Fig. 7: Schematic diagrams of the PPI corrosion mechanisms.

a The PPI corrosion mechanism for CS Cu in HNO3; b simplified models showing the diffusion pathways for species under different geometrical conditions; the corrosion process for c LT, and d HT CS Cu. Arrows in a III indicate the corrosion propagation caused by the ORR (green) and catalytic cycles (blue). Arrows in b represent possible diffusion directions, with the purple and black ones denoting directions into the bulk solution and to the Cu surface, respectively.