Solid Oxide Fuel Cell Module Research Articles

Comprehensive Analysis of a Tubular, Reversible Solid Oxide Fuel Cell By Using a 3-D Computational Fluid Dynamics Model

Hydrogen technology has recently gained wide attention in the field of renewable energy. This technology needs to either consume hydrogen to generate electricity or produce the gas to store energy. A reversible solid oxide fuel cell (SOFC) can perform the two tasks by simply changing its operating conditions. Experiments can determine the performance of the SOFC but has economic limitations in changing its design parameters. A computational fluid dynamics (CFD) model, on the other hand, can test various design options at a relatively low cost. This study performed a CFD analysis of a tubular, reversible cell in its SOFC and SOEC modes in COMSOL Multiphysics 5.3. The model performed calculations by considering fluid dynamics, mass diffusion, heat transfer, and electrochemistry. The calculation results were then compared with experimental data to verify the model at various values of the cell voltage. The results showed that the hydrogen, steam, oxygen, and nitrogen distributions had certain, distinguishable effects from the model parameters. The results agreed with those from the literature both qualitatively and quantitatively. The IV data of the model matched with the experimental IV curves to an acceptable degree, further supporting the credibility of the model. Other authors who seek to model a tubular SOFC in the future can refer to this study as a reference. The results are also important in designing and building a stack of tubular, reversible SOFCs because the design parameters of the current cell can be adjusted to result in a more suitable cell for the stack build-up.

La0.8Sr0.2Co0.8Ni0.2O3-δ impregnated oxygen electrode for H2O/CO2 co-electrolysis in solid oxide electrolysis cells

High-temperature H2O/CO2 co-electrolysis through reversible solid oxide electrolysis cell (SOEC) provides potentially a feasible and eco-friendly way to convert electrical energy into chemicals stored in syngas. In this work, La0.8Sr0.2Co0.8Ni0.2O3-δ (LSCN) impregnated Gd0.1Ce0.9O1.95 (GDC)-(La0.8Sr0.2)0.95MnO3-δ (LSM) composite oxygen electrode is studied as high-performance electrode for H2O/CO2 co-electrolysis. The LSCN impregnated cell exhibits competitive performance with the peak power density of 1057 mW cm−2 at 800 °C in solid oxide fuel cell (SOFC) mode; in co-electrolysis mode, the current density can reach 1.60 A cm−2 at 1.5 V at 800 °C with H2O/CO2 ratio of 2/1. With LSCN nanoparticles dispersed on the surface of GDC-LSM to maximize the reaction active sites, the LSCN impregnated cell shows significant enhanced electrochemical performance at both SOEC and SOFC modes. The influence of feed gas composition (H2O-H2-CO2) and operating voltages on the performance of co-electrolysis are discussed in detail. The cell shows a very stable performance without obvious degradation for more than 100 h. Post-test characterization is analyzed in detail by multiple measurements.

Elementary reaction modeling of reversible CO/CO2 electrochemical conversion on patterned nickel electrodes

CO/CO2 are the major gas reactant/product in the fuel electrode of reversible solid oxide cells (RSOC). This study proposes a two-charge-transfer-step mechanism to describe the reaction and transfer processes of CO-CO2 electrochemical conversion on a patterned Ni electrode of RSOC. An elementary reaction model is developed to couple two charge transfer reactions, C(Ni)+O2−(YSZ) ↔ CO(Ni)+(YSZ) +2e− and CO(Ni)+O2−(YSZ) ↔ CO2(Ni)+(YSZ)+2e−, with adsorption/desorption, surface chemical reactions and surface diffusion. This model well validates in both solid oxide electrolysis cell (SOEC) and solid oxide fuel cell (SOFC) modes by the experimental data from a patterned Ni electrode with 10 μm stripe width at different pCO (0–0.25 atm), pCO2 (0–0.35 atm) and operating temperature (600-700 °C). This model indicates SOEC mode is dominated by charge transfer step C(Ni)+O2−(YSZ)↔CO(Ni)+(YSZ) +2e−, while SOFC mode by CO(Ni)+ O2−(YSZ)↔CO2(Ni)+(YSZ)+2e− on the patterned Ni electrode. The sensitivity analysis shows charge transfer step is the major rate-determining step for RSOC, besides, surface diffusion of CO and CO2 as well as CO2 adsorption also plays a significant role in the electrochemical reaction of SOEC while surface diffusion of CO and CO2 desorption could be co-limiting in SOFC.

Electrochemical performance and stability of cobalt-free Ln1.2Sr0.8NiO4 (Ln=La and Pr) air electrodes for proton-conducting reversible solid oxide cells

Cobalt-free Ruddlesden-Popper structured Ln1.2Sr0.8NiO4 (Ln = La and Pr) have been synthesized by a modified Pechini method, moreover, their thermal and electrochemical properties as well as performance of cells with proton-conducting electrolytes have been investigated. Experimental results reveal that the thermal expansion coefficients of Ln1.2Sr0.8NiO4 are close to those of Ba(Ce,Zr)O3-based proton conductors. The polarization resistances of symmetrical cells with La1.2Sr0.8NiO4 (LSN) and Pr1.2Sr0.8NiO4 (PSN) electrodes are as low as 0.15 and 0.23 Ω cm2 at 700 °C, respectively. Besides, Ln1.2Sr0.8NiO4 can remain stable structure over 100 h in humidified air (20 vol% H2O) at 800 °C. Furthermore, proton-conducting reversible solid oxide cells (PC-RSOCs) with LSN and PSN air electrodes exhibit maximum power densities of 0.46 and 0.35 W cm−2 in solid oxide fuel cell mode at 700 °C, respectively. Meanwhile, the same cells achieve current densities as high as 1.37 and 1.12 A cm−2 in solid oxide electrolysis cell mode at 700 °C with a given voltage of 1.3 V, respectively. In addition, both of two cells with LSN and PSN air electrodes present acceptable short-term stability under reversible operation condition. These encouraging results suggest that Ln1.2Sr0.8NiO4 could be suitable candidates of air electrodes in intermediate-temperature PC-RSOCs.

Highly Efficient, Redox-Stable, La0.5Sr0.5Fe0.9Nb0.1O3- δ Symmetric Electrode for Both Solid-Oxide Fuel Cell and H2O/CO2 Co-Electrolysis Operation

Co-free La0.5Sr0.5Fe0.9Nb0.1O3-δ (LSFNb) perovskite oxide is synthesized by the sol-gel method. LSFNb oxide exhibits good chemical and structural stability in both oxidizing and reducing atmospheres. Therefore, symmetric cells with the configuration LSFNb/LSGM/LSFNb are prepared and the electrochemical performance is evaluated for both solid oxide fuel cell (SOFC) and solid oxide electrolysis (SOEC) applications. The LSFNb symmetric electrode presents excellent catalytic activity in both SOFC and SOEC modes. At 850°C, the peak power density of the symmetric cell reaches 1157 mW cm−2 in SOFC mode, while the current density exceeds 1460 mA cm−2 at 1.3 V in SOEC mode. Under H2O/CO2 co-electrolysis at 800°C, the H2 and CO production rates reach 2.19 and 2.77 mL min−1 cm−2 at −708 mA cm−2 with nearly 100% faradaic efficiency. Moreover, the symmetric cell displays good stability under CO2 and H2O co-electrolysis, indicating that LSFNb oxide is a promising symmetric electrode material for steam and CO2 co-electrolysis as well as for regenerative fuel cells.

A Multiscale Model for Electrochemical Reactions in LSCF Based Solid Oxide Cells

Lanthanum Strontium Cobalt Ferrite (La1 − xSrxCo1 − yFeyO3 − δ or LSCF), a mixed ionic-electronic conductor is widely used as an electrode in solid oxide cells (SOCs). The reactions and transport at this oxygen electrode are complex and distributed across several length and time scales. However, a comprehensive computational model that could provide accurate and reliable linkages between different scales to predict the electrochemical characteristics of these electrodes is missing. Here, we develop a multiscale model combining density functional theory calculations, transition state theory and continuum modeling for the oxygen-based reactions at the cathode/anode in LSCF based solid oxide fuel cells (SOFC)/electrolysis cells (SOEC), to elucidate the critical reaction steps and predict the performance of the device. Density functional theory calculations were used to obtain the free energy barriers for different reaction steps while transition state theory was used to predict the reaction rate constants/diffusivities for each step based on the free energy barriers. The continuum theory utilized these reaction rate constants and diffusivities to obtain the overpotential-current density relations. The proposed multiscale model yields a quantitative agreement with the overpotential-current density data from experiments. The results indicate that oxygen exchange at the LSCF surface, rather than the triple-phase boundary, is the main contributing reaction pathway for a single phase LSCF electrode. For the entire cathodic and anodic reaction pathway, the reaction step involving the splitting of the surface peroxo units into oxo units under SOFC mode or the combination of surface oxo units into peroxo units under SOEC mode is the rate-limiting reaction step, and the diffusion of oxide ions in bulk LSCF is the rate-limiting diffusion step. We also predict that the SrO terminated LSCF surface is not an efficient surface structure for oxide ion diffusion.

Mechanism for reversible CO/CO2 electrochemical conversion on a patterned nickel electrode

The patterned Ni negative electrode on single-crystal YSZ in CO-CO2 atmosphere is investigated in both the solid oxide fuel cell (SOFC) and solid oxide electrolysis cell (SOEC) modes. The effects of the temperature T, partial pressure of CO and CO2 (pCO and pCO2) on the electrochemical performance are measured to obtain the intrinsic kinetic parameters by natural logarithm linear fitting. The strong dependency of surface diffusion resistance on pCO implies that surface diffusion could be related to CO(Ni). The electrochemical performance had an obviously positive correlation with T and pCO. The limitation of CO2 adsorption leads to a weak dependency of polarization on pCO2. The electrochemical performance of SOEC mode in the atmosphere without CO is 1.21 times higher than that in the atmosphere without CO2, which implies that CO electrochemical reduction could be more significant than CO2 electrochemical reduction in the patterned Ni electrode. An analytical calculation is performed for the speculation of rate-limiting steps. In the SOFC mode, CO oxidation into CO2 is speculated to be rate-determining, besides, adsorbed carbon oxidation into CO could be also non-ignorable. In the SOEC mode, CO reduction into carbon could be more probably the major electrochemical reaction on the pure Ni surface.

Reversible H2/H2O electrochemical conversion mechanisms on the patterned nickel electrodes

The patterned nickel (Ni) electrode enables to quantify the triple-phase boundary (TPB) length and Ni surface area as well as exclude the interference of bulk gas diffusion. In this study, the patterned Ni electrodes are investigated in both the solid oxide fuel cell (SOFC) and solid oxide electrolysis cell (SOEC) modes at the atmosphere of H2O/H2. The experimental test shows the patterned Ni electrode keeps stable and intact only at the specific operating condition due to instability of Ni at the H2O-containing atmosphere. The effects of the temperature, partial pressure of H2O and H2 on the electrochemical performance are measured. The electrochemical performance has a positive correlation with the temperature, partial pressure of H2 and H2O. Further, the experimental results are compared with the mechanism containing two-step charge-transfer reaction used in the existing literature. An analytical calculation is performed to indicate the rate-limiting steps may be different for SOFC and SOEC modes. In SOFC mode, H2 electrochemical oxidation could be dominated by both charge transfer reaction at low polarization voltage and by the charge-transfer reaction H(Ni) + O2−(YSZ) → OH−(YSZ) + (Ni) + e− at high polarization voltage, however in SOEC mode, H2O electrochemical reduction is considered to be dominated by H2O(YSZ) + (Ni) + e− → OH−(YSZ) + H(Ni).

Development of a Highly Efficient SOFC Module Using Two‐stage Stacks and a Fuel Regeneration Process

AbstractA solid oxide fuel cell (SOFC) module using two‐stage stacks and a fuel regeneration process between them was developed in this study for the first time, to the best of the authors' knowledge. Upon configuring the first‐stage and second‐stage stacks and a steam reformer between them in the SOFC module, a gross output power of DC 2.27 kW was generated with gross power generation efficiency of DC 69.2% (lower heating value (LHV)), at a total fuel utilization rate of 86.3%. This technology enables operation at a very high total fuel utilization rate even while operating the stacks at a moderate fuel utilization rate (below 70%). Considering an auxiliary device loss (6%) and inverter loss (5%), the net power generation efficiency is estimated to be AC 61.8% (LHV); hence, the module is considered to exhibit a high power generation efficiency. Further increases in the power generation efficiency could be realized in the future by removing the CO2 from the anode off‐gas during the fuel regeneration process and/or operating the stacks at higher temperatures by decreasing heat leakage from the module.

Reaction Mechanism and Rate-Determining Step Speculation of Reversible CO/CO2 Electrochemical Conversion on the Nickel Patterned Electrodes

The nickel(Ni)-patterned electrode enables researchers to quantify the triple-phase boundary (TPB) length and Ni surface area, exclude the influence of bulk gas diffusion and clearly separate the active regions of the chemical/electrochemical reactions. This tool has been studied for identifying the reaction mechanism in SOFC but rarely in SOEC. In this study, the Ni-patterned electrodes with the stripe width of 100 μm were tested in both the solid oxide fuel cell (SOFC) and solid oxide electrolysis cell (SOEC) modes at the atmosphere of H2O/H2 and further H2O/CO2/H2/CO. The experimental test shows the stability of the Ni-patterned electrode in the H2O/H2 atmosphere was much poorer than that in the CO/CO2 atmosphere due to the nickel reacting with steam. Thus, the Ni-patterned electrode needed to operate at a temperature of ≤700oC with the inlet H2/H2O molar ratio of >7 and the current-applied time shouldn’t be over 5 h to keep the accuracy of the TPB length and Ni surface area. The effects of the temperature, partial pressure of H2O and H2 are investigated. The activation energy of the Ni-patterned electrodes was 0.386 eV. The electrochemical performance had a positive correlation with both the partial pressure of H2 and H2O, especially showed higher sensitivity to the partial pressure of H2O. Further, a possible mechanism of the H2O/H2 electrochemical conversion was proposed according to the experimental data and existing literature, which contains two-step charge-transfer reaction: H(Ni)+O2-(YSZ)OH-(YSZ)+(Ni)+e- and H(Ni)+OH-(YSZ)H2O(YSZ)+(Ni)+e-. Based on the experiments, an analytical calculation was performed to investigate the rate-determining steps in the Ni-patterned electrodes by bridging the connection between the kinetic parameters and operating conditions. The results indicate the rate-limiting steps may be different for the SOFC and SOEC modes. In SOFC mode, the H2 electrochemical oxidation could depend more on the charge-transfer reaction H(Ni)+O2-(YSZ)→OH-(YSZ)+(Ni)+e-, however in SOEC mode, the rate-determining step of the H2O electrochemical reduction should be H2O(YSZ)+(Ni)+e-→OH-(YSZ)+H(Ni). In this way, a reversible mechanism could be applied for reversible SOFC (RSOFC) to describe the conversion between hydrogen and steam by different charge-transfer-reaction domination in the SOFC and SOEC mode. Figure 1

Green Industrial Hydrogen via Reversible High-Temperature Electrolysis

With its roadmap for moving to a competitive low-carbon economy in 2050, the European Commission sets greenhouse gas emissions targets for different economic sectors. A main challenge will be the integration of renewable energy sources into industrial processes to reduce carbon dioxide emissions. The vision of the GrInHy project is to provide ‘green’ hydrogen via electrolysis using renewable electricity and to provide grid management services as reversible generator in the iron and steel works of Salzgitter Flachstahl GmbH (Germany). Because a significant share of the energy input can be provided in the form of waste heat, high-temperature electrolysis is able to achieve highest electrical system efficiencies and, therefore, is one of the most promising technologies to fulfill this vision. The GrInHy project targets the industrial integration and validation of a high temperature electrolysis with a nominal electrolyser power of 150 kWAC in one scalable module. Based on steam, the project aims at an overall electrical efficiency of more than 80 %LHV. Other objectives are to proof a system lifetime over 7,000 hours and stack lifetimes over 10,000 hours with a degradation lower than 1 %/1000 hours. The prototype is designed as reversible generator (RSOC). In the Solid Oxide Electrolyser Cell (SOEC) mode hydrogen can be produced, whereas the Solid Oxide Fuel Cell (SOFC) mode is able to generate electricity from hydrogen or natural gas. The system consists of the RSOC Unit delivered by Sunfire and the Hydrogen Processing Unit (HPU) delivered by Boeing Research and Technology Europe (Figure 1). Both are integrated in 2 separate 20’ containers including all auxiliary systems. The RSOC shall utilize steam and electricity from the onsite power plant to generate hydrogen. Hydrogen is fed to the HPU which compresses the hydrogen to minimal 8 bar(g) and removes the remaining steam by pressure swing absorption to fulfil the quality criteria “5.0”. Afterwards dry hydrogen is injected an existing ring pipeline that supplies a variety of processes at the steel work. The RSOC prototype is based on a stack unit comprising 1440 3YSZ-ESC-cells. Those cells are set up in 6 Interchangable Modules (ICM) each containing 240 cells. The system is supplied with cold feed gases and/or steam from a so called Coldbox that realizes the fluid controls. The feed gases are further processed and preheated to operating temperature in two separate highly integrated Hotboxes. Each Hotbox supplies 3 of the 6 ICMs with educt gases and recuperates heat from the product gases. For operation in SOFC mode with natural gas, a steam reformer is integrated which uses gas electrode off-gas for humidification. In this mode, the system reaches a power output of 25 kWAC in completely automated operation. At full load the efficiency is > 50 % based on the lower heating value. Details from the system operation in natural gas fuel cell mode (NG-FC), in hydrogen fuel cell (H2-FC) mode and in electrolyser mode (EL) will be presented. In hydrogen fuel cell mode the nominal power is 30 kWAC at an efficiency of more than 45 %LHV. In electrolyser mode the system consumes approx. 50 kg/h steam and 150 kWAC electrical power to produce 40 Nm³/h hydrogen with an overall efficiency of more than 80 %LHV. The RSOC is also able to operate in overload and is therefore able to reach up to 50 Nm³/h hydrogen output at an AC power input of approximately 200 kWAC. This is currently the largest high temperature electrolyser module worldwide. Figure 1

Solid Oxide Cell Degradation Operated in Fuel Cell and Electrolysis Modes: A Comparative Study on Ni Agglomeration and LSCF Destabilization

Ceramic high-temperature fuel cells and electrolysers are efficient energy conversion systems for electrical power generation and hydrogen production. Their core components are constituted by a stack of electroactive Solid Oxide Cells (SOCs) in which the electrochemical reactions take place. Thanks to their flexibility, the same stack can be alternatively operated in both fuel cell and electrolysis modes. However, the insufficient durability of SOCs still constitutes a major limitation for the technology. The present study addresses this issue and aims to bring some new insights on the effect of the Solid Oxide Fuel Cell (SOFC) versus Solid Oxide Electrolysis Cell (SOEC) operating modes on degradation of a typical Ni-YSZ//YSZ//CGO//LSCF-CGO cell. The electrochemical degradations are generally attributed to several underlying phenomena such as electrode microstructural evolution, material chemical decomposition or electroactive sites poisoning by contaminants. Among them, it is generally considered that Ni agglomeration in the Ni-YSZ cermet and Lanthanum Strontium Cobalt Ferrite (LSCF) material destabilization are two prevalent mechanisms involved in the cell performance deterioration. Therefore, these two mechanisms have been specifically investigated by a coupled approach of long-term testing in both SOFC and SOEC modes (1000 ≤ t (h) ≤9000) and post-test characterizations. The experimental results have then been analyzed in the frame of an in-house multi-scale model with the purpose to interpret them and to quantify the effect of material ageing on cell performances. The extent of Ni agglomeration has been characterized by three-dimensional electrode reconstructions obtained by X-ray nano-holotomography at European Synchrotron Radiation Facility (ESRF) (on the new Nano-Imaging beamline ID16A-NI). The new set-up and protocol enable the reconstructions of valuable 3D volumes (Fig. 1) with a large field of view (~50 µm) along with a high spatial resolution (~50 nm). The electrode morphological properties, which have been measured on the 3D volumes, have revealed a substantial Ni coarsening over time at 850°C and 750°C, whereas no Ni depletion was detected at the electrolyte interface. The increase of the Ni particle size is found to induce a decrease in both (i) the density of Triple Phase Boundary (TPBs) lines and (ii) the interfacial surface area between Ni and gas. Moreover, it was found that the Ni/YSZ interfacial surface area does not evolve during the experiments. This statement indicates that the ceramic backbone in the cermet prevents a massive Ni agglomeration at the SOFC/SOEC operating temperature. The compilation of all experimental data have allowed fitting the parameters of a physically-based law for Ni coarsening that was introduced in the modelling framework. The simulations have revealed that Ni agglomeration explains around 20-25% of the electrochemical degradation at 850°C after 1000 hrs of operation. However, the electrode microstructural evolution is found not to be affected by the cell polarizations. Therefore, the mechanism cannot explain the higher degradation rates recorded in electrolysis mode compared to the fuel cell ones. To explain the impact of the operating modes (SOFC or SOEC) on the degradation rates, several post-test analyses (i.e. Scanning Electron Microscopy, Transmission Electron Microscopy, X-ray µfluorescence and µdiffraction techniques) have been employed to investigate the phase reactivity in the region of the CGO barrier layer. The characterizations have revealed that Sr diffusion across the barrier layer and formation of SrZrO3 secondary phase occur mainly during electrolysis operation, whereas the process is very limited in fuel cell mode (Fig. 2). As a consequence, LSCF destabilization is found not to be involved in the degradation of cell performances during fuel cell operation while it could explain the highest degradation rates recorded in electrolysis mode. The post-test analyses have also revealed a diffusion and an accumulation of Co in the region of the barrier layer which is concomitant with the formation of SrZrO3. The formation of these Co-rich segregates in contact with SrZrO3 grains have been identified as cobalt-ferrite type compound. The in-house multi-scale model has been used to interpret the role of the cell operating mode on the LSCF destabilization mechanism. The cell polarization curves and the local quantities within the O2 electrode have been computed in both fuel cell and electrolysis modes. The simulations have shown that the electrolysis operation leads to a strong depletion of oxygen vacancies in the LSCF material. It has been proposed that the depletion in oxygen vacancies under electrolysis polarization could drive the Sr release from the structure, and in turn, could explain the experimental results. Based on this proposition, a possible mechanism for the LSCF destabilization and SrZrO3 formation has been detailed. Figure 1

Reaction Mechanism and Rate-Determining Step Speculation of Reversible CO/CO2 Electrochemical Conversion on the Nickel Patterned Electrodes

The nickel (Ni) patterned electrode enables to quantify the triple-phase boundary (TPB) length and Ni surface area as well as exclude the interference of bulk gas diffusion. In this study, an analytical calculation based on the oxygen spillover mechanism is performed by assuming one elementary reaction as the rate-limiting reaction and the others in the equilibrium state to bridge the connection among the polarization resistance, charge transfer coefficient and partial pressure of CO/CO2 based on Butler-Volmer equation. The analytical calculation is compared with the experimental data of the Ni patterned electrode published in previous paper(1) to investigate the rate-limiting steps in both the solid oxide fuel cell (SOFC) and solid oxide electrolysis cell (SOEC) modes. In SOFC mode, CO oxidation into CO2 is speculated to be the major electrochemical reaction, besides, adsorbed carbon could also be oxidated into CO. In SOEC mode, the limitation of CO2 adsorption may inhibit CO2 electrochemical reduction, thus, CO reduction into carbon could be more probably be the major electrochemical reaction.

Environomic design for electric vehicles with an integrated solid oxide fuel cell (SOFC) unit as a range extender

This article investigates an innovative concept of vehicle propulsion. An electric vehicle with limited battery packs is coupled with an innovative converter – a Solid Oxide Fuel Cell with gas turbines system (SOFC- GT). This energy integrated converter is characterized by high energetic efficiency – around 70%, which includes also the integrated on board fuel reforming. Thus, the concept presents the advantage to extend the vehicle basic electric range thanks to this highly efficient converter. A second advantage is the reforming of a liquid fuel on board. Thus the H2 storage is avoided. The liquid fuel is methane produced from biomass and liquefied at 200 bars pressure in the vehicle tank. The vehicle concept is modeled under Matlab/Simulink as a serial range extender. The innovative conversion system of the integrated reforming, SOFC and gas turbines modules (GT) is modeled with a map based approach. The range extender is so introduced into a standard electric vehicle. The innovative range extender vehicle is thus optimized according to techno-economic and environmental criteria. The optimization is performed on the vehicle for optimal mobility service.

Dynamic model with experimental validation of a biogas-fed SOFC plant

The dynamic model of a poly-generation system based on a biogas-fed solid oxide fuel cell (SOFC) plant is presented in this paper. The poly-generation plant was developed in the framework of the FP7 EU-funded project SOFCOM (www.sofcom.eu), which consists of a fuel-cell based polygeneration plant with CO2 capture and re-use. CO2 is recovered from the anode exhaust of the SOFC (after oxy-combustion, cooling and water condensation) and the Carbon is fixed in the form of micro-algae in a tubular photobioreactor.This work focuses on the dynamic operation of the SOFC module running on steam-reformed biogas. Both steady state and dynamic operation of the fuel cell stack and the related Balance-of-Plant (BoP) has been modeled in order to simulate the thermal behavior and performance of the system.The model was validated against experimental data gathered during the operation of the SOFCOM proof-of-concept showing good agreement with the experimental data. The validated model has been used to investigate further on the harsh off-design operation of the proof-of-concept.Simulation results provide guidelines for an improved design of the control system of the plant, highlighting the feasible operating region under safe conditions and means to maximize the overall system efficiency.

High-performance oxygen electrode for reversible solid oxide cells with power generation and hydrogen production at intermediate temperature

Reversible solid oxide cells (RSOCs) can work for power generation by converting fuel chemical energy to electric energy as solid oxide fuel cells (SOFCs) and for hydrogen production by converting excess electrical power to chemical energy as solid oxide electrolysis cells (SOECs). In this work, the possibility of using impregnated La0.8Sr0.2Co0.8Ni0.2O3−δ-Ce0.9Gd0.1O2−δ (LSCN-GDC) as oxygen electrode in RSOCs is investigated. The button cells with Ni-YSZ hydrogen electrode, YSZ electrolyte and impregnated LSCN-GDC oxygen electrode are fabricated. In the SOFC mode, cell with impregnated LSCN-GDC electrode shows an impressive power density of 1.336 W cm−2 at 800 °C and the polarization resistance is 0.100 Ω cm2 under open circuit condition, approximately the same as the value in the SOEC mode at applied current density of 0.2 A cm−2. In the SOEC mode, the variable operating parameters are optimized to obtain the maximum hydrogen production and minimum energy consumption. The remarkable current density reaches 2.34 A cm−2 at 1.6 V when measured at 800 °C with 90 vol% absolute humidity (AH). The polarization degradation behavior of LSCN-GDC oxygen electrode under electrolysis mode is analyzed in detail by estimating the three-phase boundary (TPB) change of the oxygen electrode.

Effect of Chromium Poisoning on Performances of Lscf-SDC Composite Oxygen Electrodes Under Reversible Operation of Solid Oxide Cells

Solid oxide cells (SOCs) are high-temperature electrochemical energy conversion and storage devices, which can be operated under solid oxide electrolysis cell (SOEC) mode to produce pure hydrogen from water vapor with high efficiency. SOCs can also be operated in reverse under solid oxide fuel cell (SOFC) mode, providing high-energy conversion efficiency to convert hydrogen fuel to electricity. Similar to SOFCs, cost-effective metallic (alloy) can be used as interconnects for planar-type SOCs operated at reduced temperatures (≤ 800 °C). However, without an effective protective coating on the Cr-containing alloy, volatile Cr-containing species are generated at high temperatures in oxidizing atmosphere. It has been recognized that several oxygen electrodes such as Sr-doped LaMnO3 (LSM) or La0.6Sr0.4Co0.2Fe0.8O3 - δ (LSCF) suffer from a serious Cr-poisoning.1–3 We have recently succeeded in improving the reversible performances of the single-layer LSCF-Ce0.8Sm0.2O1.9 (SDC) composite O2 electrode with SDC interlayer at 800 and 900 °C,4–6 compared with those of an identical-type electrode in our previous work.7 Though the degradation of the LSM or LSCF electrodes by Cr-poisoning has been studied under either SOFC or SOEC operation mode, separately, to the best of our knowledge, the Cr-poisoning have not been investigated on SOCs under simultaneously reversible operation of SOFC/SOEC modes. Here, we examined for the first time the effect of Cr-poisoning on the performances of LSCF-SDC oxygen electrodes under simultaneously cathodic and anodic polarization conditions in the presence of Fe-Cr alloy. A symmetrical cell [LSCF-SDC ǀSDC interlayerǀ ScSZ electrolyte ǀSDC interlayerǀ LSCF-SDC] was prepared.4,5 Here, we briefly describe the protocol. The SDC interlayer was deposited on both sides of the scandia-stabilized zirconia (ScSZ, (ZrO2)0.89(Sc2O3)0.10(CeO2)0.01) electrolyte by spin coating of Ce(III) 2-ethylhexanoate and Sm(III) 2-ethylhexanoate mixed solution, followed by heat-treatment at 1050 oC for 2 h. The LSCF-SDC paste (60:40 volume ratio) was tape-casted onto the SDC interlayer and heat-treated at 1050 oC for 1 h. The air reference electrode consisted of a Pt wire wound around the ScSZ disk. A commercial Fe-Cr alloy (RA446, 23–27 wt% Cr, Rolled Alloy, Canada) was used as the metallic interconnect without any protective coating. The interconnect plate (12 × 12 × 4 mm) was machined with gas channels on one side. Air was supplied to both electrodes at a flow rate of 100 mL min−1. The as-prepared symmetrical cell was sandwiched with two Fe-Cr interconnect plates, which were also acting as the current collectors. After a constant current density operation at 0.5 A cm−2 and 800 oC for 100 h, the IR-free polarization curves of both electrodes were measured. Hereinafter, the electrodes polarized anodically (O2 evolution) and cathodically (O2reduction) for 100 h will be denoted as electrode A and electrode C, respectively. Figure 1 shows the polarization curves of electrode A and electrode C with and without Fe-Cr interconnect plate at 800 oC. When operated with Pt current collectors (without any Fe-Cr alloy), very high performance of both electrode A and electrode C was observed even after 100 h (negligibly small degradation). In contrast, after operation with Fe-Cr alloy interconnects, the overpotential at both electrodes significantly increased due to Cr-poisoning. While the difference in the anodic overpotential between electrode A and C was relatively small in the O2 evolution reaction, electrode A showed much larger overpotential than that of electrode C in the O2 reduction, specifically at high current densities. This could suggest that Cr-containing oxides deposited in the pores2 might block the O2diffusion path. Analyses of the electrode morphology are under progress. This work was supported by the funds for “ALCA” from Japan Science and Technology Agency.

Study of reversible solid oxide fuel cell with different oxygen electrode materials

This study reports the manufacturing of its core device–hydrogen electrode supported cell of reversible solid oxide fuel cell (RSOFC) with use of different oxygen electrode (La0.8Sr0.2MnO3−δ = LSM, La0.8Sr0.2MnO3/yttria stabilized zirconia = LSM/YSZ) and its operation under solid oxide fuel cell (SOFC) and solid oxide electrolyzer cell (SOEC) mode. In order to lower difficulties during cell assembly, acceptable curvature of hydrogen electrode supported cell is accomplished with improvement of manufacturing process. Also reported are the resulting performances, both in SOEC and SOFC modes, as a function of its operating parameters such as temperature. We found that the RSOFC performance improved with increasing temperature for all oxygen electrodes–LSM, LSM + YSZ. SOFC performance with oxygen electrode–LSM is a better option while SOFC/SOEC recycling with oxygen electrode-LSM/YSZ is more durable. Identical material composition and no obvious weak connection between oxygen electrode-LSM/YSZ and electrolyte after SOFC/SOEC cycling tests are the main reasons leading to minor performance drops compared to that with electrode – LSM.

Durability test on coral Ce0.9Gd0.1O2-δ-La0.6Sr0.4Co0.2Fe0.8O3-δ with La0.6Sr0.4Co0.2Fe0.8O3-δ current collector working in SOFC and SOEC modes

This work presents a 790h durability test performed on a solid oxide cell. An innovative Ce0.9Gd0.1O2-δ-La0.6Sr0.4Co0.2Fe0.8O3-δ oxygen electrode with coral microstructure was deposited on a solid oxide fuel cell (SOFC) anode supported with 8mol.% yttria-stabilized zirconia (8YSZ) electrolyte. An initial cell potential was found to be 817mV at 773 °C under synthetic air on the oxygen electrode side, and pure hydrogen (500NmL.min−1) on the hydrogen electrode side, under 0.5A.cm−2 current density in SOFC. The initial cell potential in the solid oxide electrolysis cell (SOEC) was 1200mV at 773°C under synthetic air on the oxygen electrode side and a mixture of steam/hydrogen (80 %/20 %, respectively) on the hydrogen electrode side under −0.75 and −0.5 A.cm−2 current density. The cell resistance progressively increased during the durability test. The increase at the high frequency range was mainly responsible for an increase in total cell resistance. This frequency range was associated with the blocking effect on the oxygen electrode/electrolyte interface. U-j curves showed reversibility of the current loading from −0.75 to 0.5A.cm−2. SEM observations indicated cracks in the 8YSZ electrolyte and the detachment of the oxygen electrode.

Planar SOFC system modelling and simulation including a 3D stack module

A solid oxide fuel cell (SOFC) system consists of a fuel cell stack with its auxiliary components. Modelling an entire SOFC system can be simplified by employing standard process flowsheeting software. However, no in-built SOFC module exists within any of the commercial flowsheet simulators. In Amiri et al. (Comput. Chem. Eng., 2015, 78:10–23), a rigorous SOFC module was developed to fill this gap. That work outlined a multi-scale approach to SOFC modelling and presented analyses at compartment, channel and cell scales. The current work extends the approach to stack and system scales. Two case studies were conducted on a simulated multilayer, planar SOFC stack with its balance of plant (BoP) components. Firstly, the effect of flow maldistribution in the stack manifold on the SOFC's internal variables was examined. Secondly, the interaction between the stack and the BoP was investigated through the effect of recycling depleted fuel. The results showed that anode gas recycling could be used for managing the gradients within the stack, while also improving fuel utilisation and water management.