On the Homogeneity of a Cobalt-Based Water Oxidation Catalyst

The homogeneity of molecular Co-based water oxidation catalysts (WOCs) has been a subject of debate over the last 10 years as assumed various homogeneous Co-based WOCs were found to actually form CoOx under operating conditions. The homogeneity of the Co­(HL) (HL = N,N-bis­(2,2′-bipyrid-6-yl)­amine) system was investigated with cyclic voltammetry, electrochemical quartz crystal microbalance, and X-ray photoelectron spectroscopy. The obtained experimental results were compared with heterogeneous CoOx. Although it is shown that Co­(HL) interacts with the electrode during electrocatalysis, the formation of CoOx was not observed. Instead, a molecular deposit of Co­(HL) was found to be formed on the electrode surface. This study shows that deposition of catalytic material is not necessarily linked to the decomposition of homogeneous cobalt-based water oxidation catalysts.