Enhanced photoelectrochemical water splitting from Si quantum dots/TiO₂ nanotube arrays composite electrodes

Graphical abstract: Si quantum dots were firstly applied to modify TiO₂ nanotubes and enhanced visible light response was demonstrated for the resulted Si QDs/TiO₂ nanocomposite. Si QDs are promising in photoelectrochemical water splitting and photocatalysis since their low cost, abundance and environmentally-friendliness. - Highlights: • A novel nanocomposite Si QDs/TiO₂ nanotubes was fabricated and characterized. • Enhanced photoelectrochemical water splitting was firstly demonstrated for Si QDs/TiO₂. • The visible light response of TiO₂ increased with the presence of Si QDs. - Abstract: This work firstly introduced Si quantum dots (QDs) to modify TiO₂ nanotube arrays for photoelectrochemical water splitting. A systematic study using surface and optical characterization tools reveals the nature of the combination of Si QDs and TiO₂ nanotube arrays. Scanning electron microscopy and X-ray photoelectron spectroscopy results show that Si QDs were assembled on the surface of vertically aligned TiO₂ nanotube arrays. The UV–vis diffuse reflectance spectra indicate the improved visible light absorbance. The enhanced photoelectrochemical water splitting was demonstrated under visible light illumination and the photocurrent density was 1.6 times larger than that of pristine TiO₂ electrodes. Electrochemical impedance behavior was measured for the electrodes and the impedance is slightly reduced for the nanocomposite electrode with the presence of Si QDs. This work demonstrated that Si QDs would be a novel and effective choice for improving the utilization of visible light for TiO₂ nanotubes