Methanol Oxidation at Pt−Cu, Pt−Ni, and Pt−Co Electrode Coatings Prepared by a Galvanic Replacement Process

Abstract

Platinized Cu, Ni, and Co deposits have been formed on glassy carbon (GC) electrode substrates by a two-step process, whereby a controlled amount of the transition metal was electrodeposited onto GC and subsequently partially exchanged for Pt upon immersion of the Cu/GC, Ni/GC, and Co/GC electrodes into a chloroplatinic acid solution. The spontaneous partial replacement of the transition metal by Pt resulted in Pt(Cu)/GC, Pt(Ni)/GC, and Pt(Co)/GC electrodes whose composition and depth profile were obtained by energy-dispersive spectrometry (EDS) and sputter-etch Auger electron spectroscopy (AES). Following electrochemical conditioning (involving electrode exposure to the oxygen and hydrogen evolution potential regimes), all deposits displayed typical Pt surface electrochemistry in acid solutions. Pt(Cu) catalysts exhibited enhanced electrocatalytic activity for methanol oxidation both during voltammetric and constant potential experiments. The behavior of Pt(Ni) and Pt(Co) depended on the method of assessment; in short-term voltammetric experiments, they were inferior to pure Pt, whereas in long-term constant potential experiments they outperformed it. The superior methanol oxidation activity of Pt(Cu) among all catalysts tested is interpreted in terms of the effect of Cu, Ni, and Co on methanol dissociative chemisorption and CO poison removal at/from the Pt surface.