H:ZnO Nanorod-Based Photoanode Sensitized by CdS and\nCarbon Quantum Dots for Photoelectrochemical Water Splitting

Abstract

We report a promising simple strategy\nfor improving the performance\nof the photoanode for photoelectrochemical (PEC) water splitting.\nZnO nanorods on an indium tin oxide glass substrate were synthesized\nby a hydrothermal method following calcinations in air at 500 °C\nfor 2 h and pure ambient hydrogen at atmospheric pressure at 400 °C\nfor 30 min. The hydrogenated ZnO (H:ZnO) sample shows an enhanced\nphotocurrent in comparison to that of ZnO nanorods. To enhance the\nabsorption in the visible light and near-infrared regions, H:ZnO nanorods\nwere sensitized by cadmium sulfide (CdS) nanoparticles and carbon\nquantum dots (CQDs). The H:ZnO nanorod film sensitized in this way\nexhibited significantly improved PEC properties after treatment with\nambient nitrogen at 400 °C for 30 min. The optimized H:ZnO nanorod\nsample sensitized by CdS and CQDs yields a photocurrent density of\n∼12.82 mA/cm² at 0 V (vs saturated calomel electrode\n(SCE)) in 0.25 M Na₂S and 0.35 M Na₂SO₃ solution under the illumination of simulated solar light (100 mW/cm² from a 150 W xenon Arc lamp source). The optimal structure\nshows a solar-to-hydrogen conversion efficiency of ∼3.85% (at\n−0.67 V vs SCE). The H₂ gas generation obtained\nusing this optimal structure consisting of H:ZnO nanorods sensitized\nby CdS and CQDs was 7.04 mL/cm² in 1 h. The morphology\nand properties of the samples were examined by scanning electron microscopy,\nX-ray diffraction, transmission electron microscopy, ultraviolet–visible\nabsorption, and electrical measurements.