Regulating spatial charge transfer over intrinsically ultrathin-carbon-encapsulated photoanodes toward solar water splitting

Abstract

Photoinduced charge separation and transfer have been deemed the core factors affecting the efficiency of photoelectrocatalysis; precisely modulating the spatial migration of photo-induced charge carriers to the ideal reaction sites is of paramount importance for boosting the solar conversion efficiency of photoelectrochemical (PEC) cells. In this work, a combinatorial strategy has been developed to progressively construct highly efficient charge transport channels on the quintessential electrochemically anodized one-dimensional semiconductor framework (TiO₂ nanotube arrays, TNTAs) by in situ annealing-induced intrinsic ultrathin carbon encapsulation. Antimony sulfide (Sb₂S₃) nanocrystals were subsequently attached to the interior and exterior surfaces of the carbon-encapsulated TNTA (C–TNTA) substrate forming a well-defined ternary photoanode (C–Sb₂S₃–TNTA) capable of triggering smooth and cascade electron transfer. Cooperativity stemming from intrinsic carbon encapsulation on the surface for fast electron transport in conjunction with Sb₂S₃ photosensitization for substantial visible light harvesting endows the C–Sb₂S₃–TNTA heterostructure with markedly enhanced solar-powered PEC water dissociation performances, conspicuously exceeding its single and binary counterparts. Furthermore, a hole transport pathway was further constructed by site-selective incorporation of an oxygen evolving catalyst (Co-Pi) in the ternary system via a photo-assisted electrodeposition or electrodeposition approach, which contributes to more enhanced separation efficiency and prolonged lifetime of photo-induced charge carriers together with improved photostability. It is expected that our work would afford a new frontier to intelligently mediate the spatial directional flow of photogenerated charge carriers and rationally construct efficient charge transport channels on the semiconductor-based photoelectrodes for high-efficiency solar energy harvesting and conversion.