Nitesh
Choudhary
ab,
Shiva
Singh
a,
Gaurav
Malik
b,
Shakshi
Bhardwaj
a,
Siddharth
Sharma
b,
Akshay
Tomar
b,
Sheetal
Issar
b,
Ramesh
Chandra
*b and
Pradip Kumar
Maji
*a
aDepartment of Polymer and Process Engineering, Indian Institute of Technology Roorkee, Saharanpur Campus, Saharanpur-247001, India. E-mail: Ramesh.chandra@ic.iitr.ac.in; Tel: +91-9897031912
bInstitute Instrumentation Centre, Indian Institute of Technology, Roorkee 247667, India. E-mail: pradip@pe.iitr.ac.in; Tel: +91-7895965010
First published on 2nd July 2024
Adopting a green and environmentally friendly strategy requires the development of supercapacitor electrodes using sustainable, renewable, and environmentally beneficial materials. Chemically stable and renewable cellulose-based supercapacitors need high-quality carbon materials with excellent mechanical and electrical characteristics to create a three-dimensional network-based electrode. Nevertheless, using cellulose as a supercapacitor electrode with enhanced electrochemical characteristics presents a difficulty. This paper describes creating and producing electrodes for supercapacitors using nano-composites consisting of wrapped-around single-walled carbon nanotubes to improve performance. The electrode's optimal electrochemical characteristics were achieved by using a concentration of 9 wt% MACNC/CNT nanocomposites. The proposed electrode material for the MACNC-based flexible supercapacitor assembly demonstrates outstanding electrochemical stability and effective electrochemical performance. When tested in a three-electrode cell configuration, it achieves an areal capacitance of 1389.202 mF cm−2 at a current density of 0.02 A cm−2, with 74.6% cyclic retention after 12000 cycles. This study effectively converted agricultural waste into high-performing supercapacitor electrodes using a simple and cost-efficient method. This innovative design and outstanding electrochemical performance show great promise in using environmentally friendly materials to improve nanocellulose-based sustainable energy storage systems.
The electrochemical and structural properties of their electrode materials significantly impact the key features of energy storage devices. While activated carbon (AC) is commonly used as the electrode material in energy storage devices, its commercialization has been hindered by low energy and power densities caused by high equivalent series resistance.3 The energy and power densities of commercially available electrochemical capacitors based on AC electrodes are thus restricted to 1 to 10 W h kg−1 and 2 to 10 kW kg−1, respectively. To enhance the energy and power densities of SCs, single-walled carbon nanotubes (SWCNTs) offer a promising alternative as electrode materials. CNTs possess excellent conductivity, significant specific surface area, low mass density, and remarkable mechanical strength.4 Furthermore, cellulose exhibits remarkable physical/chemical/thermal properties that make it suitable for various applications in energy, sensors, medical devices, transistors, actuators, electric heaters, electromagnetic interference (EMI) shielding materials, and hybrid applications, particularly in the nanoscale domain.5–10
Additionally, it possesses exceptional mechanical properties and abundant active sites.11 These qualities make it a promising candidate for acting as a binder or active material when combined with different electrochemical constituents.12,13 It has become a trend to utilize waste materials for high-end applications, taking the context of sustainability and economic viability into account. Such waste materials are generally rich in cellulose content, which can be utilized for versatile applications.
Utilizing biomass-derived carbon materials as binder-free, freestanding electrodes is a particularly promising approach, as it eliminates the need for additional inactive components and enables high mass loading while maintaining excellent electrochemical properties.14 Cellulose is a natural, renewable, and biodegradable material, making cellulose-based binders an environmentally friendly alternative to conventional binders like polyvinylidene difluoride (PVDF), which is essential for sustainable energy solutions by minimalizing the use of different hazardous chemicals and offering a more biocompatible alternative to conventional polymers for energy storage devices.15 Recently, Guo et al. observed a simple yet effective method for bonding binders and electrolytes, which remarkably improved the cycle stability of high-capacity anodes utilizing K+ ions.16
The CNF binder retains BN-Ac's micropores and improves wettability, while the PVDF binder fills micropores and hinders ion-conductive pathways. The as-synthesized BN-Ac/CNF exhibits a capacitance of 268.4 F g−1 at 5 A g−1, which is 1.4 times higher than that of BN-Ac/PVDF. In addition, the energy/power density improves for replacing PVDF with CNF and outstanding capacitance and decreased bulk electrolyte resistance application of CNF in energy devices.17
Their mechanical characteristics, including their flexibility and tensile strength, also contribute to the improved cyclic performance of SC electrodes. The strong hydrogen bonding network within the CNC helps maintain the electrode's structural integrity during charge–discharge cycles, leading to enhanced stability and longer lifespan.18 Han et al. observed that upon surface coating of the PANI shell, the proposed PANI@CNT–CNC/PVA–PAA nanofibrous membranes show a large porosity, excellent tensile strength of ∼54.8 MPa, and an electroconductivity of ∼0.44 S m−1 and capacitance of 164.6 F g−1 with 91% retention after 2000 cycles.19
When cellulose is defined as having at least one dimension less than 100 nm, it is referred to as nanocellulose (NC). It can be obtained from various sources, including bio, agricultural, and plant wastes.20 Using top-down synthetic approaches involving various chemical and physical procedures, NC can be produced from cellulose-rich biomass, such as pea hull waste, pineapple peel,12,20 areca nut husk,21 cotton,22 and many more.23
The remarkable flexibility, affordable cost, renewable nature, and environmental friendliness of cellulose make it a crucial component in developing diverse electrode materials, separators, and electrolytes for flexible SCs.9,24 As an electrode material, hydrophilic NC prevents the aggregation of active materials like CNT and enhances electrode wettability for absorbing liquid electrolytes. As a separator, NC creates a porous structure that allows electrolyte ions to move more efficiently, increasing energy storage efficiency. Islam et al. proposed NC as a separator material in their study because of its strong ion conductivity and weak electron conductivity. The transport of electrolyte ions is facilitated by the porous structure created by NC acting as a separator, increasing energy storage efficiency.25
Besides serving as an electrode and separator, NC also exhibits excellent potential as an electrolyte. Recently, Chen et al. reported that hydrogel electrolytes with excellent mechanical performance, good repairability, adhesion ability, and promising electrochemical performance could be obtained using hydrophobic interactions.26 Overall, cellulose is a very promising material for improving the efficiency and environmental sustainability of SCs because of its availability, porosity, mechanical strength, biocompatibility, ion conductivity, and sustainability.
Utilizing agricultural waste materials to extract NC offers a viable waste management and environmental protection approach. NC, upon its surface tuning with charged moieties, exhibits favorable characteristics that render it suitable for various electrochemical and energy storage applications. The reactive surfaces, abundant in –OH groups, offer several hybridization possibilities with other active materials for creating composite electrodes/separators/electrolytes based on nanocellulose. Hence, NC is a desirable material for flexible energy storage devices.27 Its carbon content, high aspect ratios, and ease of surface modification make it an excellent starting material for producing carbon electrodes with large pore structures, surface areas, and adjustable microstructures.28 On the other hand, NC has also been discovered to contribute to achieving an advanced specific capacitance of the nano-composite electrodes by reducing the stacking of nanosheets and facilitating the ion movement of electrolytes.29
Additionally, it is a strong support in the arrangement of CNT sheets. Besides these qualities, the combination results in decreased electrode conductivity, requiring additional modifications to offset the loss of conductivity. To meet this requirement, it is crucial to have an ideal concentration of modified CNC and CNT, as conducting polymers (rGO) can enhance the conductivity of active materials and introduce pseudo-capacitance.30 This incorporation effectively mitigates the restacking of CNT sheets, improving the interaction between the electrode and electrolyte. Consequently, such an approach enables the attainment of superior electrochemical performance.
Researchers have explored various surface modification techniques to improve CNC's conductivity and electrochemical performance, like TEMPO-mediated oxidation to introduce carboxylic groups on the CNC surface and sulfonation, acetylation, and silylation to further functionalize the CNC surface.31 These surface alterations enhance the compatibility and interaction between CNC and conductive polymers or other active materials in electrode composites. The novelty of the preparation method is the modification of cellulose by an MA moiety and incorporation with an SWCNT sheet, its use of a hybrid composite as an electrode composite with the CNT sheet, and the assessment of the proposed composites' electrochemical performance and thermal stability.
In this study, a novel renewable, eco-friendly, cost-effective, and agriculture-waste-based electrode, which does not contain any binders, i.e. a binder-free electrode, is fabricated for application in supercapacitors. The fabrication includes coating the SWCNT using MA-modified CNC. This combination prevents the stacking of CNT sheets, establishes a framework for arranging them, and incorporates pseudo-capacitance. The optimized concentration of binary nano-composites (9 wt% MACNC/SWCNT) had the best electrochemical properties. CNT can also raise the thermal stability and conductivity of the material.32 This study converts waste materials into efficient electrode materials and enhances the electrochemical properties of CNC-based SC electrodes derived from agricultural waste. The electrochemical performance of the produced MACNC/SWCNT ternary nano-composite was assessed as an electrode material for SCs using 1 M Li2SO4 electrolyte. This allows for the creation of eco-friendly and cost-effective electrodes for high-performance SCs.
Fig. 1 (a) Modification of CNC with maleic anhydride via a chemical process. (b) Proposed reaction scheme of maleic anhydride (MA) grafted on cellulose and MACNC. |
The dry powder of the extracted CNC (1.0 g) was dissolved in 20 ml DMF using a bath sonicator to modify their surface using maleic anhydride (MA). After adding 8.0 g of MA sample to the suspension, it was stirred for about half an hour, or until the MA completely dissolved. The surface tuning was done for 7–8 h with continuous stirring in an oil bath at 110 °C. The mixture was stirred for two hours before being centrifuged for twenty minutes at 8000 rpm after the reaction, and 100 ml of ethanol was added. After recovering the sediment, it was re-diluted with 150 ml of purified ethanol. Three further centrifugal cleanses were carried out to eliminate any remaining unreacted MA and DMF. Lastly, distilled water was used to disperse the MACNC which was then freeze-dried. Fig. 1(a) depicts the suggested reaction route for MA modification, and Fig. 1(b) predicts the chemical reaction between cellulose and MA and synthesized MACNC.
The electrode was fabricated using the following procedure: synthesis of MACNC solution, electrode dip-coating, drying, and sample preparation. The first step involved the synthesis of a modified cellulose nanocrystal (MACNC) solution. A specific area of the electrode was then dipped overnight in various concentrations of the MACNC solution. The MACNC solution was subjected to constant magnetic stirring for 2 h during this process. After the overnight dipping, the electrode samples were removed from the MACNC solution and placed in an oven for drying. The dried electrode samples were then ready for further use and characterization as shown in Scheme 1, which illustrates an electrode fabrication scheme with different wt% and then evaluates their electrochemical measurements for optimization.
Scheme 1 Illustration of an electrode fabrication scheme with different composites and their electrochemical measurements. |
The voltage range for CV was −0.6 V to +0.6 V, i.e., the potential window is 1.2 V, with several scan rates used. The specific capacitance, power/energy density, and cyclic efficiency were determined by eqn (S1)–(S3)† mentioned in ESI† sections. Due to its strong ionic character, 1 M Li2SO4 solution was used as the electrolyte for the experimental work.
The hydrophilicity of the membranes was increased by incorporating CNC or functionalized CNTs, which could also impact the surface characteristics of the MA-grafted CNC/CNT composite. In combination with CNC-based electrode materials, further research is needed to investigate the performance of other electrolyte types, such as organic solvents, ionic liquids, and solid-state electrolytes. The search results indicate that aqueous electrolytes like Li2SO4, sodium sulfate (Na2SO4), and potassium sulfate (K2SO4) have been explored for CNC-based electrodes. The performance of these aqueous electrolytes is influenced by the mobility and size of the alkali metal ions, with Li+ exhibiting the best capacitance and charge propagation properties. Aqueous electrolytes can provide good ionic conductivity and compatibility with CNC-based electrodes, making them a suitable choice.
Fig. 2 (a) ATR-FTIR spectra; (b) X-ray diffraction (XRD) results of cellulose nanocrystals (CNC) and maleic anhydride cellulose nanocrystals (MACNC). |
The intensity of the anomeric carbon (C–H) vibration of β-glycosidic links between the cellulose units at 897 cm−1 reduces from CNC to MACNC after the chemical alteration, and it does not overlap, in contrast to C–Hn (n = 1, 2) stretching. This is attributed to the sensitivity of the gluco pyranose ring to change in pendant groups, which indicates the chemical structural change on modification. Indeed, a strong appearance of intense change in transmittance at 1720 cm−1 in MACNC corresponds to the carboxyl group (–O–CO), establishing the formation of ester linkage on the surface of cellulose molecules.39 Additionally, upon modification with MA, the vinyl group (CC) is responsible for the peak at 1634 cm−1. These findings show that MA may be successfully grafted onto the CNC surface.
The CNT sample images showed that the CNT assembled to form a 3D network with high porosity and excellent conductivity. To make it sustainable and sustain its porosity, the FESEM images of the CNC/CNT composite are also presented in Fig. 3. For the MACNC/CNT composite, better wrapping of MACNC over CNT sheets can be observed, which confirms the uniform and homogeneous interaction between them. It shows a unique 3D network topology with high porosity and excellent physical and mechanical durability. The high level of MACNC adhesion on the CNT's surface makes it promising for practical applications. According to the findings, CNTs' hydrophobic and poor solubility characteristics cause them to clump together (aggregate) and entangle.43 The entangled nanotubes in these CNT aggregates create vacant regions that are difficult for a viscous fluid to disperse. The CNC/CNT composites reveal that due to the incorporation of cellulose on the CNT surface, they are not fully covered. Still, in the composite with 9 wt% MACNC, as presented in Fig. 3(a–e), the nanosheets are covered entirely and uniformly with MACNC. Further addition of MACNC may become extra layers on the already attached cellulose on the CNT surface, disturbing the surface homogeneity.
The components that are present in the samples have been identified through the use of energy-dispersive X-ray (EDX) analysis. The cellulose and composite sheet's EDX spectra reveal two prominent O and C peaks (as seen in Fig. 3(f–h)).
The low mass/volume energy density, poor cycle stability, and limited capacitance of CNC/CNT electrode materials make them unsuitable for large-scale applications. As a result, several research studies have effectively enhanced the electrochemical efficiency of the SC by creating richer pore architectures, raising the specific surface area, and combining it with pseudo-capacitive materials. Furthermore, adding conductive materials can improve the electrolyte's adsorption capacity and lower the interface resistance between the electrode and the electrolyte, improving the electrode's electrochemical stability, rate, and cycle stability.42
Thus, the modification of cellulose with MA is required to improve performance. We attribute the MACNC/CNT-based electrode's superior capacitance performance to (i) high active-material mass loadings, (ii) the freestanding electrode's high active surface area, which offers more redox sites for charge storage, (iii) the increased interfacial contact between the porous surface and the electrolyte, (iv) the excellent wettability of the electrode, and (v) the high electrochemical performance, which facilitated quick charge transport. The amount of material deposited on the CNT film was evaluated by measuring the weight of the SWCNT sheet film before and after the MACNC deposition. The weight percentage of MACNC (WMACNC%) was estimated at ∼70%, and mass loading is 25.34 mg on the surface of the (1 cm × 1 cm) CNT sheet, as discussed in the ESI† of the revised manuscript. Further, the thickness of active material loading on the proposed 9 wt% MACNC/CNT films is 20–30 μm and typically measured using cross-sectional analysis techniques, such as SEM, as shown in Fig. S4† in the ESI,†i.e., SEM cross-section of the 9 wt% MACNC/CNT proposed electrode material.
The proposed electrode material shows good capacitive behavior and electrochemical performance compared to CNC/CNT and CNT electrodes, EIS, CV, and GCD, and the graph between scan rate and energy density is shown in Fig. 4. The graph between the scan rate and specific capacitance of all the prepared electrode samples is displayed in Fig. S5† in the ESI.†
In addition, the Nyquist plot was plotted using EIS to examine the prepared nano-composite ion diffusion and charge transport behavior. As the Nyquist plot reveals, the X-axis indicates the resistive behavior, while the slope represents the excellent capacitance performance of the electrodes. Here, the observed plot illustrates that the as-prepared MACNC/CNT composite shows outstanding charge transfer ability in comparison to the two other samples of CNC, as shown in Fig. 4. Furthermore, at low frequencies, the sloping line of the prepared electrode suggests an approximately ideal capacitive behavior. The lower resistance and more significant slope indicated that the composite electrode possesses superior electrochemical performance than the others. The electrochemical properties, including areal capacitance and energy density, of CNT, CNC/CNT, and MACNC at a scan rate of 0.002 V s−1 are represented in Table 1.
Electrode sample | Scan rate (V s−1) | Areal capacitance (mF cm−2) | Energy density (μW h cm−2) |
---|---|---|---|
CNT | 0.02 | 441.798 | 88.3596 |
CNC/CNT | 0.02 | 320.88 | 64.176 |
MACNC/CNT | 0.02 | 644.46 | 128.892 |
For the CV curves, all the curves showed analogous rectangle shapes, indicating that the composite (MACNC/CNT) sample exhibited superior pseudo-capacitance in comparison to others, which can also be proved by CV, GCD, and EIS curves (Fig. 4). In addition, this composite also provides a noticeable areal capacitance and energy density of 270.8903 mF cm−2 and 54.1780 mW h cm−2 at a current density of 0.005 A cm−2 respectively. In contrast, the CNC/CNT electrode shows the areal capacitance of 138.9813 mW h cm−2 and 64.176 μW cm−2 at the same current density. This result illustrates that the proposed MACNC/CNT composite shows the best electrochemical performance for SC applications.
Finally, the outstanding electrochemical characteristics of the proposed MACNC/CNT electrode may be attributed to the combined effect of several reasons like the superficial electron transportation due to reversible redox reactions of SWCNT and MACNC, the removal of the restacking tendency of SWCNT by incorporating cellulose, resulting in a conductive and porous 3D network microstructure based composite electrode, because cellulose-based materials produce a suitable diffusion pathway for the ions of electrolyte, resulting in overall superior electrochemical performance of the supercapacitive composite electrode.
Fig. 5 CV curve of the (a) 3 wt%, (b) 6 wt%, (c) 9 wt%, and (d) 12 wt% MACNC/CNT at different scan rates, namely 0.01 V s−1, 0.02 V s−1, 0.05 V s−1, 0.1 V s−1, 0.2 V s−1 and 0.5 V s−1. |
The further addition of MACNC varied from 3 wt% to 12 wt%. The decrement of electrochemical performance beyond 9 wt% and excellent areal and specific capacitance comes at optimum 9 wt% MACNC/CNT, as displayed in Fig. 5(a–d).
The fabrication of 9 wt% MACNC to CNT surfaces has been observed to exhibit exceptional electrochemical behavior due to factors such as strong interaction modified CNC and CNTs leading to a more stable and uniform distribution of CNTs within the MACNC matrix,47 enhanced mechanical/thermal properties of the CNT-based nano-composites,47–49 optimized porosity and high surface area,50 which facilitates the adsorption of electrolyte ions thereby enhancing the performance.51 These findings suggest that the 9 wt% cellulose content may be an optimal choice, and the optimal charge transfer can be attributed to the synergistic effect of MACNC and CNTs, which can lead to enhanced electrochemical performance, as shown in Fig. 5(c).
The detailed calculation in tabulated form as area, capacitance, and energy density of other wt% has been provided in Tables S2–S5 of the ESI section S3.† The electrochemical performance of 9 wt% MACNC/NCT was examined by CV/GCD curves of these samples, which were recorded at different scan rates and current density, respectively, using an aqueous 1 M Li2SO4 electrolyte, as depicted in Fig. 6(a and b). The graph between power density and current density, the relation between energy density and power density (Ragone plot), and the graph of energy density with current density and scan rate, as shown in Fig. 6(c–f) and Table 2, show the calculated value of areal capacitance and energy density from cyclic voltammetry. Notably, all the analyzed samples exhibited symmetrical and analogous rectangular curves, which indicate the possession of fast reaction kinetics. Direct mixing of CNT and MACNC forms a porous matrix that facilitates electrolyte infiltration and improves electronic conduction.
9 wt% CV scan rate (V s−1) | Area | Capacitance (mF cm−2) | Energy density (μW h cm−2) |
---|---|---|---|
0.005 | 0.00579 | 1389.202 | 277.84032 |
0.01 | 0.00532 | 638.9299 | 127.78598 |
0.02 | 0.00906 | 543.44243 | 108.68849 |
0.05 | 0.01264 | 303.46244 | 60.69249 |
0.1 | 0.01408 | 169.00158 | 33.80032 |
0.2 | 0.01508 | 90.46439 | 18.09288 |
Furthermore, the redox peaks observed in CV curves indicate the co-existence of electric double-layer capacitive behavior and pseudo-capacitance. The proposed electrodes showed a specific capacitance of 62 F g−1 at a current density of 0.005 A g−1, and the gravimetric power density and energy density are 819 W kg−1 and 14.8 W h kg−1, respectively. Further, the electrode exhibited a maximum areal capacitance of 1389.202 mF cm−2 with a voltage window of 1.2 V calculated from curves.
It has been observed that 9 wt% MACNC/CNT gave the best electrochemical performance due to the synergistic effect of the carboxylic group on the surface of cellulose (MACNC) and high surface area of CNT, enhancing the overall faradaic performance of the electrode material.
The presence of the –COOH group can improve the wettability of the electrode and promote better ion transport. At the same time, the CNT sheet can provide a conducive environment for efficient electron transport in the system. The intercalation of Li+ ions with the composite from the 1 M Li2SO4 electrolyte can also influence the faradaic mechanism. Fig. 7(a and b) illustrate the chemical structure of MACNC and adsorption mechanisms involving Li ions on the material surface and the carboxylic acid group of MACNC. The possible proposed mechanism of the carboxylic group present on the surface of the cellulose nanocrystals and CNTs with the Li2SO4 electrolyte is shown in Fig. 7.
Following the GCD curves, all the samples displayed almost symmetrical triangular shapes, indicating the materials' reversible electrochemical process. This is a clear indication of excellent capacitance behavior. The capacitance and power density at 0.02 A cm−2 current density were calculated from GCD curves to be 34.88167 mF cm−2 and 12000 μW cm−2, respectively, and at a current density of 0.05 A cm−2, capacitance and power density were 68.72 mF cm−2 and 30000 μW cm−2 respectively. Furthermore, the charge/discharge curve also suggested the highly reversible redox reaction-based faradaic pseudo-capacitance behavior, which originated from the addition of MACNC.
The above section shows the graph obtained from the above-mentioned table, which shows the energy density of the proposed 9 wt% MACNC/CNT electrode at various scan rates.
The development of high-performance energy storage materials is crucial for the advancement of renewable energy technologies. Modified CNC has emerged as a promising candidate for enhancing the electrochemical properties of CNT or other composites. This research study investigates the optimal ratio of MACNC/CNT for electrochemical performance. It discusses the results in the context of existing literature, as shown in Table S6† (in the ESI). Table S6† and Fig. 8 present a comparison of the electrode materials used, as well as their areal capacitance, energy, and power density at several scan rates and current densities, with the present study and other materials that have been previously described.
Fig. 8 Radar (spider plot) comparison plot of the MACNC/CNT hybrid sheet composite with other works in the literature. |
An essential way to assess an electrode's electrochemical performance and appropriateness for SC usage is through cycle performance analysis. Using GCD experiments at a current density of 0.02 A cm−2, the cycling stability of 9 wt% MACNC/CNT was assessed. As depicted in Fig. 9, the capacitance efficiency, retention ratio, or coulombic efficiency (%) versus cycle number for the 9 wt% MACNC/CNT electrode was 74.6% after 12000 cycles. In this regard, cellulose, a naturally occurring, renewable, nontoxic polymer, has offered a cohesive, durable, and mechanically stable electrode structure with less electrode cracking or delamination during cycling.
The initial ∼2 wt% loss between 140 and 240 °C can be attributed to the evaporation of tightly bound moisture to the carboxyl groups and the decarboxylation of substituted maleic anhydride in the disordered regions,52,53 which can be corroborated by the decrement of the crystallinity index (C. I.) of MACNC from the XRD analysis. The DTA curve reached a steady state between 240 and 250 °C before the accelerated decomposition began at 250 °C. The maximum weight loss between 250 and 400 °C corresponds to the depolymerization and cleavage of glycosidic linkages of cellulose with a maximum degradation temperature of 320 °C. The single ultimately synthesized MACNC and deprivation of CNC indicate a controlled degree of substitution and narrow size distribution of nanocellulose, as displayed in Fig. S7† thermal stability – TGA and DTG curves of CNC and MACNC and Fig. S8† thermal stability – TGA and DTG curves of CNT (blue color), CNC/CNT (pink color), and MACNC/CNT (green color), in the ESI.† Using traditional H2SO4 improves the suspension stability at the expense of thermal stability, differentiating between the ordered and amorphous regions, leading towards a wide distribution spread, which constrained the nanocrystals for thermal applications. With HCl, the nanocrystals are not distinguished into two areas of thermal degradation and exhibit a higher C. I. with a narrow distribution.54,55 Somseemee et al. modified the CNC with maleic anhydride, which was extracted from H2SO4, which displayed a two-stage degradation between 220 and 300 °C and 330 and 400 °C with two DTA peaks at 270 and 350 °C, which is in agreement with the statements mentioned above.56
The extracted CNC has exhibited a single-step degradation, unlike the CNC isolated through H2SO4, which displays a multi-stage degradation profile.57 The isolated CNC via HCl showed a relatively higher onset temperature (250 °C) than CNC extracted through H2SO4. Unlike CNC from H2SO4, the maximum degradation temperature (351 °C) with a maximum weight loss of 86 wt% was in the region between 250 and 400 °C. This can be attributed to the absence of sulfate groups (–OSO3−), which decreases activation energy for pyrolysis. However, CNC modified with the MA moiety displayed a multi-step degradation with two peaks in the DTA curve at 144 °C and 322 °C. Eventually, the residual char of MACNC and CNC is 2 wt% and 7 wt%, respectively, and the DTA peak at 555 °C could correspond to the degradation of interior nanocrystals, which are not modified.
MACNC | Maleic anhydride-tuned cellulose nanocrystals |
SWCNT | Single-walled carbon nanotubes |
EES | Electrochemical energy storage |
SC | Supercapacitors |
AC | Activated carbon |
EMI | Electromagnetic interference |
NC | Nanocellulose |
CNT | Carbon nanotubes |
rGO | Reduced graphene oxide |
CNC | Cellulose nanocrystals |
MA | Maleic anhydride |
EIS | Electrochemical Impedance Spectroscopy |
HCl | Hydrochloric acid |
CPC | Chemically purified cellulose |
DMF | Dimethyl formamide |
CV | Cyclic voltammetry |
GCD | Galvanostatic charge–discharge |
FE-SEM | Field emission scanning electron microscopy |
C. I. | Crystallinity index |
AFM | Atomic force microscopy |
TGA | Thermal gravimetric analysis |
RMS | Root Mean Square |
ATR-FTIR | Attenuated total reflectance-Fourier-transform infrared spectroscopy |
Ag/AgCl | Silver/silver chloride |
XRD | X-ray diffraction |
R sk | Skewness |
R ku | Kurtosis value |
EDX | Energy dispersive X-ray spectroscopy |
DTA | Derivative thermogravimetry |
C s | Specific capacitance |
PVDF | Polyvinylidene difluoride |
BN-Ac/CNF | Binders for biochar/cellulose nanofiber |
PVA–PAA-PANI | Poly(vinyl alcohol)/poly(acrylic acid) |
Footnote |
† Electronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d4se00286e |
This journal is © The Royal Society of Chemistry 2024 |