Alfred Larsson, Andrea Grespi, Ožbej Vodeb, Karen van den Akker, Auden Ti, Claire Berschauer, Alexandra Imre, Philip Miguel Kofoed, Estephanía Lira, Mahesh Ramakrishnan, Stuart Ansell, Justus Just, Henrik Grönbeck, Ulrike Diebold, E. Lundgren, L. R. Merte, Dušan Strmčnik, Rik V. Mom, Marc T. M. Koper
saturation. Furthermore, we show that the oxide coverage increases with upper vertex potential, slower scan rates, and extended hold times at OCP, illustrating how oxides inhibit ORR during fuel cell start-up. Crucially, we demonstrate that the ORR onset is delayed until these oxides are reduced, establishing a direct, negative relationship between oxide coverage and ORR activity. This reveals a revised mechanism in which the potential-determining step is the reduction of surface oxides, and the slow kinetics of this restructuring ultimately determine when surface sites become catalytically available.