Reduced graphene oxide/silicon nanowire heterostructures with enhanced photoactivity and superior photoelectrochemical stability

Silicon nanowires (SiNWs) have been widely explored as light harvesting antenna in photocatalysts due to their ability to absorb broad solar spectrum, but are typically limited by poor photoelectrochemical stability. Here we report the synthesis of reduced graphene oxide-SiNW (rGO-SiNW) heterostructures to achieve greatly improved photocatalytic activity and stability. The SiNWs were synthesized through a metal-assisted electroless etching process, and functionalized with reduced graphene oxide (rGO) flakes through a chemical absorption process. Here the rGO can not only function as a physical protection layer to isolate the SiNWs from the harsh electrochemical environment, but also serve as a charge mediator to facilitate the charge separation and transport processes. Furthermore, the rGO may also function as the redox catalysts to ensure efficient utilization of photo-carriers for the desired chemical reactions. Photocatalytic dye degradation studies show that the photoactivity of the heterostructures can be significantly enhanced with an initial activation process and maintained without apparent decay over repeated reaction cycles. Electrochemical and photochemical studies indicate that the enhanced photoactivity and photostability can be attributed to the more efficient separation of photoexcited charge carriers in SiNWs, and the reduced self-oxidation on SiNWs surface during the photocatalytic dye degradation process. The ability to significantly improve the photocatalytic activity and stability in rGO-SiNW heterostructures can not only open up more opportunities in the application of silicon based photocatalysts/photoelectrodes for solar energy harvesting, but also provide new insights in the stabilization of other unstable photocatalytic systems.