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Zusammenfassung:
Although quasi-amorphous Ir-oxohydroxides have repeatedly been identified as superior oxygen evolution reaction (OER) electrocatalysts, an exact description of the performancerelevant species has so far remained a challenge. In this context, we
report on the characterization of hydrothermally prepared IrIII/IV-oxohydroxides exhibiting exceptional OER-performance. It was found that holes in the O2p states of IrIII/IV-oxohydroxides result in reactive OI--species identified by characteristic NEXAFS-features. A prototypical titration reaction based on CO as a probe molecule shows that these OI--species are highly susceptible to nucleophilic attack at room temperature. Similarly to pre-activated oxygen involved in the biological OER in Photosystem II, the electrophilic OI--species evidenced in IrIII/IV-oxohydroxides are suggested to be precursors to species involved in the O-O bond formation during electrocatalytic OER. CO-titration also highlights a link between OER-performance
and the surface/sub-surface mobility of OI--species. The superior electrocatalytic properties of IrIII/IV-oxohydroxides are thus explained
by their ability to accommodate pre-activated electrophilic OI--species
able to migrate within the lattice.