Proton-conducting Solid Oxide Fuel Cells Research Articles

The effect of calcination temperature on the electrochemical properties of La0.3Sr0.7Fe0.7Cr0.3O3−x (LSFC) perovskite oxide anode of solid oxide fuel cells (SOFCs)

A series of perovskite structure anode materials, LSFC, was successfully prepared by a glycine combustion process and further calcined at different temperatures. The electrochemical properties of anodes prepared at various calcination temperatures (1100°C, 1200°C and 1300°C) were investigated. The calcination temperature had no significant influence on the morphology of the material but showed obvious influences on the particle sizes and electrochemical properties of the materials. Higher calcination temperature results in sharper X-ray diffractometer (XRD) diffraction peaks of the materials with larger particle sizes and higher electrical conductivity. However materials calcined at higher temperature had much smaller BET surface area resulting in lower triple phase boundary (TPB). The electrochemical performance test exhibited that LSFC anode material sintered at 1100°C exhibited the smallest area specific resistance (ASR) value in H2 at operating temperatures from 700 to 900°C. For proton conducting SOFCs (PC-SOFCs) fed by syngas, the cell with anode calcined at 1100°C also showed highest power density output of 120mW/cm2 at 750°C, which was almost three times higher than that of the cell with anode calcined at 1300°C.

Modeling of Proton-Conducting Solid Oxide Fuel Cells Fueled with Syngas

Solid oxide fuel cells (SOFCs) with proton conducting electrolyte (H-SOFCs) are promising power sources for stationary applications. Compared with other types of fuel cells, one distinct feature of SOFC is their fuel flexibility. In this study, a 2D model is developed to investigate the transport and reaction in an H-SOFC fueled with syngas, which can be produced from conventional natural gas or renewable biomass. The model fully considers the fluid flow, mass transfer, heat transfer and reactions in the H-SOFC. Parametric studies are conducted to examine the physical and chemical processes in H-SOFC with a focus on how the operating parameters affect the H-SOFC performance. It is found that the presence of CO dilutes the concentration of H2, thus decreasing the H-SOFC performance. With typical syngas fuel, adding H2O cannot enhance the performance of the H-SOFC, although water gas shift reaction can facilitate H2 production.

Investigation of A-site deficient Ba0.9Co0.7Fe0.2Nb0.1O3−δ cathode for proton conducting electrolyte based solid oxide fuel cells

A novel cathode material for proton conducting electrolyte based solid oxide fuel cells (SOFCs) of A-site deficient Ba0.9Co0.7Fe0.2Nb0.1O3−δ (BCFN) has been synthesized and characterized. The A-site deficient BCFN has demonstrated a thermal expansion coefficient (TEC) similar to that of BaZr0.1Ce0.7Y0.2O3−δ (BZCY) electrolyte, enhanced oxygen reduction activity and chemical stability. The application of BCFN in proton-conducting electrolyte-based SOFCs has been investigated, and the SOFCs with Ni-BZCY|BZCY|BCFN configuration demonstrate maximum cell power outputs of 180, 240 and 300 mW cm−2 at 600, 650 and 700 °C, respectively. The cell polarization resistance is as low as 0.951, 0.387 and 0.201 Ω cm2 under open circuit voltage (OCV) at 600, 650 and 700 °C, respectively. The cell maximum power density increases from 300 to 356 mW cm−2 at 700 °C after over 118 h operating under a constant current of 300 mA cm−2.

Effects of Particle Size and Size Distribution on the Percolation Behavior of Composite Proton Conducting Solid Oxide Fuel Cells Cathode

The cathode is the key in improving the performance of solid oxide fuel cells (SOFCs) at an intermediate temperature (IT). High performance cathode requires not only large amount of reaction sites, but also efficient transport of gases, electrons and ions, which are characterized by the percolation properties of the cathode. In this paper, the effects of cathode material properties and microstructures on percolation behavior of a composite SOFC cathode are analyzed by a 3D numerically morphological dilation method with controlling contact angles between two types of particles. The proposed model is validated by comparing the present simulation results with data from our previous kinetic Monte Carlo (KMC) simulations. The model is used for calculating the effective conductivity and percolation behaviors of proton-conducting SOFC (H-SOFCs) cathode. Detailed simulations are conducted under different parameters (mean particle radius of composite cathode, volume fraction of electrode and electrolyte materials, bulk material conductivities) to investigate their effects on the important effective ionic conductivity and percolation behavior of the cathode at an IT. The results could help design high performance H-SOFC electrodes.

Insights into CO poisoning in high performance proton-conducting solid oxide fuel cells

High performance anode supported proton-conducting solid oxide fuel cells (PC-SOFC) were fabricated and their performance in syngas was studied. PC-SOFC button cells produced a maximum power density of 812 mW cm−2 in H2 at 750 °C. It was found that the CO-containing feed streams could drastically degrade the performance of PC-SOFC. Based on the experimental results and the theoretical analysis, the detailed process of the CO-induced Ni catalyst deactivation was identified. This process could be divided into three distinguishable stages during the continuous exposure of the Ni catalyst in the CO-containing environment. The first stage could be described using the CO surface active site blocking mechanism, which was further confirmed by CO/H2 competitive adsorption model. The second stage deactivation was proposed to be related to the carbon deposition at TPB (Triple-phase Boundary). The deactivation during this stage was accelerated by the electrochemical conversion of H2. The last stage was attributed to the coking of Ni catalyst and the resulted metal dusting effect.

The effect of particle size on the performance of LSFC perovskite anode of proton conducting solid oxide fuel cell (PC-SOFC)

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Co-Generation of Electricity and CO from Syngas Via Proton-Conducting Solid Oxide Fuel Cells

High performance anode supported proton conducting solid oxide fuel cells (SOFCs) are fabricated and tested in syngas, which enable effective utilization of H2 as fuel. The proposed co-production of concentrated CO and electricity using SOFCs is investigated. The presence of CO in the anode feed does not decrease fuel cell performance considerably and it is found that in the anode effluent, the CO is concentrated whereas H2 is selectively removed with reasonable power output.

A chemically stable electrolyte with a novel sandwiched structure for proton-conducting solid oxide fuel cells (SOFCs)

A chemically stable electrolyte structure was developed for proton-conducting SOFCs by using two layers of stable BaZr0.7Pr0.1Y0.2O3−δ to sandwich a highly-conductive but unstable BaCe0.8Y0.2O3−δ electrolyte layer. The sandwiched electrolyte structure showed good chemical stability in both CO2 and H2O atmosphere, indicating that the BZPY layers effectively protect the inner BCY electrolyte, while the BCY electrolyte alone decomposed completely under the same conditions. Fuel cell prototypes fabricated with the sandwiched electrolyte achieved a relatively high performance of 185mWcm−2 at 700°C, with a high electrolyte film conductivity of 4×10−3Scm−1 at 600°C.

Catalytic surface promotion of highly active La0.85Sr0.15Cr0.8Ni0.2O3−δ anodes for La5.6WO11.4−δ based proton conducting fuel cells

La0.85Sr0.15CrO3−δ (LSC), La0.85Sr0.15Cr0.8Ni0.2O3−δ (LSCN) and LSCN infiltrated with Ni nanoparticles were tested as anodes for symmetrical cells based on La5.6WO11.4−δ (LWO) protonic electrolyte. These chromite-based electrode materials are compatible with LWO material, in contrast to the widely used NiO. Under typical anode reducing conditions, Ni is segregated from the LSCN lattice on the grain surface as metallic Ni nanoparticles, which are proved to be compatible with LWO in reducing conditions. These Ni nanoparticles become the catalytic active sites for the H2 oxidation reaction in proton conducing anodes and the electrode performance is substantially improved regarding to pure LSC. Ni nanoparticle infiltration further improves the catalytic promotion of the anode, reducing the polarization resistance (Rp) previously limited by low frequency surface related processes. Indeed, the Rp values achieved for LSCN infiltrated with Ni, e.g. 0.47Ωcm2 at 700°C, suggest the practical application of this kind of anodes in proton conducting solid oxide fuel cells (PC-SOFC).

The Effect of Particle Size on the Performance of LSFC Perovskite Anode of Proton Conducting Solid Oxide Fuel Cell (PC-SOFC)

A promising and stable perovskite structure anode material La0.3Sr0.7Fe0.7Cr0.3O3-x (LSFC) prepared by a glycine nitrate process was applied as the anode catalyst of a proton conducting solid oxide fuel cell (PC-SOFC). The particle size of the anode material could be controlled by varying the calcination temperatures. The influence of particle sizes on electrochemical performances had been studied. It was shown that the higher calcination temperature resulted in larger LSFC particles, which decreased the PC-SOFC performance significantly.

High-performance anode-supported solid oxide fuel cells based on nickel-based cathode and Ba(Zr0.1Ce0.7Y0.2)O3−δ electrolyte

Iron-stabilized lanthanum nickelate oxide with a perovskite structure, LaNi0.6Fe0.403−δ(LNF), was prepared by a citrate–nitrate process and evaluated as the cathode component of a proton-conducting SOFC based on a Ba(Zr0.1Ce0.7Y0.2)O3−δ (BZCY) electrolyte. XRD analysis shows that LNF reacts with BZCY to form a K2NiF4-type phase in the course of cathode calcination, but remains chemically well compatible with BZCY at the operating temperature. A single cell was assembled and tested using humidified hydrogen as fuel gas and atmospheric air as the oxidant. The matching thermal expansion coefficient (TEC), high conductivity and good catalytic activity of the LNF cathode enable the cell to generate high power densities and low polarization resistances. At 700°C, the peak power density is 668mWcm−2 and the polarization resistance is 0.046Ωcm2. This work confirms that LNF may be a prospective cathode material for BZCY proton-conducting electrolytes.

Investigation of a proton-conducting SOFC with internal autothermal reforming of methane

This study presents a performance analysis of a proton-conducting SOFC (SOFC-H+) with internal reforming of methane. The autothermal reforming within the SOFC-H+ stack is considered to be a potential solution of the carbon formation problem facing in operation of internal steam reforming SOFC-H+. A one-dimensional, steady-state model of the SOFC-H+ coupled with a detailed electrochemical model is employed to investigate its performance in terms of power density and fuel cell efficiency. The simulation results show that when SOFC-H+ is operated under an autothermal reforming environment, the presence of carbon monoxide, which is a major cause of carbon formation, in the fuel cell stack decreases. Effect of key operating parameters, such as temperature, steam-to-carbon and oxygen-to-carbon feed ratios, current density and fuel utilization, on the SOFC-H+ performance in terms of electrical efficiencies and energy demand is also investigated. The results indicate that operating temperatures have strong influence on SOFC-H+ performance, carbon monoxide production and heat generation.

Proton-Conducting Solid Oxide Fuel Cells Fed by Syngas and its Degradation Mechanisms

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Proton-Conducting Solid Oxide Fuel Cells with Yttrium-Doped Barium Zirconate for Direct Methane Operation

Electrochemical performance and feasibility of proton-conducting solid oxide fuel cells (SOFCs) using methane (CH4) fuel were investigated. At high fuel utilization, higher protonic transport number of electrolytes enables higher open-circuit voltage (OCV) when hydrogen (H2) is the fuel. In contrast, a high oxide ionic transport number is needed when CH4 is the fuel. Conductivities of each charge carrier of an yttrium-doped barium zirconate (BZY) electrolyte were therefore estimated by measuring the OCV under various partial pressures. A dense BZY electrolyte was obtained by the addition of 0.6 mol% nickel (Ni). This electrolyte exhibited protonic- and oxide ionic-mixed conductivity; in particular, these conductivities were similar to each other at 800–900°C, indicating high efficiency. A Ni/BZY anode enabled stable operation of a proton-conducting SOFC using 3% humidified CH4 fuel. The maximum power density of this SOFC was 2.35 mW cm−2 at 900°C and 1.69 mW cm−2 at 800°C, which were higher than that using a platinum anode. The activation energy for electrode polarization of the Ni/BZY anode using 3% humidified CH4 fuel was similar to that using 3% humidified H2 fuel, indicating that H2 via decomposition of CH4 was the main reactant on the Ni/BZY anode.

Optimization of the Lanthanum Tungstate/Pr2NiO4 Half Cell for Application in Proton Conducting Solid Oxide Fuel Cells

AbstractLa6WO12, recently reformulated La28–xW4+xO54+3x/2 exhibits a good level of protonic conductivity and chemical stability toward acidic gases. It is therefore a potential material for use as electrolyte in proton conducting solid oxide fuel cells (PC‐SOFC). Pr2NiO4 is a cathode material tested for SOFC in which proton conductivity has been demonstrated recently. In this study, compatibility between lanthanum tungstate and praseodymium nickelate has been investigated by powder X‐ray diffraction (XRD). Microstructure of symmetrical cells based on the lanthanum tungstate and Pr2NiO4 has been analyzed by scanning electron microscopy (SEM) and performance of the cathode has been evaluated by electrochemical impedance spectroscopy (EIS) through the value of the area specific resistance (ASR). To optimize the ASR value, different parameters were modified such as the Pr2NiO4 calcination temperature, the firing temperature of the symmetrical cells, the thickness of the Pr2NiO4 layer, and the composition of the composite cathode. An ASR value of 0.46 Ω cm2 at 700 °C has been obtained showing that lanthanum tungstate electrolyte associated with Pr2NiO4 cathode is a promising half cell for application in PC‐SOFC.

Interfacial Charge Transfer and Chemical Bonding in a Ni–LaNbO4Cermet for Proton-Conducting Solid-Oxide Fuel Cell Anodes

In this work, we present an atomic scale study of the structural and chemical characteristics of interfaces between Ni and LaNbO4 grains in Ni–LaNbO4 cermets, a model composite material for anodes in proton-conducting solid-oxide fuel cells (SOFC). Electron energy loss spectroscopy (EELS) performed in an aberration-corrected scanning transmission electron microscope reveals the absence of reaction or interdiffusion layers at the interface. Changes in the valence state of Ni as well as in the electronic structure of La, reflected by changes in the EELS fine features at the interface, are shown to be related to charge transfer across the interface. The experimental results are in excellent agreement with ab initio calculations based on density functional theory, which predict that direct chemical bonds are formed between the metal and the ceramic at this abrupt interface, resulting in a redistribution of electronic charge across the interface.

A Novel BaCo0.4Fe0.4Zr0.2O3-δ Cathode for Intermediate Temperature Proton-Conducting SOFC

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Electrochemical properties of composite fuel cell cathodes for La5.5WO12−δ proton conducting electrolytes

New composite cathodes for proton conducting solid oxide fuel cells (PC-SOFCs) based on the novel La5.5WO12−δ (LWO) electrolyte have been developed. First the applicability of LWO as a protonic electrolyte has been proved by recording the OCV in a Pt/LWO/Pt cell as a function of the temperature, matching the expected Nernst voltage. In order to improve the electrode performance on LWO PC-SOFCs, composite cathodes have been prepared by mixing the La0.8Sr0.2MnO3−δ (LSM) electronic phase with the LWO protonic phase. The ceramic–ceramic (cer–cer) composites have been electrochemically studied as cathodes on LWO dense electrolytes in symmetrical cells. Different ratios of both phases and two different electrode sintering temperatures (1050 and 1150 °C) have been studied. Electrochemical impedance spectroscopy (EIS) analysis has been carried out in the temperature range 700–900 °C under moist (2.5% H2O) atmospheres. Different oxygen partial pressures (pO2) have been employed in order to characterize the processes (surface reaction and charge transport) taking place at the composite cathode. A substantial improvement in the cathode performance has been attained by the addition of the LWO protonic phase into the LSM electronic material. From the electrochemical analysis it can be inferred that electrode enhancement is principally ascribed to the increase in the three-phase-boundary length, which enables electrochemical reactions to occur along the thickness of the electrode.

Evaluation of molybdenum carbide as anode catalyst for proton-conducting hydrogen and ethane solid oxide fuel cells

Electrochemical performance, impedance spectroscopy and carbon tolerance analysis show, for the first time, that molybdenum carbide has great potential for application as anode catalyst in proton-conducting solid oxide fuel cells. Ethylene and stable power density are coproduced from ethane in proton-conducting SOFC with molybdenum carbide as anode catalyst and BCZY as electrolyte.

Electrochemical characterization of YBaCo 3ZnO 7+ δ as a stable proton-conducting SOFCs cathode

YBaCo 3ZnO 7+ δ (YBCZ) was synthesized and used as the cathode materials for proton-conducting SOFCs successfully. The single cell, consisting of a BaZr 0.1Ce 0.7Y 0.2O 3− δ (BZCY7)–NiO anode substrate, a BZCY7 anode functional layer, a BZCY7 electrolyte membrane and an YBCZ cathode layer, was assembled and tested from 600 to 700 °C with humidified hydrogen (∼3% H 2O) as the fuel and static air as the oxidant. An open-circuit potential of 0.98 V and a maximum power density of 307 mW cm −2 at 700 °C were obtained. The measured results indicated that YBCZ has the potential to be a cathode material for proton-conducting SOFCs.