Reduced graphene oxide/silicon nanowire hetero- structures with enhanced photoactivity and superior photoelectrochemical stability Xing Zhong 1,§ , Gongming Wang 1,§ , Benjamin Papandrea 1 , Mufan Li 1 , Yuxi Xu 1 , Yu Chen 2 , Chih-Yen Chen 1 , Hailong Zhou 1 , Teng Xue 2 , Yongjia Li 2 , Dehui Li 1 ,Yu Huang 2,3 , and Xiangfeng Duan 1,3 (  ) 1 Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, California 90095, USA 2 Department of Materials Science and Engineering, University of California, Los Angeles, California 90095, USA 3 California Nanosystems Institute, University of California, Los Angeles, California 90095, USA § These authors contributed equally to this work. Received: 9 January 2015 Revised: 5 April 2015 Accepted: 14 April 2015 © Tsinghua University Press and Springer-Verlag Berlin Heidelberg 2015 KEYWORDS graphene, silicon nanowire, photocatalyst, photoactivity, stability ABSTRACT Silicon nanowires (SiNWs) have been widely studied as light harvesting antennas in photocatalysts due to their ability to absorb broad-spectrum solar radiation, but they 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 not only functions as a physical protection layer to isolate the SiNWs from the harsh electrochemical environment but also serves as a charge mediator to facilitate the charge separation and transport processes. Furthermore, the rGO may also function as a redox catalyst 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 photo- electrochemical 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 of the surface of the SiNWs during the photocatalytic dye degradation process. The ability to significantly improve the photocatalytic activity and stability in rGO-SiNW heterostructures can not only lead to more opportunities for the application of silicon-based photocatalysts/ photoelectrodes for solar energy harvesting but also provide new insights into the stabilization of other unstable photocatalytic systems. Nano Research DOI 10.1007/s12274-015-0790-2 Address correspondence to xduan@chem.ucla.edu