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 CoO x under operating conditions. The homogeneity of the Co(H L ) (H L = 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 CoO x . Although it is shown that Co(H L ) interacts with the electrode during electrocatalysis, the formation of CoO x was not observed. Instead, a molecular deposit of Co(H L ) 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.