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Ternary transition metal sulfides embedded in graphene nanosheets as both anode and cathode for high-performance asymmetric supercapacitors Wei Liu, Hao Niu, Jiao Yang, Kui Cheng, Ke Ye, Kai Zhu, Guiling Wang, Dianxue Cao, and Jun Yan Chem. Mater., Just Accepted Manuscript • Publication Date (Web): 04 Jan 2018 Downloaded from http://pubs.acs.org on January 4, 2018
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Chemistry of Materials
Ternary transition metal sulfides embedded in graphene nanosheets as both anode and cathode for high-performance asymmetric supercapacitors Wei Liu, Hao Niu, Jiao Yang, Kui Cheng, Ke Ye, Kai Zhu, Guiling Wang, Dianxue Cao and Jun Yan* Key Laboratory of Superlight Materials and Surface Technology, Ministry of Education, College of Material Science and Chemical Engineering, Harbin Engineering University, Harbin 150001, China ABSTRACT: Owing to their low electronegativity, excellent electrical conductivity, high specific capacitance and rich electrochemical redox sites, various transition metal sulfides have attracted numerous attention as promising pseudocapacitive electrode materials for supercapacitors. However, the relatively poor electrical conductivity and large volume changes seriously hinder their further commercial applications. Herein, ternary Co0.33Fe0.67S2 nanoparticles are in situ embedded in-between graphene nanosheets through a facile one-step hydrothermal approach to form sandwich-like composite. Thanks to the unique and robust structure, the graphene nanosheet/Co0.33Fe0.67S2 composite (GCFS-0.33) exhibits high specific capacitance (310.2 C g-1 at 2 mV s-1) and superb rate capability (61.8 % at 200 mV s-1) in 3 M KOH aqueous electrolyte. With transition metal sulfides simultaneously as both positive and negative electrodes, for the first time, an aqueous asymmetric supercapacitor (ASC) has been fabricated by using GCFS-0.33 composite as the negative electrode and sulfidized graphene/CoNiAl-layered double hydroxides as the positive electrode with well-separated potential windows. Our fabricated ASC could deliver a superior energy density of 66.8 Wh kg-1 at a power density of 300.5 W kg-1 and still retain 13.1 Wh kg-1 even at a high power density of 29.4 kW kg-1, which is highly comparable with the previously reported transition-metal-sulfide-based ASC devices. Moreover, the as-fabricated ASC cell displays impressive long-term cycling stability with a capacitance retention of 102.2 % in comparison with the initial capacitance after 10000 cycles. This versatile synthetic strategy can be readily extended to synthesize other transition-metal-sulfide-based composites with excellent electrochemical performances.
■ INTRODUCTION With the rapid development of global economy, increasingly depleted fossil fuels and ever-worsening environmental pollution, energy crisis is undoubtedly one of the most urgent and critical issues faced currently by our modern society.1 The growing and urgent future energy consumption requirements have triggered a worldwide 'gold rush' in developing environmentally benign, efficient and low-cost devices for energy production and storage.2 Among various energy storage technologies and devices, supercapacitors have attracted intensive attention owing to their ultrahigh power density, fast charge/discharge rates, superb cycling stability and environmental friendliness.3 However, most of the commercially available supercapacitors still suffer from relatively lower energy density (
