Photoanode/Electrolyte\nInterface Modification for\nEfficient Hydrogen Evolution in Cu<sub>2</sub>SnS<sub>3</sub> Dots-Sensitized\nSolar PEC Cells

It is proven through transmission electron microscope\n(TEM) analysis\nthat solar sensitizer Cu<sub>2</sub>SnS<sub>3</sub> (CTS) dots prepared\nvia the hot-injection route are nonspherical, polyhedral nanocrystals\nwith the size of ∼11 nm. CTS dots were deposited into a porous\nTiO<sub>2</sub> layer to form CTS/TiO<sub>2</sub>, an effective type\nII heterojunction in photoanodes. The electronic and energy band structures\nof TiO<sub>2</sub> and CTS were studied by the plane-wave ultrasoft\npseudopotential method based on density functional theory (DFT) and\nverified by ultraviolet–visible (UV–vis) spectroscopy.\nUV–vis and Photoluminescence (PL) spectra show that the CTS/TiO<sub>2</sub> photoanode exhibits wider visible-light absorption as well\nas lower charge recombination. ZnS quantum dots (QDs) deposited on\nthe CTS/TiO<sub>2</sub> photoanode through the in situ successive\nion layer adsorption and reaction (SILAR) method as the passivation\nlayer can inhibit the reverse carrier transfer and increase the photocurrent\ndensity by building a potential barrier on the CTS/TiO<sub>2</sub> photoanode and electrolyte interface. When 2-layer ZnS QDs are deposited,\nthe maximum photocurrent density of the photoelectrochemical (PEC)\ncell composed of a ZnS/CTS/TiO<sub>2</sub> photoanode, a Pt counter\nelectrode, and Na<sub>2</sub>SO<sub>4</sub> solution electrolyte is\n8.43 mA/cm<sup>2</sup> and the maximum applied bias photon-to-current\nefficiency (ABPE) is 7.79%. Under 1 sun (AM 1.5, 100 mW/cm<sup>2</sup>) with 0.6 V bias, its hydrogen yield reached 125.7 μmol·cm<sup>–2</sup> after 4 h with the rate of 31.4 μmol·cm<sup>–2</sup>·h<sup>–1</sup> in contrast to the yield\nof 107.86 μmol·cm<sup>–2</sup> with the rate of\n21.3 μmol·cm<sup>–2</sup>·h<sup>–1</sup> for the CTS/TiO<sub>2</sub> photoanode.