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Fe3O4@Carbon Nanosheets for All-Solid-State Supercapacitor Electrodes Huailin Fan, Ruiting Niu, Jiaqi Duan, Wei Liu, and Wenzhong Shen ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b05415 • Publication Date (Web): 13 Jul 2016 Downloaded from http://pubs.acs.org on July 14, 2016
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ACS Applied Materials & Interfaces
Fe3O4@Carbon Nanosheets for All-Solid-State Supercapacitor Electrodes ＆
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Huailin Fan,†‡ Ruiting Niu, Jiaqi Duan,† Wei Liu†‡ and Wenzhong Shen*†
†State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan, 030001, PR China ‡University of Chinese Academy of Sciences, Beijing, 100049, PR China ＆State Key Laboratory of Separation Membranes and Membrane Processes, Institute of Functional Fiber, School of Materials Science and Engineering, Tianjin Polytechnic University, Tianjin 300387, China. ※ College of Environmental and Chemical Engineering, Shanghai University, Shanghai, 200444, PR China. KEYWORDS: carbon nanosheets, iron oxide, supercapacitors, energy storage, self-assembly ABSTRACT: Fe3O4@carbons nanosheets composites were synthesized using ammonium ferric citrate as Fe3O4/carbon precursor and graphene oxide as structure-directing agent under hydrothermal process. The surface chemical compositions, pore structures and morphology of the composite were analyzed and characterized by nitrogen adsorption isotherms, TG analysis, FT-IR, X-ray photoelectron energy spectrum, transmission electron microscope and scanning electron microscope images. The composites showed excellent specific capacitance of 586 F/g, 340 F/g at 0.5 A/g and 10 A/g. The all-solid-state asymmetric supercapacitor device assembled using carbons nanosheets in-situ embedded Fe3O4 composite and porous carbon showed a largest energy density of 18.3 Wh/kg at power density of 351 W/kg in KOH/PVA gel electrolyte. The synergism of high special surface to volume ratio, mesoporous structure, graphene-based conduction paths and Fe3O4 nanoparticle
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provided a high surface area of ion-accessibility, high electric conductivity, the utmost utilization of Fe3O4 and resulted in excellent specific capacitance, outstanding rate capability and cycling life as all-solid-state supercapacitor electrodes. INTRODUCTION All-solid-state supercapacitors are novel and high-efficiency storing energy equipment, which have attracted significant concerns due to their potential applications in portable, wearable and roll up displays, as well as the additional merits of lightweight, outstanding safety, environmental friendliness and flexible energy storage applications excepting for common supercapacitors of high power ratings, long cycle life and quick charging capacity.1-3 In accordance with the charge storage mechanism, energy is stored in supercapacitors of electric double layer capacitors (EDLC) or Faradaic redox capacitors. The capacitance of EDLC derives from the ion adsorption and desorption at the surface of electrode, and porous carbon, graphene and carbon nanotube are always selected as electrode materials; while the Faradaic capacitors are based on redox reactions and conductive polymers or transition-metal oxide such as RuO2, MnO2, and FeOx are always selected as electrode materials.4-6 The carbon materials provide higher power, but bear lower energy density on account of the limited electrical charge separation at the interface between electrolyte and electrode materials; the metal oxides provide higher energy density, but lower power suffering from the rate of redox reactions. Carbon materials surface were modified with N, B, S or P heteroatoms to boost the energy density of electric double layer capacitors7-9, which can not only boost the capacitance by pseudocapacitive effect but also improve the electronic conductivity and surface wettability. It is worthy to
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ACS Applied Materials & Interfaces
develope composite supercapacitor electrode consisting of carbon materials and transition metal oxide. For carbon–metal oxide compound, the carbon skeletons act as the structure support of metal oxides preventing agglomerating and insuring sufficient utilization of metal oxides at redox reactions, meanwhile provide the intense electronic migrating channels to benefit the rate capability and power density at large charge-discharge current remedying low conductivity of metal oxides. The metal oxides in composite electrodes contribute to high energy density from storing charge of redox reactions. The composite electrodes exert the advantages and alleviate the defects of carbon and transition metal oxides. Much effort was conducted on constructing nano-composites of carbon and transition metal oxides10-17 as supercapacitor electodes to investigate the synergistic effect of carbon and transition metal oxides. Among them, FeOx have been widely received significant attention owing to their cheap, low environment impact and high theoretical capacity, and carbon-FeOx composites as electrode materials for supercapacitors have been extensively investigated.18-20 For example, FeOx-doped graphene showed expected capacitance and high energy density, but its capacitance significantly decreased with cycle life increasing18,
21, 22
. Various porous carbon materials like microporous
carbon20, macroporous carbon23, carbon nanofibers24 and mesoporous carbon25 have been composited with FeOx, however, their didn’t completely displayed the potential capacitance of FeOx (
