Core-Shell Pd 9 Ru@Pt on Functionalized Graphene for Methanol Electrooxidation

Abstract

© 2018 The Electrochemical Society. A simple but effective electrochemical route to functionalize graphene is demonstrated. Cyclic voltammetric sweeps (CV) are performed in a 0.5 M H 2 SO 4 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, Pd 9 Ru nanoparticles with an average size of 3–4 nm are synthesized and impregnated on functionalized graphene (FGN). To prepare core-shell electrocatalysts, Pd 9 Ru/FGN is subjected to Cu underpotential deposition followed by a galvanic displacement reaction to deposit a Pt monolayer on the Pd 9 Ru surface (Pd 9 Ru@Pt). The as-synthesized sample (Pd 9 Ru@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 Pd 9 Ru@Pt/FGN shows a value that is 1.5-fold larger than that of Pd 9 Ru@Pt on untreated graphene (Pd 9 Ru@Pt/GN). In the durability tests, Pd 9 Ru@Pt/FGN and Pd 9 Ru@Pt/GN demonstrate losses in the ECSA of 14.9% and 30.3%, respectively.