A novel approach to synthesize an efficeint CoWO4 water oxidation catalyst derived from polyoxometalate

Abstract

Electrochemical or photoelectrochemical water splitting enables eco-friendly production of fuels and thus has drawn enormous attentions across the world. For its practical application, however, water oxidation catalysts (WOCs) should be employed to facilitate the four-electron water oxidation reaction, which is the rate-determining step. Conventionally, ruthenium and iridium oxide has attracted great interests because of their high catalytic activity and stability. Nevertheless, these transition metals are not only costly and but also unsustainable . Here, we report a novel method to synthesize an efficient and stable CoWO4-based-WOC from cobalt-based polyoxometalates, [Co4(H2O)2(PW9O34)2]10- (Co4POM). Simple annealing process leads to conversion of Co4POM to CoWO4-based-WOC with an enhanced catalytic activity for water oxidation. It was found that a phase transition from amorphous to crystalline CoWO4 (c-CoWO4) occurs between 400°C and 500°C and that amorphous CoWO4 (a- CoWO4) exhibited a higher catalytic activity than c-CoWO4. Based on these results, we deposited CoWO4-based-WOCs on hematite by layer-by-layer assembly of Co4POM and subsequent heat treatment to fabricate an efficient hematite-based photoanode for solar water oxidation. We found that the photoelectrochemical performance of the hematite photoanode was significantly improved after the decoration with a-CoWO4 WOC in terms of photocurrent density and onset potential. We believe that out findings can suggest simple way to synthesize efficient and stable WOCs and to deposit them on photoelectrode for enhanced water oxidation reaction.