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The present work focuses on the synthesis of hybrid La2CoCrO6/Co3O4/rGO composite via solvothermal technique for supercapacitor application. X-ray diffraction, field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, Brunauer-Emmett-Teller (BET), and Barrett-Joyner-Halenda analyses are employed to assess phase structure, morphology, chemical state, surface area, and porosity of synthesized materials, respectively. The formation of mesoporous spheres is confirmed through FESEM and BET analysis. The inclusion of redox additive KMnO4 in KOH electrolyte enhances the accessibility of electrochemical sites in the mesoporous spheres of the La2CoCrO6/Co3O4/rGO electrode, resulting in excellent charge storage. Electrochemical analysis of the La2CoCrO6/Co3O4 exhibits specific capacitance of 633.2 F/g at 2 A/g in a redox electrolyte (6 M KOH + 0.05 M KMnO4) with capacitive retention of approximately 81 % over 5000 cycles. Furthermore, the addition of rGO improves the overall performance of La2CoCrO6/Co3O4/rGO composite (763.9 F/g at 2 A/g with capacitive retention of approximately 86 %). The electrochemical analysis of hybrid La2CoCrO6/Co3O4/rGO composite showed improved performance, owing to the synergy of double perovskite (La2CoCrO6), cobalt oxide (Co3O4), and reduced graphene oxide (rGO). These findings suggest promising applications for the material in advanced energy storage devices.

This work investigates the electrochemical behavior of hybrid supercapacitors with carbon-based electrodes of different porosity using 5M NaNO3 + 0.5M KBr electrolyte to optimize energy storage processes. Three types of carbon materials were synthesized: activated carbon from rice husk (RH) with a specific surface area of ~2300 m2/g and pore size < 1 nm, and templated carbons from magnesium citrate (MP-8) and glucose with SiO2 as a template (G7), having surface areas of 1976 and 1320 m2/g and pore sizes of 3.4 and 7 nm, respectively. The microporous structure of activated carbon (AC) obtained from RH shows limitations in the diffusion of electrolyte ions, which affects the charge-discharge kinetics. In contrast, the larger mesoporous structures of templated carbons promoted better adsorption and ion transport, significantly affecting the dynamics of redox reactions. The RH/MP-8 hybrid capacitor, combining high surface area and large pore size, demonstrated a 54% increase in specific capacitance, 128% increase in specific energy and 51% increase in energy efficiency at high current densities of 5 A/g, comparing to the symmetric RH/RH hybrid capacitor. This study highlights the critical importance of the relationship between electrode pore structure and electrolyte composition for optimizing supercapacitor performance, which provides valuable information for the development of efficient energy storage technologies.

With the continuous advancement in the dual-carbon strategy, the upswell in the demand for renewable energy sources has motivated extensive research on the development of novel energy storage technologies. As a new type of energy storage device, carbon-based redox-enhanced supercapacitors (RE-SCs) are designed by employing soluble redox electrolytes into the existing devices, exploiting the merits of the diffusion-controlled faradaic process of the redox electrolyte at the surface of carbon electrodes, thus leading to improved energy density without the cost of power density. During the past years, great progress has been made in the design of novel redox electrolytes and the configuration of new devices. However, the development of these systems is plagued by severe self-discharge. Herein, a comprehensive picture of the fundamentals, together with a discussion and outline of the challenges and future perspectives of RE-SCs, are provided. We highlight the impacts of redox electrolytes on capacitance, energy density, and power output. Notably, the self-discharge behavior owing to the introduction of redox electrolyte and its mechanism are also discussed, followed by a summary of the strategies from materials to system optimization. Furthermore, possible directions for future research are discussed.

In the present study, an iodide/triiodide (I−/I3−) redox couple is used in hybrid electrochromic devices (ECDs), and the effects of the applied bias potential and bias time on device performance are studied. An applied bias potential of ~1 V is sufficient to achieve an initial contrast ratio of 8:1 in less than 5 min. Increasing both the bias potential and bias time results in an enhancement in loss reactions at the WO3/electrolyte interface, rather than improving optical performance. Moreover, long-term performance depends on the testing procedure (regularly cycling or after storage), while the formation of iodine (I2) decreases the initial transparency of the ECDs and affects their overall performance. However, its formation cannot be avoided, even without cycling the ECDs, and the restoration of the optical performance can take place only when the electrolyte is replaced with a fresh one. Finally, a new methodology is applied for calculating the loss current, and a suggestion is made to avoid a common mistake in calculating the coloration efficiency of these hybrid ECDs.

Supercapacitors (SCs) have attracted widespread attention due to their short charging/discharging time, long cycle life, and good temperature characteristics. Electrolytes have been considered as a key factor affecting the performance of SCs. They largely determine the energy density based on their decomposition voltage and the power density from their ionic conductivity. In recent years, redox electrolytes obtained a growing interest due to an additional redox activity from electrolytes, which offers an increased charge storage capacity in SCs. This article summarizes the latest progress in the research of redox electrolytes, and focuses on their properties, mechanisms, and applications based on different solvent types available. It also proposes potential solutions for how to effectively increase the energy density of the SCs while maintaining their high power and long life.

The one of the most important issues in constructing light-harvesting photovoltaic (PV) systems with a charge storage element is its reliable and uninterrupted use in highly variable and weather-dependent conditions in everyday applications. Herein, we report the construction and applicability evaluation of a ready-to-use portable solar charger comprising a silicon solar cell and an enhanced energy hybrid supercapacitor using activated carbon electrodes and iodide-based aqueous electrolyte to stabilise the PV power under fluctuating light conditions. The optimised electrode/electrolyte combination of a supercapacitor was used for the construction of a 60 F/3 V module by a proper adjustment of the series and parallel connections between the CR2032 coin cells. The final photo-rechargeable device was tested as a potential supporting system for pulse electronic applications under various laboratory conditions (temperature of 15 and 25 °C, solar irradiation of 600 and 1000 W m−2).

The cooperative effects between the PANI (polyaniline)/nano-NiO (nano nickel oxide) composite electrode material and redox electrolytes (potassium iodide, KI) for supercapacitor applications was firstly discussed in this article, providing a novel method to prepare nano-NiO by using β-cyelodextrin (β-CD) as the template agent. The experimental results revealed that the composite electrode processed a high specific capacitance (2122.75 F·g−1 at 0.1 A·g−1 in 0.05 M KI electrolyte solution), superior energy density (64.05 Wh·kg−1 at 0.2 A·g−1 in the two-electrode system) and excellent cycle performance (86% capacitance retention after 1000 cycles at 1.5 A·g−1). All those ultra-high electrical performances owe to the KI active material in the electrolyte and the PANI coated nano-NiO structure.

Redox electrolytes can provide significant enhancement of capacitance for supercapacitors. However, more important promotion comes from the synergetic effect and matching between the electrode and electrolyte. Herein, we report a novel electrochemical system consisted of a polyanilline/carbon nanotube composite redox electrode and a hydroquinone (HQ) redox electrolyte, which exhibits a specific capacitance of 7926 F/g in a three-electrode system when the concentration of HQ in H2SO4 aqueous electrolyte is 2 mol/L, and the maximum energy density of 114 Wh/kg in two-electrode symmetric configuration. Moreover, the specific capacitance retention of 96% after 1000 galvanostatic charge/discharge cycles proves an excellent cyclic stability. These ultrahigh performances of the supercapacitor are attributed to the synergistic effect both in redox polyanilline-based electrolyte and the redox hydroquinone electrode.