Photoanode/Electrolyte Interface Modification for Efficient Hydrogen Evolution in Cu 2 SnS 3 Dots-Sensitized Solar PEC Cells.

It is proven through transmission electron microscope (TEM) analysis that solar sensitizer Cu ₂ SnS ₃ (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 TiO ₂ layer to form CTS/TiO ₂ , an effective type II heterojunction in photoanodes. The electronic and energy band structures of TiO ₂ 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/TiO ₂ photoanode exhibits wider visible-light absorption as well as lower charge recombination. ZnS quantum dots (QDs) deposited on the CTS/TiO ₂ 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/TiO ₂ 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/TiO ₂ photoanode, a Pt counter electrode, and Na ₂ SO ₄ solution electrolyte is 8.43 mA/cm ² and the maximum applied bias photon-to-current efficiency (ABPE) is 7.79%. Under 1 sun (AM 1.5, 100 mW/cm ² ) 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/TiO ₂ photoanode.