Linking Composition, Structure and Thickness of CoOOH layers to Oxygen Evolution Reaction Activity by Correlative Microscopy

Abstract The role of β‐CoOOH crystallographic orientations in catalytic activity for the oxygen evolution reaction (OER) remains elusive. We combine correlative electron backscatter diffraction/scanning electrochemical cell microscopy with X‐ray photoelectron spectroscopy, transmission electron microscopy, and atom probe tomography to establish the structure–activity relationships of various faceted β‐CoOOH formed on a Co microelectrode under OER conditions. We reveal that ≈6 nm β‐CoOOH(01 0), grown on [ 0]‐oriented Co, exhibits higher OER activity than ≈3 nm β‐CoOOH(10 3) or ≈6 nm β‐CoOOH(0006) formed on [02 ‐ and [0001]‐oriented Co, respectively. This arises from higher amounts of incorporated hydroxyl ions and more easily reducible Co III −O sites present in β‐CoOOH(01 0) than those in the latter two oxyhydroxide facets. Our correlative multimodal approach shows great promise in linking local activity with atomic‐scale details of structure, thickness and composition of active species, which opens opportunities to design pre‐catalysts with preferred defects that promote the formation of the most active OER species.