Carbon corrosion and platinum nanoparticles ripening under open circuit potential conditions

This study bridges the structural and the chemical properties of a high surface area carbon support (Vulcan XC72) used in proton-exchange membrane fuel cells and its resistance to corrosion under open circuit potential (OCP). Inks composed of Pt/XC72 electrocatalysts, Nafion® ionomer and water were aged for 3.5 years under air atmosphere. These conditions cause a mixed potential produced by simultaneous carbon support corrosion and oxygen reduction on Pt. Raman, X-ray photoelectron and Fourier Transform infrared spectroscopy measurements show that the amorphous domains of the Vulcan XC72 support are preferentially oxidized into CO2 during the first 1.5 years of aging at OCP. A much sluggish corrosion rate of the organized domains of the Vulcan XC72 support is observed by Raman and X-ray photoelectron spectroscopy measurements. Fourier-Transformed infrared spectroscopy results indicate that the corrosion of the organized domains of the carbon support produces mostly oxygen-bearing carbon surface groups, and to a minor extent, CO2 molecules at U = 0.80 V vs. RHE. Electron microscopy and electrochemical techniques were used to monitor the morphological changes of the Pt nanoparticles over time, resulting from the Pt-catalysed carbon corrosion.

► Degradation mechanism of Pt/Vulcan XC 72 nanoparticles at open circuit potential.
► The amorphous domains of Vulcan XC 72 are easily oxidized into CO2.
► CO2 formation is kept to a low extent on the organized domains of Vulcan XC 72.
► The Pt-catalysed carbon corrosion yields aggregation/detachment of the Pt particles.