Reduced TiO2 Nanorods Decorated with Carbon Nanodots for Photoelectrochemical Water Oxidation

Abstract

The formation of composite materials with carbon nanodots (CNDs) and electrochemical reduction of metal oxide semiconductors are attractive strategies to increase the performance of photoelectrochemical water oxidation. Here, both strategies were used with TiO2 photoelectrodes to analyze their role separately and when combined. For this purpose, TiO2 nanorods were synthesized on fluorine-doped tin oxide (FTO) substrates by a hydrothermal route; after that, TiO2 was subjected to electrochemical reduction by applying a constant potential, and finally, carbon nanodots were incorporated into the TiO2 surface by immersion of the TiO2 samples in a CND solution. The resulting photoelectrodes were characterized by different microscopy, spectroscopy, and electrochemical techniques. The results indicate that the electrochemical reduction allows to increase the lifetime of the electrons in the semiconductor, decreases the charge-transport resistance in the bulk of TiO2, and improves the water oxidation kinetics. In the case of the incorporation of CNDs on the TiO2 surface, it contributes to enhancing the separation of the electron-hole pairs and leads to a lower charge-transfer resistance from the photoelectrode to the electrolyte. In this way, the photocurrent of TiO2 (at 1.23 V vs RHE) had an increase of 36% with electrochemical reduction, 64% with CND decoration, and 103% with a combination of both strategies. These results are important to understand the role of electrochemical reduction and CND decoration in photoelectrochemical systems.