Nanoporous Pd-Cu thin films as highly active and durable catalysts for oxygen reduction in alkaline media

Abstract

A facile electrochemical etching approach was developed and implemented to enhance the electrocatalytic performance of Pd-Cu films for oxygen reduction reaction (ORR) in alkaline media. The nanoporous (np) Pd-Cu was synthesized through electrochemical de-alloying of pre-deposited Pd-Cu films. Scanning electron microscopy (SEM) with energy dispersive spectroscopy was employed to confirm the residual amount of Cu in the np structure. The accordingly prepared np catalysts showed excellent ORR activity up to 1.11 A/mgPd at a potential of 0.9 V vs. RHE which is around 22-times and 6.2-times higher than that of a plain Pd film and commercial Pd/C catalyst, respectively. The ORR activity enhancement is attributed to the unique porous structure, large Pd surface area, and modified electronic structure of Pd with residual Cu as confirmed by the SEM, hydrogen underpotential deposition, and CO stripping characterizations. The np Pd-Cu catalyst also showed excellent durability which is manifested by a negligible decrease in the half-wave potential (4 mV negative shift) after 10,000 potential cycles in alkaline media. These findings provide insights into the rational design of an electrocatalyst's structure utilizing an electrochemical de-alloying method to achieve high atomic utilization and improved catalytic performance.