Degradation kinetics of Pt during high-temperature PEM fuel cell operation part II: Dissolution kinetics of Pt incorporated in a catalyst layer of a gas-diffusion electrode

Abstract

This paper presents the experimentally studied degradation of a gas-diffusion electrode under a potentiostatic regime. The experimental conditions corresponded to the operation of a high-temperature fuel cell with a proton-exchange membrane, e.g. in 99.6 wt% H3PO4, at a temperature of 160 °C. A one-dimensional mathematical model of the degradation of a gas-diffusion electrode was validated using experimental data and utilised for determination of kinetics data of the electrochemical dissolution of Pt. The mathematical model predicted a general mechanism of Pt degradation during electrode polarisation, comprising the electrochemical oxidation of the surface of smaller nanoparticles to PtO, followed by the chemical dissolution of PtO to Pt2+(sol) and electrochemical reduction of the formed Pt2+(sol) on the bare Pt surface of larger nanoparticles. The intensity of degradation varied with the electrode polarisation potential. At potentials close to 0.7 V vs. dynamic hydrogen electrode (DHE), only small nanoparticles were dissolved, while at potentials close to 1 V vs. DHE, Pt dissolution took place on a wider range of nanoparticle sizes, resulting in a higher concentration of Pt2+(sol) on the electrode and, consequently, in a higher rate of nanoparticle growth. The mathematical model presented can be used, with modifications, to make an approximate estimate of the extent of degradation and Pt nanoparticle size distribution in a gas-diffusion cathode, depending on the polarisation potential within the range of 0.7–1 V vs. DHE.