Carbon Nanodots Assisted Surface Engineering of GaN Photoanodes for Efficient and Stable Photoelectrochemical Water Oxidation

The process of transferring high-quality graphene-based films onto the surface of the electrode is very complicated and is one of the main bottlenecks in using graphene or graphene-based protecting layers with semiconductors that are electrochemically vulnerable in harsh pH conditions. To address this, an approach is implemented for direct deposition of carbon nanodots on the surface of GaN electrodes, instead of graphene films. Instead of isolating the GaN surface from the electrolyte, the carbon nanodots function as a catalyst, expediting charge transfer at the electrode/electrolyte interface. This fast charge-transfer process prevents accumulation of photoholes on the GaN surface, thereby improving stability. These photoholes, formed in the presence of basic electrolytes, are considered to be the main reason for photocorrosion. The effect of the surface dispersion of the carbon nanodots on the overall performance of the electrode is also studied. A significant improvement in the photocurrent density (0.44 mA cm(-2) at 1.23 V vs RHE) is obtained for the optimized sample as compared to that of the bare GaN sample (0.34 mA cm(-2) at 1.23 V vs RHE). Moreover, the stability performance is also improved, with almost 87% retention of the initial current value after 3 h of chronoamperometric measurements.