Confining Redox Electrolytes in Functionalized Porous Carbon with Improved Energy Density for Supercapacitors

Recent advances in supramolecular self-assembly derived materials for high-performance supercapacitors

The key preponderance of supramolecular self-assembly strategy is its ability to precisely assemble various functional units at the molecular level through non-covalent bonds to form multifunctional materials. Supramolecular materials have the merits of diverse functional groups, flexible structure, and unique self-healing properties, which make them of great value in the field of energy storage. This paper reviews the latest research progress of the supramolecular self-assembly strategy for the advanced electrode materials and electrolytes for supercapacitors, including supramolecular self-assembly for the preparation of high-performance carbon materials, metal-based materials and conductive polymer materials, and its beneficial effects on the performance of supercapacitors. The preparation of high performance supramolecular polymer electrolytes and their application in flexible wearable devices and high energy density supercapacitors are also discussed in detail. In addition, at the end of this paper, the challenges of the supramolecular self-assembly strategy are summarized and the development of supramolecular-derived materials for supercapacitors is prospected.

Atypical performance of CoO-accelerated interface tweaking in hierarchical cobalt phosphide/oxide@P-doped rGO heterostructures for hybrid supercapacitors

Designing two-dimensional (2D) heterostructures based on suitable energy materials is a promising strategy to achieve high-performance supercapacitors with hybridized transition metal and carbonaceous-based electrodes. The influence of each component and its content on the capacitor performance necessitates deeper insights. In this study, a 2D/2D heterostructure made of hierarchical pseudocapacitive cobalt phosphide/oxide and P-doped reduced graphene oxide (PrGO) nanosheets (CoP/CoO@PrGO) was fabricated using porous zeolitic-imidazolate framework precursor. The decoration of 2D leaf-like CoP/CoO hybrid onto PrGO could create a unique interface with a large number of active sites, CoO-driven creation of pseudocapacitive surface PO_x species, and high P content (∼3 at.%) in PrGO, thus promoting the Faradaic reaction, electrical conductivity, and overall charge storage. This framework yields a high specific capacitance of 405 F g^-1 at 5 A g^-1 and excellent cycling stability (over 100 % after 10,000 cycles), superior to those of pristine CoP@PrGO (300 F g^-1 at 5 A g^-1). Furthermore, the fabricated asymmetric supercapacitor delivers reasonable energy density of 4.2 Wh kg^-1 at a power density of 785 W kg^-1 and cycling stability of ∼100 % after 10,000 cycles. Therefore, CoP/CoO@PrGO with its unique interfacial properties can promote the development of heterostructure electrode for high-performance supercapacitors.

Nanostructured Poly(3,4-ethylenedioxythiophene) Coatings on Functionalized Glass for Energy Storage

Conducting polymers rise among some of the most promising transparent supercapacitor electrode materials due to high conductivity, environmental stability, light weight, and ease of synthesis. A major challenge for depositing conducting polymers on a glass substrate is the lack of molecular interactions between organic and inorganic moieties resulting in poor adhesion and low cycling stability of the electrode. We present a synthetic approach by covalently linking poly(3,4-ethylyenedioxythiophene) (PEDOT) and glass through Friedel-Crafts alkylation on a self-assembled diphenyldimethoxysilane monolayer. This method obviates the need for a conductive FTO or ITO coating, enabling the fabrication of current collector-free planar supercapacitor electrodes on any glass surface. The electrode produced from our vapor-phase synthesis is coated with a highly conductive nanofibrillar PEDOT film (sheet resistance 2.1 Ω/□) possessing a gravimetric capacitance of ∼200 F/g. Our PEDOT planar supercapacitor possesses outstanding stability (86% capacitance retention after 50,000 cycles). We also fabricate a proof-of-concept transparent tandem supercapacitor on PEDOT-coated glass using 3D-printed frames that supplies enough voltage and current to light up a blue light-emitting diode (LED).

Understanding the Operating Mechanism of Aqueous Pentyl Viologen/Bromide Redox-Enhanced Electrochemical Capacitors with Ordered Mesoporous Carbon Electrodes

Compared to traditional electric double-layer capacitors, redox-enhanced electrochemical capacitors (redox-ECs) show increased energy density and steadier power output thanks to the use of redox-active electrolytes. The aim of this study is to understand the electrochemical mechanisms of the aqueous pentyl viologen/bromide dual redox system at the interface of an ordered mesoporous carbon (CMK-8) and improve the device performance. Cells with CMK-8 carbon electrodes were investigated in several configurations using different charging rates and potential windows. The pentyl viologen electrochemistry shows a mixed behavior between solution-based diffusion and adsorption phenomena, with the reversible formation of an adsorbed layer. The extension of the voltage window allows for full reduction of the viologen molecules during charge and a consequent increase in the specific discharge energy delivered by the cell. Investigation of the mechanism indicates that a 1.5 V charging voltage with a 0.5 A g^-1 charging rate and fast discharge rate produces the best overall performance.

Tailoring the capacitive performance of ZnCo2O4 by doping of Ni2+ and fabrication of asymmetric supercapacitor

The specific capacity of ZnCo2O4 tailored effectively by doping with Ni2+

Hierarchically Engineered Nanocarbon Florets as Bifunctional Electrode Materials for Adsorptive and Intercalative Energy Storage

Three-dimensional dendritic nanostructured carbon florets (NCFs) with tailored porosity are demonstrated as electrochemically versatile electrodes for both adsorptive and intercalative energy storage pathways. Achieved through a single-step template-driven approach, the NCFs exhibit turbostratic graphitic lamellae in a floral assembly leading to high specific surface area and multi-modal pore distribution (920 m²/g). The synergism in structural and chemical frameworks, along with open-ended morphology, enables bifunctionality of hard carbon NCFs as symmetric adsorptive electrodes for supercapacitors (SCs) and intercalation anodes for hybrid potassium-ion capacitors (KICs). Flexible, all-solid-state SCs through facile integration of NCF with the ionic-liquid-imbibed porous polymeric matrix achieve high-energy density (20 W h/kg) and power density (32.7 kW/kg) without compromising on mechanical flexibility and cyclability (94% after 20k cycles). Furthermore, NCF as an anode in a full-cell hybrid KIC (activated carbon as cathode) delivers excellent electrochemical performance with maximum energy and power densities of 57 W h/kg and 12.5 kW/kg, respectively, when cycled in a potential window of 1.0-4.0 V. The exceptional bifunctional performance of NCF highlights the possibility of utilizing such engineered nanocarbons for high-performance energy storage devices.

High Entropy Oxides-A Cost-Effective Catalyst for the Growth of High Yield Carbon Nanotubes and Their Energy Applications

This report anticipates a thorough strategy for the utilization of high entropy oxide (HEO) nanoparticles (1) as a cost-effective catalyst for the growth of high yield carbon nanotubes (CNTs), resulting in HEO-CNT nanocomposites, and (2) the implementation of HEO-CNT nanocomposites for energy applications such as electrochemical capacitors (ECs). In the first step, HEO nanoparticles were synthesized by a simple sol-gel autocombustion method and then the as-synthesized HEO nanoparticles were ground and used as the catalyst for the growth of CNTs by chemical vapor deposition technique. The as-grown CNTs (HEO-CNT nanocomposite) exhibited unexpectedly high yield, a superior specific surface area of ∼151 m² g^-1, and encapsulation and diffusion of the catalyst throughout the HEO-CNT nanocomposite, providing remarkably high mechanical strength, which make them a promising candidate for energy applications. To study the electrochemical activity of the HEO-CNT nanocomposite, half-cell and full-cell ECs were assembled in different electrolytes. Stupendously, a complete 100% capacitance retention and a Coulombic efficiency up to 15 000 cycles were realized for the HEO-CNT nanocomposite-based full-cell EC assembled in the polyvinyl alcohol/H₂SO₄ hydrogel electrolyte. Additionally, a high specific capacitance value of 286.0 F g^-1 at a scan rate of 10 mV s^-1 for the HEO-CNT nanocomposite-based full-cell EC assembled in the [BMIM][TFSI] electrolyte with a wide potential window of 2.5 V is reported. Also, high energy density and power density of ∼217 W h kg^-1 and ∼24 521 W kg^-1, respectively, are reported. Furthermore, the HEO-CNT nanocomposite-based full-cell EC assembled in the [BMIM][TFSI] electrolyte can successfully light up a red light-emitting diode, demonstrating great potential of the HEO-CNT nanocomposite in the various energy applications.

Monodisperse Carbon Sphere-Constructed Pomegranate-Like Structures for High-Volumetric-Capacitance Supercapacitors

Porous carbons have been extensively studied in supercapacitors. However, it remains a grand challenge for porous carbons to achieve a volumetric capacitance ( C_v) of over 200 F cm^-3 because of the low intrinsic density and limited capacitance. Herein, we propose a pomegranate-like carbon microsphere (PCS) constructed by monodisperse, submicron, N-doped microporous carbon spheres for high-volumetric-capacitance supercapacitors. The assembly of submicron carbon spheres into pomegranate-like structures significantly reduces the required binder amount (2.0 wt %) for electrode preparation, diminishes the interparticle resistance, and most importantly, endows the PCS with a high packing density (0.75 g cm^-3). Benefited from the high surface area (1477 m² g^-1), N-doping (3.0 wt %), and high packing density, the PCS demonstrates a high C_v (254 F cm^-3), four times that of unassembled monodisperse carbon spheres. This work opens a new avenue to enhance the C_v of porous carbons without compromising the rate capability or cyclability.

Nanosheets of nickel, cobalt and manganese triple hydroxides/oxyhydroxides as efficient electrode materials for asymmetrical supercapacitors

An in situ method to fabricate thin nanosheets of Nickel, Cobalt and Manganese composite for charge storage applications is reported.

Molecular engineering of supercapacitor electrodes with monodispersed N-doped carbon nanoporous spheres

Water phase synthesis of polytriazine nanospheres as the high-nitrogen content carbon spheres precursor for a high-performance EDLC electrode.