Nanostructured copper molybdates as promising bifunctional electrocatalysts for overall water splitting and CO2reduction

Overall water splitting and CO2 reduction are two very important reactions from the environmental viewpoint. The former produces hydrogen as a clean fuel and the latter decreases the amount of CO2 emissions and thus reduces greenhouse effects. Here, we prepare two types of copper molybdate, CuMoO4 and Cu3Mo2O9, and electrochemically investigate them for water splitting and CO2 reduction. Our findings show that Cu3Mo2O9 is a better electrocatalyst for full water splitting compared to CuMoO4. It provides overpotentials, which are smaller than the overpotentials of CuMoO4 by around 0.14 V at a current density of 1 mA cm-2 and 0.10 V at -0.4 mA cm-2, for water oxidation and hydrogen evolution reactions, respectively. However, CuMoO4 adsorbs CO2 and the reduced intermediates/products more strongly than Cu3Mo2O9. Such different behaviors of these electrocatalysts can be attributed to their different unit cells.