Nanocellulose based functional materials for supercapacitor applications

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 sup

Review Article

Nanocellulose based functional materials for supercapacitor

applications

a Centre for Functional Materials, Christian College, Chengannur University of Kerala, 689122, India

b Department of Chemistry, Christian College, Chengannur University of Kerala, 689122, India

c Department of Economics, Christian College, Chengannur University of Kerala, 689122, India

a r t i c l e i n f o

Article history:

Received 8 January 2019

Received in revised form

30 April 2019

Accepted 3 June 2019

Available online xxx

Keywords:

Nanocellulose

Supercapacitor

a b s t r a c t

Environmental protection and renewable sources for energy conversion and storage remain an important topic nowadays Major challenges of the 21stcentury 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/)

1 Introduction

In recent time we have seen considerable improvements in the

living standard which doubtlessly could be attributed to the

inno-vation 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

pro-gressing 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

revolu-tionary 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

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 prop-erties have made super capacitors capable offilling the gap between batteries and conventional capacitors [4] Currently, polymeric materials for super capacitor applications have gained wide atten-tions because of their properties, such asflexibility, lightweight, and stable cycling performance[5] Further, redox active polymers due

to their recyclability and sustainability are better and safer re-placements for heavy metals in battery electrodes [6] Since the future generation electronics industry needs to be highly sustain-able there must be extraordinary and visustain-able efforts for the devel-opment of low-cost, lightweight, environment-friendly, high-performance super capacitors and batteries [7] Among bio-polymers, natural polysaccharides are being developed as sub-stitutes to synthetic materials for electrochemical devices [4] Nanocellulose, is a structural polysaccharide that has gained much attentions nowadays due to its renewability, inherent biocompati-bility and biodegradabiocompati-bility, cost-effectiveness, natural abundance

* 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.

Contents lists available atScienceDirect Journal of Science: Advanced Materials and Devices

j o u r n a l h o m e p a g e : w w w e l s e v i e r c o m / l o c a t e / j s a m d

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/ ).

and eco-friendly nature[8] Cellulose is an odourless,

biodegrad-able, 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)/nano-crystalline 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 repeatingb-D

-glucopyranose units, covalently connected throughb-1, 4 glycosidic

bonds (Fig 1)[10] A large number of hydrogen bonds exist intra and

inter molecularly and yield different cellulosic structures

Nano-cellulose offers a unique combination of properties including

flex-ible surface chemistry, transparency, low thermal expansion, high

elasticity, anisotropy and the ability to bind to other conductive

materials, enabling extensive application inflexible 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 inFig 2

Integrating nanocelluloses into energy-related devices would

definitely inspirate research in the area of eco-friendly materials

and wefind it very promising to address the important

environ-mental concerns In addition, a cellulose expresses itself as a low

cost material with large-scale promises [17] With the

cellulose-related 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

cellulose-based 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

experi-mental evaluation of their thermo-optic properties using the

thermal lensing technique We were able to develop an UV

pro-tection 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 thefield of energy-related devices, especially

in the development of supercapacitors

2 Cellulose-based functional materials

Cellulose is one of the most abundant natural organic polymers

on the Earth and is usually extracted from plants, agricultural

by-products, woods etc.[4] The properties of a cellulose and cellulose

derived materials can be enhanced by functionalizing it with

suitable materials [20] or through structural modifications for specific applications Cellulose nanofibres (CNF) (<100 nm width) were synthesized very recently in our laboratory using raw cotton

as the source material through green techniques (Fig 4) In-depth investigations were carried out to evaluate their thermo-optical properties and ultraviolet blocking capabilities Ultra-sensitive dual beam mode matched thermal lensing technique was used for the measurement of thermo- optical properties (Fig 5) The low ther-mal diffusivity (2.61  10 8 m2/s) and thermal conductivity (0.108 W/mK) value of the system indicated its thermal insulation behavior Further, highly transparent plasmon-enhanced ultravio-let radiation blocking CNF-PVA films (Fig 6) for environmental applications were developed and we found that the UV blocking capability of the synthesizedfilms is almost the same as that of commercialfilms available in the market With our current interest

on the development of functionalized nanocellulose based systems for energy storage applications, the development of functionalized nanocellulose based aerogels for supercapacitor applications is underway in our lab This review therefore has been carried out to bring a fresh picture of nanocellulose based supercapacitors, which

we believe, is highly significant in the present scenario

3 Cellulose based supercapacitors Supercapacitors, also called ultracapacitors or electrochemical capacitors, offer a promising approach to meet the growing power demands owing to their high power density, superior rate capa-bility, quick charging/discharging rate, long cycle life, simple prin-ciples, fast dynamics of charge propagation and low maintenance cost[21] These supercapacitors are classified into electrical double layer capacitors, which store energy through electrostatically accumulated charges at the electrode/electrolyte interface and pseudo capacitors based on fast redox reactions at the electrodes for huge pseudo capacitance [22] There are also hybrid super-capacitors comprising of both types of electrodes thereby combining both double layer capacitive and pseudocapacitive charging and discharging schemes Such supercapacitors have high energy density, high power density and high cycling stability With these developments the supercapacitors are proficient to bridge the gap between the batteries/fuel cells (with high energy density) and the conventional capacitors (with high power density)[23,24] For electro-chemical double layer supercapacitors a large specific sur-face area is favorable as it delivers more space for the adsorption of the electrolyte ions Highly porous materials that possess high mechanical strength and large surface area, such as aerogels and films, can be synthesized by combining with nanocelluloses[25] This type of porous structures reveal a great potential as substrates Table 1

Primary characteristics of cellulose types [13e15]

Material Crystallinity Surface area [m 2 g 1 ] Young's Modulus [GPa] Average size

Diameter length Cellulose micro fibres (CMF) <60% <1 20e60 10mm >10mm Cellulose nano fibres (CNF) 50% z 90% z100 50e160 10e80 nm <10mm Cellulose nano crystals (CNC) z90% z200 50e140 5e30 nm z100 nm

Fig 1 Structure of celluloses.

J Jose et al / Journal of Science: Advanced Materials and Devices xxx (xxxx) xxx 2

Fig 2 Various preparation methods of nanocelluloses [adapted from reference [16] ].

Fig 3 Scopus database on the research output in form of research articles using

celluloses and supercapacitors as keywords. Fig 4 HR-TEM image of CNF prepared from cotton.

forflexible supercapacitors[29]and their efficiencies modified by

doping with carbon conductive materials like CNTs [26,27] and

graphene oxides (GO)[28]

Though cellulose-based materials are environmental friendly

the chemical processes involved in its preparation indicates a threat

to the ecology Therefore, while designing the green energy storage

devices, one has to focus more on reducing the effect of chemical

treatments Koga and co-workers successfully converted recycled

waste pulp-fibres and single-layer GO sheets into a cellulose paper/

Reduced Graphene oxide (RGO) composite using a blend of

papermaking process andflash reduction techniques (Fig 7) The

room temperature, additive free, and millisecond time scale

reduction of GO was achieved in the composite by irradiating with

high intensity pulsed light This cellulose paper/RGO composite

electrode gave a high specific capacitance of 177 F/g It was

suc-cessfully applied for an all-paper basedflexible supercapacitor that

provided a capacitance of 212 F/g[30]

The extraction of cellulosefibres from waste paper, and

subse-quent application in supercapacitor electrodes is proposed as a cost

effective route for developing energy storage devices with

improved performance[32] Habio Su et al demonstrated an all

solid state symmetricflexible supercapacitor based on the office

waste paper fibers/reduced graphene oxide/manganese dioxide

(PF/RGO/MnO2) which acts as both the positive and negative

electrodes Flexible PF/RGO/MnO2electrodes with a good physical

flexibility and excellent mechanical strength were fabricated via a

simple solution phase assembly and vacuum filtration method

without using any binding agents Moreover, owing to the

advan-tages of large surface area and microfibers present in paper fiber,

the PF based hybrid flexible electrodes show a high specific

capacitance of 410 F,g 1 at 0.8 A,g 1 and retain 93% of the

capacitance over 5000 cycles, and display an outstanding electro-chemical performance In addition, the assembled solid-state symmetric supercapacitors exhibit a high energy density (19.6 Whkg 1at 400 Wkg 1) and an excellent cycling stability of 85.3% retention even after 2000 folding and bending cycles These investigations, thus, demonstrate a renewable method of turning waste into wealth and deliver a new method to fabricate the sus-tainable and self-supporting paper-based supercapacitor for the application inflexible energy storage devices[33]

In a pioneering work, Zhe Weng and his co-workers[34] re-ported a simple and scalable method to fabricate graphene-cellulose paper (GCP) membranes that act as freestanding and binder-free electrodes forflexible supercapacitors The electrical conductivity of the GCP membrane shows great stability with a reduction of only 6% after being bent 1000 times Thisflexible GCP electrode has a high capacitance per geometric area of 81 mFcm 2, which is equivalent to a gravimetric capacitance of 120 Fg 1of graphene, and retains>99% of the capacitance over 5000 cycles Under highlyflexible conditions, the supercapacitors exhibit a high capacitance per geometric area of 46 mFcm 2for the complete device All these results indicate that polymer supercapacitors made using GCP membranes are versatile

The fabrication of supercapacitors and lithium ion batteries using commercial paper sheets that were coated with aqueous Carbon Nanotube (CNT) ink using sodium dodecyl benzene sulfo-nate (SDBS) as surfactant was introduced by Cui and team[35] The process was based on a simple Meyer rod coating process in line with the main principles of green chemistry The method implied ways to reduce the consumption of organic solvents, usage of low energy intake processes avoiding high temperature or high pres-sure since paper absorbs water easily and binds to CNTs The resulting conductive paper exhibitedflexibility and good mechan-ical strength as well Supercapacitors based on CNT conductive paper also displayed a specific capacitance of 200 Fg 1 and the stable cycling life over 40000 cycles Later, the same team coated single-walled CNTs (SWCNTs) onto cottonfibres and attained a highly electrically conductive interconnecting network [36] Supercapacitors made with such electrodes had excellent cycling performance (good capacity retention after 35000 cycles) and a specific capacitance of 70e80 Fg 1 Due to these properties, the combination of the cotton/SWCNT electrodes into the wearable electronics was proposed widely Kang et al developed a solid state flexible supercapacitor by coating CNT onto office papers using the drop-dry method using gel electrolytes with ionic liquid (i.e fumed silica nanopowders were mixed with ionic liquid, 1-ethyl-3-methylimidazolium) Even though the supercapacitor exhibited excellent stability, flexibility and a specific capacitance of about

135 Fg 1, the approach was a pull out from green chemistry prin-ciples as the use of ionic liquids is debatable due to their unsafe synthesis[37] Later, a simple route to obtain three dimensional, lightweight, hybrid aerogels possessing excellent capacitance retention at charge/discharge rates required for aflexible energy storage device was proposed by Xuan Yang et al in their work They demonstrated the use of CNC aerogels as universal substrates by incorporating polypyrrole nanofibers (PPy-NF), polypyrrole-coated carbon nanotubes (PPy-CNT), and spherical manganese dioxide nanoparticles (MnO2-NP), during the aerogel assembly[38] Lee et al demonstrated a new green method of cellulose acti-vation using coffee In their work they soaked a piece of paper in the espresso coffee which acted as a natural activating agent followed

by a pyrolysis to give paper derived carbons (EKACs) Potassium ions being the core ingredients in the espresso coffee play an important role in augmenting the pyrolysis kinetics and achieving a porous structure and a specific capacitance of 131 Fg 1at a scan rate of 1.0 mVs 1 was obtained All the flexible paper

super-Fig 5 Thermal lensing plot of CNF.

Fig 6 UV/Visible spectrum showing transparency of the PVA/CNF/AgNP film.

J Jose et al / Journal of Science: Advanced Materials and Devices xxx (xxxx) xxx 4

capacitors were fabricated by assembling the EKAC/CNT mixture

embedded paper towel as the electrode, the PVA/KOH mixture

paper towel as the electrolyte and polydimethylsiloxane infiltrated

paper towel as the packing substance This coffee mediated

acti-vation of cellulose and the resultant super-capacitor provide a new

material and an environmental friendly power source[39]

Conductive polymers are usually the polymers with highly

p-conjugated polymeric chains and among these polymers the most

widely used ones include polypyrrole (PPy, 0.3e100 Scm 1),

poly-aniline (PANI, 0.01e5 Scm 1), polyacetylene (PA, 3e1000 Scm 1),

polythiophene (PTh, 2e150 Scm 1), poly (phenylenevinylene) (PPV,

10 3- 100 Scm 1) and their derivatives [40] These conductive

polymers have been widely studied for use in sensors,

electro-chemical capacitors, fuel cell electrodes, batteries, memory devices,

andfield emission devices[41] In recent years, significant research

efforts have been made to fabricate conductive nanocomposites by

combining conductive polymers (especially PPy and PANI) with

nanocelluloses The major issue that restricts the performance of

nanocellulose/conductive polymer composites as super-capacitor

electrodes is their low conductivity which lies in the range of

0.02 Scm 1 to 5.1 Scm 1[42] To surmount this problem, Wang

et al.[43]employed well precise core sheath structured conductive

nanocomposites by covering a homogeneous layer of PPy on

nanocellulosefibers and the as prepared composites achieved an

outstanding conductivity about 77 Scm 1 (Fig 8) A very general

approach of increasing the conductivity is to introduce conductive

materials into the composites, like carbon based materials The

incorporation of carbon-based conducting components in

nanocellulose-based composites is appealing due to their low cost

and excellent conductive nature (electrical conductivity up

to ~ 108S,m 1for graphene[44]and ~105Sm 1for graphite)[45]

NC-based aerogels as substrates of energy devices have drawn great

attentions [47e49] due to their interesting properties, such as

highly porous structure, large specific surface area and very low

density An interesting example is the Covalently Cross-linked CNF

aerogels produced by Zhang et al.[48], which can retain its shape in water due to the interaction between water and the cellulose, specifically through the hydrogen bonds

Flexible solid-state CNF-based aerogel supercapacitors with silver and PANI nanoparticles deposited on aerogel were prepared

by Zhang et al.[49]and it was observed that the relatively high specific capacitance (176 mF cm 2at 10 mV s 1) of the as fabricated supercapacitors remained the same when they were bent with different bending radii Exceptionally lightweight aerogels of CNC prepared by Yang et al.[38]were considered as universal 3D sub-strates for nanosized materials in SCs, such as PPy nanofibers, PPy coated CNTs and MnO2 nanoparticles The resultant composites

Fig 7 Preparation of the composite derived from single layer GO and recycled cellulose pulp fibres by papermaking and successive flash reduction processes Adapted from reference [31]

Fig 8 PPy polymerization in the presence of equal amounts of pristine CNCs and PVP/ CNCs with a cartoon demonstrating the two extremely different morphologies of the end products Adapted from reference [46]

were lightweight and exhibited great mechanical properties, as

indicated inFig 9 It could remain intact when being compressed in

air or in an aqueous electrolyte without breaking and recover its

original shape on the removal of the force making it a promising

material for supercapacitor applications

Carbonization of nanocellulose materials could be yet another tactic of exploiting nanocellulose in supercapacitors Due to their high conductivities, stability and versatile structures, carbon mate-rials have countless potential in the application as supercapacitor electrode materials[50e52] In order to increase the accessibility to

Fig 9 Photograph emphasizing the lightweight nature of a hybrid aerogel resting on top of a feather (left); Photograph of cyclic compression tests in saturated Na 2 SO 4 solution at 0% (middle) and 80% (right) strain Adapted from reference [38]

Fig 10 (1) Photograph of a BC pellicle (2) SEM image of the N,P-co-doped carbon nanofiber surface (inset: the typical sample, 2.7  1.2 cm 2 ) (3) SEM image of the inner of the N,P-co-doped carbon nanofiber (N,P-CNF) (4) HRTEM image of the N,P-CNF Adapted from reference [61]

Table 2

Performance of some cellulose based supercapacitors.

Electrode material Specific capacitance (F g 1 ) Power density Energy density Capacitance retention References rGO/CNC hybrid fibre 123.3 at current density

0.1 A g 1

496.4 mW cm 3 5.1 mWh cm 3 e [62]

Cellulose Paper/CNTs/MnO 2 (P-CM) 295 (10 mVs 1 scan rate) 96

(200 mVs 1 )

283.63 kW kg 1 32.91 Wh kg 1 95.4% capacity retention after

2000 cycles

[65] Polyester textile/CNTs//CNT (T- CMC) e e e 62% at 12500th Cycle [65] Nanocomposite paper (CNT cellulose-RTIL) 36 1.5 kW kg 1 13 Wh kg 1 100th Cycles [66] Graphite/Ni/Co 2 NiO 4 -CP (cellulose paper)

(positive electrode) and graphite/Ni/AC-CP

(negative electrode)

1737 25.6 kW kg 1 80 Wh kg 1 <4% capacitance loss after

20000 Cycles

[67]

Graphene-cellulose paper (GCP) membranes 120 retains > 99% capacitance over

5000 cycles

[22] cellulose Nanofibril (CNF)/reduced graphene

oxide (RGO)/carbon nanotube (CNT) hybrid

aerogels

252 F g 1 at a discharge current density of 0.5 A g 1

9.5 mW cm 2 28.4mWh cm 2 >99.5% of the capacitance was

retained after 1000 charge discharge cycles at a current density of 1 A g 1

[68]

Meso-microporous carbon prepared by the

combination of a template method and

chemical activation with cellulose and

lignosulphonate

286 F g 1 at a current density of 0.25 A g 1

Cellulose Nanofibers (CNFs)/molybdenum

disulfide (MoS 2 )/reduced graphene oxide

(RGO) hybrid aerogel

916.42 F g 1 8.56 mW cm 2 45.7 mW h cm 2 >98% after 5000 charge

edischarge cycles at a current density of 0.5 mA cm 2

[70]

J Jose et al / Journal of Science: Advanced Materials and Devices xxx (xxxx) xxx 6

the electrolyte and electrochemical activities, carbon materials of

high specific surface area, high porosity and containing more

oxidative groups are required This improves its supercapacitive

behavior, particularly since the mesoporous structure of the carbon

nanofibers improves the uptake of the electrolyte solution and

simplifies the ion transport kinetics [53] Compared to the

poly-acrylonitrile or polybenzimidazole, nanocellulose is supposed to be a

better source of activated carbon because of its small size, unique

porous structure and it is sourcing from inexhaustible natural

re-sources[54] Furthermore, celluloses in nanoscale show the features

of the structural similarity and the ease of graphitization[55]

It has been shown that the electrical and chemical properties of

carbon nanomaterials can be tailored by the heteroatom

sub-stitutions, most importantly of Nitrogen, Phosphorus, Sulfur and

Iodine[56] These heteroatom-doped nanoscale carbon materials

have attracted immense attentions in energy storage device

ap-plications since it could increase the surface wettability, the

elec-trical conductivity and the electro-donor tendency [57,58]

Nitrogen, in particular, is considered to be capable of enhancing the

capacitance since N-containing functional groups can offer more

redox pseudo capacitance[59] A common approach adopted to

introduce nitrogen into carbon matrices is the pyrolysis of a carbon

precursor coated with nitrogen-containing polymer like PPy and

PANI An asymmetric supercapacitor was prepared by Chen et al

with bacterial cellulose derived carbon nanofiber/MnO2 and

nitrogen-doped carbon nanofiber as electrodes [60] In their

research, the carbon nanofiber obtained by the cellulose pyrolysis

at 1000C was dipped into an urea solution at 180C for 12 h to

develop nitrogen-doped composites Such a device had an

outstanding potential space of 2 V and provided an energy density

of 32.91 Whkg 1 Different hetero-atoms were further introduced

onto the cellulose derived carbon in their investigations[61]

Cel-lulose slices were immersed into H2PO4, NH4H2PO4 and H3PO4/

H3BO4to synthesize the doped; the N, co-doped; and the B,

P-co-doped carbon fibers, respectively, via the carbonization at

800C under N2 All elements were distributed evenly on the

car-bonfibers, as shown in Fig 10 As expected, the corresponding

supercapacitors exhibited good super capacitive performance

The performance of cellulose based supercapacitors based on

the previously reported data is summarized inTable 2

4 Outlooks and conclusion

The main focus of our review was to bring about a broad outlook

on the applications of nanocellulose based materials in energy

related areas in general and in supercapacitors in particular A

general picture of cellulose based functional materials is also

included in the review Definitely, challenges do exist and

signifi-cant research efforts are needed to overcome these challenges in

order to develop materials for sustainable applications A basic

understanding will definitely reveal the extraordinary application

potentials of cellulose nanomaterials in energy and environmental

applications As exemplified in this article, nanocelluloses hold an

incredible value and application potential as supercapacitors With

advanced preparation, processing and characterization techniques,

cellulose nanomaterials may soon become a significant and potent

multifunctional material with a huge potential for supercapacitor

applications

Conflicts of interest

The authors declare that there is no conflict of interest regarding

the publication of this paper

Acknowledgments The authors are thankful to The Science Engineering Research Board (SERB), Government of India forfinancial assistance in the form of research grant EMR/2017/000178

References [1] K Tan, S Heo, M Foo, I.M Chew, C Yoo, An insight into nanocellulose as soft condensed matter: challenge and future prospective toward environmental sustainability, Sci Total Environ 650 (2019) 1309e1326

[2] B Dunn, H Kamath, J.M Tarascon, Electrical energy storage for the grid: a battery of choices, Science 334 (2011) 928e935

[3] J.M Tarascon, M Armand, Issues and challenges facing rechargeable lithium batteries, Nature 414 (2001) 359e367

[4] M.M P
erez-Madrigal, M.G Edo, C Alem
an, Powering the future: application of cellulose-based materials for supercapacitors, Green Chem 18 (2016) 5930e5956

[5] H Nishide, K Oyaizu, Toward flexible batteries, Science 319 (2008) 737e738 [6] P Poizot, F Dolhem, Clean energy new deal for a sustainable world: from

non-CO 2 generating energy sources to greener electrochemical storage devices, Energy Environ Sci 4 (2011) 2003e2019

[7] Z Wang, P Tammela, M Strømme, L Nyholm, Cellulose-based super-capacitors: material and performance considerations, Adv Energy Mater 7 (2017) 1700130

[8] T Abitbol, A Rivkin, Y Cao, Y Nevo, E Abraham, T Ben-Shalom, et al., Nanocellulose, a tiny fiber with huge applications, Curr Opin Biotechnol 39 (2016) 76e88

[9] X Wang, C Yao, F Wang, Z Li, Cellulose-based nanomaterials for energy applications, Small 14 (2017) 1702240

[10] S Liu, D Tao, H Bai, X Liu, Cellulose-nanowhisker-templated synthesis of titanium dioxide/cellulose nanomaterials with promising photocatalytic abilities, J Appl Polym Sci 126 (2012) E282eE290

[11] M P€a€akk€o, J Vapaavuori, R Silvennoinen, H Kosonen, M Ankerfors,

T Lindstr€om, et al., Long and entangled native cellulose I nanofibers allow flexible aerogels and hierarchically porous templates for functionalities, Soft Matter 4 (2008) 2492e2499

[12] L Hu, G Zheng, J Yao, N Liu, B Weil, M Eskilsson, et al., Transparent and conductive paper from nanocellulose fibers, Energy Environ Sci 6 (2013) 513e518

[13] D Klemm, F Kramer, S Moritz, T Lindstr€om, M Ankerfors, D Gray, et al., Nanocelluloses: a new family of nature-based materials, Angew Chem Int.

Ed 50 (2011) 5438e5466 [14] X Yang, E.D Cranston, Chemically cross-linked cellulose nanocrystal aerogels with shape recovery and superabsorbent properties, Chem Mater 26 (2014) 6016e6025

[15] S.J Eichhorn, R.J Young, The Young's modulus of a microcrystalline cellulose, Cellulose 8 (2001) 197e207

[16] J Rojas, M Bedoya, Y Ciro, Current trends in the production of cellulose nanoparticles and nanocomposites for biomedical applications, Cellul Fun-dam Asp Curr Trends 8 (2015) 193e228

[17] A Tayeb, E Amini, S Ghasemi, M Tajvidi, Cellulose nanomaterialsebinding properties and applications: a review, Molecules 23 (2018) 2684

[18] A Russo, B.Y Ahn, J.J Adams, E.B Duoss, J.T Bernhard, J.A Lewis, Pen-on-paper flexible electronics, Adv Mater 23 (2011) 3426e3430

[19] L Nyholm, G Nystr€om, A Mihranyan, M Strømme, Toward flexible polymer and paper-based energy storage devices, Adv Mater 23 (2011) 3751e3769

[20] D Klemm, B Heublein, H.-P Fink, A Bohn, Cellulose: fascinating biopolymer and sustainable raw material, Angew Chem Int Ed 44 (2005) 3358e3393 [21] Y Wang, Y Song, Y Xia, Electrochemical capacitors: mechanism, materials, systems, characterization and applications, Chem Soc Rev 45 (2016) 5925e5950

[22] W Chen, H Yu, S.-Y Lee, T Wei, J Li, Z Fan, Nanocellulose: a promising nanomaterial for advanced electrochemical energy storage, Chem Soc Rev.

47 (2018) 2837e2872 [23] C Largeot, C Portet, J Chmiola, P.-L Taberna, Y Gogotsi, P Simon, Relation between the ion size and pore size for an electric double-layer capacitor,

J Am Chem Soc 130 (2008) 2730e2731 [24] S.G Kandalkar, D.S Dhawale, C.-K Kim, C.D Lokhande, Chemical synthesis of cobalt oxide thin film electrode for supercapacitor application, Synth Met.

160 (2010) 1299e1302 [25] J Cai, S Liu, J Feng, S Kimura, M Wada, S Kuga, et al., Celluloseesilica nanocomposite aerogels by in situ formation of silica in cellulose gel, Angew Chem Int Ed 51 (2012) 2076e2079

[26] X Zhang, Z Lin, B Chen, S Sharma, C Wong, W Zhang, et al., Solid-state, flexible, high strength paper-based supercapacitors, J Mater Chem 1 (2013) 5835e5839

[27] Y.J Kang, S.-J Chun, S.-S Lee, B.-Y Kim, J.H Kim, H Chung, et al., All-solid-state flexible supercapacitors fabricated with bacterial nanocellulose papers, carbon nanotubes, and triblock-copolymer ion gels, ACS Nano 6 (2012) 6400e6406

[28] K Gao, Z Shao, J Li, X Wang, X Peng, W Wang, et al., Cellulose

nanofiberegraphene all solid-state flexible supercapacitors, J Mater Chem 1

(2013) 63e67

[29] X Lu, M Yu, G Wang, Y Tong, Y Li, Flexible solid-state supercapacitors:

design, fabrication and applications, Energy Environ Sci 7 (2014) 2160e2181

[30] Y Gao, W Zhang, Q Yue, B Gao, Y Sun, J Kong, et al., Simple synthesis of

hierarchical porous carbon from Enteromorpha prolifera by a self-template

method for supercapacitor electrodes, J Power Sources 270 (2014) 403e410

[31] H Koga, H Tonomura, M Nogi, K Suganuma, Y Nishina, Fast, scalable, and

eco-friendly fabrication of an energy storage paper electrode, Green Chem 18

(2016) 1117e1124

[32] Y.N Sudhakar, D.K Bhat, M Selvakumar, Ionic conductivity and dielectric

studies of acid doped cellulose acetate propionate solid electrolyte for

supercapacitor, Polym Eng Sci 56 (2016) 196e203

[33] H Su, P Zhu, L Zhang, F Zhou, G Li, T Li, et al., Waste to wealth: a sustainable

and flexible supercapacitor based on office waste paper electrodes,

J Electroanal Chem 786 (2017) 28e34

[34] Z Weng, Y Su, D.-W Wang, F Li, J Du, H.-M Cheng, Grapheneecellulose

paper flexible supercapacitors, Adv Energy Mater 1 (2011) 917e922

[35] L Hu, J.W Choi, Y Yang, S Jeong, F La Mantia, L.-F Cui, et al., Highly

conductive paper for energy-storage devices, Proc Natl Acad Sci Unit States

Am 106 (2009) 21490e21494

[36] M Pasta, F La Mantia, L Hu, H.D Deshazer, Y Cui, Aqueous supercapacitors on

conductive cotton, Nano Res 3 (2010) 452e458

[37] W Liu, X Yan, J Lang, C Peng, Q Xue, Flexible and conductive nanocomposite

electrode based on graphene sheets and cotton cloth for supercapacitor,

J Mater Chem 22 (2012) 17245e17253

[38] X Yang, K Shi, I Zhitomirsky, E.D Cranston, Cellulose nanocrystal aerogels as

universal 3D lightweight substrates for supercapacitor materials, Adv Mater.

27 (2015) 6104e6109

[39] D Lee, Y.-G Cho, H.-K Song, S.-J Chun, S.-B Park, D.-H Choi, et al.,

Coffee-driven green activation of cellulose and its use for all-paper flexible

super-capacitors, ACS Appl Mater Interfaces 9 (2017) 22568e22577

[40] Y Shi, L Peng, Y Ding, Y Zhao, G Yu, Nanostructured conductive polymers for

advanced energy storage, Chem Soc Rev 44 (2015) 6684e6696

[41] C Li, H Bai, G Shi, Conducting polymer nanomaterials: electrosynthesis and

applications, Chem Soc Rev 38 (2009) 2397e2409

[42] S Li, D Huang, J Yang, B Zhang, X Zhang, G Yang, et al., Freestanding

bac-terial celluloseepolypyrrole nanofibres paper electrodes for advanced energy

storage devices, Nano Energy 9 (2014) 309e317

[43] H Wang, L Bian, P Zhou, J Tang, W Tang, Coreesheath structured bacterial

cellulose/polypyrrole nanocomposites with excellent conductivity as

super-capacitors, J Mater Chem A 1 (2013) 578e584

[44] E Lago, P.S Toth, G Pugliese, V Pellegrini, F Bonaccorso, Solution blending

preparation of polycarbonate/graphene composite: boosting the mechanical

and electrical properties, RSC Adv 6 (2016) 97931e97940

[45] H.O Pierson, Handbook of Carbon, Graphite, Diamonds and Fullerenes:

Pro-cessing, Properties and Applications, William Andrew, 2012

[46] X Wu, J Tang, Y Duan, A Yu, R.M Berry, K.C Tam, Conductive cellulose

nanocrystals with high cycling stability for supercapacitor applications,

J Mater Chem A 2 (2014) 19268e19274

[47] K Gao, Z Shao, X Wang, Y Zhang, W Wang, F Wang, Cellulose nanofibers/

multi-walled carbon nanotube nanohybrid aerogel for all-solid-state flexible

supercapacitors, RSC Adv 3 (2013) 15058e15064

[48] W Zhang, Y Zhang, C Lu, Y Deng, Aerogels from crosslinked cellulose nano/

micro-fibrils and their fast shape recovery property in water, J Mater Chem.

22 (2012) 11642e11650

[49] X Zhang, Z Lin, B Chen, W Zhang, S Sharma, W Gu, Y Deng, Solid-state

flexible polyaniline/silver cellulose nanofibrils aerogel supercapacitors,

J Power Sources 246 (2014) 283e289

[50] L Dai, D.W Chang, J.-B Baek, W Lu, Carbon nanomaterials for advanced

energy conversion and storage, Small 8 (2012) 1130e1166

[51] L.-F Chen, X.-D Zhang, H.-W Liang, M Kong, Q.-F Guan, P Chen, et al., Synthesis of nitrogen-doped porous carbon nanofibers as an efficient elec-trode material for supercapacitors, ACS Nano 6 (2012) 7092e7102 [52] J Cai, H Niu, Z Li, Y Du, P Cizek, Z Xie, et al., High-performance super-capacitor electrode materials from cellulose-derived carbon nanofibers, ACS Appl Mater Interfaces 7 (2015) 14946e14953

[53] V Kuzmenko, A.M Saleem, H Staaf, M Haque, A Bhaskar, M Flygare, et al., Hierarchical cellulose-derived CNF/CNT composites for electrostatic energy storage, J Micromech Microeng 26 (2016) 124001

[54] Z.-Y Wu, C Li, H.-W Liang, J.-F Chen, S.-H Yu, Ultralight, flexible, and fire-resistant carbon nanofiber aerogels from bacterial cellulose, Angew Chem.

125 (2013) 2997e3001 [55] L Deng, R.J Young, I.A Kinloch, A.M Abdelkader, S.M Holmes, D.A De Haro-Del Rio, et al., Supercapacitance from cellulose and carbon nanotube nano-composite fibers, ACS Appl Mater Interfaces 5 (2013) 9983e9990 [56] D Jana, C.-L Sun, L.-C Chen, Kuei-Hsien Chen, Effect of chemical doping of boron and nitrogen on the electronic, optical, and electrochemical properties

of carbon nanotubes, Prog Mater Sci 58 (2013) 565e635 [57] B Xu, D Zheng, M Jia, G Cao, Y Yang, Nitrogen-doped porous carbon simply prepared by pyrolyzing a nitrogen-containing organic salt for supercapacitors, Electrochim Acta 98 (2013) 176e182

[58] J Han, G Xu, B Ding, J Pan, H Dou, D.R MacFarlane, Porous nitrogen-doped hollow carbon spheres derived from polyaniline for high performance supercapacitors, J Mater Chem 2 (2014) 5352e5357

[59] X.Y Chen, C Chen, Z.J Zhang, D.H Xie, X Deng, Nitrogen-doped porous carbon prepared from urea formaldehyde resins by template carboniza-tion method for supercapacitors, Ind Eng Chem Res 52 (2013) 10181e10188

[60] L.F Chen, Z.-H Huang, H.-W Liang, Q.-F Guan, S.-H Yu, Bacterial-cellulose-derived carbon nanofiber@ MnO2 and nitrogen-doped carbon nanofiber electrode materials: an asymmetric supercapacitor with high energy and power density, Adv Mater 25 (2013) 4746e4752

[61] L.F Chen, Z.-H Huang, H.-W Liang, H.-L Gao, S.-H Yu, Three-dimensional heteroatom-doped carbon nanofiber networks derived from bacterial cellu-lose for supercapacitors, Adv Funct Mater 24 (2014) 5104e5111 [62] G Chen, T Chen, K Hou, W Ma, M Tebyetekerwa, Y Cheng, et al., Hydrophilic graphene/cellulose nanocrystal fiber-based electrode with high capacitive performance and conductivity, Carbon 127 (2018) 218e227

[63] K.K Liu, Q Jiang, C Kacica, H.G Derami, P Biswas, S Singamaneni, Flexible solid-state supercapacitor based on tin oxide/reduced graphene oxide/bac-terial nanocellulose, RSC Adv 8 (2018) 31296e31302

[64] Y Yang, C Chen, D Li, Electrodes based on cellulose nanofibers/carbon nanotubes networks, polyaniline nanowires and carbon cloth for super-capacitors, Mater Res Express 6 (2018) 035008

[65] Z Gui, H Zhu, E Gillette, X Han, G.W Rubloff, L Hu, S.B Lee, Natural cellulose fiber as substrate for supercapacitor, ACS Nano 7 (2013) 6037e6046 [66] V.L Pushparaj, M.M Shaijumon, A Kumar, S Murugesan, L Ci, R Vajtai, et al., Flexible energy storage devices based on nanocomposite paper, Proc Natl Acad Sci Unit States Am 104 (2007) 13574e13577

[67] J.X Feng, S.H Ye, A.L Wang, X.F Lu, Y.X Tong, G.R Li, Flexible cellulose paper-based asymmetrical thin film supercapacitors with high-performance for electrochemical energy storage, Adv Funct Mater 24 (2014) 7093e7101

[68] Q Zheng, Z Cai, Z Ma, S Gong, Cellulose nanofibril/reduced graphene oxide/ carbon nanotube hybrid aerogels for highly flexible and all-solid-state supercapacitors, ACS Appl Mater Interfaces 7 (2015) 3263e3271 [69] Z Zhao, S Hao, P Hao, Y Sang, A Manivannan, N Wu, et al., Lignosulphonate-cellulose derived porous activated carbon for supercapacitor electrode,

J Mater Chem 3 (2015) 15049e15056 [70] Y Lv, L Li, Y Zhou, M Yu, J Wang, J Liu, et al., A cellulose-based hybrid 2D material aerogel for a flexible all-solid-state supercapacitor with high specific capacitance, RSC Adv 7 (2017) 43512e43520

J Jose et al / Journal of Science: Advanced Materials and Devices xxx (xxxx) xxx 8