Ultrafast Charge Separation for Full Solar Spectrum-Activated Photocatalytic H2 Generation in a Black Phosphorus–Au–CdS Heterostructure

Two-dimensional layered black phosphorus (BP) with a tunable band gap of 0.3–2.0 eV has received great interest in broad-spectrum-active photocatalysis, but rapid charge recombination limits its potential applications. Herein, we report that BP quantum dots (QDs) work as active photosensitizer in a ternary heterostructure consisting of BP QDs, Au nanorods (NRs), and CdS nanowires (NWs), which efficiently photocatalytically generates H2 at full solar spectrum, especially in the near-infrared (NIR) region. The superior performance of the BP–Au–CdS heterostructure arises from the overall photoabsorption contribution, the dual role (electron relay and plasmonic electron donor) of Au NRs, as well as the appropriate band alignment and strong coupling between the three components. Tracking the electron and hole transfers via femtosecond transient absorption spectroscopy shows a unidirectional electron flow from BP to Au and then to CdS, which has been achieved by the high conduction band level of BP, the well-harnessed work function match in BP–Au, and the well-established Schottky barrier in Au–CdS heterojunction.