Efficient Nickel Foam-Supported Ternary Cu ₂ ZnSnS ₄ /Ag/PANI Photocathode for Hydrogen Evolution in Pt-free Solar Tandem PEC Cells

To address the challenges of high cost and the environmental concerns associated with noble metals and toxic elements-based conventional photocathode materials in photoelectrochemical (PEC) cells, an efficient noble metal/toxic element-free solar-driven PEC water-splitting device based on a ternary Cu2ZnSnS4/Ag/polyaniline (CZTS/Ag/PANI) heterostructure photocathode has been constructed with nickel foam (NF) as the substrate via a two-step in situ reaction route. CZTS nanoparticles (NPs) with band gap ∼1.2 eV possess light absorption in the visible region and PANI exhibits exceptional charge transport capability with catalytically active sites in high density. The incorporation of Ag NPs enhances visible light absorption and, especially, boosts the separation and injection efficiency of carriers due to the surface plasmon resonance (SPR) effect. The synergistic interaction among the ternary composites not only amplifies light absorption but also suppresses carrier recombination, and the CZTS/Ag/PANI photocathode achieved a maximum photocurrent density of 26.65 mA/cm2 with high stability, representing the best photoelectric performance in recent reports. After constituting with the CTS/TiO2/FTO photoanode, the CZTS/Ag/PANI photocathode-based tandem cell reached a hydrogen evolution yield of 206.25 μmol/cm2 for 4 h, superior to the 162.05 μmol/cm2 of the Pt sheet electrode-based cell under 1 sun with 0.6 V bias, and, especially, showed a comparable stability of photocurrent density in the total 32-h hydrogen evolution process. This work provides a feasible strategy to replace the traditional high-cost noble-metal electrodes in solar PEC cells to achieve efficient solar-to-hydrogen conversion.