Modulating the Schottky barrier heights of plasmonic metal/semiconductor heterojunctions by graphene substrates for boosting photocatalytic water oxidation

Abstract

Construction of plasmonic metal/semiconductor heterojunctions represents a promising approach to extending the light absorption range and simultaneously maintaining the high redox potentials of photogenerated carriers. However, unsuitable Schottky barrier height (ΦB) blocks the metal-to-semiconductor injection of hot electrons and increases the probability of their recombination with hot holes. Herein, a verstile protocol is demonstrated to address this issue based on the introduction of a reduced graphene oxide (rGO) substrate. As a proof-of-concept design, a Au/TiO2/rGO stacked photocatalyst is fabricated with TiO2 sandwiched between rGO and Au. In this smart design, rGO with work function smaller than that of Au upshifts the Fermi level of Au/TiO2 and reduces the ΦB between Au and TiO2. As a result, the hot electron injection efficiency from plasmonic Au to the conduction band of TiO2 is greatly augmented, increasing the number of separated hot holes participating in H2O oxidation. Profitting from the enhanced utilization of hot carriers, the Au/TiO2/rGO delivers markedly improved photocatalytic activity in O2 evolution as compared with Au/TiO2. This work provides us guidance to build high-efficient plasmonic photocatalysts for renewable fuel production and highlights the importance in reinforcing the separation and transfer of hot charges.