Superior visible light hydrogen evolution of Janus bilayer junctions via atomic-level charge flow steering

Although photocatalytic hydrogen evolution (PHE) is ideal for solar-to-fuel conversion, it remains challenging to construct a highly efficient PHE system by steering the charge flow in a precise manner. Here we tackle this challenge by assembling 1T MoS(2) monolayers selectively and chemically onto (Bi(12)O(17)) end-faces of Bi(12)O(17)Cl(2) monolayers to craft two-dimensional (2D) Janus (Cl(2))-(Bi(12)O(17))-(MoS(2)) bilayer junctions, a new 2D motif different from van der Waals heterostructure. Electrons and holes from visible light-irradiated Bi(12)O(17)Cl(2) are directionally separated by the internal electric field to (Bi(12)O(17)) and (Cl(2)) end-faces, respectively. The separated electrons can further migrate to MoS(2) via Bi–S bonds formed between (Bi(12)O(17)) and MoS(2) monolayers. This atomic-level directional charge separation endows the Janus bilayers with ultralong carrier lifetime of 3,446 ns and hence a superior visible-light PHE rate of 33 mmol h(−1) g(−1). Our delineated Janus bilayer junctions on the basis of the oriented assembly of monolayers presents a new design concept to effectively steer the charge flow for PHE.