Sustainable Materials for Electrochemcial Capacitors E-Book

• Herausgeber: John Wiley & Sons
• Kategorie: Fachliteratur
• Sprache: Englisch

Seitenzahl: 975

Veröffentlichungsjahr: 2023

Beschreibung

Sustainable Materials for Electrochemical Capacitors The book highlights the properties of sustainable materials for the production of commercial electrochemical capacitors. Sustainable Materials for Electrochemical Capacitors details the progress in the usage of ubiquitous environmentally sustainable materials. Due to their cost effectiveness, flexible forms, frequent accessibility, and environmentally friendly nature, electrochemical capacitors with significant surface areas of their carbon components are quite common. Many novel ways for using bio-derived components in highly efficient electrochemical capacitors are being established as a consequence of current research, and this book provides details of all these developments. The book provides: * A broad overview of properties explored for the development of electrochemical capacitors; * Introduces potential applications of electrochemical capacitors; * Highlights sustainable materials exploited for the production of electrochemical capacitors; * Presents commercial potential of electrochemical capacitors. Audience This is a useful guide for engineers, materials scientists, physicists, and innovators, who are linked to the development and applications of electrochemical capacitors.

Leseprobe

Scrivener Publishing100 Cummings Center, Suite 541JBeverly, MA 01915-6106

Publishers at ScrivenerMartin Scrivener ([email protected])Phillip Carmical ([email protected])

Sustainable Materials for Electrochemical Capacitors

Edited by

Inamuddin

Department of Applied Chemistry, Aligarh Muslim University, Aligarh, India

Tariq Altalhi

Department of Chemistry, College of Science, Taif University, Saudi Arabia

and

Sayed Mohammed Adnan

Department of Chemical Engineering, Aligarh Muslim University, Aligarh, India

This edition first published 2023 by John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, USA and Scrivener Publishing LLC, 100 Cummings Center, Suite 541J, Beverly, MA 01915, USA© 2023 Scrivener Publishing LLCFor more information about Scrivener publications please visit www.scrivenerpublishing.com.

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Library of Congress Cataloging-in-Publication Data

ISBN 978-1-394-16623-7

Cover images: Pixabay.ComCover design by Russell Richardson

Preface

Electrochemical capacitors are ideal for a wide range of elevated operations due to the highly adjustable qualities of the materials employed in their production. Many regard them as effective alternatives to conventional capacitors and batteries due to their ability to enhance the system according to the anticipated power/energy characteristics. Electrochemical capacitors with considerable surface areas of their carbon components are desirable, because of their cost effectiveness, adjustable forms, frequent availability, and environmental friendliness. As a result of recent research, many unique approaches for employing bio-derived components in highly efficient electrochemical capacitors are under development.

This book summarizes the progress in the usage of ubiquitous environmentally sustainable materials.

Chapter 1 describes the eco-friendly electrode materials used in electrochemical supercapacitor devices. The techniques of synthesis, characterization, and electrochemical performance of carbon-based, metal oxide-based, and carbon/metal oxide composite electrode materials are explained. Moreover, this chapter highlights the pros, cons, and future perspectives of eco-friendly supercapacitor electrode materials.

Chapter 2 discusses the importance of supercapacitor devices among energy storage devices. This chapter examines various environmental waste-derived carbon nanomaterials and general preparation methods, activation processes, recent advancements, challenges, and future perspectives.

Chapter 3 discusses the fabrication of metal hydroxide through precipitation, consolidation, ion exchange, sonochemical, hydrothermal, and polyol synthesis. Primary topics include the applications in nanotechnology, electrochemistry, pharmaceutical, and wastewater treatment. Furthermore, examples of metal hydroxide are summarized, along with the advantages and drawbacks in humans and animals.

Chapter 4 describes the nature, classifications, and various Porous Organic Polymers (POP). These POPs’ history, chemistry, inner classifications, and synthetic strategies are discussed. POPs possess the advantages of both porous materials and conventional polymers, and have tunable natural porous size, shape, and morphology, which can be expanded for application in material chemistry and biology.

Chapter 5 explains the classification of naturally occurring polymeric materials that are employed for hydrogel fabrication, along with the diverse properties and various synthesis techniques of hydrogels. This chapter closely focuses on the utilization of hydrogels in electrochemical supercapacitors.

Chapter 6 details the progress of ionic liquids as new green electrolytes for supercapacitors. Topics include the research progress and future directions of pure ionic liquids, functional ionic liquids, mixed systems of ionic liquids and ionic liquids, mixtures of ionic liquids, and organic solvents or salts as super-capacitor electrolytes.

Chapter 7 focuses on different kinds of sustainable binders used for the construction of electrochemical capacitors. Furthermore, it discusses the properties of binders, the mechanism involved in the binding process, as well as various classifications of binding materials. Issues related to the use of conventional binders are also presented.

Chapter 8 discusses the use of non-flammable fluorinated electrolytes for electrochemical capacitors and their drawbacks. The primary focus is to give an overview of alternative fluorine-free sustainable electrolyte materials, categorizing them, and comparing their performance to fluorinated electrolytes. In addition, additives that can improve the performance of sustainable fluorine-free electrolytes are briefly discussed.

Chapter 9 outlines various electrolytes suitable for high-performance electrochemical supercapacitors. Topics includes electrolyte classification, types, with examples and the supercapacitor characteristics that are influenced by the nature of electrolytes employed.

Chapter 10 describes how biodegradable electrolytes can eliminate the use of fossil fuels, and their classes corresponding to manufacturing methods. Also included are the properties of biodegradable electrolytes, the factors that influence their ionic conduction, and the application of biodegradable electrolytes in fuel cells, batteries, and supercapacitors.

Chapter 11 explores the importance of supercapattery devices among the energy storage devices, such as batteries and capacitors. The chapter encompasses their working mechanisms, along with the various electrode materials, such as metal-based, carbon-based, and polymer-based materials and their composites. Furthermore, it concerns the utilization, advantages, and hassles of supercapattery devices.

Chapter 12 explains the supercapacitors which are electrochemical energy storage devices that can cover the power/energy gap between conventional capacitors and batteries/ fuel cells. The choice of electrode material and electrolyte directly influences its performance. Ceramic-based materials are very promising, and this chapter deals with the various advances and challenges of using ceramic-based materials as supercapacitor electrodes.

Chapter 13 discusses the many doping techniques that are utilized to create sustainable functional materials for next-generation supercapacitors, including N-, S-, B-, and P-doped and co-doped carbon materials. This chapter goes into great detail about the intriguing effects of heteroatom doping with carbon on supercapacitors. Furthermore, it provides a thorough assessment of the electrochemical performance of mono- or multi-doped carbon composites acting as superior electrodes in energy storage systems.

Chapter 14 discusses the rapid development of wearable supercapacitors in practical applications. Additionally, the synthetic processes for material fabrication is explained with important examples. Specific emphasis is placed upon integrated devices and their applications with supercapacitors as a power source.

Chapter 15 has covered the history and process of electrospinning. The electrospinning process’s working parameters, like solution, processing, and ambient parameters, are thoroughly described. Moreover, the preparation, pore-formation, and modification processes of electrospun polymer nanofibers are extensively discussed. An emphasis is placed upon the most recent and important developments in electrospun nanofiber applications.

Chapter 16 reviews the use of polysaccharides-based electrolytes and electrodes for electrochemical applications. This covers the use of polysaccharides for electrolyte synthesis— from salt-in-polymer-electrolyte to polymer-in-salt-electrolyte range—and electrode synthesis to obtain hierarchical electrodes with the suitable distribution of micro and mesopores using external- and self-templates. Nitrogen/oxygen-doped electrode synthesis is also summarized.

Chapter 17 highlights advanced polymer inks for printable supercapacitors. The working principles of supercapacitors are discussed. Printing technologies for fabricating supercapacitors, such as screen printing, inkjet printing, and 3D printing are emphasized.

Chapter 18 describes the significance, tunable parameters, and different synthesis techniques of activated carbon from biomass for supercapacitor application. Moreover, it provides a detailed description of the constituents, applications, advantages, and limitations of a few major sources, like plant, animal, and microorganism-derived carbon as electrode material, as reported in recent literature.

Our thanks go to Wiley and Scrivener Publishing for their continuous support and guidance.

Inamuddin

Department of Applied Chemistry, Zakir Husain College of Engineering and Technology, Aligarh Muslim University, Aligarh, India

Tariq Altalhi

Department of Chemistry, College of Science, Taif University, Taif, Saudi ArabiaSayed Mohammed Adnan

Department of Chemical Engineering, Zakir Husain College of Engineering and Technology, Aligarh Muslim University, Aligarh, India

1Sustainable Materials for Electrochemical Supercapacitors: Eco Materials

R. Kumar and R. Thangappan*

Advanced Functional Materials for Energy Research Lab, Department of Energy Science & Technology, Periyar University, Salem, Tamil Nadu, India

Abstract

Electrochemical storage systems like secondary batteries and ultra-capacitors need continual performance development due to the long-term demand for rechargeable devices with a high specific energy and rapid charging. Supercapacitors are a recent development for electrochemical energy storage devices. Electrode materials have a lot of interesting features, like a wide active area, high electrical, chemical, and mechanical properties. That kind of makes this a great material for supercapacitor devices. The most prominent factor of electrode materials is that they are environment friendly and non-toxic. Thereby further, recent researchers are working to develop eco-friendly materials for supercapacitor electrode materials by using the bio waste and waste product extracts. In this chapter fully focused on eco-friendly electrode materials for supercapacitors application. Then, the electrode materials synthesis method, characterization, and electrochemical performance are discussed. The electrode materials were categorized into three parts: carbon-based, metal oxide-based, and carbon/metal oxide composite. Furthermore, the future perspectives of electrochemical energy storage devices are addressed.

Keywords: Carbon, metal oxide, composite, eco materials, supercapacitor

1.1 Introduction

In the present century, renewable energy is beginning to replace fossil fuels and nonrenewable energy sources. When energy production is a necessity, as well as energy storage is very important. Now, people used to the two major types of electrochemical energy storage systems like battery and ultra-capacitor [1]. Figure 1.1 plots a comparison of energy and power density for different devices that store energy. The batteries have limited specifications of low charge–discharge time, restricted life, and large mass in the portable devices. Now, the modern technology of energy storage material is supercapacitor. It’s have an enhanced high power, low weight, flexible, inexpensive and eco-friendly storage device compared to battery [2]. The supercapacitor as so called as an ultra-capacitor. According to the storage mechanism, it’s classified those three types such as electrostatic double layer capacitance (non-faradic), electrochemical pseudocapacitance (faradic) and hybrid supercapacitor (faradic & non-faradic). In hybrid supercapacitor have electrostatic and electrochemical storage mechanism. Moreover, electrical double layer capacitance act on isolating charges at the conductive interface and pseudo capacitors store charges through reverse reduction and oxidation reactions at the electro active surface [3, 4]. EDLC has carbon related electrode materials included activated carbon, carbon nanotubes (CNT) and graphene [5–7]. Nevertheless, conductive polymers and transition metal oxides/hydroxides can be used as pseudo-capacitor positive terminal [8, 9]. Figure 1.2 depicted that different type’s electrode material for the supercapacitor applications.

Figure 1.1 Energy versus power plot for various energy storage devices.

Figure 1.2 Various electrode materials for electrochemical supercapacitor.

An important function for the supercapacitor device has been played by the working electrode and the electrolyte. In particular, electrode materials must have vital features of low cost, high active surface area, high output power, and large duration [10]. The performance of active materials are depending upon the electron conductivity path way and structural of the electrode materials. Furthermore, the nanostructure of these materials was important in deciding electrochemical performance. Nanostructured electrode materials are divided into four different sorts of dimensionality, including 0D, 1D, 2D, and 3D [11, 12]. Recently, researchers have become interested in using biomass and green synthesis materials in supercapacitor electrode. The creation of a bio waste-based supercapacitor electrode material serves to supports in waste disposal by transforming waste into a valuable product of supercapacitor technology. Nevertheless, several harmful chemical agents or rigorous techniques have been utilized to prepare the materials for supercapacitors. Thus, green technology that uses electrochemical energy to reserve materials is evaluated from the perspectives of biomass sources and manufacture. Biomass has been processed in two distinct processes: pyrolysis and extract. Biomass-produced electrode materials are ideal for supercapacitor device because of their high active surface and rapid cycle durability [13].

In this chapter, recent advances on the synthesis methods, material structures, large contact surface, and electrochemical behavior of eco-friendly active electrode for supercapacitor application were discussed. Moreover, the electrochemical features of electrode materials including such specific capacity, cyclic stability, power, and energy density also reported. In this study, classified to three different types of environmental friendly supercapacitor anode and cathode like carbon based materials, metal oxides based material and both of them composite materials.

1.2 Eco-Carbon-Based Electrode Materials

Carbon is a vital component in the lives of human people as well as in the functioning of our current ecology and it is numerous in the environment. Since carbon related materials had a lot of effective surface area and electron conduction, when mostly used anode materials are graphene, carbon nanotubes, activated carbon and carbon aerogel [14]. Some of the researchers find to the waste material or green synthesis of electrode materials. Firstly, Kotchaphan Kanjana et al. eco-friendly synthesized using rubber seed shells, durian shells and palm petiole shells derived activated carbon in supercapacitor device. The activated carbon was made using an environmental friendly self-activation process with KOH as an alkali activator. The activated carbon derived from durian shell (DS) had the large capacitance of 178 Fg-1 and the highest cyclic stability tested to 4000 continuous charging and discharging cycles between the potentials of -0.2 to 0.2 V. This DS AC features a number of flakes on smooth surface, high porosity distribution, good electrochemical energy storage and charge carrier balance. Finally, it was concluded that the concentration of KOH had a significant impact on the porous morphology, more active area, crystalline phase, and graphitization mechanism, determining the supercapacitor performance of the produced electrode. There are several active agents included therein, although the KOH activator has gained significant interest due to its environmental friendliness as compared to other activating agents [15]. Moreover, Meenaketan Sethi et al. reported porous graphene has been synthesized that eco-friendly method of without using any toxic chemicals. A solvothermal method has been maintained at the common temperature for different time duration such as 16 to 32 hrs. The morphology structure of porous like graphene sheet is shown in Figure 1.3A (a, b). The porous graphene sheets (PG28) have a total active place of 420 m2g-1 and obtained large specific capacity of 666 Fg-1 at 5 mVs-1 in positive potential window. After completing the 10,000 continuous GCD cycle, the PG 28 sample had 87% stability retention. Figure 1.3B (a–c) the resultant PG 28 electrode was tested for the symmetric supercapacitor application such as CV, GCD, and EIS. The symmetric device supports a high energy value of 26.3 Wh kg-1 and a peak power value of 6120 W kg-1. Over the 5000 continuous cycles of galvanostatic charge-discharge, the PG 28 symmetrical supercapacitor electrodes preserved 93% of their initial capacitance value as shown in Figure 1.3B (d). The hierarchical porous structure PG 28 electrode material exhibited outstanding performance because it had a high active surface area and offered open ways but also a conductive path way for effective charge storage and ion movement [16]. Then Guoxiong Zhang et al. examined activated carbon from bamboo by carbonization and activation method. Various temperatures were kept during the carbonization process, with temperatures ranging from 700°C to 1000°C. Whereas prepared AC material at carbonized 900°C would have an effective highly porous structure with a high outermost layer of 2221.1 m2 g-1, the excellent specific capacitive of 293 F g-1 at current range of 0.5 Ag -1 and wonderful rate capability in 3 M KOH aqueous electrolyte solution. Assembled Symmetric device of the optimal electrode obtained an energy and power density (10.9 Wh/kg and 63 W/kg) and outstanding continuous cycle of 91.8% over 10000 cycle loops [17].

Figure 1.3 (A). (a, b) FESEM and TEM image of porous graphene sheet. (B). Electrochemical results of (a) CV, (b) GCD, (c) EIS and (d) cyclic stability for symmetrical supercapacitor fabricated from PG 28 electrode.

Reproduced with permission [16]. Copyright 2019, Elsevier.

Divyashree A et al. produced that porous carbon nanosphere by pyrolysis method with three various types of coconut waste such as fiber (CF), leaves (CL) and stick (CS), respectively. The average particle size of the carbon spheres derived from coconut fiber approximately 20 nm and three different types of coconut waste derived carbon nanosphere SEM image shown in Figure 1.4 (a–c). Furthermore, the leaves and stick have a similar circular shape with particle sizes range between 30 to 60 nm. The pyrolysis used CF, CL, and CS coconut waste derived into carbon spheres had particle areas of 7 m2/g, 4 m2/g and 8 m2/g, respectively. The synthesized wastes are tested in the electrochemical studies. Further the results show that the waste-derived electrode materials have high specific capacitance of 236, 116, and 208 Fg-1 from coconut fiber, leaves, and sticks, respectively [Figure 1.4 (d)]. Due to the fact that 2D flaks are coated with spheres, coconut fiber displayed a high capacitance and stability when compared to other waste [18]. Moreover, Xiao-Qiang Lin et al. fabricated to innovative, cost effective and environmental friendly electrode materials for supercapacitor application from Konjaku flour in way of precarbonization and KOH activation method. The precarbonized porous bio carbon was classified by different KOH activated agent concentrations, such as 3:1, 5:1, and 7:1. The surface study revealed that the surface of the 5:1 bio carbon approximately 1403 m2g-1. The 5:1 ratio of porous bio carbon displayed a maximum capacity of 216 F/g and a cyclic stability of 93.7 percent over 5000 cycles. Additionally, the symmetric device reached power/energy densities of 2.5 kW kg-1/ 9.2 Wh kg-1 in 6 M KOH + 0.5 mM PPD electrolytes. Therefore, Konjaku flour derived porous bio carbon based electrode material was excellent supercapacitor device materials [19]. Then, Xiao-Li Su et al. used carbonization and KOH active process to synthesize loofah sponge-derived activated carbons. The activated carbons produced are categorized according to their amount of KOH activation. Now, porous structure SAC-4 electrode materials have been obtained an extremely large surface area of 2718 m2g-1 according to the BET analysis. The prepared electrode sample has been tested for the electrochemical studies, compared to the different ratios of KOH activation electrodes; SAC-4 achieved a large capacitive of 309.6 Fg-1 at a current density of 1 Ag-1 in a three-electrode configuration with 6 M KOH electrolyte solution. With the 1 M Na2SO4 electrolyte, the symmetric device demonstrates power and energy output of 160 W/kg and 16.1 Wh/kg [20].

Figure 1.4 (a–c) scanning electron microscope images of coconut fiber (CF), coconut leaves (CL) and coconut stick (CS), respectively. (d) Specific capacitance of three different coconut wastes. (e) Capacitance retention of coconut fiber current density of 2.5 A/g for 5,000 cycles.

Reproduced with permission [18]. Copyright 2016, Elsevier.

Sultan Ahmed et al. synthesized an activated carbon by using of Butnea monsperma flower pollens via thermal activation method and carbonized with ZnCl2 activation agent. ZnCl2was added in various concentrations to the raw material of Butnea monsperma flower pollens. When compared to the other concentrations, the 1:2 ratio of AC produced the highest surface area of 1422.66 m2g-1. The activated carbon electrode of 1:2 showed a high capacitive of 130 Fg-1 and stability of more than 99 % in aqueous electrolyte for more than 10,000 cycles. Additionally, the large energy and power values of 19 kW/kg and 42 Wh/kg were determined [21]. Furthermore Yan Han et al. has been prepared the activated carbon from the Fish gill by using carbonization and KOH activation. At a mass ratio of 1:1, the pre-carbonized sample was combined with KOH and optimized for that device application. Fish gill derived Sheet like structures of activated carbon have high surface area due to found of oxygen and nitrogen functional groups. The AC nanosheets are exhibited the high specific capacitance of 334 F/g at 2 A/g and excellent cyclic stability in 6 M potassium hydroxide. Because of the synergistic effect of these properties on ion diffusion, transport and adsorption, and charge storage, the Fish gill derived activated carbon outperforms most bio-derived activated carbons. As prepared the eco-friendly material eligible to the supercapacitor electrode material [22]. Nannan Guo et al. synthesized environmental friendly material of tremella [Figure 1.5A (a)] derived activated carbon by using carbonization process and KOH activation. The activated carbon gets a high specific surface of 3760 m2 g-1. After that KOH etching process, the activated carbons have a smooth surface and highly porous structure SEM shown in Figure 1.5A (b–f). By using the pyrolysis process the gas and unwanted particles are fully decomposed in the carbon surface. Compared to the different ratio of KOH activation, the ratio of 1:5 obtained the high capacitance value of 71 F g-1 at a current density 1 A g-1 in electrolyte solution of 6 mol of potassium hydroxide [Figure 1.5B (a–c)]. The symmetric supercapacitor was tested with three different electrolyte solutions: 6 mol potassium hydroxide (1V), 1 mol sodium sulfate (1.6 V), and neat 1-ethyl-3-methylimidazolium tetrafluoroborate (3V). The same anode and cathode terminal device displays a better energy and power value of 65.6 W h kg-1 and 19,700 W kg-1 [23].

The innovative bio char was created by extracting activated carbon from poultry litter waste. The poultry litters are then transformed to bio char via the pyrolysis process. Following that, the bio char was exposed to a chemical activation and carbonization procedure. Finally, the process obtained activated carbon with a 3000 m2/g surface area. Daniele Pontirol et al. tested two different types of eco-friendly electrolyte in this two electrode configuration such as KOH and Na2SO4 respectively. The electrolyte of KOH and Na2SO4 reached the capacitance of 22 and 164 F/g [24]. There are several activating agents utilized in the carbonization process, whereas Feiqiang Guo et al. produced activated carbon from peanut shell using a bimetallic active agent. The activators, in order, are the compounds with the formulas ZnCl2/MgCl2, FeCl3/MgCl2, and FeCl3/ZnCl2. Using BET surface analysis; the FeCl3/MgCl2 activation of carbon reveals a highly porous structure with a particle area of 1401.45 m2 g-1. As prepared sample was achieved the specific capacitance (247.28 F/g at 1 A/g) and excellent cyclic loops. A symmetric supercapacitor with two activated carbon electrodes showed energy value of 32.7 Wh kg-1 and high power value of 588.3 W kg-1 [25]. The several types of carbon-based electrode materials obtained from biomass are reported in Table 1.1. According to the reviewed literatures above, biomass-derived carbon-based materials are suitable materials. Because, the porous shape that allows for ion movement and electrical interaction this positive findings suggest that activated biomass carbon compounds might be useful in supercapacitors.

Figure 1.5 (A). (a) Image of tremella (b-f) SEM image of Biomass derived activated carbon. (B). (a–c) Electrochemical studies of activated carbon in 6 M KOH.

Reproduced with permission [23]. Copyright 2017, Elsevier.

Table 1.1 Different types of bio waste derived carbon based electrode material in supercapacitor devices.

Source of electrode material

Surface area (m

2

g

-1

)

Ionic solution

Specific capacitance (Fg

-1

)

Power density (W kg

−1

)

Energy density (W h kg

−1

)

Ref.

Bamboo

3000

6M KOH

300

-

-

[

41

]

European deciduous trees

614

1 M H

2

SO

4

24

500

0.53

[

42

]

Tectona grandis

leaf

514

1 M H

2

SO

4

168

-

-

[

11

]

Sapindus trifoliatus

nut shells

786

6M KOH

240.8

400

30

[

43

]

Hibiscus sabdariffa

fruits

1720.46

2 M KOH

194.50

225

13.10

[

44

]

Willow catkins

645

6M KOH

340

-

-

[

45

]

Tree bark

1018

1 M Na

2

SO

4

114

-

-

[

46

]

Finger grass flower

637.1

6 M KOH

315

6100

13.18

[

47

]

Tea waste

1610

6 M KOH

332

-

-

[

48

]

Momordica charantia

1126

1 M H

2

SO

4

186

6000

23

[

49

]

Mangosteen peel

2623

6 M KOH

357

401

17.28

[

50

]

Eucalyptus globulus seed

2388.38

1 M KOH

150

-

-

[

51

]

Potato peel

1911.5

1 M Na

2

SO

4

323

800

45.5

[

52

]

Cotton

1508

6 M KOH

278

-

-

[

53

]

Jujube fruits

1135

6 M KOH

460

629

23.7

[

54

]

Albizia flowers

2757.63

6 M KOH

406

429

26.3

[

55

]

Solanum lycopersicum

leaves

325.046

1 M H

2

SO

4

345

61.34

43.13

[

56

]

Bean sprouts

397.15

1 M KOH

203.8

-

-

[

57

]

1.3 Eco-Metal Oxide-Based Electrode Materials

Mostly, the behavior of ultra-capacitor is depends by the electrodes material composition. As a consequence, the scientists are researching highly active electrode for electrochemical energy storage. Commonly, the electrode materials should be low cost, environmental friendliness then high performance but some metal oxides have a highly toxic nature. The researchers have now contributed to the development of environmental friendly materials and green synthesis process. H.M. Abuzeid et al. synthesized α-MnO2 from orange byproduct such like orange peel and orange juice using a green synthesis process. The MnO2 was produced using a green approach that uses less solvents and organic substrates, which saves resources and costs, and also minimizes the toxicity of those substances. Disposable by-products were also used in the process. Orange juice and peel extract are used as a reducing agent to convert KMnO4 to MnO2 electrode material. Finally, to obtain orange peel extract, this has a greater surface area than orange juice extract. The performance of the cyclic voltammetry was evaluated throughout a potential range of -0.2 to 1.2 in 0.5 mol of sodium sulfate electrolyte. The orange peel extract produced MnO2 reached the specific capacity of 139 F g-1 at the current value of 0.5 A g-1. MnO2 has been synthesized as an electrode material in a variety of ways, however this approach allows for the simple synthesis of MnO2 for supercapacitor applications [26]. Likewise, Chae Eun Lee et al. developed on the pseudocapacitor properties of iron doped cerium oxide materials through the use of an environmentally friendly co-precipitation method. Then Iron particles are doped to the pure CeO2 in the ratio of 1%, 5% and 10% respectively. Compared to the pure and Fe doped CeO2, 10% of Fe doped CeO2 exhibit the large capacitance value of 559 F g-1 at current range of 1 Ag-1. The capacity of iron doped cerium oxide exceeds 4.6 times than the pure cerium oxide. For the reason of iron particles significantly increase the capacitance of CeO2 electrode materials [27]. Whereas, G. Theophil Anand et al. generated ZnO nanoparticles using Prunus dulcis (almond gum) by green synthesis method. In this CV study, the possible window of 0 to 0.8 was examined using a variable scan rate. According to the pseudocapacitor mechanism in between of electrode and electrolyte, as a scan rate has been increased current also increased in CV analysis. So green synthesis approach of ZnO nanoparticle are best electrode material for supercapacitor applications [28]. Furthermore, H. E. Nsude et al. produced CuFeS2 nanoparticles from touch me not (Mimosa pudica) leaves extract via a simple synthesis process with different annealed temperature. The four different temperatures are without annealed, 200°C, 250°C, and 300°C, respectively. As prepared electrode of CuFeS nanoparticles at 250°C obtained the extreme capacitance of 501.4 F g-1. By using a green2 synthesis approach, touch me not (Mimosa pudica) leaves extract have the best reducing agent for nanomaterial’s production without polluting the environment [29]. Manab Kundu et al. also investigated NiO nanoparticles as electrode materials for supercapacitors. NiO was synthesized using Hydrangea paniculata flower extracts in a green synthesis process [Figure 1.6A (a)]. The average particle size of NiO nanoparticles was determined to be 33 nm in this TEM analysis [Figure 1.6A (b)], with an outer area of 78.472 m2 g-1. Figure 6B (a) depicts the CV curves of NiO nanoparticles at different scan rates in a applied voltage value of 0 to 0.5 V. Due to the high outer layer area of nickel oxide nanoparticles and the quick ion in rate of electronic diffusion during the faradic reduction and oxidation process, the anodic peaks shift positively while the cathodic peaks shift negatively in this CV curve. The galvanostatic charging/discharging curve was utilized to evaluate the capacitance of the NiO nanoparticle electrode material [Figure 1.6B (b)]. The green synthesis NiO nanoparticle electrode material obtained the specific capacitance of 752 Fg-1 at a current density of 2Ag-1. Additionally, the NiO-NPs electrodes exhibit excellent continuous GCD up to 5000 cycles at 10 Ag-1. Hydrangea paniculata flower extract was used as a nanoparticle conversion technology and achieved the best performance for supercapacitor studies [30].

Anacyclus pyrethrum plant extract were employed as a reducer in an involved to naturally synthesis RuO2 nanoparticles and analyzed the electrochemical capability of RuO2 nanoparticles. Due to the fact that Anacyclus pyrethrum is an Indian herbal plant, it is readily accessible in markets. In TEM investigation, the average particle size of RuO2 approximately 13 nm. RuO2 active material coated on the surface of carbon conducting medium checked in a three electrode configuration, and the nanoparticles achieved an excellent capacitance rate of 209 F g-1 at a scan rate of 5 mV/s in 0.5 M of Na2SO4 ions conductive solution. Long-term cyclic loops of 98 % has been maintained in the electrode material over 1000 charge discharge loops [31]. E. Ismail et al. created a bio-synthesis technique for RuO2 nanoparticles using Aspalathus linearis natural extract. This extract serves as the green synthesis method’s redox and capping agent. The bio synthesis technologies are harmless and safe for the environment. The electrode setup was analyzed in the 0 to 0.5 V potential ranges. RuO2 electrode material was deposited on the nickel foam surface, as well as the NiF/RuO2 electrode attained highest specific capacitive value of 750 F g-1 at 10 Ag-1 and long-term cycling stability of 97% capacitance retained after 500 charge–discharge loops in 2 M potassium hydroxide. The porous nature of NiF/RuO2 nanoparticles had outstanding performance, because the effective charge transfer and diffused ion in between of electrode and electrolyte surface [32]. Moreover, Irum Shaheen et al. examined the sol–gel fabrication of a ZnO–Co3O4 nanocomposite with E. cognata organic components. For the synthesis of nanomaterial, E. cognate acts as a binding agent and a reducer. The produced ZnO–Co3O4 nanocomposite exhibited significant homogeneity in particle arrangement with a porous structure. Preferably, the ZnO–Co3O4 nanocomposite should get a single particle size of 20 nm. The composite’s specific capacitance was determined with cyclic voltammetry and found out to have been 165 F g-1. The GCD graph was also used to compute an power and energy value of 7500 W/kg and 4.1 W h/kg. As an end, E. cognate is now one of the organic reducing agents used during fabrication of supercapacitor electrodes [33]. Furthermore, using a nontoxic aqueous phyto extract of guava leaves, Priyanka Lamba et al. produced NiO nanoparticles for use as supercapacitor electrodes. As a reducing and capping agent, guava leaf extract was added. The electrochemical properties of NiO nanoparticle electrodes were studied using 1, 5, 10, 15, and 20 mol of KOH ionic solution. The specific capacity of 85.31 Fg-1 in 5 M potassium hydroxide aqueous electrolyte at 2 mVs-1 demonstrates the supercapacitors strong capacitive performance. As a consequence, the performance of the electrode materials would be determined by the electrolyte solution [34]. Likewise, N. Matinise et al. used Moringa oleifera extract to create unique ZnFe2O4 nanocomposites. A green chemistry technique was used for the manufacture of ZnFe2O4 nanocomposite for electrochemical applications, which used Moringa Oleifera leaf extract as both a reducing and capping agent. The Glassy carbon electrode (GCE) supported ZnFe2O4 nanocomposites directly acted as the working electrode. Glassy carbon electrode (GCE) based ZnFe2O4 nanocomposites served as the working electrode directly. The CV performance of the GCE/ZnFe2O4 electrode was determined across a potential range of 0–0.6 V [35]. Pseudocapacitor electrodes have recently been employed in supercapacitors. Because the performance of synthesized metal oxide-based electrodes is higher than that of other electrode materials. Eco friendly metal oxides are achieved the remarkable performance for electrochemical supercapacitor and reduce the environmental effects. So the recent researchers are now developing the environmental friendly electrode materials for energy storage materials.

Figure 1.6 (A). (a) Hydrangea paniculata flower and extracts (b) TEM image of NiO nanoparticles. (B). (a) CV at various scan rate (b) GCD at various current value.

Reproduced with permission [30]. Copyright 2021, Elsevier.

1.4 Eco-Carbon-Based Material/Metal Oxide Composite Electrode Materials

According to the aforementioned literatures, supercapacitor electrode materials based on carbon and metal oxide are created using waste materials and an environmentally acceptable synthesis approach. The researchers have indeed led to the advancement of a hybrid supercapacitor electrode material made of carbon-based materials and metal oxide composites. Because the hybrid composite electrode blends EDLC and Pseudocapacitance behaviors, it seems to have a high specific capacitance. C. Sasirekha et al. explored the eco-friendly preparation of ZnO/Carbon nanocomposite for supercapacitor electrode material in sol-gel method with sucrose as a capping agent. The ZnO nanoparticles are completely coated with carbon, which aids in effective charge transfer from the electrode/ electrolyte contact. The CV and GCD of Pure Zink oxide and ZnO/Carbon composite terminals been studied at various scan rates and current densities in 1.0 M Na2SO4 at potentials ranging from 0 to 0.8V. According to the GCD curve, the ZnO/carbon composite does have a maximum capacity of 820 F/g at 1 A/g. The cyclic stability of composites attained 92 % capacitance retention after 400 loops. In a symmetric supercapacitor, the same two ZnO/carbon composite electrode materials demonstrate a capacitance of 92 F g-1 at current density of 2.5 A g-1 and an output energy of 32.78 W h kg-1. For electrochemical devices, the ZnO/carbon composite was shown to have a high capacitance and a long lifespan [36]. Moreover, Y. N. Sudhakar et al. created rGO from Piper nigrum and CuO composite as anode for electrochemical capacitors. While maintaining the overall weight of the composite constant, several ratios of reduced graphene oxide–CuO nanocomposites were synthesized, namely 1:3 ratio, 1:2 ratio, 1:1 ratio, 2:1 ratio, 3:1 ratio, 4:1 ratio, 5:1 ratio, and 6:1 ratio. The morphological study of the reduced graphene oxide –CuO nanocomposite reveals that the CuO nano-leaves are well distributed over the rGO surface as leaves with equal sizes of around 100 nm. The electrode material was tested with several electrolyte solutions, including sodium sulfate, phosphoric acid, sulfuric acid, and (9:1) sulfuric acid: phosphoric acid. Comparing pure rGO and CuO electrodes, the 3:1 reduced graphene oxide/CuO nanocomposite had lower resistance and greater capacitive. For supercapacitors, the acid combination (9:1) was acceptable electrolyte. However, the symmetrical supercapacitor has a capacity of 137 F g-1, and its cyclic stability is steady for charge–discharge cycles of up to 5,000 cycles [37].

Whereas, L. Jia et al. fabricated green synthesis technique of ultrafine porous carbon and MnO2 nanowire as a anode and cathode material for asymmetric supercapacitors. Porous boron, nitrogen double doped carbon aerogel synthesized from the methyl cellulose. Importantly, this layered material minimized aggregation while increasing the effective area of contact, which resulted in exceptional electrochemical characteristics. The composite working electrode had the high specific capacitance of 338 F g-1 at a current density of 1 A g-1. Under a broad voltage ranging from 0 to 1.8 V, the built ASC device demonstrated an ultra-energy density of 27.75 Wh kg-1 and an output power of 1.35 kW kg-1. In this device demonstrated excellent cycle life, with just a 4.4 percent capacity reduction over 2000 cycles [38]. In particular, low cost, and eco-friendly single step synthesis process of NiO nanoparticles from Opuntia ficus-indica leaf juice for asymmetric pseudocapacitors has been developed by S.S. Gunasekaran et al. Opuntia ficus-indica is a polyphenolic plant that includes a variety of flavonoids and phenolic acids. The extract’s phenolic components, flavonoids, lipids, amino acids and proteins function as a capping and reducing reagent during the NiO nanoparticle manufacturing process. Figure 1.7a an illustrated the production method for NiO nanoparticles, whereas Figure 1.7b illustrates the surface shape of manufactured NiO nanoparticles. NiO nanoparticles were synthesized and shown a large capacity of 644 Fg-1 at a current value of 0.5 Ag-1 as determined by the CV and GCD curves of electrochemical capacitor investigation [Figure 1.7c (i & ii)]. The assembled asymmetric supercapacitor device (NiO//AC) with carbon and as-prepared Nickel oxide nanoparticles as an anode and cathode terminals, demonstrated an exceptional energy value of 25 Wh kg-1 and a large power value of 40 W kg-1 with a capacitive retention of 96.5 % even over 10,000 cycles. Due to its various oxidation states, this NiO is suitable for high-efficiency electrochemical energy storage using a green manufacturing method based on leaf extracts [39]. Further, Sherief A. Al Kiey produced NiO/porous structured carbon composites using an easy and eco-friendly method based on banana peel waste materials. The NiO/pores carbon have a large outer area of 1187 m2/g according to BET surface analysis. Since prepared samples have a similar specific surface area, ions are more accessible at the electrode/electrolyte contact. The NiO/pores carbon composite displays an extraordinary specific capacity of 811 F/g at 1 A/g, a ultra-rate capability of 84.55 % retention at 10 A/g, and excellent cycle stability over 1000 cycles. The activation of banana peels is a novel approach for preparing supercapacitor electrodes [40].

Figure 1.7 (a) Green synthesis of nickel oxide nanoparticle by using Opuntia ficus-indica leaves extract (b) FESEM image of NiO nanoparticles (c) (i) Cyclic voltammetry and (ii) Galvanostatic charging/ discharging of NiO electrode material.

Reproduced with permission [39]. Copyright 2017, Elsevier.

1.5 Conclusion