Black Phosphorus Revisited: A Missing Metal-Free Elemental Photocatalyst for Visible Light Hydrogen Evolution.

Metal-free elemental photocatalysts for hydrogen (H2 ) evolution are more advantageous than the traditional metal-based inorganic photocatalysts since the nonmetal elements are generally cheaper, more earth-abundant, and environmentally friendly. Black phosphorus (BP) has been attracting increasing attention in recent years based on its anisotropic 2D layered structure with tunable bandgap in the range of 0.3-2.0 eV; however, the application of BP for photocatalytic H2 evolution has been scarcely reported experimentally although being theoretically predicted. Herein, for the first time, the visible light photocatalytic H2 evolution of BP nanosheets prepared via a facile solid-state mechanochemical method by ball-milling bulk BP is reported. Without using any noble metal cocatalyst, the visible light photocatalytic hydrogen evolution rate of BP nanosheets reaches 512 µmol h-1 g-1 , which is ≈18 times higher than that of the bulk BP, and is comparable or even higher than that of graphitic carbon nitrides (g-C3 N4 ).