Electrochemical Synthesis of an Alcohol-Tolerant Platinum-Based Material for the Oxygen Reduction Reaction

Abstract

A prevalent problem in direct alcohol fuel cells (DAFCs) is the crossover of alcohol, which usually floods the cathode compartment and its effects reflect in the decrease of cell performance in terms of efficiency. This is due to the interference of alcohol molecules on the electrocatalyst surface during the oxygen reduction reaction (ORR), causing a competition between them. As this consequence is directly related to the low selectivity of catalyst, an alcohol-tolerant material is necessary; in order to inhibit its deactivation because of oxidized species on the electrode surface. Some approaches to avoid such decrease in activity consists in the incorporation of a secondary metal in the electrocatalyst with the aim of promoting selectivity. Furthermore, the implementation of bimetallic materials leads to the decrease in the Pt loading, as it represents a higher cost of the catalyst; in summary, the best option consists in preparing bimetallic mixtures. In the present work, Pt and Pt/Ag materials were synthesized by cyclic voltammetry (VC) and its behavior in basic medium was evaluated for the oxygen reduction reaction (ORR) in absence and in presence of 0.1 M of methanol, ethanol, ethylene glycol and glycerol. The results demonstrated that the use of PtAg as cathode electrode achieved higher selectivity and better performance compared with Pt catalyst in the presence of alcohol fuels. While Pt preferred to oxidize these fuels instead of taking the ORR, PtAg only carried out the ORR. The activity of PtAg catalyst towards oxygen reduction reaction resulted in an overpotential of 90 mV compared with pure Pt, after the electrochemical activation. Pt showed no tolerance to any tested alcohol-based fuels but, PtAg exhibited excellent tolerance to methanol, ethanol and ethylene glycol.