To further accelerate exciton dissociation and restrain charge recombination, Zscheme photocatalytic systems (Figure ) have been widely developed as effective devices to separately generate H 2 and O 2 on different interfaces and show higher solarto-hydrogen conversion efficiency than that of a single photocatalyst . have recently demonstrated that nanojunction of B-doped carbon nitride nanolayer and bulk carbon nitride show higher incident photon-to-current efficiency than that of carbon nitride film . By employing time-dependent ab initio nonadiabatic molecular dynamics, Zhang et al. have predicted that Z-scheme heterostructure of monolayer BCN and C 2 N (Figure ) possess high interface electron-hole recombination rate and is a promising photocatalyst for overall water splitting . Aside from effective exciton dissociation, fast charge migration is also essential to guarantee high Q.E. of photocatalytic water splitting, which determines the rate of electron and hole transfer to adsorbed molecules or co-catalysts. For 2D polymers, the exciton mobility is limited to in-plane transfer, where the insufficient interaction of πelectronic building units usually results in low charge carrier mobilities . A high degree of π-conjugation and crystallinity of 2D polymers yields band dispersion and therefore enhances charge carrier mobilities . Dong and co-workers have recently summarized the internal and external modification strategies to optimize the carrier mobility of 2D g-C 3 N 4 . For instance, the in-plane carrier transfer of g-C 3 N 4 can be effectively improved by expanding the π-electron delocalization via introducing aromatic groups or embedding aromatic rings , which in turn enhances photocatalytic performance for hydrogen evolution.