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

Abstract

We report a promising simple strategy for improving the performance of the photoanode for photoelectrochemical (PEC) water splitting. ZnO nanorods on an indium tin oxide glass substrate were synthesized by a hydrothermal method following calcinations in air at 500 °C for 2 h and pure ambient hydrogen at atmospheric pressure at 400 °C for 30 min. The hydrogenated ZnO (H:ZnO) sample shows an enhanced photocurrent in comparison to that of ZnO nanorods. To enhance the absorption in the visible light and near-infrared regions, H:ZnO nanorods were sensitized by cadmium sulfide (CdS) nanoparticles and carbon quantum dots (CQDs). The H:ZnO nanorod film sensitized in this way exhibited significantly improved PEC properties after treatment with ambient nitrogen at 400 °C for 30 min. The optimized H:ZnO nanorod sample sensitized by CdS and CQDs yields a photocurrent density of ∼12.82 mA/cm2 at 0 V (vs saturated calomel electrode (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 shows a solar-to-hydrogen conversion efficiency of ∼3.85% (at −0.67 V vs SCE). The H2 gas generation obtained using this optimal structure consisting of H:ZnO nanorods sensitized by CdS and CQDs was 7.04 mL/cm2 in 1 h. The morphology and properties of the samples were examined by scanning electron microscopy, X-ray diffraction, transmission electron microscopy, ultraviolet–visible absorption, and electrical measurements.