Electrodeposited AgPd alloy coatings as efficient catalysts for the ethanol oxidation reaction

Abstract

The Pd and three AgPd alloy layers (AgPd1, AgPd2 and AgPd3) were electrodeposited onto Au disc electrodes from the solution containing high concentration of chloride ions (>12 M). All coatings were investigated by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), anodic linear sweep voltammetry (ALSV), while their surface composition was investigated by X-ray photoelectron spectroscopy (XPS). The AgPd1 and AgPd2 samples were electrodeposited at different constant current densities (-0.178 mA cm(-2) and -0.415 mA cm(-2) respectively) to the charge of -0.2 C cm(-2) (thickness similar to 0.18 mu m) at a stationary disc electrode, while the sample AgPd3 was electrodeposited to the charge of -3.0 C cm(-2) (thickness similar to 2.8 mu m) at a constant current density of -7.0 mA cm(-2) under the conditions of convective diffusion. Samples AgPd1 and AgPd2 had similar morphologies of low roughness, while the morphology of AgPd3 was characterized by large crystals and higher roughness. The most active and the most poisoning tolerant coatings for ethanol oxidation reaction (EOR) are the AgPd3 and AgPd1 alloy samples, containing 72.6 at.% Ag - 27.4 at.% Pd and 84.7 at.% Ag - 15.2 at.% Pd respectively (XPS analysis). In this study, we demonstrated for the first time that the activity for the EOR at AgPd alloys was closely related to the amount of non-reduced Ag2O (most probably as Ag - hydroxide). Accordingly, all AgPd alloy samples had to be cycled in the potential region of Ag2O formation and reduction before the investigation of the EOR, in order to provide their catalytic activity towards the EOR.