Intermediate-range structure of self-assembled cobalt-based oxygen-evolving catalyst.

Continual improvements in solar-to-fuels catalysis require a genuine understanding of catalyst structure-function relationships, not only with respect to local order, but also intermediate-range structure. We report the X-ray pair distribution function analysis of the nanoscale order of an oxidic cobalt-based water-splitting catalyst and uncover an electrolyte dependence in the intermediate-range structure of catalyst films. Whereas catalyst films formed in borate electrolyte (CoB(i)) exhibit coherent domains consisting of 3-4 nm cobaltate clusters with up to three layers, films deposited in phosphate electrolyte (CoP(i)) comprise significantly smaller clusters that are not coherently stacked. These structural insights are correlated with marked differences in activity between CoP(i) and CoB(i) films.