Degradation kinetics of Pt during high-temperature PEM fuel cell operation part I: Kinetics of Pt surface oxidation and dissolution in concentrated H3PO4 electrolyte at elevated temperatures

Abstract

In this work, a combined approach, utilising both experimental cyclic voltammetry and mathematical modelling, was adopted in order to determine the kinetics of Pt oxidation to PtO and chemical dissolution of PtO to Pt2+ in concentrated H3PO4 at elevated temperatures. Experimental cyclic voltammograms were corrected for chemical dissolution of PtO based on a charge balance calculation and the corresponding kinetic constant was evaluated. The corrected voltammograms were compared with the results of a 0-dimensional dynamic model of electrochemical Pt oxidation and the kinetic parameters of this reaction were evaluated. Finally, the two surface reactions were integrated into a mathematical model. This model is able to simulate cyclic voltammograms of Pt in concentrated H3PO4 electrolyte within the temperature range of 120–160 °C. It was shown that Pt electrochemical oxidation is the dominating reaction on the Pt surface, based on total recorded charge. However, the chemical dissolution of PtO is by no means negligible, since as much as 10% of the PtO monolayer formed can chemically dissolve under specific conditions.