Janus MSiSnN4(M= Mo; W):High efficiently overall water splitting photocatalyst triggered by the intrinsic electric field

•A local electric field exists in the janus monolayers, which favours a good separation of photoelectrons and holes in space and overcoming the photocatalytic material's band gap limiting requirement.•Janus MSiSnN4 (M= Mo; W) systems have a suitable band edge position (span the redox position of water), as well as the ample electron mobility and outstanding visible light optical absorption capacity(ηSTH = 23.12 % for WSiSnN4; ηSTH = 32.91 % for MoSiSnN4).•WSiSnN4 can make HER and OER processes occur spontaneously under light in acidic solutions(pH=0–7), demonstrating excellent photocatalytic performance of overall water splitting. Photocatalytic hydrolysis is one of the most effective ways for hydrogen fuel as a strategy for turning solar energy into hydrogen fuel. Two-dimensional(2D) Janus materials with an out-of-plane polarized electric field not only help to promote photogenerated carrier separation and migration but also alter the alignment of water splitting potentials, which enhances photo-oxidation and retains efficient absorption of visible light. In this manuscript, a systematic first-principles analysis was conducted on the WSn2N4 and MSiSnN4 (M= Mo; W) system. The results show that Janus MSiSnN4 (M= Mo; W) systems have a suitable bandgap and band edge position (span the redox position of water), as well as the ample electron mobility(>200 cm2V−1s−1) and outstanding visible light optical absorption capacity(η’STH = 23.12 % for WSiSnN4; η’STH = 32.91 % for MoSiSnN4). The oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) Gibbs free energy changes of WSiSnN4 show that it can make HER and OER processes occur spontaneously under light in acidic and neutral solutions, demonstrating excellent photocatalytic performance. [Display omitted]