Efficient photon harvesting and charge collection in 3D porous RGO-TiO₂ photoanode for solar water splitting

Highlights: • 3D porous photoanode was fabricated via hydrothermal assembly of RGO and TiO₂ NPs. • Optimized photoanode yields an impressive photoconversion efficiency of 0.5%. • Enhanced photon-harvesting and charge collection contribute to PEC activity. • The multi-channel electron transfer with positive NIR thermal effect was highlighted. The construction of photonic nanosystems with highly accessible photon harvesting and charge collection attracts intense interest in the fields of photovoltaic and photoelectrochemical (PEC) cells. It is desirable to build three-dimensional (3D) porous photoelectrodes that ensure high active surface area and promote light-trapping, charge separation and transport. Herein, we execute the hierarchical assembly of reduced graphene oxide (RGO) and scattered TiO₂ nanoparticles (NPs) to fabricate a heterogeneous 3D porous photoanode, which yields a high photocurrent density of 2.59 mA cm⁻² at a low bias of 0.6 V (vs. Ag/AgCl) with an impressive solar-to-hydrogen conversion efficiency of 0.5% for water splitting without the need of any sacrificial reagents. The significantly increased PEC activity in RGO-TiO₂ composite photoanode relative to TiO₂ NPs-based analogues is demonstrated to be benefit from the positive roles of 3D rGO framework in confining the incident light, promoting electron transport, activating thermal effect, improving catalyst loading and electrolyte penetration.