Nanoscale PAPER Cite this: Nanoscale, 2016, 8, 6629 Received 15th January 2016, Accepted 23rd February 2016 DOI: 10.1039/c6nr00400h www.rsc.org/nanoscale Oxygen reduction catalyzed by gold nanoclusters supported on carbon nanosheets† Qiannan Wang,‡ a Likai Wang,‡ a Zhenghua Tang,* a,b Fucai Wang, c Wei Yan, a Hongyu Yang, a Weijia Zhou, a Ligui Li, a Xiongwu Kang a and Shaowei Chen* a,d Nanocomposites based on p-mercaptobenzoic acid-functionalized gold nanoclusters, Au 102 ( p-MBA) 44 , and porous carbon nanosheets have been fabricated and employed as highly efficient electrocatalysts for oxygen reduction reaction (ORR). Au 102 ( p-MBA) 44 clusters were synthesized via a wet chemical approach, and loaded onto carbon nanosheets. Pyrolysis at elevated temperatures led to effective removal of the thiolate ligands and the formation of uniform nanoparticles supported on the carbon scaffolds. The nano- composite structures were characterized by using a wide range of experimental techniques such as trans- mission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, UV-visible absorption spectroscopy, thermogravimetric analysis and BET nitrogen adsorption/ desorption. Electrochemical studies showed that the composites demonstrated apparent ORR activity in alkaline media, and the sample with a 30% Au mass loading was identified as the best catalyst among the series, with a performance comparable to that of commercial Pt/C, but superior to those of Au 102 nanoclusters and carbon nanosheets alone, within the context of onset potential, kinetic current density, and durability. The results suggest an effective approach to the preparation of high-performance ORR catalysts based on gold nanoclusters supported on carbon nanosheets. Introduction Developing effective energy technologies to eliminate our dependence on fossil fuels has been attracting a great deal of interest in recent decades. Towards this end, proton exchange membrane fuel cells represent a unique, promising alternative, 1–4 which entail two major reactions, oxidation of small organic molecule fuels at the anode and oxygen reduction at the cathode. Yet, because of the sluggish electron- transfer kinetics and complex reaction pathways, oxygen reduction reaction (ORR) at the cathode has long been recog- nized as a major bottleneck that impedes the fuel cell perform- ance. Pt and Pt-based alloys have been used extensively as the catalysts of choice for ORR. 5–9 However, the limited reserves and high costs of Pt have significantly hampered the wide- spread commercial applications of fuel cells. Therefore, con- tinuous efforts are urgently needed to develop readily available, cost-effective catalysts with activity comparable to or even better than that of commercial Pt/C. 10–18 Within this context, gold nanoclusters have attracted par- ticular attention as efficient catalysts for ORR, where strong core size effects have been observed. 19–21 However, gold nanoclusters are in general unstable and tend to dissolve and/ or aggregate into larger particles during sample processing and electrochemical reactions. 20 To mitigate this issue, a variety of substrates have been used to support and stabilize gold nanoclusters, such as graphene, 21,22 mesoporous carbons, 23 TiO 2 , 24 CeO 2 , 25 and others. 26 Among these, carbon nanosheets represent a unique addition with a high surface area, excellent electrical conductivity, and robust electrochemi- cal stability. 27 This is the primary motivation of the present study. In this study, nanocomposites based on p-mercaptobenzoic acid-functionalized Au 102 nanoclusters, Au 102 ( p-MBA) 44 , and porous carbon nanosheets have been fabricated and employed as highly efficient electrocatalysts for ORR. The gold nano- clusters were prepared by a wet chemical method and loaded onto carbon nanosheets. Pyrolysis at controlled temperatures (600 °C) led to effective removal of the organic capping ligands such that gold nanoparticles were in intimate contact with the carbon scaffolds. Electrochemical studies of the resulting † Electronic supplementary information (ESI) available: Additional experimental data and discussion. See DOI: 10.1039/c6nr00400h ‡ These authors contributed. a New Energy Research Institute, School of Environment and Energy, South China University of Technology, Guangzhou Higher Education Mega Centre, Guangzhou, 510006, P. R. China. E-mail: zhht@scut.edu.cn b Guangdong Provincial Key Laboratory of Atmospheric Environment and Pollution Control, Guangzhou, Guangdong 510006, P. R. China c Zijin Mining Group Co. Ltd, Shanghang, Fujian 364200, P. R. China d Department of Chemistry and Biochemistry, University of California, 1156 High Street, Santa Cruz, California 95064, USA. E-mail: shaowei@ucsc.edu This journal is © The Royal Society of Chemistry 2016 Nanoscale, 2016, 8, 6629–6635 | 6629 Published on 25 February 2016. Downloaded by University of California - Santa Cruz on 17/03/2016 15:20:39. View Article Online View Journal | View Issue