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 degreesC in hydrogen. The examined porous anodes are a Ni/Zr0.92Y0.16O2.08 (Ni/YSZ) cermet, a Ni/Ce0.9Gd0.1O1.95 (Ni/CGI) cermet, a Ce0.6Gd0.4O1.8 (CG4) ceramic, a La0.75Sr0.25Cr0.97V0.03O3 (LSCV) ceramic and a Ti-0.22 Y0.16Zr0.92O2.52 (TiYSZ) ceramic, Addition of small amounts ( approximate to I w/o) of Ni to the electrode surface is found to improve electrode performance on mixed electronic and ionic conductors (MIEC's), distinctly in the low-frequency part of the impedance spectra. An effect of isotope exchange (H-2/H2O to D-2/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, (C) 2002 Elsevier Science B.V. All rights reserved.