Alkaline fuel cells and electrolyzers attract increasing attention of the electrochemical community, and one of their supposed advantages is their larger electrode materials stability than for their proton-exchange membrane analogues. However, stability of the core materials of fuel cells and electrolyzers in alkaline environment is not granted and remains understudied so far.Herein, using in situ Fourier-transform infrared spectroscopy (FTIR), identical-location transmission electron microscopy (IL-TEM), X-ray photoelectron spectroscopy (XPS) and CO ads stripping techniques, we provide physical and chemical evidences that Pt-based nanocatalysts catalyze the electrochemical corrosion of the carbon support (Vulcan XC72). This is due to more facile oxidation of oxygen-containing surface groups of the carbon support upon adsorption of hydroxyl groups on the Pt-based surface. The degradation mechanism is, to some extent, similar for other carbon-supported Pt group metal (PGM) electrocatalysts. We propose that the extent of degradation of PGM/C nanoparticles in alkaline electrolytes scales with the electrocatalyst's activity to electrooxidize CO, thereby providing a marker of the materials propensity to degradation in alkaline environment.

It is usually believed that carbon‐supported electrocatalysts are stable in alkaline environment, owing to the better thermodynamics stability of many metals and oxides at high pH. By focusing on a selected literature review concerning Pt/C and Pd/C nanoparticles, and in particular from identical‐location transmission electron microscopy (ILTEM), it is demonstrated that this “common knowledge” is erroneous in aqueous alkaline electrolytes: both Pt/C and Pd/C suffer pronounced loss of electrochemical surface area (ECSA), and the latter is linked to the detachment of the metal nanoparticles from the carbon support. Raman and X‐ray photoelectron spectroscopy show that these severe degradations are neither linked to massive corrosion of the carbon support nor to an overall change in carbon chemistry, but instead to a very localized corrosion of the carbon in the vicinity of the metal nanoparticles, leading to nucleation and growth of solid carbonate (when the electrolyte contains alkali metal cations), which expels the metal nanoparticles from their support. The mechanisms and extent of degradation depend on the nature of the metal nanoparticles, but also on their texture and on the nature of the support onto which they are immobilized.