4 in a reducing atmosphere. Promising electrode performances have been obtained for a solid oxide steam electrolyser based on this composite cathode.

Assessment of Pressure Effects on High Temperature Steam Electrolysis Based on Solid Oxide Technology

To manage the grid with renewable electrical sources and ensure their storage, hydrogen chains have to be considered. However, hydrogen must be pressurized before being used or stored. The first levels of compression are less energetic for liquids than for the hydrogen gas, therefore the electrolysis of steam directly under pressure has to be studied. On one hand, with the solid oxide technology, the Open Circuit Voltage (OCV) presents the drawback of increasing with pressure. On the other hand, the pressure might improve the reactive species supply to the electrochemical sites and reduce the related losses. Thus, what are the electrolysis performances under pressure? And is there an energetic gain at the system level to produce pressurized hydrogen? In this context, experimental and modelling approaches have been adopted in order to understand the basic underlying mechanisms of pressurized electrolysis operation. In this frame, SOEC performance tests were realized under pressure in the range of 1 to 10 bars on two types of single commercial cells. They were based on conventional materials and differentiated by their microstructure. Concerning the set-up, the test platform requirements were achieved by developing an innovative mechanical design associated to a specific steam management. Moreover, a previously proposed electrochemical model of solid oxide electrolysis cell was adapted to take into account the pressure effects. The model allows computing all the most important operation parameters such as local current densities, local molar fraction, overpotentials and also the cell microstructural parameters [1]. According to the complete I-V curves from 0 to -1.3 A/cm2 at 800°C with high steam conversion, it has been observed that OCVs respect the Nernst relation under pressure while the limit current appears at higher current values. This work shows that the hydrogen production can be increased thanks to a 10 bars operation at the autothermal voltage. Moreover, these trends have been analyzed with the model. The impact of pressure on the electrochemical performances is much more important in the range of 1 to 5 bars than above. In our experimental conditions, the diffusion improvement in the porous cathode alone can explain this behavior. Finally, the impact of each microstructural parameter on the cell performances with pressure is discussed. The research leading to these results has received funding from the European Union's Seventh Framework Programme (FP7/2007-2013) Fuel Cells and Hydrogen Joint Undertaking (FCH-JU-2013-1) under grant agreement 621173. [1] J. Laurencin, D. Kane, G. Delette, J. Deseure, F. Lefebvre-Joud, Modelling of solid oxide steam electrolyser : impact of the operating conditions on hydrogen production, 2011, Journal of Power Sources, 196, 2080-2093. Figure 1

Scandium-Doped LSM Anode for Steam Electrolysis in a Proton-Conducting Solid Oxide Electrolyzer

Perovskite La0.8Sr0.2MnO3-δ has been widely used as anode for proton conducting solid oxide steam electrolyzer; however, the insufficient catalytic activity still restricts the activity for electrochemical oxidation of steam. In this work, Sc-doped anode material La0.8Sr0.2Mn1-xScxO3-δ (x=0, 0.02, 0.05, 0.08, 0.1) with the aim of enhancing anode performance is studied. Combined characterization using XRD, TEM, XPS, SEM and EDS confirmed the successful partial replacement of Mn by Sc in B site. The doping of Sc remarkably improves ionic conductivity while accordingly decreases the mixed conductivity due to the increase of oxygen vacancies indicated by TGA and XPS. Electrochemical measurements and ionic conductivity measurements demonstrate LSMS0.05 has the most optimized polarization properties. With LSMS0.05 anode, the Faradic efficiency is maximized to 80% and accordingly enhanced by 25% compared with the electrolyzer with LSM anode for high temperature steam electrolysis by exposing anode to 5%H2O/air.

The Effects of Operating Conditions on the Performance of a Solid Oxide Steam Electrolyser: A Model‐Based Study

AbstractTo support the development of hydrogen production by high temperature electrolysis using solid oxide electrolysis cells (SOECs), the effects of operating conditions on the performance of the SOECs were investigated using a one‐dimensional model of a cathode‐supported planar SOEC stack. Among all the operating parameters, temperature is the most influential factor on the performance of an SOEC, in terms of both cell voltage and operation mode (i.e. endothermic, thermoneutral and exothermic). Current density is another influential factor, in terms of both cell voltage and operation mode. For the conditions used in this study it is recommended that the SOEC be operated at 1,073 K and with an average current density of 10,000 A m–2, as this results in the stack operating at almost constant temperature along the cell length. Both the steam molar fraction at the inlet and the steam utilisation factor have little influence on the cell voltage of the SOEC but their influence on the temperature distribution cannot be neglected. Changes in the operating parameters of the SOEC can result in a transition between endothermic and exothermic operation modes, calling for careful temperature control. The introduction of air into the anode stream appears to be a promising approach to ensure small temperature variations along the cell.

Modelling of solid oxide steam electrolyser: Impact of the operating conditions on hydrogen production

A 2D multi-physic in-house-model has been developed to analyse the performances of Solid Oxide Electrolysis Cell (SOEC) stack. This model encompasses a combined electrochemical and thermal description of the electrolyser. An analytical solution for multi-species diffusion across the porous cathode has been implemented in the model. This numerical tool is useful to provide all the important parameters of the stack operation: distribution of temperature, heat fluxes, local current densities, gas concentrations and overpotentials. Simulations show that thermal equilibrium of the stack is strongly dependant on radiative heat losses, whereas convective heat transfers are limited. In the exothermic operation mode, the cell warming depends on the radiation efficiency. A parametric study has been carried out to analyse SOEC irreversible losses. It is found that the anode activation overpotential is significant, whereas the polarisation due to the cathode activation remains much more limited. Anode concentration overpotentials are found to be insignificant whatever the operating condition. Cathode concentration overpotentials are found to be moderate in the case of Electrolyte Supported Cell (ESC), while they can increase drastically with current density in the case of Cathode Supported Cell (CSC). Addition of diluent gases into the H 2, H 2O mixture is found to increase the concentration overpotentials.

Performance and Aging of Microtubular YSZ‐based Solid Oxide Regenerative Fuel Cells

AbstractFuel electrode supported microtubular solid oxide fuel cells (SOFC) fabricated at ICMA have been characterised in both solid oxide steam electrolyser (SOEC) and fuel cell modes. The cells consists of a fuel electrode supporting tube of Ni/YSZ with 40% porosity, ∼400 μm thickness, 2.4 mm diameter and 100–150 mm length, a 15 μm thick YSZ electrolyte and a 50 vol% LSM/YSZ composite air electrode of 20 μm thickness and LSM/YSZ (80/20 vol%) up to 2 cm2 area as current collector in the air side. Platinum paste and wires were used as interconnectors in the air chamber and Ni felt in the fuel side. SOFC and SOEC experiments were performed at temperatures between 750 and 950 °C using synthetic air in the oxygen electrode and different partial pressures of steam in the fuel side. Analysis of the polarisation contributions to the j–V curve in FC operation mode was performed using theoretical models, as discussed in the text. The effect of the steam concentration and temperature on the electrolysis and fuel cell experiments is presented and discussed. The cells are reversible in both modes of operation at low fuel conversion rates. According with previous observations, when cells are operated at high steam conversion rates the cell voltage tends to saturate. Irreversible damage was observed by SEM at the YSZ–oxygen electrode interface after operation, probably due to the electrolyte reduction produced at high voltages.

Evaluation and calculation on the efficiency of a water electrolysis system for hydrogen production

With the help of the typical model of a water electrolysis hydrogen production system, which mainly includes the electrolysis cell, separator, and heat exchangers, three expressions of the system efficiency in literature are compared and evaluated, from which one reasonable expression of the efficiency is chosen and directly used to analyze the performance of a water electrolysis hydrogen production system under different operation conditions. Several new configurations of a water electrolysis system are put forward and the problem how to calculate the efficiencies of these configurations is solved. Moreover, a solid oxide steam electrolyzer system (SOSES) for hydrogen production is taken as an example to expound that the different configurations of a water electrolysis system should be adopted for different operation conditions. The results obtained here may provide some guidance for the optimum design and operation of water electrolysis systems for hydrogen production.