Deep reconstruction of transition metal molybdate@hydroxide heterostructure triggered by anion-exchange reaction as high efficiency water oxidation electrocatalyst

Abstract

Developing an efficient strategy to facilitate deep reconstruction of precatalysts to generate more active sites is crucial for fabricating efficient OER-catalysts but remains challenging. Here, an anion-exchange strategy is reported to achieve the complete reconstruction of cobalt molybdate (CoMoO4·nH2O) by engineering the ultrathin Co(OH)2 nanosheets in situ growing on CoMoO4·nH2O. The leaching of molybdate during anion-exchange reaction favors the formation of the loose hierarchical nanostructure, which facilitates deep reconstruction of precatalyst under electro-oxidation conditions. In-situ and ex-situ techniques demonstrate that CoMoO4·nH2O@Co(OH)2 undergoes four stages of reconstruction, and the reconstruction degree depend on the electrolyte and the bias voltage. After reconstruction, more CoOOH species are generated in the reconstructed CoMoO4·nH2O@Co(OH)2 compared with the reconstructed CoMoO4·nH2O, which is ascribed to the preferential conversion of amorphous Co(OH)2 to β-Co(OH)2 and CoOOH under alkaline conditions. As a result, the reconstructed CoMoO4·nH2O@Co(OH)2 catalyst exhibits the significantly enhanced OER activity and excellent long-term durability. This study provides an effective strategy to construct the highly efficient OER electrocatalyst, and investigated the origin of catalytic activity through deep self-reconstruction.