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 ).