Direct Detection of Surface Species Formed on Iridium Electrocatalysts during the Oxygen Evolution Reaction

The effect of surface orientations on the formation of iridium oxide species during the oxygen evolution reaction (OER) remains yet unknown. Herein, we use a needle-shaped iridium atom probe specimen as a nanosized working electrode to ascertain the role of the surface orientations in the formation of oxide species during OER. At the beginning of electrolysis, the top 2-3 nm of (024), (026), (113), and (115) planes are covered by IrO-OH, which activates all surfaces towards OER. A thick subsurface oxide layer consisting of sub-stoichiometric Ir-O species is formed on the open (024) planes as OER proceeds. Such metastable Ir-O species are thought to provide an additional contribution to the OER activity. Overall, this study sheds light on the importance of the morphological effects of iridium electrocatalysts for OER. It also provides an innovative approach that can directly reveal surface species on electrocatalysts at atomic scale.

Automated summary

The effect of different surface orientations on the formation of iridium oxide species during the oxygen evolution reaction (OER) was studied using a needle-shaped iridium atom probe specimen as a nanosized working electrode. It was found that a thick subsurface oxide layer consisting of sub-stoichiometric Ir-O species on the open (024) planes contributes additional activity to the OER process. This study highlights the importance of surface morphological effects on iridium electrocatalysts for OER and provides a new method to directly reveal surface species on electrocatalysts at the atomic scale.