Direct Z‑Scheme Water Splitting Photocatalyst\nBased on Two-Dimensional Van Der Waals Heterostructures

Abstract

Mimicking\nthe natural photosynthesis in plants, Z-scheme water\nsplitting is a promising strategy to improve photocatalytic activity.\nSearching for the direct Z-scheme photocatalysts is urgent and the\ncrucial factor for the photocatalytic efficiency is the photogenerated\nelectron–hole (<i>e–h</i>) recombination rate\nat the interface of two photosystems. In this report, based on time-dependent <i>ab initio</i> nonadiabatic molecular dynamics (NAMD) investigation,\nwe first report a two-dimensional (2D) metal-free van der Waals (vdW)\nheterostructure consisting of monolayer BCN and C₂N as\na promising candidate for direct Z-scheme photocatalysts for water\nsplitting. It is shown that the time scale of <i>e–h</i> recombination of BCN/C₂N is within 2 ps. Among such <i>e–h</i> recombination events, more than 85% are through\nthe <i>e–h</i> recombination at the interface. NAMD\nsimulations based on frozen phonon method prove that such an ultrafast\ninterlayer <i>e–h</i> recombination is assisted by\nintralayer optical phonon modes and the interlayer shear phonon mode\ninduced by vdW interaction. In these crucial phonon modes, the interlayer\nrelative movements which are lacking in traditional heterostructures\nwith strong interactions, yet exist generally in various 2D vdW heterostructures,\nare significant. Our results prove that the 2D vdW heterostructure\nfamily is convincing for a new type of direct Z-scheme photocatalysts\nsearching.