Mixed conductor anodes: Ni as electrocatalyst for hydrogen conversion

Five types of anodes for solid oxide fuel cells (SOFC) are examined on an yttria-stabilised zirconia (YSZ) electrolyte by impedance spectroscopy at 850 °C in hydrogen. The examined porous anodes are a Ni/Zr0.92Y0.16O2.08 (Ni/YSZ) cermet, a Ni/Ce0.9Gd0.1O1.95 (Ni/CG1) cermet, a Ce0.6Gd0.4O1.8 (CG4) ceramic, a La0.75Sr0.25Cr0.97V0.03O3 (LSCV) ceramic and a Ti0.22Y0.16Zr0.92O2.52 (TiYSZ) ceramic. Addition of small amounts (≈1 w/o) of Ni to the electrode surface is found to improve electrode performance on mixed electronic and ionic conductors (MIECʹs), distinctly in the low-frequency part of the impedance spectra. An effect of isotope exchange (H2/H2O to D2/D2O) is observed for all anodes. The low-frequency limitation is suggested to be hydrogen adsorption and/or dissociation on the surface of MIEC electrodes.