Electrochemical Water Oxidation Catalysis Beginning with Co(II) Polyoxometalates: The Case of the Precatalyst Co4V2W18O6810–

Abstract

The question is addressed of whether the cobalt polyoxometalate (Co-POM) precatalyst Co4V2W18O6810– (hereafter Co4V2W18) is a stable, homogeneous water oxidation catalyst under electrochemically driven conditions and in 0.1 M pH 5.8 and 8.0 NaPi buffer as well as pH 9.0 sodium borate (NaB) buffer. This question is of considerable interest since Co4V2W18 has been reported to be highly stable and a 200-fold faster water oxidation catalyst than its P congener Co4P2W18O6810– (hereafter Co4V2W18), for reasons that were not specified. The nature of the true water oxidation catalyst with Co4V2W18 as the starting material is of further fundamental interest because a recent report reveals that the 51V NMR peak at ca. −507 ppm assigned by others to Co4V2W18 and used to argue for its solution stability is, instead, correctly assigned to the highly stable cis-V2W4O194–, in turn raising the question of the true stability of Co4V2W18 under water oxidation catalysis conditions. A battery of physical methods is used to a...