Boosting Charge Separation in NiS/C3N4 Type-II Heterojunction for Efficient Photoelectrocatalytic Water Reduction

To tackle the intrinsic limitations of fast charge recombination and sluggish reaction kinetics in carbon nitride (C3N4) for photoelectrocatalytic (PEC) water reduction reaction, we constructed a NiS/C3N4 heterojunction photoelectrode via a sequential approach combining chemical vapor deposition and hydrothermal treatment. Compared with pristine C3N4, the introduction of NiS significantly reduced interfacial charge transfer resistance and effectively suppressed the photogenerated carrier recombination. Among all compositions investigated, the NiS-0.2 photoelectrode demonstrated a maximum photocurrent density of −13.44 mA cm−2 at −0.8 V vs. RHE, representing a more than 6.7-fold enhancement in comparison to bare C3N4 (−2.00 mA cm−2). This remarkable improvement is attributed to the construction of an efficient type-II heterojunction between C3N4 and NiS. Under the driving force of the internal electric field at the interface, photoinduced electrons migrate from the conduction band of C3N4 to NiS, whereas holes move from the valence band of NiS to C3N4. This spatial separation mechanism, coupled with the role of NiS as an efficient active site for the water reduction reaction, synergistically enhances the overall PEC performance. This work offers a rational and feasible approach for designing efficient, stable, and cost-effective C3N4-based photoelectrodes.