Engineering Oxygen Vacancies in Mesocrystalline CuO Nanosheets for Water Oxidation

Tailoring relatively inert Cu oxides for high-performance oxygen evolution reaction (OER) electrocatalysts is of great practical significance but extremely challenging. Herein, CuO MCSs enriched with O vacancies have been fabricated via an appealing metal–organic framework (MOF)-based topotactic alkalization route for the first time. Mechanism analysis indicates that the formation of the CuO mesocrystal superstructure undergoes a gradual structural evolution from nanocrystal to nanobelt and then to nanosheet with escalating order. The porous two-dimensional nanosheet coupled with mesocrystal characteristic endows CuO MCSs with rich surface active sites and significantly improved electric conductivity. When served as an OER electrocatalyst in the alkaline media, the CuO MCS exhibits an overpotential of 304 mV at 10 mA cm–2 and a stable delivery of the OER current for more than 15 h, which surpasses most of the Cu oxide OER electrocatalysts ever reported. Theoretical calculations indicate that high OER activity of CuO MCSs can be traced to the modified electronic structure caused by the O vacancies, resulting in much enhanced Cu 3d–O 2p covalency as well as lifted d-band center, which alters CuO MCSs into a half-metallic nature with optimized binding strength toward O-containing intermediates for OER. This work could provide valuable insights into the design of other MOF-derived advanced catalysts for OER and beyond.