In-situ construction of metallic Ni3C@Ni core–shell cocatalysts over g-C3N4 nanosheets for shell-thickness-dependent photocatalytic H2 production

[Display omitted] The highly active and stable shell-thickness-controlled Ni3C@Ni core–shell co-catalysts could achieve the shell-thickness-dependented photocatalytic H2 evolution over the g-C3N4 nanosheets. •The in-situ construction of Ni3C@Ni core–shell cocatalysts was first reported.•The exact active sites over Ni3C@Ni core–shell co-catalysts were revealed.•The Schottky-based heterojunctions with improving charge transfer channels were carefully addressed.•The H adsorption and Gibbs free energies, and H2-evolution kinetics were verified.•Shell-thickness-dependented Photocatalytic H2 Production was achieved. Herein, we designed the shell-thickness-controlled Ni3C@Ni/g-C3N4 photocatalysts with intimate Schottky-junctions by an in situ high-temperature transformation strategy. Meanwhile, we found that the cocatalysts with optimized Ni shell-layer thickness of 15 nm could achieve the best visible-light photocatalytic H2-production performance of 11.28 μmolh−1, with an apparent quantum yield (AQY) of 1.49 % at 420 nm, which was 16 times higher than that of Ni3C/g-C3N4. Moreover, an excellent stability is achieved. The well-defined density functional theory (DFT) calculations indicate that the “TOP_C1” sites of Ni3C@Ni can exhibit the H adsorption and Gibbs free energies of -0.07eV and 0.18 eV, respectively, which should be hydrogen-evolution active sites instead of two “HOLLOW” sites. Interestingly, the intimate Schottky-junctions, could hinder rapid charge recombination, increase reactive sites, boost catalytic kinetics and passivate unstable surface of Ni3C, thus achieving shell-thickness-dependent hydrogen evolution. Therefore, the Ni3C@Ni core–shell cocatalysts will open a new avenue for robust solar fuel production.