CoP imbedded g-C₃N₄ heterojunctions for highly efficient photo, electro and photoelectrochemical water splitting

Nanorod-like CoP nanoparticles were fabricated from different precursors of Co(OH)₂ and Co₃O₄ by gas-solid reaction, then further embedded into g-C₃N₄ nanosheets to form intimate heterojunctions via the (011) crystal planes of CoP nanoparticles. The heterojunction hybrid obtained from Co(OH)₂ exhibits superior activity in photo, electro and photoelectrochemical water splitting processes. In photocatalytic water half-splitting for hydrogen evolution reaction, the as-obtained 0.5% CoP-CN achieved a rate at 959.4 μmol·h^-1·g^-1 and 59.1 μmol·h^-1·g^-1 when irradiated by simulated sunlight and visible light respectively, almost 3.1 times and 15.8 times that of pristine g-C₃N₄, For photocatalytic water full-splitting, a stoichiometric evolution of H₂ (14.7 μmol·h^-1·g^-1) and O₂ (7.6 μmol·h^-1·g^-1) was observed on 3%Pt-0.5% CoP-CN composite. The onset potential for electrochemical HER process was drastically reduced after deposition with 0.5% CoP. Meanwhile, a higher photocurrent response and larger anodic photocurrent was detected over 0.5% CoP-CN photoanode during the photoelectrochemical water splitting process, relative to pristine g-C₃N₄ and its analogues. The comprehensive enhancements for catalytic activity of 0.5% CoP-CN could be attributed to its reduced over-potentials, more negative photo-reductive potentials, boosted interfacial charge transfer efficiency, as well as a much higher solar to hydrogen efficiency. The contrastive redox roles of CoP in both photocatalytic water half-splitting and full-splitting processes have been fully explored and revealed. This design on covalent organic framework of highly efficient CoP-based heterojunctions holds great promise for direct water splitting applications in utilizing solar energy.