Two-dimensional heterojunction g-C3N4/BCN was constructed via thermal polymerization process. The formed two-dimensional heterostructure could enhance the interfacial contact area between BCN and porous g-C3N4 as well as shorten the photogenerated charge carriers transfer time and distance. The two-dimensional g-C3N4/BCN heterojunction photoanode shows enhanced photoelectrochemical (PEC) performance for water splitting under visible-light irradiation, which primarily originates from the improved charge transfer and separation, and prolonged lifetime of electrons. Under the visible light irradiation, the g-C3N4/BCN heterojunction sample yields a photocurrent density of similar to 0.62 mA cm(-2) at 1.23 V vs. RHE, which is about eight times as many as that of CN (0.08 mA cm(-2)) electrode at the same conditions. In addition, the possible electron transfer model and mechanism of PEC water splitting for H-2 evolution have been discussed. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.