New layered semiconductors for efficient photoelectrochemical hydrogen and oxygen generation

Photocatalytic water splitting to produce H-2 and O-2 with semiconductor photocatalysts provides an attractive solution to global energy and environmental problems. The development of photocatalysts with high efficiency, availability, and stability under wide solar spectrum is paramount for the practical application of this technology. Nitrogen doping and preparation of materials with desirable crystal structure and morphology are two important strategies of fine-tuning the properties of semiconductor photocatalysts. In the present work, by synchronizing the two strategies, photocatalysts with typical structures were doped with nitrogen with the aim of realizing efficient water splitting under wide solar spectrum. After nitrogen doping, the absorption of the as-obtained N-doped photocatalysts was extended from the UV to the visible region. The doped photocatalysts exhibited not only increased visible light absorbance but enhanced photocatalytic hydrogen or oxygen production under light irradiation, in comparison to that of undoped parent compound. DFT calculations indicated that the top of the valence band is composed of N2p states mixed with pre-existing O2p states, which moved the valence band maximum (VBM) upwards, as a result, decreasing the band gap of the parent oxide photocatalysts tremendously. The unique structures of the pristine materials were found to facilitate the homogeneous of nitrogen nitrogen in the whole materials by offering excellent pathways for nitrogen doping process. This work highlighted the importance of crystal structures on the doping of nitrogen, paving a new way for developing novel functional photocatalytic materials.