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

The role of beta-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 beta-CoOOH formed on a Co microelectrode under OER conditions. We reveal that approximate to 6 nm beta-CoOOH(01 1? ${\bar{1}}$ 0), grown on [ 1?21? ${\bar{1}2\bar{1}}$ 0]-oriented Co, exhibits higher OER activity than approximate to 3 nm beta-CoOOH(10 1? ${\bar{1}}$ 3) or approximate to 6 nm beta-CoOOH(0006) formed on [02 2?1] ${\bar{2}1]}$ - and [0001]-oriented Co, respectively. This arises from higher amounts of incorporated hydroxyl ions and more easily reducible Co-III-O sites present in beta-CoOOH(01 1? ${\bar{1}}$ 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.

Automated summary

We investigated the relationship between crystallographic orientations of beta-CoOOH and catalytic activity for the oxygen evolution reaction (OER). We found that beta-CoOOH(01 1? ${\bar{1}}$ 0) grown on [ 1?21? ${\bar{1}2\bar{1}}$ 0]-oriented Co exhibited higher OER activity compared to beta-CoOOH(10 1? ${\bar{1}}$ 3) grown on [02 2?1] ${\bar{2}1]}$ -oriented Co or beta-CoOOH(0006) grown on [0001]-oriented Co. This is due to the presence of higher amounts of hydroxyl ions and more easily reducible Co-III-O sites in beta-CoOOH(01 1? ${\bar{1}}$ 0). Our findings offer opportunities for designing pre-catalysts with preferred defects to promote the formation of the most active OER species.