Carbon quantum dots as novel sensitizers for photoelectrochemical solar hydrogen generation and their size-dependent effect

As a result of global energy needs, much research has been devoted to the conversion of solar energy to various usable forms, such as chemical energy in the form of hydrogen via water splitting. To make the conversion methods efficient, economically practical, and industrially scalable, sensitizers capable of utilizing visible and near infrared (IR) light need to be developed. Herein, water-soluble, colloidally stable carbon quantum dots (CQDs) are successfully synthesized by a facile one-step alkali-assisted electrochemical method. Owing to their broad visible light absorption, upconversion luminescence properties and efficient electron injection to TiO2, these CQDs can be used as the sensitizer for photoelectrochemical cells and show an optimized photocurrent of 1.2 mA cm−2 at 0 V versus Ag/AgCl under 100 mW cm−2 simulated sunlight. The above results indicate that the elementally abundant and environmentally friendly CQDs, as a novel sensitizer, can surely be employed to make full use of the visible spectrum of sunlight for their application in photovoltaic devices. (paper)