Vanadium oxide electrodes for low temperature solid oxide fuel cells

Abstract

Thin film solid oxide fuel cells (µ-SOFCs), which use electrodes and electrolyte films with thicknesses of the order of tens of nanometers, have demonstrated power densities above 0.5 W/cm2 at temperatures below 600°C. The decrease of the operating temperature of SOFCs opens up the possibility of using them as power sources in mobile applications, but also allows demonstrating new power source operational capabilities enabled by the use of non-traditional SOFC materials. In this respect, we have recently demonstrated that using vanadium oxide on the anode-side of µ-SOFCs allows storing energy to continue generating power for short time periods in the absence of fuel. In the present contribution, we explore in detail the influence of the stoichiometry of as-deposited thin film vanadium oxide anodes on the performance of µ-SOFCs. Vanadium oxide films were deposited by reactive magnetron sputtering without external heating. Different oxygen concentrations in the sputtering chamber allowed obtaining different stoichiometries in the as-deposited films, as indicated by x-ray photoelectron spectroscopy and x-ray diffraction. The stoichiometry was varied from V metal to V2O5. V and VO films were crystalline while other as-deposited vanadium oxide stoichiometries were amorphous. µ-SOFCs with yttria-stabilized zirconia electrolyte, porous platinum cathode, and anodes with different vanadium oxide stoichiometries were fabricated and tested at temperatures between 150 and 440°C. Composition effects on open circuit voltage and peak power performance will be considered in depth in connection with the electrocatalytic activity of the oxide electrodes