Solution-phase vertically growth of aligned NiCo2O4 nanosheets arrays on Au nanosheets with weakened oxygen-hydrogen bond for photocatalytic oxygen evolution
Vertical heterojunctions of two-dimensional (2D) semiconducting materials have attracted more and more research interests recently due to their unique optical, electrical, catalytic properties and potential applications. Although great progress has been achieved, vertical integration of layered materials formed by 2D semiconductor nanosheets and 2D plasmatic metal nanosheets remains a huge challenge. Here, we demonstrate for the first time solution-phase growth of vertical plasmatic metal-semiconductor heterostructures in which aligned NiCo2O4 nanosheets arrays vertically grow on single Au nanosheet, forming vertically aligned NiCo2O4-Au-NiCo2O4 sandwich-type heterojunctions with hierarchical open channels. Such vertical NiCo2O4-Au-NiCo2O4 heterojunctions can effectively promote the separation and transfer of photoinduced charge. Density-functional theory (DFT) studies and time-resolved transient absorption spectroscopy show that the electrons transfer from NiCo2O4 to Au, and the formation of heterojunction weakens the H-O bond of H2O. Due to the unique structure and component superiority, the vertical NiCo2O4-Au-NiCo2O4 heterojunctions exhibit significant activity with a O2 production rate up to 33 μmol·h-1 and long-term stability for photocatalytic water oxidation. We measured apparent quantum efficiency (AQE) of 21.9% for NiCo2O4-Au-NiCo2O4 heterojunctions at the wavelength λ = 450 ± 10 nm, which is higher than that of NiCo2O4 nanosheets (10.9%), Au nanosheets (0.96%) and other photocatalysts. The present study paves the way for the controlled synthesis of novel vertical heterojunctions based on 2D semiconductor nanosheets and 2D metal nanosheets for efficient photocatalysis.