Constructing Multifunctional Metallic Ni Interface Layers in the g-C3N4 Nanosheets/Amorphous NiS Heterojunctions for Efficient Photocatalytic H2 Generation.

The construction of exceptionally robust and high-quality semiconductor-cocatalyst heterojunctions remains a grand challenge toward highly efficient and durable solar-to-fuel conversion. Herein, novel graphitic carbon nitride (g-C3N4) nanosheets decorated with multifunctional metallic Ni interface layers and amorphous NiS cocatalysts were fabricated via a facile three-step process: the loading of Ni(OH)2 nanosheets, high-temperature H2 reduction, and further deposition of amorphous NiS nanosheets. The results demonstrated that both robust metallic Ni interface layers and amorphous NiS can be utilized as electron cocatalysts to markedly boost the visible-light H2 evolution over g-C3N4 semiconductor. The optimized g-C3N4-based photocatalyst containing 0.5 wt % Ni and 1.0 wt % NiS presented the highest hydrogen evolution of 515 µmol g-1 h-1, which was about 2.8 and 4.6 times as much as those obtained on binary g-C3N4-1.0%NiS and g-C3N4-0.5%Ni, respectively. Apparently, the metallic Ni interface layers play multifunctional roles in enhancing the visible-light H2 evolution, which could first collect the photogenerated electrons from g-C3N4, and then accelerate the surface H2-evolution reaction kinetics over amorphous NiS cocatalysts. More interestingly, the synergetic effects of metallic Ni and amorphous NiS dual-layer electron cocatalysts could also improve the TEOA-oxidation capacity through upshifting the VB levels of g-C3N4. Comparatively speaking, the multifunctional metallic Ni layers are dominantly favorable for separating and transferring photoexcited charge carriers from g-C3N4 to amorphous NiS cocatalysts owing to the formation of Schottky junctions, whereas the amorphous NiS nanosheets are mainly advantageous for decreasing the thermodynamic overpotentials for surface H2-evolution reactions. It is hoped that the implantation of multifunctional metallic interface layers can provide a versatile approach to enhance the photocatalytic H2 generation over different semiconductor-cocatalyst heterojunctions.