Surface-Modified Rod-Like Cd _<i>x</i> Zn _{1– <i>x</i>} S QDs-Sensitized Photoanode in Solar PEC Cell for Enhancing Yield and Stability of Hydrogen Evolution

The rod-like Cd_<i>x</i>Zn_1-<i>x</i>S quantum dots (CZS QDs) with a low length-diameter ratio (13:3.5 nm) and high uniformity in shape and size were successfully synthesized by a hot-injection process for hydrogen evolution in solar photoelectrochemical (PEC) cells. Compared with traditional sphere-like QDs with an average diameter of ∼4.5 nm, these rod-like CZS QDs with a low length-diameter ratio sensitized TiO₂/FTO (F-doped SnO₂) glass photoanode show higher absorptance in the visible region and photocurrent density. However, the electron-hole recombination does not increase apparently due to their similar PL spectra. ZnS QDs were deposited on a CZS QDs-sensitized TiO₂/FTO photoanode via an in situ SILAR process to improve photoelectrical properties by inhibiting reversed current and increasing bulk charge separation efficiency and hydrophilicity of the photoanodes. However, excess ZnS QDs will impair the photoelectrical performance due to the decrease of surface injection efficiency caused by too many introduced surface defects. The bias voltage plays the primary role of overpassing the potential barrier as well as providing weak electric catalysis in PEC hydrogen evolution. The decrease of the length-diameter ratio of rod-like CZS QDs has not only enhanced PEC efficiency but also ensured considerable stability of the cells in H₂ evolution. The PEC cell consisting of 8ZnS/CZS/TiO₂ and a Pt counter electrode realizes ∼46% improvement in hydrogen evolution yield and rate compared with the CZS/TiO₂ photoanode-based cell under one sun (AM 1.5 G, 100 mW/cm²) at 0.8 V bias, and especially exhibits significantly high stability, with 87.4% hydrogen production efficiency retained after a total 20 h PEC hydrogen evolution process.