The accelerated stress test AST performed

Overall, the procedures are similar to those performed in Ref. [31], except Nafion® polymer electrolyte is used instead of 1 mol L−1 sulfuric acid solution: the working electrode remained at the interface with a 115 Nafion® membrane in the absence of any liquid electrolyte during the whole AST and ORR characterizations. In all cases (dry cell and aqueous H2SO4 electrolyte solution), the temperature was similar (T = 298 ± 2 K) during the AST and ORR characterization, which enables comparing the tests on the basis of the presence/absence of excess liquid water.