A copper–palladium/reduced graphene oxide composite as a catalyst for the oxygen reduction reaction

Abstract

Replacing expensive platinum in electrocatalytic materials by cheaper and readily available alternatives is a paramount task in hydrogen-based energetics. In this study, we synthesize a copper–palladium nanostructured catalyst with lowered palladium content on a reduced graphene oxide support (RGO/CuPd), and compare its catalytic activity in the oxygen reduction reaction (ORR) against the monometallic analogues RGO/Cu and RGO/Pd. The products are fully characterized by a set of instrumental methods, including TGA, XRD, XPS, and TEM. The chemical form of metals in all the three composite materials is different. In RGO/Cu, copper exists in the form of single Cu²⁺ ions chemically bound to the RGO surface. In RGO/Pd, palladium forms metallic nanoparticles. In RGO/CuPd, part of Cu²⁺ covers the RGO surface, similar to RGO/Cu, but another part forms alloyed nanoparticles with Pd. The catalytic properties of the prepared materials are tested by CV, chronoamperometry, and the actual membrane electrode assemblies. Interestingly, even noble-atom-free RGO/Cu demonstrated catalytic activity toward the ORR. The most efficient material was still pure palladium-based RGO/Pd. However, replacing half of expensive Pd by Cu in RGO/CuPd only slightly lowered the catalyst efficiency; the maximum current densities for RGO/CuPd and RGO/Pd were respectively 124 and 136 mA cm⁻², and the power densities were respectively 55.8 and 59.6 mW cm⁻². The discovered synergistic effect between Cu and Pd opens the route for developing platinum-free, low-noble-metal-content catalytic systems for the ORR.