Reactive Electrophilic OI− Species Evidenced in High‐Performance Iridium Oxohydroxide Water Oxidation Electrocatalysts

• Published in: ChemSusChem 2017-12, Vol.10 (23), p.4786-4798
• Main Authors: Massué, Cyriac, Pfeifer, Verena, van Gastel, Maurice, Noack, Johannes, Algara‐Siller, Gerardo, Cap, Sébastien, Schlögl, Robert
• Format: Article
• Language: English
• Subjects: Electrocatalysts; electrochemistry; energy storage; Fine structure; Iridium; Oxidation; oxygen; Oxygen evolution reactions; Titration; water splitting
• ISSN: 1864-5631; 1864-564X
• DOI: 10.1002/cssc.201701291

Although quasi‐amorphous iridium oxohydroxides have been identified repeatedly as superior electrocatalysts for the oxygen evolution reaction (OER), an exact description of the performance‐relevant species has remained a challenge. In this context, we report the characterization of hydrothermally prepared iridium(III/IV) oxohydroxides that exhibit exceptional OER performances. Holes in the O 2p states of the iridium(III/IV) oxohydroxides result in reactive OI− species, which are identified by characteristic near‐edge X‐ray absorption fine structure (NEXAFS) features. A prototypical titration reaction with CO as a probe molecule shows that these OI− species are highly susceptible to nucleophilic attack at room temperature. Similarly to the preactivated oxygen involved in the biological OER in photosystem II, the electrophilic OI− species evidenced in the iridium(III/IV) oxohydroxides are suggested to be precursors to species involved in the O−O bond formation during the electrocatalytic OER. The CO titration also highlights a link between the OER performance and the surface/subsurface mobility of the OI− species. Thus, the superior electrocatalytic properties of the iridium (III/IV) oxohydroxides are explained by their ability to accommodate preactivated electrophilic OI− species that can migrate within the lattice. Water way to do it: Quasi‐amorphous iridium(III/IV) oxohydroxides exhibit exceptional performances as electrocatalysts for the oxygen evolution reaction (OER). The study of their electronic structures suggests that their superior electrocatalytic performances are linked to their ability to accommodate preactivated electrophilic OI− species, which can migrate within the lattice.