Core-Shell Pd9Ru@Pt on Functionalized Graphene for Methanol Electrooxidation

Abstract

A simple but effective electrochemical route to functionalize graphene is demonstrated. Cyclic voltammetric sweeps (CV) are performed in a 0.5 M H2SO4 aqueous solution on electrodes consisting of carbon cloth, graphene, and Nafion ionomer. Upon exposure to ambient oxygen, the formation of hydroxyl radicals from the oxygen reduction reaction during the CV cycles initiates the decomposition of the Nafion ionomer, which produces oxygenated functional groups on the graphene surface. Using contact angle measurements and X-ray photoelectron spectroscopy, various amounts of Nafion ionomer are explored to determine the optimum conditions for graphene functionalization. Afterwards, Pd9Ru nanoparticles with an average size of 3–4 nm are synthesized and impregnated on functionalized graphene (FGN). To prepare core-shell electrocatalysts, Pd9Ru/FGN is subjected to Cu underpotential deposition followed by a galvanic displacement reaction to deposit a Pt monolayer on the Pd9Ru surface (Pd9Ru@Pt). The as-synthesized sample (Pd9Ru@Pt/FGN) exhibits enhanced performance in methanol electrooxidation, which includes a better activity and lower susceptibility to poisoning by intermediates. The electrochemically active surface area (ECSA) of Pd9Ru@Pt/FGN shows a value that is 1.5-fold larger than that of Pd9Ru@Pt on untreated graphene (Pd9Ru@Pt/GN). In the durability tests, Pd9Ru@Pt/FGN and Pd9Ru@Pt/GN demonstrate losses in the ECSA of 14.9% and 30.3%, respectively.