Dalton Transactions PAPER Cite this: Dalton Trans., 2016, 45, 9646 Received 1st February 2016, Accepted 2nd May 2016 DOI: 10.1039/c6dt00449k www.rsc.org/dalton Molybdenum diselenide/reduced graphene oxide based hybrid nanosheets for supercapacitor applications† Suresh Kannan Balasingam,‡ a,b Jae Sung Lee c and Yongseok Jun* b In the present study, molybdenum diselenide/reduced graphene oxide (MoSe 2 /rGO) nanosheets were synthesized via a facile hydrothermal process and the electrochemical performance of the nanosheets was evaluated for supercapacitor applications. The MoSe 2 nanosheets were uniformly distributed on the surface of the rGO matrix. The MoSe 2 /rGO nanosheet electrode exhibited an enhanced specific capaci- tance (211 F g -1 ) with excellent cycling stability, compared with pristine MoSe 2 . The enhanced electro- chemical performance of the MoSe 2 /rGO nanosheet electrode is mainly attributed to the improved electron and ion transfer mechanism involving the synergistic effects of pseudocapacitance (from the MoSe 2 nanosheets) and the electric double layer charge (EDLC, from the rGO nanosheets) storage behav- ior. These results demonstrate that the enhanced electrochemical performance of MoSe 2 /rGO nanosheets could be obtained via a facile and scalable approach. 1 Introduction The recent development of modern electronic devices and the progressive research on renewable energy-based electro- chemical energy conversion systems have fuelled the drive toward advanced high-performance energy storage devices. Among the various types of energy storage devices, super- capacitors have been recognized as one of the most promising candidates for high-power applications such as hybrid-electric vehicles, portable electronics, digital communications, and renewable-energy systems due to their outstanding properties, including high power density, long cycle life, fast charge/ discharge rate, and better safety. 1–6 In general, supercapacitors can be classified into two categories based on the charge storage mechanism: electrochemical double layer capacitors (EDLCs: where ion adsorption occurs at the electrode/electro- lyte interface) and pseudocapacitors (involving fast faradaic charge transport reactions). 5,7,8 Electrode materials for EDLCs are usually carbon-based materials such as activated carbon, carbon nanotubes, carbon nanofibers, and graphene. 9–12 However, the specific capacitance of carbon-based materials is generally low due to the limited specific surface area and non- uniform pore size distribution of these materials, which in turn limits the effective utilization of these electroactive materials in supercapacitors. 13,14 On the other hand, tran- sition metal oxides, 15–17 metal hydroxides, 18–20 conducting polymers, 4 and transition metal dichalcogenides 21,22 have been widely used as electrode materials for pseudocapacitors due to their much higher specific capacitance. Although, pseudocapacitors generally have high specific capacitance, the poor cycling stability and low conductivity of the pseudocapaci- tive materials limit their practical application in the energy storage field. 23,24 In order to overcome these issues as well as to achieve an enhanced electrochemical performance, novel hierarchical hybrid nanostructures combining EDLCs and pseudocapacitors have emerged, where these systems have a large surface area, good electrical conductivity, and a short path for ion diffusion. Recently, transition metal dichalcogenides (TMDCs), MX 2 (M = Mo, W; X = S, Se), with a layered structure (analogous to graphene) have emerged as one of the most prominent candi- dates for energy storage, catalysis, photo-transistors, and sensor systems due to their unique crystal structures and diverse material properties. 21,22,25–28 In these materials, metals and chalcogens interact via strong chemical bonds in the molecular layers, whereas the individual layers interact via weak van der Waals forces, forming a graphene-like layered † Electronic supplementary information (ESI) available. See DOI: 10.1039/ C6DT00449K ‡ Present address: Department of Materials Science and Engineering, Faculty of Natural Sciences and Technology, Norwegian University of Science and Techno- logy (NTNU), Trondheim 7491, Norway. E-mail: suresh.k.balasingam@ntnu.no a Department of Chemistry, School of Molecular Sciences, Ulsan National Institute of Science and Technology (UNIST), Ulsan 44919, Republic of Korea b Department of Materials Chemistry & Engineering, Konkuk University, Seoul 05029, Republic of Korea. E-mail: yjun@konkuk.ac.kr; Tel: +82-2450-0440 c School of Energy and Chemical Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan 44919, Republic of Korea 9646 | Dalton Trans. , 2016, 45, 9646–9653 This journal is © The Royal Society of Chemistry 2016 Published on 06 May 2016. Downloaded by Norwegian University of Science and Technology on 12/06/2016 23:07:21. View Article Online View Journal | View Issue