Tartaric Acid as an Interfacial Bridge: Constructing a Tight SnS₂/CdIn₂S₄ Junction for Efficient Photoelectrochemical Water Oxidation

Strengthening the interfacial interaction of heterojunction photoanodes is an important route to efficient photoelectrochemical (PEC) water splitting. Herein, a SnS₂/CdIn₂S₄ heterojunction photoanode is fabricated by a two-step solvothermal method, in which tartaric acid (TA) acts as an interfacial bridge to regulate the growth of SnS₂ on trapezoid-like CdIn₂S₄. The optimized photoanode delivers a photocurrent density of 5.93 mA cm⁻² at 1.23 V vs. RHE, approximately 6.9 times that of pristine CdIn₂S₄ (0.86 mA cm⁻²), with a maximum applied bias photon-to-current efficiency (ABPE) of 2.81%. Electrochemical impedance spectroscopy shows a reduced charge-transfer resistance, and time-resolved photoluminescence reveals a prolonged carrier lifetime. Density functional theory calculations indicate the proposed interfacial charge-transfer mechanism: the work-function difference between SnS₂ (6.12 eV) and CdIn₂S₄ (3.95 eV) drives interfacial electron transfer from CdIn₂S₄ to SnS₂, the charge density difference reveals electron accumulation on the SnS₂ side and depletion on the CdIn₂S₄ side, with the interfacial charge transfer increasing from 0.33 to 0.39 e⁻ after TA bridging, and the projected density of states (PDOS) evidences a strong electronic interaction across the junction. This organic-molecule-assisted interfacial bridging offers a facile route for designing the interfaces of sulfide photoanodes.