Synergistic interfacial engineering of Ag/Cu3BiS3/g-C3N4 photocathode for boosting bias-free solar PEC hydrogen evolution.

The development of efficient and low-cost photocathodes is critical for the commercial advancement of solar photoelectrochemical (PEC) cells for water-splitting hydrogen evolution applications. Herein, Ag/Cu3BiS3/graphitic-C3N4 (g-C3N4) composite photocathode was fabricated using the two-step in-situ growth approach, serving as an alternative to conventional noble metal counter electrodes. Within this configuration, Cu3BiS3 nanomaterial (CBS) acts as the principal light-harvester responsible for the generation of photo-induced excitons, while CBS/g-C3N4 heterojunction facilitates efficient charge separation. Simultaneously, Ag forms Schottky junctions with CBS to promote directional electron extraction and transport, and especially, its surface plasmon resonance (SPR) effect further enhances exciton separation efficiency. Consequently, this multiphase synergistic system optimizes charge generation, separation and transfer processes. PEC measurements reveal the half-cell solar-to‑hydrogen conversion efficiency (STH) reaching 4.37%, representing the highest reported value to date for hydrogen evolution in solar bias-free PEC cells. Furthermore, when integrated with MnS/CdSe/TiO2 photoanode, the assembled tandem PEC device demonstrates markedly superior performance, achieving the hydrogen evolution yield of 350.92 μmol/cm2 over 4 h period relative to Pt sheet counter electrode-based cell (252.52 μmol/cm2). The stability assessments conducted over 32 h indicated that H2 yield decreased approximate 9.6%. This work presents viable strategy for substituting noble-metal electrodes in stable PEC hydrogen evolution systems.