Dissolution-Induced Surface Roughening and Oxygen Evolution Electrocatalysis of Alkaline-Earth Iridates in Acid

Alkaline and alkaline-earth iridates have garnered much attention, as they can outperform traditional IrO2 for oxygen evolution electrocatalysis under acidic conditions. Despite the advantages of their catalytic properties and significant reduction of Ir utilization, dissolution of alkaline and alkaline-earth elements into acid media can be a serious drawback that may confine long-term applications. By using atomic-column-resolved scanning transmission electron microscopy, we demonstrate the surface variations of three alkaline-earth iridates, AIrO(3) (A = Sr or Ba). Directly identifying the structural transformation into metastable nanocrystallites or an amorphous state, we elucidate that substantial surface roughening can be induced by alkaline-earth elemental leaching. In particular, similar to 20-fold increases in the active surface area in pseudocubic SrIrO3 and monoclinic BaIrO3 are notable structural features. Our findings emphasize both the impact of surface structure on the overall catalytic activity and consequently the important control of chemical leaching to attain a high surface area in iridate-based catalysts.