CO Electrochemical Oxidation on Ni Patterned Anodes for Assessing Solid Oxide Fuel Cell Kinetics

Abstract

To eliminate complications associated with gas-phase transport in porous SOFC anodes, microfabricated Ni patterned anodes on YSZ electrolytes have been studied with impedance spectroscopy and voltammetry to evaluate CO electrochemical oxidation under dry and wet conditions. The patterned anodes provide a measure for approximating charge transfer rates per length of three-phase boundary. Adding ~ 3% H2O (by mole) to CO/CO2 anode flows increases exchange current densities by approximately 1.5X for temperatures between 700 and 800 {degree sign}C. This suggests that water gas shift does create adsorbed H on the Ni electrocatalyst for increased charge transfer rates. However, comparison with H2 exchange current densities indicates that CO electrochemical oxidation is still the dominant source of Faradaic current. Analysis of the measured impedance spectra for the dry and wet CO/CO2 anode flows reveals that both high-frequency charge transfer activation and low-frequency adsorption and surface diffusion are contributing significantly to the measured anode overpotentials.