Effect of Acid Washing on the Oxygen Reduction Reaction Activity of Pt-Cu Aerogel Catalysts

Developing highly active and durable oxygen reduction reaction (ORR) catalysts is crucial to reduce the cost of polymer electrolyte fuel cells (PEFCs). To meet those requirements, unsupported Pt-Cu alloy nanochains (aerogels) were synthesized by a simple co-reduction route in aqueous solution and their structure was characterized by X-ray absorption spectroscopy and scanning transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy. These catalysts exceeded the ORR activity of commercial Pt/C catalysts by more than 100% in rotating disk electrode (RDE) experiments and met the corresponding US DOE target for automotive PEFC implementation, thereby qualifying as very promising materials. The behavior of Pt-Cu aerogels under PEFC operation conditions was mimicked by acid washing experiments which showed that the Cu content in the alloy phase and ORR activity decrease through this step. Comparing composition, structure and ORR activity for various specimens, the Cu content in the alloy phase was identified as the main descriptor of ORR activity. An almost linear correlation was found between those two parameters and complemented by supporting data from the literature.