Controllable Synthesis of Metallic Ni3P–Ni Spheres on Graphitic Carbon Nitride Nanosheets to Promote Photocatalytic Hydrogen Generation

To achieve the construction of efficient photocatalytic H2 generation systems, developing highly active and durable earth-abundant H2 generation cocatalyst is still a challenge. In this paper, we construct a noble-metal-free Ni3P–Ni composite, which displays strong chemical stability and high-efficiency as a cocatalyst to enhance the visible-induced photocatalytic activities in H2 generation of g-C3N4. Ni3P–Ni/g-C3N4 is prepared by one-step annealing of amorphous Ni–P nanoparticles and g-C3N4. The result verifies that both Ni3P and metallic Ni worked as electron cocatalysts and significantly enhanced the visible light H2 generation over g-C3N4. The optimum composite 2.0 wt.% Ni3P–Ni/g-C3N4 exhibits a high H2 generation rate of 203.3 μmol g−1 h−1, which is 1.6, 2.7, and 53.5 times as much as those obtained on Ni3P/g-C3N4, Ni/g-C3N4, and pure g-C3N4 respectively. Photoluminescence and photoelectrochemical analysis confirm that the metallic Ni plays multifunctional roles in boosting the H2 generation under visible light, which could both accept the photo-generated electrons from g-C3N4 and enhance the electron transfer to Ni3P for further H2 generation. This investigation provides a route to the rational design and development of earth-abundant metal phosphide and metal composites, which could be utilized as noble-metal-free cocatalysts for the improvement of H2 generation activity. Spherical Ni3P–Ni particles with metallic Ni spread over the inner and outer surface of Ni3P sphere was synthesized and hybrid with g-C3N4. The specific structure of spherical Ni3P–Ni leads to adequate contact area between ternary Ni3P, Ni, and g-C3N4. Ni with high electrical conductivity could act as an electron transfer bridge between g-C3N4 and Ni3P, leading to effective charge separation and enhanced photocatalytic hydrogen generation.