CoWO4-based Water Oxidation Catalyst Derived from Polyoxometalates

Abstract

We report herein the synthesis of CoWO4-based water oxidation catalysts (WOCs) derived from cobalt-based polyoxometalate (CoPOM). CoPOM with a molecular formula of Co4(H2O)2(PW9O34)2]10- is a well-known homogeneous WOC. For its versatile application, however, its integration with a heterogeneous electrode/photoelectrode is critically required. We found that CoPOM can be readily converted to more efficient CoWO4-based catalyst and integrated with a substrate by simple annealing process. According to our results, CoWO4 catalysts can have both amorphous and crystalline phase, depending on the annealing temperature. We found that amorphous CoWO4 formed at a relatively low temperature has much higher catalytic activity than pristine CoPOM and crystalline CoWO4. The performance was found to be closely related to the distance between the nearest cobalt ions. Based on these findings, we could fabricate both an anode and a photoanode for water oxidation by integrating CoWO4 on the carbon felt electrode and Fe2O3 photoanode, respectively. We believe that our findings can suggest simple way to synthesize efficient and stable WOCs for enhanced PEC system to accelerate solar energy storage.