Solid Oxide Fuel Cell Module Research Articles

Results for a Fuel Cell System Consisting of an SOFC Fed by an Adiabatic Pre-Reforming Fuel Processor With European Standard Road Diesel

Abstract In the near future, ships will need more efficient power generation technologies for auxiliary power supply than those used currently. In the project SchiffsIntegration BrennstoffZelle (SchIBZ), a fuel cell system is being developed to increase the electrical efficiency of on-board power supply systems. In order to avoid the limitation of hydrogen storage, the on-site fuel processing of hydrocarbons offered an opportunity for the hydrogen supply of fuel cell systems to be operated in remote locations. As fuel standard European road diesel was processed with the process of adiabatic pre-reforming, a steam-reforming derivate. A solid oxide fuel cell (SOFC) was coupled with this fuel processor and was fed with standard European diesel fuel. Two flexible test rigs were developed to test the fuel processor and the SOFC either combined or independently. During combined operation, the SOFC modules were fed with feedstock gas from the fuel processor, which ran on standard European diesel fuel. Combined operation of both test rigs at steady state was achieved for more than 1000 h. For the whole experimental runtime, the fuel processor delivered sufficient feedstock quality for the SOFC, and no significant voltage degradation (about 0.5 %) of the SOFC modules was observed over 1000 h of operation. This low value of degradation is known for the operation of SOFC with pure hydrogen and methane without impurities.

Conventional and Advanced Biomass Gasification Power Plants Designed for Cogeneration Purpose

In this paper conventional and advanced biomass gasification power plants designed for small cogeneration application are defined. The CHP plants consist of a gasification unit, that employs a downdraft gasifier, and a power unit based on a microturbine in the case of conventional configuration, and on a solid oxide fuel cell module, in the case of advanced configuration. The plants are sized to supply about 100kW of electrical power.In order to investigate and to analyze the performances of the two plant configurations, in terms of thermal and electrical efficiencies, numerical models have been developed by using thermochemical and thermodynamic codes.

Mechanism and Kinetics of Ni-Y2O3-ZrO2 Hydrogen Electrode for Water Electrolysis Reactions in Solid Oxide Electrolysis Cells

Ni-Y2O3 stabilized ZrO2 (Ni-YSZ) cermet is the most commonly used hydrogen electrode for hydrogen oxidation reaction (HOR) under solid oxide fuel cell (SOFC) mode and water reduction reaction (WRR) under solid oxide electrolysis cell (SOEC) mode. Here we studied the electrocatalytic activity of Ni-YSZ electrodes as a function of Ni content, water concentration and dc bias for WRR and HOR under SOEC and SOFC modes, respectively. The activity of Ni-YSZ cermet increases significantly with the increase of YSZ content due to the enhanced three phase boundaries (TPB). The electrode activity for the WRR and in less degree for the HOR increases with the increase of steam concentration. The electrode polarization resistance, RE, for the WRR increases with the dc bias, while in the case of HOR, RE decreases with the dc bias, demonstrating that kinetically the WRR and HOR is not reversible on the Ni-YSZ cermet electrodes under SOFC and SOEC operation modes. The WRR can be described by two electrode processes associated with the H2O adsorption and diffusion on the oxygen-covered Ni or YSZ surface in the vicinities of TPB, followed by the charge transfer. The significant increase of high frequency electrode polarization resistance, RH and in much less extent low frequency electrode polarization resistance, RL with the dc bias indicates that the water electrolysis reaction is kinetically controlled by the reactant supply (e.g., the adsorbed H2O species) limited charge transfer process.

Sensitivity Analysis for the Efficiency Improvement of a Light Integrated Gasification Fuel Cell Power Plant

The solid oxide fuel cell (SOFC) is recognized as one of high efficiency plants of electricity generation for a sustainable future system with low environmental effects. In term of fuel flexibility, SOFC is suitable for direct use of syngas from a coal gasification plant. The application of integrated SOFC in coal gasification based power plant, such as a light integrated gasification fuel cell (L-IGFC) power plant, could be one of the most promising coal energy conversions system providing high electrical efficiency with low CO2 emitted to the atmosphere. The system consists of a coal gasifier and intermediate temperature SOFC module on the top of a steam turbine. The syngas produced by pressurized coal gasifier is used in SOFC module after heat recovery units and cleaning processes. To minimize exergy loses in the plant, the dry gas desulfurization (DGD) unit which can operate at elevated operating temperature and pressure are adopted. The heat generated by SOFC module can be utilized by the heat recovery steam generator providing high quality steam for a steam turbine. In this work, thermodynamic analysis is carried out to develop process integration of the L-IGFC plant. The overall plant analysis of a baseline system design is performed by identifying the major factors effecting plant performance by using the Aspen Plus simulation. The Aspen plus simulation is then used to perform parametric analysis to identify optimum values for the maximum system efficiency. Modifications to the baseline system design are made in order to determine the most viable system designs based on maximizing total system efficiency.

Electrochemical Characterization of Ni/Y2O3-ZrO2 Hydrogen Electrode for Water Splitting in Solid Oxide Electrolysis Cells

Ni-Y2O3 stabilized ZrO2 (Ni-YSZ) cermet is a widely used hydrogen electrode for solid oxide fuel cells (SOECs), but detailed studies regarding the water splitting processes are scarce. Here we report the preliminary results on the electrocatalytic activity of Ni-YSZ hydrogen electrode in the SOEC mode as a function of operating temperature and water concentration. The electrode activity for the water splitting reaction is strongly influenced by the water concentration and dc bias. The electrochemical performance for the water splitting reaction increases with the increase of water concentration. On the other hand, the electrode polarization resistance increases gradually with the increase of dc bias regardless of the H2O content, which is particularly pronounced in the low frequency impedance process related to the H2O dissociative adsorption and diffusion processes. The reaction mechanism and kinetics of the H2O dissociation reaction on Ni-YSZ hydrogen electrodes are discussed.

Carbon Tolerant Electrodes for SOFC and Reversible SOFC (RSOFC) Cells Operating on Carbon Containing Fuels

Solid Oxide Fuel Cells (SOFC) and Electrolyzers (SOEC) hold great potential for the security of energy sector, providing solutions for efficient power generation and production of hydrogen and synthesis gas. A challenging barrier for the successful implementation of SOFC and SOEC technologies, remains the long term stability under realistic operating conditions by the effective control and minimization of degradation due to carbon built up. The problem arise from the fact that the commonly used anode cermets, e.g. Ni-YSZ and Ni-GDC, are prone to carbon deposition onto nickel, as a result of the Boudouard reaction (CH4cracking, disproportionation of CO), leading to low activity and fast degradation. In this study, a class of Au-modified commercially available NiO/GDC and NiO/YSZ cermet powders has been developed and studied for their performance and tolerance to carbon deposition, operating as SOFC anodes for CH4 steam reforming, as well as bi-functional electrodes in a Regenerative SOFC operating on the CO2 cycle (SOEC mode: electrolysis of CO2, SOFC mode: electrochemical reaction of CO and oxygen for power generation). In- situ HT-XRD tests revealed that the presence of Au, in an optimum nominal loading of 3wt%, affects the Ni crystal phase and has a significant positive effect in inhibiting carbon deposition. The results from cell testing in the temperature range of 800-1000°C, showed promising, stable performance of electrodes under carbon forming conditions (e.g. H2O/CH4=0.25, CO or CO/CO2mixtures of 0.7/0.3). The work is supported by the FCHJU project T-CELL (298300).

Reversible Fuel Cells with Tri-Layer Electrolytes

Reversible solid oxide fuel cells (SOFC) are operated as solid oxide fuel cells and as solid oxide electrolyzer cells (SOEC). In SOFC mode, hydrogen is consumed at the fuel electrode to convert chemical energy of fuel oxidation into water vapor. In SOEC mode, water vapor is decomposed at the fuel electrode to generate hydrogen under an applied DC voltage. Much of the reported work on reversible solid oxide cells is based on yttria-stabilized zirconia (YSZ) electrolyte, Ni + YSZ fuel electrode, and a perovskite-based oxygen electrode. At high operating voltages in the SOEC mode, cell degradation can occur which involves oxygen electrode delamination, formation of cracks within the electrolyte, and also reduction of the electrode near the fuel electrode. The higher the applied voltage, the greater is the propensity to degradation. These observations are consistent with the chemical potential of oxygen in the electrolyte exceeding both electrode bounds under an applied voltage. It has been shown that a small amount of electronic conductivity can minimize degradation. The principal role of electronic conductivity is to smoothen out the variation in oxygen chemical potential through the electrolyte such that it does not exceed electrode bounds. YSZ-based electrolyte if doped with sufficient amount of CeO2 can create significant electronic conductivity such that the electrolyte becomes a mixed ionic electronic conductor. Doping with ceria also lowers the ionic transference number of the electrolyte. A possible bi-layer electrolyte consists of a thin layer of YSZ (or another purely oxygen ion conductor) deposited on a mixed ionic electronic conducting material. As long as electronic conduction through the blocking layer is negligible, the overall ionic transference number of the bi-layer electrolyte can approach unity. In this paper, theoretical analysis of the bi-layer electrolyte for reversible cells is presented. Two configurations of the bi-layer electrolyte are investigated. (1) The electron blocking layer adjacent to the oxygen electrode. (2) The electron blocking layer adjacent to the fuel electrode. For both configurations, the spatial distribution of oxygen chemical potential through the bi-layer electrolyte in both the SOFC and the SOEC modes are evaluated. The ionic transference number of the MIEC part of the bi-layer electrolyte is varied over a wide range. Theoretical analysis shows that such bi-layer electrolyte cells should exhibit good performance characterstics and excellent stability. The net variation of the oxygen chemical potential through the bi-layer electrolyte is determined as a function of transport properties of both layers, electrode polarizations and interfacial resistances to electron transfer.

Three-Dimensional Computational Fluid Dynamics Modelling for a Planar Solid Oxide Fuel Cell of a New Design

The aim of the work is to investigate the electrochemical processes of a planar Solid Oxide Fuel Cell (SOFC) and to estimate the performance of a novel SOFC design. The design involves cross-flow bipolar plates. Flow channels were designed to connect pairs of four orifices at the corners of the SOFC plates. Each of the bipolar plates has an air channel system on one side and a fuel channel system on the other side. One pair of channels in adjacent plates is used for the air flow along the cathode electrode, the other for the fuel flow along the anode of each cell. A schematic of the design proposed by Bossel [1] is shown in Fig. 1. Figure 1. A schematic of the proposed planar SOFC design: (a) cathode side view, (b) anode side view [1] A three-dimensional Computational Fluid Dynamics (CFD) model for an anode-supported planar SOFC with complex bipolar plates has been developed using the ANSYS Fluent code with additional Fuel Cell Tools module. The conservation equations of mass, momentum, energy and species as well as electrochemical models were solved for the fuel cell. The distributions of temperature and gas flow through the gas channels and PEN (positive electrode/electrolyte/negative electrode) structure were studied. The results identified the most susceptible areas for significant increase of the temperature at high current density, which can lead to hot spots formation and destruction of the electrodes. Knowledge of such parameters as the flow fields, pressure losses or temperature variation over the fuel cell area allowed to validate the effectiveness of the new SOFC design and is useful in further design modification. Acknowledgments The research programme leading to these results received funding from the European Union’s Seventh Framework Programme (FP7/2007-2013) for the Fuel Cells and Hydrogen Joint Technology Initiative under grant agreement no [325323]. Acknowledgments are due to the partners of SAFARI project. The work was also financed from the Polish research funds awarded for the project No. 3043/7.PR/2014/2 of international cooperation within SAFARI in years 2014-2016. [1] U. Bossel, Rapid startup SOFC modules, Energy Procedia, 28, 2012, 48-56. DOI: 10.1016/j.egypro.2012.08.039. Figure 1

Large size biogas-fed Solid Oxide Fuel Cell power plants with carbon dioxide management: Technical and economic optimization

This article investigates the techno-economic performance of large integrated biogas Solid Oxide Fuel Cell (SOFC) power plants. Both atmospheric and pressurized operation is analysed with CO2 vented or captured. The SOFC module produces a constant electrical power of 1 MWe.Sensitivity analysis and multi-objective optimization are the mathematical tools used to investigate the effects of Fuel Utilization (FU), SOFC operating temperature and pressure on the plant energy and economic performances. FU is the design variable that most affects the plant performance. Pressurized SOFC with hybridization with a gas turbine provides a notable boost in electrical efficiency. For most of the proposed plant configurations, the electrical efficiency ranges in the interval 50–62% (LHV biogas) when a trade-off of between energy and economic performances is applied based on Pareto charts obtained from multi-objective plant optimization. The hybrid SOFC is potentially able to reach an efficiency above 70% when FU is 90%. Carbon capture entails a penalty of more 10 percentage points in pressurized configurations mainly due to the extra energy burdens of captured CO2 pressurization and oxygen production and for the separate and different handling of the anode and cathode exhausts and power recovery from them.

High Temperature Micro‐Fan for Solid Oxide Fuel Cell Applications

AbstractThe possibility of using a μ‐fan in tubular solid oxide fuel cells module (SOFC‐M) is shown. The μ‐fan is placed instead of the ejector and fulfills its role. The main advantages of this solution are: lower power demanded by the fuel compressor (blower), more stable working characteristics, and the possibility of more accurate control of the recycled part of the anode gas during part load operation. A comparison of two SOFC‐Ms, with and without the ejector, is also shown and commented.

Sensitivity Analysis for the Efficiency Improvement of a Light Integrated Gasification Fuel Cell Power Plant

The solid oxide fuel cell (SOFC) is recognized as one of high efficiency plants of electricity generation for a sustainable future system with low environmental impact. In term of fuel flexibility, SOFC is suitable for direct use of syngas from a coal gasification plant. The application of integrated SOFC in coal gasification based power plant, such as a light integrated gasification fuel cell (L-IGFC) power plant, could be one of the most promising coal energy conversions system providing high electrical efficiency with low CO2 emitted to the atmosphere. The system consists of a coal gasifier and SOFC module on the top of a steam turbine. The sensitivity analyses of major operating parameters were performed using the developed model. The results indicated that the L-IGFC plant could achieve electrical efficiency in the range of 46.35- 60.32% in lower heating value.

Study of reversible SOFC/SOEC based on a mixed anionic-protonic conductor

This paper deals with the fabrication and electrochemical study of a high temperature solid electrolyte supporting cell operating as SOFC (Solid Oxide Fuel Cell) and SOEC (Solid Oxide Electrolysis Cell). The cell is based on a dual membrane (DM) electrolyte design, advantageously separating the cell into three different chambers: hydrogen side, oxygen side, and dual membrane (DM), where H2O production or splitting takes place in SOFC or SOEC mode respectively. The supporting electrolyte consists of a dense/porous/dense tri-layer, exclusively made of BaCe0.85Y0.15O3−δ (monolithic design), which is a mixed anionic-protonic conductor. The assembly was fabricated by tape casting, adding pore formers to control porosity. The cell was then electrochemically studied under different operating conditions of temperature, overpotentials and gas feeding, either in SOFC and SOEC mode. From the results presented here, it can be observed that, in spite of dense and thick electrolyte layers and platinum electrodes, the electrochemical study of the cell showed: (i) promising power density, (ii) interesting SOFC/SOEC operating mode reversibility, (iii) proved H2O production in the porous dual membrane when the cell operates as a fuel cell, and proved splitting of the H2O molecules contained in the porous dual membrane when the cell operates as an electrolyser. Investigations of cell performance degradation were also conducted.

Conceptual design of light integrated gasification fuel cell based on thermodynamic process simulation

Abstract Integration of solid oxide fuel cell (SOFC) in coal gasification power plant technology would be one of the most promising technology in the coal utilization for power generation. The clean syngas from gas cleanup unit serves as fuel for SOFC in integrated gasification fuel cell power plant. The heat generated by SOFC can be utilized by heat recovery steam generator to drive steam turbine for electricity production. In this study, proposed plants consisting of coal gasifier and SOFC on the top of a steam turbine (ST), called light integrated gasification fuel cell (L-IGFC), are investigated thermodynamically by using Aspen Plus software to evaluate their performance. The analyses are based on the SOFC module considering ohmic, activation and concentration losses at a certain current density of the cell operating at the intermediate temperature. The influences of gas cleanup unit models were also investigated. The results indicated that the proposed atmospheric L-IGFC plant could achieve electrical efficiency in the range of 39–46.35% in lower heating value.

A CASE STUDY OF USING ENHANCED INTERCONNECT CHANNEL GEOMETRIES ON HEAT AND MASS TRANSFER CHARACTERISTICS OF ANODE-SUPPORTED PLANAR SOFC

The role of enhanced heat transfer inside interconnect channels for improved convective cooling and thermal management of planar solid oxide fuel cells (SOFCs) is investigated. A case study of two different geometries (sinusoidal wavy or corrugated walls and offset-and- interrupted walls) is presented for a uniform electrochemical reaction rate with constant flow of moist hydrogen and air. The coupled heat and mass transfer is modeled by three-dimensional, steady-state equations for mass, momentum, energy, species transfer, and electrochemical kinetics, in which the porous-layer flow is in thermal equilibrium with the solid matrix and is coupled with the electrochemical reaction rate. The heat and mass transfer rates through the interconnect ducts as well as the electrodes on both the anode and cathode sides are computationally obtained. The temperature field and species mass distributions, along with variations in the friction factor and heat transfer coefficients describe the performance of the two flow-channel geometries. The relative thermal and hydrodynamic behavior is compared with that in plain rectangular-duct interconnects to evaluate their convective-cooling performance. The results demonstrate that the offset interrupted-wall geometry yields better cooling of the SOFC module.

Investigating parametric effects on performance of a high-temperature URSOFC

Summary The aim of this paper is to investigate the effects of variable parameters on the performance of a unitized regenerative solid oxide fuel cell (URSOFC) using a two-dimensional axisymmetric simulation model. This model was validated using the performance curves of an in-house button-type URSOFC. The parameters studied include the operating temperature and the porosity, tortuosity, and grain diameter of the electrodes while the URSOFC is operated in the solid oxide fuel cell mode and the solid oxide electrolyzer cell (SOEC) mode. The predicted results show that the temperature and the electrode porosity have a beneficial effect on the performance of the URSOFC because of an enhancement of the electrochemical reactions and the species mass transfer, respectively. However, when the URSOFC is operated in the SOEC mode, the cell performance decreases as the electrode porosity increases. This indicates that the decreasing reaction active sites as a result of the higher porosity have a dominant effect on the performance in the SOEC mode. The cell performance also decreases as the tortuosity and grain diameter of the electrodes increase. In addition, the effect of the electrode grain diameter on the cell performance is predicted to be insignificant for the URSOFC operated in the SOEC mode. The results of investigations presented in this paper can assist in the optimal design and management of a URSOFC. Copyright © 2014 John Wiley & Sons, Ltd.

Kinetic Studies on State of the Art Solid Oxide Cells

Introduction The Solid Oxide Fuel Cell (SOFC), which converts hydrogen as well as hydrocarbon fuels directly into electricity, has demonstrated almost comparable performance when operated reversely as Solid Oxide Electrolyser Cell (SOEC) for electrical energy storage as fuels. In both applications of the technology, cell optimization and eventual commercialisation requires a sound understanding of the mechanisms that affect performance and stability. These mechanisms depend on operation conditions like temperature, gas composition, fuel utilisation and current load as well as on gradients along cell and stackand cell microstructure. This increases the complexity of the systems, such that deconvolution and analytical description of the involved mechanisms becomes a major challenge, especially if both macroscopic trends as well as fundamental chemistry are to be accommodated. The electrode reaction kinetics is one such mechanism. Experimental The investigated single cells with a 4 x 4 cm2 active electrode area are anode supported cells with Ni/3YSZ substrates (ca. 0.3 mm), Ni/8YSZ anodes (ca. 10 μm), 8YSZ electrolytes (ca. 10 μm), Ce0.9Gd0.1O2 − δ buffer layers (ca. 1 μm) and La0.6Sr0.4CoO3 − δ/Ce0.9Gd0.1O2 − δcathodes (ca. 30 μm). The cells were characterised through electrochemical impedance spectroscopy at open circuit voltage and under current load. Current/voltage characteristics were recorded at different temperatures and gas compositions. The fuel utilization and current density range were chosen to emulate practical conditions. Figure 1 displays the Distribution of Relaxation Times (DRT)1 of spectra recorded at varying current densities in SOFC mode at 700- and at 800oC ensuring a maximum fuel utilization of 60% in three different fuel electrode gas mixtures. Considering that the area beneath a peak represents the Area Specific Resistance (ASR) of the given dynamic process, it is clear that depending on operation temperature and fuel composition the processes make varying contributions to the overall cell resistance. Current vs. Overpotential Relation The ASRs of the processes were obtained through Complex Non-linear Least Squares fit of the spectra with an equivalent circuit model2. The DRT was used for pre-identification of initial fit parameters. By integration of the ASRs vs current density, the corresponding overpotential curves were obtained, as displayed in Figure 2 for the electrochemical oxidation of H2 at the Ni/YSZ electrode. (f > 103Hz in Figure 1) Figure 2 reveals that the overpotential associated with the electrochemical oxidation of H2 2 (and CO) at the Ni/YSZ electrode at all current densities increases from H2/H2O to H2/CO2 and CH4/H2/H2O fuel compositions. This is probably because in the reformate cases, H2 has to be replenished through the water gas shift reaction2 and also at equilibrium the H2/H2O case contains more H2O. The cooling effect of the endothermic steam reforming may contribute to a higher overpotential in CH4/H2/H2O mixture. Relative to the overall potential drop in the investigated current density range, it can be claimed though that under these conditions and within the limits of accuracy, the Ni/YSZ electrode displays comparable performance in the three different fuel gas compositions. Outlook In this work experimental results of investigations on cells with varying microstructure of the fuel electrode operated in H2/H2O and reformate mixtures will be presented. Detailed impedance analysis will be used to determine the current/overpotential relationships and corresponding partial pressure dependencies. This will provide a solid basis for discussion of the highly debated analytical description of the electrochemical reaction overpotential of the Ni/YSZ electrodes.

The effect of electrode infiltration on the performance of tubular solid oxide fuel cells under electrolysis and fuel cell modes

The electrochemical performance of two different anode supported tubular cells (50:50 wt% NiO:YSZ (yttria stabilized zirconia) or 34:66 vol.% Ni:YSZ) as the fuel electrode and YSZ as the electrolyte) under SOFC (solid oxide fuel cell) and SOEC (solid oxide electrolysis cell) modes were studied in this research. LSM (La0.80Sr0.20MnO3−δ) was infiltrated into a thin porous YSZ layer to form the oxygen electrode of both cells and, in addition, SDC (Sm0.2Ce0.8O1.9) was infiltrated into the fuel electrode of one of the cells. The microstructure of the infiltrated fuel cells showed a suitable distribution of fine LSM and SDC particles (50–100 nm) near the interface of electrodes and electrolyte and throughout the bulk of the electrodes. The results show that SDC infiltration not only enhances the electrochemical reaction in SOFC mode but improves the performance even more in SOEC mode. In addition, LSM infiltrated electrodes also boost the SOEC performance in comparison with standard LSM–YSZ composite electrodes, due to the well-dispersed LSM nanoparticles (favouring the electrochemical reactions) within the YSZ porous matrix.

Pressurized Regenerative Solid Oxide Cells for Electrical Energy Storage

The high potential of reversible (or regenerative) solid oxide cell (rSOCs) systems for energy storage application motivates the present study which focuses on predicting rSOC performance through mathematical modeling. An intermediate fidelity model that can be used for identifying favorable electrochemical and thermal performance of rSOCs is developed and briefly reported here. The model is employed to investigate the rSOC performance particularly for pressurized operation. It has been observed that rSOCs can benefit from pressurized operation particularly in solid oxide fuel cell (SOFC) mode of operation. In the solid oxide electrolysis (SOEC) mode there are also advantages from pressurized operation, particularly above a certain current density. It has also been observed that the SOEC performance is more affected by changing the inlet feedstock condition (pressure and temperature) than the SOFC mode at pressurized operation.

Theoretical modeling of air electrode operating in SOFC mode and SOEC mode: The effects of microstructure and thickness

A theoretical model of solid oxide cells coupled with heterogeneous elementary reactions, electrochemical reactions, electrode microstructure and mass and charge transport is developed and validated. The effects of microstructure, thickness and temperature of air electrode on the cell performance in both solid oxide electrolysis cell (SOEC) and solid oxide fuel cell (SOFC) are individually discussed. The simulation results indicate that the growth in the thickness of air electrode reduces the effect of particle diameter while dramatically enlarges the effect of porosity. The microstructure and thickness of air electrode and temperature have significantly different impacts on solid oxide cells operating in SOEC mode and SOFC mode. The results indicate that the optimizing strategy of air electrode for SOEC and SOFC should be different especially for a thicker air electrode. The proposed model can be a useful tool for bridging the electrode geometry and microstructure design and optimization.

Development of novel LSM/GDC composite and electrochemical characterization of LSM/GDC based cathode-supported direct carbon fuel cells

(La0.8Sr0.2)0.95MnO3−δ (LSM)–Gd0.1Ce0.9O2−δ (gadolinium-doped ceria, GDC) composite cathode material was developed and characterized in terms of chemical stability, sintering behaviour, electrical conductivity, mechanical strength and microstructures to assess its feasibility as cathode support applications in cathode-supported fuel cell configurations. The sintering inhibition effect of LSM, in the presence of GDC, was observed and clearly demonstrated. The mechanical characterization of developed composites revealed that fracture behaviour is directly affected by pore size distribution. The Weibull strength distribution showed that for bimodal pore size distribution, two different fracture rates were present. Furthermore, the contiguity of LSM and GDC grains was calculated with image analysis, and correlation of microstructural features with mechanical and electrical properties was established. Subsequently, an LSM/GDC-based cathode-supported direct carbon fuel cell (DCFC) with Ni/ScSZ (scandia-stabilised zirconia) anode was successfully fabricated via slurry coating and co-firing techniques. The microstructures of electrodes and electrolyte layers were observed to confirm the desired morphology after co-sintering, and a single cell was electrochemically characterized in solid oxide fuel cell (SOFC) and DCFC mode with ambient air as oxidant. The higher values of open-circuit voltage indicated that the electrolyte layer prepared by vacuum slurry coating is dense enough. The corresponding peak power densities at 850 °C were 450 and 225 mW cm−2 in SOFC and DCFC mode, respectively. Electrochemical impedance spectroscopy was carried out to observe electrode polarization and ohmic resistance.