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

Abstract

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.