More comprehensive heterojunction mechanism: Enhanced PEC properties originated from novel ZnIn2S4/Cu2S heterojunction assisted by changed surface states

The more comprehensive investigation of ZnIn2S4-based heterojunction mechanism is beneficial for rationalizing the PEC performances enhancement mechanism and optimizing the application of heterojunction. Herein, Cu2S is for the first time synthesized on ZnIn2S4 as a novel co-catalyst through in-situ ion exchange techniques. The holes are extracted and stored in ZnIn2S4/Cu2S through enhanced surface states (ss) due to the decreased holes transfer resistance to ss and improved ss capacitance, which improve the carrier separation efficiencies with the effect of built-in electric filed. With the sequential deposition of NiFe-LDH, despite the inevitable carrier recombination is caused by the conflicting chemical potentials between Cu and Ni ions at the Cu2S/NiFe-LDH interface, the carrier injection efficiency is increased to 71.60% due to the exposure of more intermediate surface states (iss). The highest photocurrent density of 1.56 mA/cm2 at 1.23 V (vs. RHE) is achieved by ZnIn2S4/Cu2S/NiFe-LDH when influence of the interface carrier recombination is counteracted by the synergistic effect containing extended light absorption, the construction of ZnIn2S4/Cu2S heterojunction and changed ss, which is 10.4 times higher than that of pristine ZnIn2S4. The work provides a more comprehensive approach to investigate the mechanism for enhanced PEC performances of ZnIn2S4-based heterojunction.