In situ electrochemical conversion of cobalt oxide@MOF-74 core-shell structure as an efficient and robust electrocatalyst for water oxidation

Abstract In recent years, applications of metal-organic frameworks (MOFs) in electrocatalysis, including hydrogen and oxygen evolution reactions, have attracted increasing attention for renewable energy conversion. Herein, the fabrication of core-shell structured Co3O4@MOF-74 catalysts is proposed and realized with the tunable thickness of MOF shell layers, where Co3O4 nanowire arrays prefabricated on Ni foam are employed as the template as well as the metal source to react with organic ligands to achieve the MOF layers. Importantly, the optimized Co3O4@MOF-74 structures exhibit much enhanced catalytic activities towards oxygen evolution reaction (OER), requiring an impressively low overpotential of 285 mV to afford a current density of 50 mA cm−2 together with a small Tafel slope of 43 mV/dec, as compared with the pristine Co3O4 sample. By investigating the Co3O4@MOF-74 structure after OER stability test, the conversion of MOF-74 into cobalt hydroxide shell layers is thoroughly characterized and confirmed, suggesting the in situ electrochemical conversion of MOF structures during the electrochemical process. All these results do not only uncover the changes in crystalline and chemical structures of MOFs for electrocatalytic reactions, but also help to comprehend and design novel MOFs as efficient and robust electrocatalysts for practical utilization.