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The most prominent and highly visible advantage attributed to supercapacitors of any type and application, beyond their most notable feature of high current capability, is their high stability in terms of lifetime, number of possible charge/discharge cycles or other stability-related properties. Unfortunately, actual devices show more or less pronounced deterioration of performance parameters during time and use. Causes for this in the material and component levels, as well as on the device level, have only been addressed and discussed infrequently in published reports. The present review attempts a complete coverage on these levels; it adds in modelling approaches and provides suggestions for slowing down ag(e)ing and degradation.

Increased energy consumption stimulates the development of various energy types. As a result, the storage of these different types of energy becomes a key issue. Supercapacitors, as one important energy storage device, have gained much attention and owned a wide range of applications by taking advantages of micro-size, lightweight, high power density and long cycle life. From this perspective, numerous studies, especially on electrode materials, have been reported and great progress in the advancement in both the fundamental and applied fields of supercapacitor has been achieved. Herein, a review of recent progress in carbon materials for supercapacitor electrodes is presented. First, the two mechanisms of supercapacitors are briefly introduced. Then, research on carbon-based material electrodes for supercapacitor in recent years is summarized, including different dimensional carbon-based materials and biomass-derived carbon materials. The characteristics and fabrication methods of these materials and their performance as capacitor electrodes are discussed. On the basis of these materials, many supercapacitor devices have been developed. Therefore, in the third part, the supercapacitor devices based on these carbon materials are summarized. A brief overview of two types of conventional supercapacitor according to the charge storage mechanism is compiled, including their development process, the merits or withdraws, and the principle of expanding the potential range. Additionally, another fast-developed capacitor, hybrid ion capacitors as a good compromise between battery and supercapacitor are also discussed. Finally, the future aspects and challenges on the carbon-based materials as supercapacitor electrodes are proposed.

Supercapacitors currently hold a prominent position in energy storage systems due to their exceptionally high power density, although they fall behind batteries and fuel cells in terms of energy density. This paper examines contemporary approaches aimed at enhancing the energy density of supercapacitors by adopting hybrid configurations, alongside considerations of their power density, rate capability, and cycle stability. Given that electrodes play a pivotal role in supercapacitor cells, this review focuses on the design of hybrid electrode structures with elevated specific capacitance, shedding light on the underlying mechanisms. Factors such as available surface area, porosity, and conductivity of the constituent materials significantly influence electrode performance, prompting the adoption of strategies such as nanostructuring. Additionally, the paper delves into the impact of novel bio-based hybrid electrolytes, drawing upon literature data to outline the fabrication of various hybrid electrode materials incorporating conducting polymers like polyaniline and polypyrrole, as well as metal oxides, carbon compounds, and hybrid electrolytes such as ionic liquids, gel polymers, aqueous, and solid polymer electrolytes. The discussion explores the contributions of different components and methodologies to overall capacitance, with a primary emphasis on the mechanisms of energy storage through non-faradic electrical double-layer capacitance and faradaic pseudo-capacitance. Furthermore, the paper addresses the electrochemical performance of hybrid components, examining their concentrations and functioning via diverse charge storage techniques.

The combination of addition of Fe (as a catalyst for graphitization) and CO 2 activation (a kind of gaseous activation) was applied to prepare a porous carbon material from bamboo powder (a waste product of superheated steam treatment). Regardless of the heat treatment temperature, many macropores were successfully formed after the heating process by removal of Fe compounds. A turbostratic carbon structure was generated in the Fe-added sample heated at 850°C. It was confirmed that the added Fe acted as a template for pore formation. Moreover, it was confirmed that the added Fe acted as a catalyst for graphitization. The resulting electrochemical performance as the electrode of an electrical double-layer capacitor, as demonstrated by cyclic voltammetry, electrochemical impedance spectroscopy, and charge–discharge testing, could be explained based on the graphitization and activation effects. Addition of Fe could affect the electrical properties of carbon material derived from bamboo.

Metal/metal oxides and conductive polymers are common supercapacitor electrode materials, revealing high power density as well as long cycle life. In composites, graphene and metal oxides displayed the combination of the excellent cycle stability of graphene and the high-capacity properties of metal oxides which remarkably improve the comprehensive properties of nanocomposites. The current developments of metal/metal oxide decorated graphene (MGr) composites in the field of electrochemical capacitors are elucidated here on account of their synergistic properties. It is demonstrated that, in comparison with their individual influences, MGr composites have attained substantial improvement in rate capability, capacity, and cycling stability. Mainly, an overview of the characteristics, preparation approaches, and application of graphene (Gr) is outlined. Mechanism of different types of electrochemical capacitance is described explicitly. Finally, the future prospects and challenges of MGr composites have been discussed for energy storage.

Supercapacitors are increasingly used for energy conversion and storage systems in sustainable nanotechnologies. Graphite is a conventional electrode utilized in Li-ion-based batteries, yet its specific capacitance of 372 mA h g−1 is not adequate for supercapacitor applications. Interest in supercapacitors is due to their high-energy capacity, storage for a shorter period and longer lifetime. This review compares the following materials used to fabricate supercapacitors: spinel ferrites, e.g., MFe2O4, MMoO4 and MCo2O4 where M denotes a transition metal ion; perovskite oxides; transition metals sulfides; carbon materials; and conducting polymers. The application window of perovskite can be controlled by cations in sublattice sites. Cations increase the specific capacitance because cations possess large orbital valence electrons which grow the oxygen vacancies. Electrodes made of transition metal sulfides, e.g., ZnCo2S4, display a high specific capacitance of 1269 F g−1, which is four times higher than those of transition metals oxides, e.g., Zn–Co ferrite, of 296 F g−1. This is explained by the low charge-transfer resistance and the high ion diffusion rate of transition metals sulfides. Composites made of magnetic oxides or transition metal sulfides with conducting polymers or carbon materials have the highest capacitance activity and cyclic stability. This is attributed to oxygen and sulfur active sites which foster electrolyte penetration during cycling, and, in turn, create new active sites.

Supercapacitors, also known as electrochemical capacitors, store energy either by the adsorption of ions (electric double-layer capacitors) or by fast redox reactions at the surface (pseudocapacitors). When high power delivery or uptake is required in electrical energy storage and harvesting applications, they can complement or replace batteries. The fundamental and applied aspects of supercapacitors have seen rapid progress in recent years. With the development of advanced nanostructured materials and a better understanding of charge storage mechanisms, significant performance improvements have been achieved. In this review, the latest advances in supercapacitors in charge storage mechanisms and electrode materials is discussed. We describe the working principle and challenges of different advanced materials used as supercapacitor electrodes and strategies to overcome these challenges. The focus is on materials like metal sulfides, metal oxides, conducting polymers, MXenes, metal–organic frameworks, and covalent organic frameworks. The performance of electrode materials is analyzed by parameters including energy density, capacitance, power density, cyclic stability, and rate capability. The prospects and challenges related to supercapacitors in applied applications are also discussed.

Transition metals are attracting numerous interests for their substantial applications in supercapacitors and as non-noble metal electrocatalyst for overall water splitting. Herein, the NiMn layer double hydroxide (NiMn-LDH) is developed using the sonochemical route at different reaction times, which act as a multifunctional electrode for supercapacitors and overall water splitting. The capacitance of layer double hydroxide (LDH) synthesized at 4 h (NiMn-LDH-4 h) of reaction time was found to be 527 F g −1 at 1 A g −1 , with 91.2% capacitance retention after 5,000 cycles at 2 A g −1 in 6 M KOH. For hydrogen and oxygen evolution reactions, the NiMn-LDH-4 h electrode exhibits a standard of 10 mA cm −2 at an overpotential of 120 mV and 296 mV, respectively, in 1 M KOH. Moreover, fabricated NiMn-LDH-4 h||NiMn-LDH-4 h electrolyzer for overall water splitting benchmarks 10 mA cm −2 at 1.6 V. The superior electrochemical properties of the NiMn-LDH electrodes might be attributed to quick diffusion paths and enhanced redox reaction of NiMn-LDH nanosheets because of the high surface area.

Supercapacitors, also called ultracapacitors or electrochemical capacitors, store electrical charge on high-surface-area conducting materials. Their widespread use is limited by their low energy storage density and relatively high effective series resistance. Using chemical activation of exfoliated graphite oxide, we synthesized a porous carbon with a Brunauer-Emmett-Teller surface area of up to 3100 square meters per gram, a high electrical conductivity, and a low oxygen and hydrogen content. This sp 2 -bonded carbon has a continuous three-dimensional network of highly curved, atom-thick walls that form primarily 0.6- to 5-nanometer-width pores. Two-electrode supercapacitor cells constructed with this carbon yielded high values of gravimetric capacitance and energy density with organic and ionic liquid electrolytes. The processes used to make this carbon are readily scalable to industrial levels.

Conducting polymer hydrogels represent a unique class of materials that synergizes the advantageous features of hydrogels and organic conductors and have been used in many applications such as bioelectronics and energy storage devices. They are often synthesized by polymerizing conductive polymer monomer within a nonconducting hydrogel matrix, resulting in deterioration of their electrical properties. Here, we report a scalable and versatile synthesis of multifunctional polyaniline (PAni) hydrogel with excellent electronic conductivity and electrochemical properties. With high surface area and three-dimensional porous nanostructures, the PAni hydrogels demonstrated potential as high-performance supercapacitor electrodes with high specific capacitance (∼480 F·g ⁻¹), unprecedented rate capability, and cycling stability (∼83% capacitance retention after 10,000 cycles). The PAni hydrogels can also function as the active component of glucose oxidase sensors with fast response time (∼0.3 s) and superior sensitivity (∼16.7 μA·mM ⁻¹). The scalable synthesis and excellent electrode performance of the PAni hydrogel make it an attractive candidate for bioelectronics and future-generation energy storage electrodes.