Graphene and Carbon Dots for Photoanodes with Enhanced Performance

Abstract

The way graphene (GDs) and carbon dots (CDs) are synthesized and combined with TiO2 determine their photoelectrochemical efficiency upon UV and visible LED lights. GDs and CDs are obtained by relatively unexplored top-down methods and conventional bottom-up methods, respectively. Top-down methods consist in the seedless growth of ZnO nanoparticles on the surface of graphene and the electrochemical cleavage of graphene grown on Ni foam. These carbon nanoparticles are later combined with TiO2 by different approaches such as solution mixing, adsorption via APTES linkers, and drop-casting on an already formed TiO2 film. Once the films are formed, they are placed into a photoelectrochemical Zahner cell and irradiated with LED lights at 450 and 360 nm. It is determined that CDs and GDs perform as efficient photosensitizers as demonstrated by an increase of ∼19- and 20-fold net photocurrent density when irradiated with UV and visible LED lights, respectively. We encountered that CDs are more sensitive upon visible light, whereas GDs promptly respond to UV light due to their difference in size-dependent band gap. Importantly, GDs obtained from seedless growth of ZnO are sensitive to both: UV and Vis LED irradiation. The combination of both nanocarbons would expand the absorption range and may be potentially used as cosensitizers toward the construction of more effective and advanced photoanodes.