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To begin with, we give a brief introduction on the necessity of ecofriendly approaches towards the development of supercapacitors that make use of nanocellulose. We then focus on various investigations that have been carried out to fabricate supercapacitors based on nanocellulose or its composites. Finally, we describe our outlook on several issues that warrant further investigations in this topic with immense potentials.
Journal of Science: Advanced Materials and Devices (2019) 333e340 Contents lists available at ScienceDirect Journal of Science: Advanced Materials and Devices journal homepage: www.elsevier.com/locate/jsamd Review Article Nanocellulose based functional materials for supercapacitor applications Jasmine Jose a, Vinoy Thomas a, *, Vrinda Vinod a, Rani Abraham b, Susan Abraham c a Centre for Functional Materials, Christian College, Chengannur University of Kerala, 689122, India Department of Chemistry, Christian College, Chengannur University of Kerala, 689122, India c Department of Economics, Christian College, Chengannur University of Kerala, 689122, India b a r t i c l e i n f o a b s t r a c t Article history: Received January 2019 Received in revised form 30 April 2019 Accepted June 2019 Available online 12 June 2019 Environmental protection and renewable sources for energy conversion and storage remain an important topic nowadays Major challenges of the 21st century that mankind has to face are certainly energy supply, its storage and conversion in a way that essentially protect the environment In this scenario the nanocellulose has come up as a sustainable and promising nanomaterial with its unique structure and remarkable properties, such as high specific modulus, excellent stability in most solvents, low toxicity and natural abundance Its ecofriendly nature, low cost, easy availability and simple synthesis techniques render the nanocellulose as a promising candidate for the fabrication of green renewable energy storage devices Herein, we present a comprehensive review of the current research activities that focus on the development of nanocellulose materials for energy storage applications, particularly on supercapacitors To begin with, we give a brief introduction on the necessity of ecofriendly approaches towards the development of supercapacitors that make use of nanocellulose We then focus on various investigations that have been carried out to fabricate supercapacitors based on nanocellulose or its composites Finally, we describe our outlook on several issues that warrant further investigations in this topic with immense potentials © 2019 The Authors Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/) Keywords: Nanocellulose Supercapacitor Introduction In recent time we have seen considerable improvements in the living standard which doubtlessly could be attributed to the innovation and development of more viable products through more efficient processes To keep this process moving we need to make use of resources that are renewable and sustainable Moreover, the technologies have reached a new era of information technology and material innovation is experiencing an unpredictable pace of progressing Numerous types of sensors, electronic devices and so on are built everyday using advanced ceramics, metals, and plastics The huge advancement of today's technology is bringing revolutionary changes to our society and along with this arises serious environmental concerns due to the generation of electronic and plastic wastes [1] The extraordinary growth in portable electronic * Corresponding author E-mail addresses: jasminejose764@gmail.com (J Jose), vinoythoma@gmail.com (V Thomas), vrindavinod.kk@gmail.com (V Vinod), raniabraham@gmail.com (R Abraham), susanmi@gmail.com (S Abraham) Peer review under responsibility of Vietnam National University, Hanoi systems during the past few decades have gained the attention of researchers in developing versatile energy storage devices, such as batteries, super capacitors, or fuel cells [2,3] Super capacitors, also termed as electrochemical double-layer capacitors, have a high capacity with a fast charge/discharge rate These interesting properties have made super capacitors capable of filling the gap between batteries and conventional capacitors [4] Currently, polymeric materials for super capacitor applications have gained wide attentions because of their properties, such as flexibility, lightweight, and stable cycling performance [5] Further, redox active polymers due to their recyclability and sustainability are better and safer replacements for heavy metals in battery electrodes [6] Since the future generation electronics industry needs to be highly sustainable there must be extraordinary and viable efforts for the development of low-cost, lightweight, environment-friendly, highperformance super capacitors and batteries [7] Among biopolymers, natural polysaccharides are being developed as substitutes to synthetic materials for electrochemical devices [4] Nanocellulose, is a structural polysaccharide that has gained much attentions nowadays due to its renewability, inherent biocompatibility and biodegradability, cost-effectiveness, natural abundance https://doi.org/10.1016/j.jsamd.2019.06.003 2468-2179/© 2019 The Authors Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/) 334 J Jose et al / Journal of Science: Advanced Materials and Devices (2019) 333e340 and eco-friendly nature [8] Cellulose is an odourless, biodegradable, hydrophilic, water insoluble material which can be obtained from plants, animals, or bacteria, and the term ‘nanocellulose’ usually refers to the cellulosic extracts or processed materials, having nano-scale structural dimensions Nanocellulose can be classified into three types: (i) cellulose nanocrystals (CNCs)/nanocrystalline cellulose (NCC) and cellulose nanowhiskers (CNWs), (ii) cellulose nanofibrils (CNFs), also referred to as nano-fibrillated cellulose (NFC), and (iii) bacterial cellulose (BC) (Table 1) [9] Chemically, a cellulose consists of linear chains of repeating b-Dglucopyranose units, covalently connected through b-1, glycosidic bonds (Fig 1) [10] A large number of hydrogen bonds exist intra and inter molecularly and yield different cellulosic structures Nanocellulose offers a unique combination of properties including flexible surface chemistry, transparency, low thermal expansion, high elasticity, anisotropy and the ability to bind to other conductive materials, enabling extensive application in flexible energy-storage devices [11,12] Extraction of nanocelluloses can be done through chemical treatment, mechanical processing, and enzymatic treatments The different methods of preparation are shown schematically in Fig Integrating nanocelluloses into energy-related devices would definitely inspirate research in the area of eco-friendly materials and we find it very promising to address the important environmental concerns In addition, a cellulose expresses itself as a low cost material with large-scale promises [17] With the celluloserelated materials gaining more and more popularity, a number of good review articles have appeared in the area of the synthesis of nanocelluloses and their properties Several reviews published in the past few years have also focused on the application of cellulosebased energy related devices, such as batteries, sensors, and other electronic systems [18] Current focus, however, seems to be in the field associated with cellulose-based sustainable supercapacitors which is fast growing with a very high progress rate Although the interest for designing cellulose based devices for energy storage applications grew fast in the recent past according to Nyholm et al [19] it is quite interesting to note (Fig 3) that investigations in the field have hardly increased since 2012 In this review, we essentially focus on the potential applications of nanocelluloses in energy-related areas, and particularly, in the field of supercapacitors Our investigations in the area were concentrated in the synthesis of nanocelluloses and the experimental evaluation of their thermo-optic properties using the thermal lensing technique We were able to develop an UV protection system using nanocellulose/PVA composites With the current experimental background and information we plan to expand our area of research and focus on the possible applications of nanocelluloses in the field of energy-related devices, especially in the development of supercapacitors Cellulose-based functional materials Cellulose is one of the most abundant natural organic polymers on the Earth and is usually extracted from plants, agricultural byproducts, woods etc [4] The properties of a cellulose and cellulose derived materials can be enhanced by functionalizing it with Fig Structure of celluloses suitable materials [20] or through structural modifications for specific applications Cellulose nanofibres (CNF) (