Durable and High-Performance Direct-Methane Fuel Cells with Coke-Tolerant Ceria-Coated Ni Catalysts at Reduced Temperatures

Unravelling the role of dopants in the electrocatalytic activity of ceria towards CO2 reduction in solid oxide electrolysis cells

CO₂ reduction in Solid Oxide Electrolysis Cells (SOECs) is a key-technology for the transition to a sustainable energy infrastructure and chemical industry. Ceria (CeO₂) holds great promise in developing highly efficient, cost-effective and durable fuel electrodes, due to its promising electrocatalytic properties, and proven ability to suppress carbon deposition and to tolerate high concentrations of impurities. In the present work, we investigate the intrinsic electrocatalytic activity of ceria towards CO₂ reduction by means of electrochemical impedance spectroscopy (EIS) on model systems with well-defined geometry, composition and surface area. Aiming at the optimization of the intrinsic catalytic properties of the material, we systematically study the effect of different dopants (Zr, Gd, Pr and Bi) on the reaction rate under varying operating conditions (temperature, gas composition and applied polarization) relevant for SOECs. The electrochemical measurements reveal the dominant role of the surface defect chemistry of the material in the reaction rate, with doping having only a mild effect on the rate and activation energy of the reaction. By analyzing the pO₂ and overpotential dependence of the reaction rate with a general micro-kinetic model, we are able to identify the second electron transfer as the rate limiting step of the process, highlighting the dominant role of surface polarons in the energy landscape. These insights on the correlation between the surface defects and the electrocatalytic activity of ceria open new directions for the development of highly performing ceria-based technological electrodes.

Low Nickel, Ceria Zirconia-Based Micro-Tubular Solid Oxide Fuel Cell: A Study of Composition and Oxidation Using Hydrogen and Methane Fuel

The study examines the effect of using low nickel (Ni) with high ceria (CeO2) anode content towards the oxidation of H2 and CH4 fuel by evaluating the activation energy of the ohmic process and charge transfer process. Using a micro-tubular solid oxide fuel cell (MT-SOFC), the anodes are made up of 50% YSZ with varying NiO:CeO2 percentages from 0% NiO, 50% CeO2 to 50% NiO, 0% CeO2. The performance is measured based on maximum power density (MPD), electrochemical impedance spectroscopy (EIS) and activation energy, Ea of the ohmic (Rohm) and charge transfer (Rct) processes. We found that by lowering the Ni content to lower than 50% NiO, anode conductivity will drop by 7-fold. An anode containing 37.5% NiO, 12.5% CeO2 yield MPD of 41.1 and 2.9 mW cm−2 when tested on H2 and CH4 fuels thus have the lowest Ni content without an abrupt negative effect on the MPD and EIS. The significant effect of conductivity drops on MPD and EIS are observed to occur at 25% NiO, 25% CeO2 and lower NiO content. However, anode content of 25% NiO, 25% CeO2 has the lowest Ea for Rct (29.74 kJ mol−1) for operation in CH4, making it the best anode composition to oxidize CH4. As a conclusion, an anode containing 25% NiO:25% CeO2:50% YSZ and 37.5% NiO:12.5% CeO2:50% YSZ shows promising results in becoming the low Ni anode for coking-tolerant SOFC.

Effects of dispersed copper nanoparticles on Ni-ceria based dry methanol fuelled low temperature solid oxide fuel cells

Methanol is an attractive energy source due to its portability and thermodynamic coke resistance by its oxygen content. In order to operate dry methanol fuel low temperature solid oxide fuel cells (LT-SOFCs), it is important to solve the problems of carbon formation and its low performance. In this study, copper impregnation was selected to decrease the carbon deposition and enhance the performance at low temperature. The interaction of copper, ceria and nickel improves CO oxidation capacity which improves coke tolerance and nano-sized nickel copper alloys improved durability and catalytic performance under methanol feed. It markedly amplified the performance about 0.4 W cm⁻² at 550 °C with the durable operation at 1.4 A cm⁻² over 50 h. Loading copper nanoparticles is promising method for Ni-ceria based LT-SOFC using methanol fuel with high performance and stable operation.

Copper impregnation was selected to decrease the carbon deposition and enhance the performance at low temperature of dry methanol fuelled low temperature solid oxide fuel cells.

An Investigation of Direct Hydrocarbon (Propane) Fuel Cell Performance Using Mathematical Modeling

An improved mathematical model was used to extend polarization curves for direct propane fuel cells (DPFCs) to larger current densities than could be obtained with any of the previous models. DPFC performance was then evaluated using eleven different variables. The variables related to transport phenomena had little effect on DPFC polarization curves. The variables that had the greatest influence on DPFC polarization curves were all related to reaction rate phenomena. Reaction rate phenomena were dominant over the entire DPFC polarization curve up to 100 mA/cm2, which is a value that approaches the limiting current densities of DPFCs. Previously it was known that DPFCs are much different than hydrogen proton exchange membrane fuel cells (PEMFCs). This is the first work to show the reason for that difference. Reaction rate phenomena are dominant in DPFCs up to the limiting current density. In contrast the dominant phenomenon in hydrogen PEMFCs changes from reaction rate phenomena to proton migration through the electrolyte and to gas diffusion at the cathode as the current density increases up to the limiting current density.

Strategies for Carbon and Sulfur Tolerant Solid Oxide Fuel Cell Materials, Incorporating Lessons from Heterogeneous Catalysis

Solid oxide fuel cells (SOFCs) are a rapidly emerging energy technology for a low carbon world, providing high efficiency, potential to use carbonaceous fuels, and compatibility with carbon capture and storage. However, current state-of-the-art materials have low tolerance to sulfur, a common contaminant of many fuels, and are vulnerable to deactivation due to carbon deposition when using carbon-containing compounds. In this review, we first study the theoretical basis behind carbon and sulfur poisoning, before examining the strategies toward carbon and sulfur tolerance used so far in the SOFC literature. We then study the more extensive relevant heterogeneous catalysis literature for strategies and materials which could be incorporated into carbon and sulfur tolerant fuel cells.