Retorting Photocorrosion and Enhanced Charge Carrier Separation at CdSe Nanocapsules by Chemically Synthesized TiO₂ Shell for Photocatalytic Hydrogen Fuel Generation

Metal chalcogenide-based semiconductor nanostructures are promising candidates for photocatalytic or photoelectrocatalytic hydrogen generation. In order to protect CdSe from photocorrosion, a layer of TiO₂ wrapped (shell) onto CdSe (core) nanocapsule via the post-synthesis process. The morphology studies confirm that a thin crystalline TiO₂ shell (3–8 nm) wrapped in all the three directions onto CdSe core and thickness of the shell can be controlled through modulating the titania precursor concentration. The feasibility of pristine CdSe nanocapsules and CdSe@TiO₂ in transforming visible light to hydrogen conversion was tested through photocatalysis reaction. The CdSe@TiO₂ nanocapsules generated a four-fold high rate of hydrogen gas (21 mmol.h⁻¹.g⁻¹cat) than pristine CdSe. In order to understand the role of shell@core, we have studied the photoelectrochemical and impedance analysis. The CdSe@TiO₂ nanocapsules showed higher photoelectric current generation and lower charge transfer resistance at electrode/electrolyte interfaces compared to pristine CdSe. These studies endorse that chemically synthesized crystalline TiO₂ shell played a multifunctional role in (a) surface passivation from photocorrosion, (b) promoting photocharge carrier separation via tunneling process between CdSe and TiO₂ interface. As a result, CdSe@TiO₂ nanocapsules showed a high conversion efficiency of 12.9 % under visible light irradiation (328 mW.cm⁻²) and a TOF of 0.05018 s⁻¹.