Alkaline fuel cells (AFCs) are relevant for niche applications, but still require enhanced performance and lifetime. Active and durable hydrogen oxidation reaction (HOR) catalysts must be developed: linking their electrochemical surface area (ECSA) loss to their HOR activity and understanding whether the ECSA loss of carbonsupported platinum group metal-based (PGM/C) HOR catalysts is irreversible (nanoparticles dissolution, detachment, Ostwald ripening) or reversible is pivotal. Using identical-location transmission electron micrographs (IL-TEM) and ECSA characterizations by "CO-like" stripping undertaken pre and post accelerated stress tests (AST), the different degradation mechanisms undergone by monometallic (Pt/C and Pd/C) and bimetallic catalysts (Pd-Pt/C and Pd-Ni/C) are unveiled. Monometallic PGM/C undergo extensive reversible poisoning and irreversible degradation upon operation at low potential, in contrast to bimetallic catalysts, which are less affected. Pd-Ni exhibits the smallest loss of ECSA PGM and HOR activity: it poorly catalyzes carbon corrosion and is hardly poisoned by "CO-like" species.