Unveiling the Bifunctional Photo/Electrocatalytic Activity of In Situ Grown CdSe QDs on g‑C₃N₄ Nanosheet Z‑Scheme Heterostructures for Efficient Hydrogen Generation

The successive ionic layer adsorption and reaction (SILAR) method was used to deposit several CdSe quantum dots (QDs) on the surface of g-C₃N₄ nanosheets. In comparison to the single moiety of g-C₃N₄, as-prepared heterostructures displayed an improved bifunctional photo- and electrocatalytic activity for oxygen (OER) and hydrogen evolution reactions (HER). Significantly, the 30 SILAR cycles optimized CdSe QDs/g-C₃N₄ heterostructure exhibited high performances and stabilities for the OER and HER reaction in alkaline conditions. The as-prepared heterostructure catalyst also exhibited an efficient photocatalytic activity toward the H₂ evolution reaction and produced 4306 μmol of H₂ gas with 23.8% of apparent quantum yield in the presence of triethanolamine as a sacrificial agent. Photoluminescence spectroscopy, electron paramagnetic resonance, and impedance spectroscopy suggest that the synergy between g-C₃N₄ nanosheets and CdSe QDs leads to higher catalytic activities, as indicated by the low overpotentials of 147 and 218 mV to obtain a 10 mA cm^–2 current density for the HER and OER reactions, respectively. Furthermore, in situ Fourier transform infrared spectroscopy, liquid chromatography–mass spectroscopy, and high-performance liquid chromatography were conducted to determine the photochemical intermediate products to confirm the successful oxidation of TEOA by capturing holes. The outcome is in accordance with the fact that the photogenerated electrons are transferred from the conduction band (CB) of g-C₃N₄ nanosheets to the valence band (VB) of CdSe QDs in a Z-scheme manner.