Photoanode/Electrolyte Interface Modification for Efficient Hydrogen Evolution in Cu₂SnS₃ Dots-Sensitized Solar PEC Cells

It is proven through transmission electron microscope (TEM) analysis that solar sensitizer Cu₂SnS₃ (CTS) dots prepared via the hot-injection route are nonspherical, polyhedral nanocrystals with the size of ∼11 nm. CTS dots were deposited into a porous TiO₂ layer to form CTS/TiO₂, an effective type II heterojunction in photoanodes. The electronic and energy band structures of TiO₂ and CTS were studied by the plane-wave ultrasoft pseudopotential method based on density functional theory (DFT) and verified by ultraviolet-visible (UV-vis) spectroscopy. UV-vis and Photoluminescence (PL) spectra show that the CTS/TiO₂ photoanode exhibits wider visible-light absorption as well as lower charge recombination. ZnS quantum dots (QDs) deposited on the CTS/TiO₂ photoanode through the in situ successive ion layer adsorption and reaction (SILAR) method as the passivation layer can inhibit the reverse carrier transfer and increase the photocurrent density by building a potential barrier on the CTS/TiO₂ photoanode and electrolyte interface. When 2-layer ZnS QDs are deposited, the maximum photocurrent density of the photoelectrochemical (PEC) cell composed of a ZnS/CTS/TiO₂ photoanode, a Pt counter electrode, and Na₂SO₄ solution electrolyte is 8.43 mA/cm² and the maximum applied bias photon-to-current efficiency (ABPE) is 7.79%. Under 1 sun (AM 1.5, 100 mW/cm²) with 0.6 V bias, its hydrogen yield reached 125.7 μmol·cm^-2 after 4 h with the rate of 31.4 μmol·cm^-2·h^-1 in contrast to the yield of 107.86 μmol·cm^-2 with the rate of 21.3 μmol·cm^-2·h^-1 for the CTS/TiO₂ photoanode.