Fabricating dual redox electrolyte to achieve ultrahigh specific capacitance and reasonable Coulombic efficiency for biomass activated carbon

One-Step Synthesis of Co-Ni-O-S Nanohybrid with Amorphous-Nanocrystalline Interwoven Architecture for High-Energy-Density Supercapacitor-Battery Hybrids

Transition metal sulfur oxides have emerged as promising candidates for advanced energy storage due to their multi-electron redox activity and tunable nanostructures. Among them, Co-Ni-O-S composites are particularly attractive for supercapacitors owing to their high energy storage density. However, conventional synthesis methods often require prolonged processing times (>10 h) or high-temperature treatments (>80 °C), which limit their practical applications. This work addresses these challenges by developing amorphous-nanocrystalline intertwined Co-Ni-O-S nanohybrid nanosheet arrays through a rapid alternating current (AC) electrodeposition method (1 h) under ambient conditions. The unique architecture combines the advantages of amorphous phases (enhanced ion diffusion pathways) and nanocrystalline domains (efficient charge transport), leading to exceptional specific capacitance of 4804 F g⁻¹ (or 959 mAh g-1, 2402 C g-1) at 1 A g⁻¹, 82.2% capacitance retention after 5000 cycles (5 A g⁻¹), and a near 100% Coulombic efficiency (CE). The assembled asymmetric supercapacitor achieves an energy density of 199.4 Wh kg⁻¹ at 754 W kg⁻¹, bridging the performance gap between batteries and conventional capacitors.

Revealing Energy Density in Porous Carbon Supercapacitors Using Hydroquinone Sulfonic Acid as Cathodic and Alizarin Red S as Anodic Redox Electrolytes

Exploration of innovative strategies aiming to boost energy densities of supercapacitors without sacrificing the power density and long-term stability is of great importance. Herein, highly porous nitrogen-doped carbon spheres (NPCS) are decorated onto the graphite sheets (GSs) through a hydrothermal route, followed by a chemical activation. The capacitive performance of the NPCS is then enhanced by hydroquinone sulfonic acid (HSQA) incorporation in both cathodic electrolyte and electrode materials. Later, NPCS are decorated with polypyrrole (PPY), in which HSQA takes a versatile role as conjugated polymer dopant and cathodic redox additive. The capacitive performance of the negative electrodes is enhanced by incorporating of alizarin red S (ARS) as anodic redox additive. Finally, PPY(HQSA)@NPCS-GS//NPCS-GS asymmetric supercapacitor is assembled and tested in dual redox electrolyte system containing HQSA-cathodic and ARS-anodic electrolytes. This device delivers a remarkable energy density of 60.37 Wh kg-1, which is close or even better than lead acid batteries. Thus, the present work provides a novel pathway to develop high energy supercapacitors using redox active electrolytes for next-generation energy storage applications.

Boosting the Capacitance of Covalent Organic Framework Supercapacitors by Hydroquinone Redox Electrolyte Addition

Rapidly escalating energy demands have spurred a relentless quest for innovative materials and methodologies in energy storage technologies. Covalent organic frameworks (COFs) have emerged as promising candidates for energy storage applications owing to their customizable structure and inherent properties, including enduring porosity and expansive surface area. In this study, we introduce imine-based COF aerogels fashioned into flexible COF electrodes, employing redox electrolytes based on hydroquinone (HQ) dissolved in H2SO4 aqueous solution and 0.25 M TBAPF6 at concentration in acetonitrile. This strategic selection of electrolytes aims to augment capacitance and energy density when compared to non-redox electrolytes. Remarkably, our COF electrodes exhibit an outstanding areal capacitance of 843 mF cm-2 when utilizing HQ with 0.10 M H2SO4, operating at 1.3 mA cm-2, while maintaining approximately 100% capacity retention after 10,000 cycles. Notably, the capacitance of the 0.38 M HQ + 0.10 M H2SO4 is eight times greater than that achieved with organic electrolytes (111 mF cm-2).

High-Performance Dual-Redox-Mediator Supercapacitors Based on Buckypaper Electrodes and Hydrogel Polymer Electrolytes

In recent years, the demand for solid, thin, and flexible energy storage devices has surged in modern consumer electronics, which require autonomy and long duration. In this context, hybrid supercapacitors have become strategic, and significant efforts are being made to develop cells with higher energy densities while preserving the power density of conventional supercapacitors. Motivated by these requirements, we report the development of a new high-performance dual-redox-mediator supercapacitor. In this study, cells were constructed using fully moldable buckypapers (BPs), composed of carbon nanotubes and cellulose nanofibers, as electrodes. We evaluated the compatibility of BPs with hydrogel polymer electrolytes, based on 1 mol L-1 H2SO4 and polyvinyl alcohol (PVA), supplemented with different redox species: methylene blue, indigo carmine, and hydroquinone. Solid cells were constructed containing two active redox species to maximize the specific capacity of each electrode. Considering the main results, the dual-redox-mediator supercapacitor exhibits high energy density of 32.0 Wh kg-1 (at 0.8 kW kg-1) and is capable of delivering 25.9 Wh kg-1 at high power demand (4.0 kW kg-1). Stability studies conducted over 10,000 galvanostatic cycles revealed that the PVA polymer matrix benefits the system by inhibiting the crossover of redox species within the cell.

Graphitic Carbon Nitride-Induced Multifold Enhancement in Electrochemical Charge Storage of CoS-NiCo2S4 for All-Solid-State Hybrid Supercapacitors

In order to improve the electro-microstructural physiognomics of electrode materials for applications in better efficiency supercapacitors, herein graphitic carbon nitride (GCN)-heterostructurized CoS-NiCo₂S₄ is designed using a controlled material growth synthesis procedure. The developed CoS-NiCo₂S₄/GCN possesses ample hydrophilicity, possible charge transfer between GCN and CoS-NiCo₂S₄, uniform phase distribution, and distinctive microstructural characteristics. The preliminary electrochemical studies in the three-electrode setup show GCN-induced lower charge transfer resistance and very unique Warburg profile corresponding to extremely low diffusion resistance in CoS-NiCo₂S₄/GCN as compared to pristine CoS-NiCo₂S₄. Furthermore, GCN is found to significantly induce surface-controlled (capacitive-type) charge storage and frequency-independent specific capacitance up to 10 Hz in CoS-NiCo₂S₄. Furthermore, the CoS-NiCo₂S₄||N-rGO and CoS-NiCo₂S₄/GCN||N-rGO all-solid-state hybrid supercapacitor (ASSHSC) devices were fabricated using N-rGO as the negative electrode material, and the inducing effect of GCN on the supercapacitive charge storage performance of the devices is thoroughly studied. Results demonstrate that the mass specific capacitance and areal capacitance of CoS-NiCo₂S₄/GCN||N-rGO are ∼2 and ∼4 times more than those of the CoS-NiCo₂S₄||N-rGO ASSHSC device, respectively. Furthermore, the CoS-NiCo₂S₄/GCN||N-rGO offers more energy density, rate energy density, and additional charge-discharge durability (over ∼10,000 cycles) than the CoS-NiCo₂S₄||N-rGO ASSHSC device. The multifold performance improvement of CoS-NiCo₂S₄ with GCN heterostructurization is ascribed to GCN-induced supplemented porosity and pore widening, ionic nonstoichiometry (Ni^2±δ, Co^2±δ, and Co^3±δ), wettability, integrated enhancement in the conductivity, and electroactive-ion accessibility in the CoS-NiCo₂S₄/GCN heterocomposite. The present study offers vital physicoelectrochemical insights toward the future development of low cost and high-performance electrode materials, and their implementation in high-rate and operationally stable all-solid-state hybrid supercapacitor devices, for application in the next-generation front-line technologies.

Facile Self-Assembly of Exfoliated Graphene/PANI Film for High-Energy Zn-Ion Micro-Supercapacitors

The Zn-ion micro-supercapacitor (ZMSC) is a promising candidate for developing miniaturized and integrated energy storage devices. To achieve high-performance functional groups with simple processing to composite with rod-like active PANI fibers, we prepared exfoliated graphene (EG) with an appropriate amount of O-containing functional groups. The appropriate O content simultaneously facilitated self-assembly of the EG and PANI fibers and maintained the electric conductivity of the composite, producing a free-standing EG/PANI film without additional conductive additives or current collectors. As an interdigital electrode for the ZMSC, the EG/PANI film showed ultrahigh capacitance of 1.8 F cm^-2 at 2.6 mA cm^-2 (361.3 F g^-1 at 0.5 A g^-1) and landmark energy density of 755.8 μWh cm^-2 at 2.3 mW cm^-2 (148.2 Wh kg^-1 at 451.7 W kg^-1). The facile preparation of the high-performance EG/PANI electrode provides a potential path for practical applications with ZMSCs.