In the past decades, the energy consumption of nonrenewable fossil fuels has been increasing, which severely threatens human life. Thus, it is very urgent to develop renewable and reliable energy storage devices with features of environmental harmlessness and low cost. High power density, excellent cycle stability, and a fast charge/discharge process make supercapacitors a promising energy device. However, the energy density of supercapacitors is still less than that of ordinary batteries. As is known to all, the electrochemical performance of supercapacitors is largely dependent on electrode materials. In this review, we firstly introduced six typical transition metal oxides (TMOs) for supercapacitor electrodes, including RuO2, Co3O4, MnO2, ZnO, XCo2O4 (X = Mn, Cu, Ni), and AMoO4 (A = Co, Mn, Ni, Zn). Secondly, the problems of these TMOs in practical application are presented and the corresponding feasible solutions are clarified. Then, we summarize the latest developments of the six TMOs for supercapacitor electrodes. Finally, we discuss the developing trend of supercapacitors and give some recommendations for the future of supercapacitors.

https://www.mdpi.com/2079-4991/11/5/1248/pdf

Transition Metal Oxide Electrode Materials for Supercapacitors: A Review of Recent Developments.

Green synthesis approaches are gaining significance as promising routes for the sustainable preparation of nanoparticles, offering reduced toxicity towards living organisms and the environment. Nanomaterials produced by green synthesis approaches can offer additional benefits, including reduced energy inputs and lower production costs than traditional synthesis, which bodes well for commercial-scale production. The biomolecules and phytochemicals extracted from microbes and plants, respectively, are active compounds that function as reducing and stabilizing agents for the green synthesis of nanoparticles. Microorganisms, such as bacteria, yeasts, fungi, and algae, have been used in nanomaterials' biological synthesis for some time. Furthermore, the use of plants or plant extracts for metal and metal-based hybrid nanoparticle synthesis represents a novel green synthesis approach that has attracted significant research interest. This review discusses various biosynthesis approaches via microbes and plants for the green preparation of metal and metal oxide nanoparticles and provides insights into the molecular aspects of the synthesis mechanisms and biomedical applications. The use of agriculture waste as a potential bioresource for nanoparticle synthesis and biomedical applications of biosynthesized nanoparticles is also discussed.

Green approaches for the synthesis of metal and metal oxide nanoparticles using microbial and plant extracts.

In the context of emerging global concerns with synthetic plastic packaging, alternative natural biodegradable packaging materials are gaining increasing attention for food packaging applications. In this study, chitosan and gelatin nanocomposite hybrid films containing green synthesized zinc oxide (ZnO) nanoparticles (NPs) were developed and microstructural properties were studied. Antimicrobial activity of the developed films was evaluated using both Gram negative (Escherichia coli) and Gram positive bacteria (Staphylococcus aureus). Green synthesis protocol was used for the precipitation of ZnO NPs using fruit extract of Cassia fistula. The as-synthesized polyhedral ZnO NPs were in the range of 20-40 nm (average size ≈29 nm). Reinforcement with ZnO NPs in the hybrid films lead to improved thermal stability, elongation-at-break (EAB), and compactness properties. The developed films with 2% and 4% ZnO NPs showed a smooth, compact, and heterogeneous surface morphology compared to the control (chitosan-gelatin hybrid) films. Disc diffusion assays showed that the nanocomposite film had significant antimicrobial activity against E. coli. The developed hybrid nanocomposite films have potential to be developed as biodegradable alternative for postharvest packaging of fresh fruits and vegetables.

https://www.mdpi.com/2304-8158/9/9/1143/pdf

Biodegradable Hybrid Nanocomposite of Chitosan/Gelatin and Green Synthesized Zinc Oxide Nanoparticles for Food Packaging.

Multifunctional ZnO nanoparticles bio-fabricated from Canna indica L. flowers for seed germination, adsorption, and photocatalytic degradation of organic dyes.

Averrhoe carrambola fruit extract assisted green synthesis of zno nanoparticles for the photodegradation of congo red dye

In the era of rapid decline of renewable sources of energy, novel supercapacitor materials are essential to provide impetus to the growing energy demands arising from the commercialization of technology towards an electric-powered future which aims at both efficient and sustainable use of energy. The inspiration is to develop materials that effect specific applications without causing any damage to the environment. The use of inherently non-conducting but biocompatible polymers that can be functionally modified are thus imperative in this respect. Here, styrene maleic anhydride (SMA) copolymer has been structurally modified with a thiadiazole moiety along with the incorporation of green synthesized ZnO nanoparticles to prepare a polymer nanocomposite. The green synthesized ZnO nanoparticles display a flake-like structure with a size of about 20 nm. UV, FT-IR and XRD analyses validates the incorporation of ZnO in to the polymer matrix to form the polymer nanocomposite. Satisfactory supercapacitor behaviour with a specific capacitance of 268.5 F g−1 at 0.1 A g−1 is estimated for the polymer nanocomposite which is larger than ZnO nanoparticles and the bare polymer. It is demonstrated that the innate conductivity of the SMA copolymer is enhanced upon modification. The materials also exhibit good cycling stability with maximum capacitance retention. The biocompatibility of the nanocomposites has been established from the preliminary cell viability studies performed on 3T6 mouse fibroblast cells. The developed material shows great promise to provide a green alternative to existing supercapacitors.

Biocompatible supercapacitor electrodes using green synthesised ZnO/Polymer nanocomposites for efficient energy storage applications


 The efficient and sustainable use of energy is highly imperative to satisfy the escalating energy demands arising from the rapid commercialization of technologies. The development of novel electrochemical energy technologies is an essential aspect in the present-day scenario of rapid depletion of existing sources of energy. Conducting polymers are promising psuedocapacitive materials with an extended delocalisation network of  electrons, flexibility to functional modifications and facile intercalation and de-intercalation of electrolyte ions. These factors enable them to possess capacitances comparable with those of metal oxides. The use of copolymers in this context is noteworthy due to their diversity of combining different types of monomer units and facile integration. Carbon based materials have also been extensively employed on account of their high power densities and large number of charge-discharge cycles. The synergism of the non-faradaic double-layer capacitance with the faradaic charge transfer has the ability to provide impressive supercapacitor properties. Different types of polymer and polymer-composites based supercapacitors have been discussed with special emphasis on implantable biomedical devices and wearable electronics.

Review— An Overview on Supercapacitors and Its Applications

Graphene–metal frameworks have been extensively studied and developed as electrode materials for next generation energy storage materials. Their high surface area and easily transformable structure enhances its specific capacitance characteristics. In the present study, graphene oxide (GO) was synthesized using Hummers method. Zinc oxide and copper oxide nanoparticles were incorporated in to the GO matrix to form mixed metal oxides. GO, GO–CuO and GO–ZnO were characterized using UV–Visible, FTIR, FT Raman spectroscopy, SEM and XRD to confirm their effective formation. The surface of the glassy carbon electrode was modified by drop casting with the samples on its surface and its electrochemical properties were studied. Cyclic Voltammetry studies were conducted at various scan rates in different electrolytes (KCl, H2SO4 and Na2SO4) and the characteristic curves were observed to be asymmetric in nature. GO–CuO exhibits the highest specific capacitance of 790 F/g at 5 mV/s in KCl. The specific capacitance of the modified electrodes was also measured using the Chronopotentiometry technique. GO–CuO nanocomposites show a maximum specific capacitance of 800 F/g at 1 A/g. The nanocomposites showed enhanced electrochemical behaviour of the nanocomposites when compared to pure GO. The nanocomposites also showed good cycling stability. The superior performance of the GO–CuO and GO–ZnO nanocomposite electrode renders it as a promising material for supercapacitors applications.

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Sohini Chakraborty

Papers

Averrhoe carrambola fruit extract assisted green synthesis of zno nanoparticles for the photodegradation of congo red dye

Biocompatible supercapacitor electrodes using green synthesised ZnO/Polymer nanocomposites for efficient energy storage applications

Review— An Overview on Supercapacitors and Its Applications

Electrolyte dependent performance of graphene–mixed metal oxide composites for enhanced supercapacitor applications

Functionalized polystyrene maleic anhydride copolymer/ZnO nanocomposites for enhanced electrochemical performance