Mixed conductor anodes: Ni as electrocatalyst for hydrogen conversion

Abstract 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/Zr 0.92 Y 0.16 O 2.08 (Ni/YSZ) cermet, a Ni/Ce 0.9 Gd 0.1 O 1.95 (Ni/CG1) cermet, a Ce 0.6 Gd 0.4 O 1.8 (CG4) ceramic, a La 0.75 Sr 0.25 Cr 0.97 V 0.03 O 3 (LSCV) ceramic and a Ti 0.22 Y 0.16 Zr 0.92 O 2.52 (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 (MIEC's), distinctly in the low-frequency part of the impedance spectra. An effect of isotope exchange (H 2 /H 2 O to D 2 /D 2 O) is observed for all anodes. The low-frequency limitation is suggested to be hydrogen adsorption and/or dissociation on the surface of MIEC electrodes.