Reverse Cell Bias for the Prevention of Ni Oxidation during Air Exposure

Abstract

The primary aim of this work was to prevent Ni oxidation by reverse biasing of the cell during air exposure at SOFC operating temperatures. As the area specific polarization resistance (Rp, inversely proportional to the H2 oxidation activity) of electrolyte-supported Ni-YSZ anodes normally decreases after a single redox cycle, the approach used here was to determine if reverse polarization during air exposure can prevent this performance enhancement. The use of a constant cathodic potential did not appear to prevent Ni oxidation, although it is likely that an insufficiently negative potential was applied. However, anode performance enhancement was prevented by the application of a constant applied current density during air exposure. However, these results are not fully conclusive, as the extent of Ni oxidation could not be determined analytically in situ. Notably, observations, such as an increase in the observed cathodic overpotential during negative biasing and the decrease in Rp after air exposure (with applied cathodic currents) still need to be understood.