The Native Oxide on Titanium Metal as a Conductive Model Substrate for Oxygen Reduction Reaction Studies

Very thin Pt layers on inexpensive substrates are promising oxygen reduction reaction (ORR) catalysts for polymer electrolyte fuel cells (PEFCs). TiOx is considered a suitable substrate but shows problems with conductivity, thus masking chemical effects by semiconductor effects (mismatch in energy states hindering electron transport). The native oxide on metallic Ti (TiOx/Ti) has been used as a novel and promising model substrate for ORR studies eliminating semiconductor effects. A high-coverage “particle” layer with high specific ORR activity was formed via electrodeposition from Ar-saturated solution. While high specific activities could be demonstrated, the concept could not be enhanced to high mass activities by limiting the Pt deposition amount. The approach to quench Pt deposition by introducing CO failed due to its adsorption to the TiOx/Ti substrate before metal deposition and thus the prevention of layer formation. A similar approach for the Pt/Au codeposition was also unsuccessful manifesting the TiOx/Ti-CO incompatibility even further.