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 (0 1 1) 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.