Datensatz

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 Ir^III/IV-oxohydroxides exhibiting exceptional OER-performance. It was found that holes in the O2p states of Ir^III/IV-oxohydroxides result in reactive O^I--species identified by characteristic NEXAFS-features. A prototypical titration reaction based on CO as a probe molecule shows that these O^I--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 O^I--species evidenced in Ir^III/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 O^I--species. The superior electrocatalytic properties of Ir^III/IV-oxohydroxides are thus explained by their ability to accommodate pre-activated electrophilic O^I--species able to migrate within the lattice.