Renewable supercapacitors based on cellulose/carbon nanotubes/[Bmim] [NTf2] ionic liquid

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Research Letter

Renewable supercapacitors based on cellulose/carbon nanotubes/[Bmim] [NTf2] ionic liquid Bruno S. Noremberg , Ricardo M. Silva, Oscar G. Paniz, and José H. Alano , Graduate Program in Materials Science and Engineering, Federal University of Pelotas, Gomes Carneiro, 1, 96010-000, Pelotas, RS, Brazil Jairton Dupont , Institute of Chemistry, Federal University of Rio Grande do Sul, Av. Bento Gonçalves, 9500, 91501-970, Porto Alegre, RS, Brazil Neftali L. V. Carreño , Graduate Program in Materials Science and Engineering, Federal University of Pelotas, Gomes Carneiro, 1, 96010-000, Pelotas, RS, Brazil Address all correspondence to Neftali L. V. Carreño at [email protected] (Received 9 November 2018; accepted 6 March 2019)

Abstract Improvement of the performance of renewable electronic devices is a crucial point for the consolidation of this emerging technology. Herein, we develop a supercapacitor based on cellulose, carbon nanotubes, and ionic liquids. A conductive paper prepared by simple acid hydrolysis of cellulose and carboxylated carbon nanotubes was used as an electrode. A cellulose sponge impregnated with 1-n-butyl-3-methylimidazolium bis(trifluoromethane sulfonyl)imide was used as a separator/electrolyte. Electrochemical tests were performed in a two-electrode cell that presented a specific capacitance of 34.37 F/g when considered the active mass and 97.9% of capacitance retention after 5000 charge/discharge cycles.

Introduction The most recurrent keywords in the scientific papers associated with cellulose are renewable materials, environmental concern, shortage of fossil fuels, low-cost, and sustainable development. It has been applied to simple and usual products such as paper to sophisticated technologies such as flexible energy storage devices,[1] humidity sensor,[2] and methanol sensors.[3] Despite all these great features mentioned, its use usually has limitations related to the durability and maintenance of high performance. An example is the use of cellulose in flexible electrodes for supercapacitors, which requires the usage of some conductive and capacitive components. Several authors have tested conductive polymers to promote electrical conductivity and flexibility.[4–6] However, the use of materials with pseudocapacitive properties tends to reduce the stability and life cycle of these devices. Since these parameters are important for real applications, their limitation may deprive its use. Therefore, this study aimed to use an effective method to promote a homogeneous and strong interaction between carbon nanotubes and cellulose, extracted from Eucalyptus. The resulting material called conductive paper was used to assembly a renewable supercapacitor. As separator and electrolyte, a cellulose sponge impregnated with 1-n-butyl-3-methylimidazolium bis(trifluoromethane sulfonyl)imide ([Bmim][NTf2]) ionic liquid (IL) was used because the IL is able to form a stable hybrid material with cellulose.[7] ILs also present excellent thermal stability and exhibit a good electrochemical performance