In Situ Formation of Efficient Cobalt-Based Water Oxidation Catalysts from Co2+-Containing Tungstate and Molybdate Solutions

Replacing rare and expensive noble-metal catalysts with inexpensive and earth-abundant ones is of great importance to split water either electrochemically or photo-electrochemically. In this study, two amorphous cobalt oxide catalysts (Co-W film and Co-Mo film) with high activity for electrocatalytic water oxidation were prepared by fast, simple electrodeposition from aqueous solutions of Na2WO4 and Na2MoO4 containing Co2+. In solutions of Na2WO4 and Na2MoO4, sustained anodic current densities up to 1.45 and 0.95 mAcm(-2) were obtained for Co-W film at 1.87 V versus a reversible hydrogen electrode (RHE) and Co-Mo film on fluorine-doped tin oxide (FTO) substrates at 1.85V versus RHE. For the Co-W film, a much higher current density of 4.5 mAcm(-2) was acquired by using a stainless-steel mesh as the electrode substrate. Significantly, in long-term electrolysis for 13 h, the Co-W film exhibited improved stability in cobalt-free buffer solution in comparison with the previously reported Co-Pi film.