Ultrahigh performance supercapacitors utilizing core-shell nanoarchitectures from a metal-organic framework-derived nanoporous carbon and a conducting polymer

Ultra-Stable High-Capacity Polythiophene Derivative for Wide-Potential-Window Supercapacitors

Conducting polymer (CP)-based supercapacitors show great promise for applications in the field of wearable and portable electronics. However, these supercapacitors face persistent challenges, notably low energy density and inadequate stability. In this study, we introduce a polythiophene derivative, designated as poly(EPE), synthesized via the electrochemical polymerization of 8-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-3,3-dimethyl-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepine (EPE). The resulting poly(EPE) polymer exhibits an exemplary 3D porous network-like structure, significantly enhancing its capacitance performance. When employed as the electrode material, the symmetric supercapacitor demonstrates an exceptionally high specific capacitance of 1342 F g-1 at a current density of 4.0 A g-1, along with impressive energy and power densities of 119.3 W h kg-1 and 38.83 kW kg-1, respectively. These capacitance values surpass those of previously reported pristine CP-based supercapacitors. Notably, the supercapacitor showcases outstanding stability, maintaining a retention rate of 92.5% even after 50,000 charge-discharge cycles. These findings underscore the substantial potential of poly(EPE) as an electrode material for the advancement of the supercapacitor technology.

High-performance electrode of ZIF-67 metal-organic framework (MOF) loaded laser-induced graphene (LIG) composite for all-solid-state supercapacitor

This work demonstrates a facile and efficient methodology to synthesize a composite material of zeolitic imidazolate frameworks (ZIFs) and laser-induced graphene (LIG). This ZIF-67 loaded LIG composite (ZIF-67/LIG) has been adequately characterized for its morphology and structure, and its electrochemical performance has been specifically examined. As supercapacitors (SCs) electrode material, the ZIF-67/LIG composite exhibits superb electrochemical performance, owing to the inherent high porosity, abundant active sites, large specific surface area of ZIF-67, and the excellent conductive three-dimensional hierarchical porous network structure provided by LIG. In three-electrode system, ZIF-67/LIG composite electrode displays outstanding areal specific capacitance (C_A) of 135.6 mF cm^-2at a current density of 1 mA cm^-2with 1 M Na₂SO₄aqueous electrolyte, which is far greater than that of pristine LIG (7.7 mF cm^-2). Furthermore, the ZIF-67/LIG composite has been fabricated into an all-solid-state planar micro-supercapacitor (MSC). This ZIF-67/LIG MSC exhibits an impressiveC_Aof 38.1 mF cm^-2at a current density of 0.20 mA cm^-2, a good cycling stability of 80.3% capacitance retention after 3000 cycles, and a high energy density of 5.29μWh cm^-2at a power density of 0.1 mW cm^-2. All electrochemical results clearly manifest that as-prepared ZIF-67/LIG composite can be a candidate in energy storage field with exciting possibilities.

Pouch-Type Asymmetric Supercapacitor Based on Nickel-Cobalt Metal-Organic Framework

Bimetal-organic frameworks (BMOFs) have attracted considerable attention as electrode materials for energy storage devices because of the precise control of their porous structure, surface area, and pore volume. BMOFs can promote multiple redox reactions because of the enhanced charge transfer between different metal ions. Therefore, the electroactivity of the electrodes can be significantly improved. Herein, we report a NiCo-MOF (NCMF) with a three-dimensional hierarchical nanorod-like structure prepared using a facile solvo-hydrothermal method. The as-prepared NCMF was used as the positive electrode in a hybrid pouch-type asymmetric supercapacitor device (HPASD) with a gel electrolyte (KOH+PVA) and activated carbon as the negative electrode. Because of the matchable potential windows and specific capacitances of the two electrodes, the assembled HPASD exhibits a specific capacitance of 161 F·g^-1 at 0.5 A·g^-1, an energy density of 50.3 Wh·kg^-1 at a power density of 375 W·kg^-1, and a cycling stability of 87.6% after 6000 cycles. The reported unique synthesis strategy is promising for producing high-energy-density electrode materials for supercapacitors.

Incorporation of α-MnO2 Nanoflowers into Zinc-Terephthalate Metal-Organic Frameworks for High-Performance Asymmetric Supercapacitors

Herein, we report the synthesis of α-MnO₂ nanoflower-incorporated zinc-terephthalate MOFs (MnO₂@Zn-MOFs) via the conventional solution phase synthesis technique as an electrode material for supercapacitor applications. The material was characterized by powder-X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy techniques. The prepared electrode material exhibited a specific capacitance of 880.58 F g^-1 at 5 A g^-1, which is higher than the pure Zn-BDC (610.83 F g^-1) and pure α-MnO₂ (541.69 F g^-1). Also, it showed a 94% capacitance retention of its initial value after 10,000 cycles at 10 A g^-1. The improved performance is attributed to the increased number of reactive sites and improved redox activity due to MnO₂ inclusion. Moreover, an asymmetric supercapacitor assembled using MnO₂@Zn-MOF as the anode and carbon black as the cathode delivered a specific capacitance of 160 F g^-1 at 3 A g^-1 with a high energy density of 40.68 W h kg^-1 at a power density of 20.24 kW kg^-1 with an operating potential of 0-1.35 V. The ASC also exhibited a good cycle stability of 90% of its initial capacitance.

Superstructures of Zeolitic Imidazolate Frameworks to Single- and Multiatom Sites for Electrochemical Energy Conversion

The exploration of electrocatalysts with high catalytic activity and long-term stability for electrochemical energy conversion is significant yet remains challenging. Zeolitic imidazolate framework (ZIF)-derived superstructures are a source of atomic-site-containing electrocatalysts. These atomic sites anchor the guest encapsulation and self-assembly of aspheric polyhedral particles produced using microreactor fabrication. This review provides an overview of ZIF-derived superstructures by highlighting some of the key structural types, such as open carbon cages, 1D superstructures, hollow structures, and the interconversion of superstructures. The fundamentals and representative structures are outlined to demonstrate the role of superstructures in the construction of materials with atomic sites, such as single- and dual-atom materials. Then, the roles of ZIF-derived single-atom sites for the electroreduction of CO₂ and electrochemical synthesis of H₂ O₂ are discussed, and their electrochemical performance for energy conversion is outlined. Finally, the perspective on advancing single- and dual-atom electrode-based electrochemical processes with enhanced redox activity and a low-impedance charge-transfer pathway for cathodes is provided. The challenges associated with ZIF-derived superstructures for electrochemical energy conversion are discussed.

An ultra-thin flexible wearable sensor with multi-response capability prepared from ZIF-67 and conductive metal-organic framework composites for health signal monitoring

Simulation of somatosensory systems in human skin with electronic devices has broad applications in the development of intelligent robots and wearable electronic devices. Here, we give an account of a new biomimetic flexible dual-mode pressure sensor, which is based on the first developed sea dandelion-like conductive metal-organic framework (cZIF-67@Cu-CAT) and the self-synthesized mechanically luminescent zinc sulfide nanoparticles and cleverly combines the microdome structure of the lotus leaf. According to finite element simulation analysis (FEA), the deformation behavior and pressure distribution of the contact interface with dandelion-like nanostructures cause the contact area of the sensor to increase rapidly and steadily with the load. It is for this reason that the piezoresistive pressure sensor has a high sensitivity of 71.74 kPa^-1 over a wide range of 0.5 to 80 kPa. More importantly, it can roughly perceive stress changes in the external environment through mechanoluminescence materials without a power supply. The ultra-thin flexible pressure sensor is suitable for sensitive monitoring of small vibrations, including wrist pulse and joint motion. Combined with Bluetooth data transmission, it is not difficult to see that the high-sensitivity ultra-thin sensor designed in this study has broad potential in the applications of bio-wearable electronics and will play an immeasurable role in various sports training and joint protection in the future.

Metal-organic frameworks and their derivatives for metal-ion (Li, Na, K and Zn) hybrid capacitors

Metal-ion hybrid capacitors (MIHCs) hold particular promise for next-generation energy storage technologies, which bridge the gap between the high energy density of conventional batteries and the high power density and long lifespan of supercapacitors (SCs). However, the achieved electrochemical performance of available MIHCs is still far from practical requirements. This is primarily attributed to the mismatch in capacity and reaction kinetics between the cathode and anode. In this regard, metal-organic frameworks (MOFs) and their derivatives offer great opportunities for high-performance MIHCs due to their high specific surface area, high porosity, topological diversity, and designable functional sites. In this review, instead of simply enumerating, we critically summarize the recent progress of MOFs and their derivatives in MIHCs (Li, Na, K, and Zn), while emphasizing the relationship between the structure/composition and electrochemical performance. In addition, existing issues and some representative design strategies are highlighted to inspire breaking through existing limitations. Finally, a brief conclusion and outlook are presented, along with current challenges and future opportunities for MOFs and their derivatives in MIHCs.

Nanocellulose/two dimensional nanomaterials composites for advanced supercapacitor electrodes

With the emerging of the problems of environmental pollution and energy crisis, the development of high-efficiency energy storage technology and green renewable energy is imminent. Supercapacitors have drawn great attention in wearable electronics because of their good performance and portability. Electrodes are the key to fabricate high-performance supercapacitors with good electrochemical properties and flexibility. As a biomass based derived material, nanocellulose has potential application prospects in supercapacitor electrode materials due to its biodegradability, high mechanical strength, strong chemical reactivity, and good mechanical flexibility. In this review, the research progress of nanocellulose/two dimensional nanomaterials composites is summarized for supercapacitors in recent years. First, nanocellulose/MXene composites for supercapacitors are reviewed. Then, nanocellulose/graphene composites for supercapacitors are comprehensively elaborated. Finally, we also introduce the current challenges and development potential of nanocellulose/two dimensional nanomaterials composites in supercapacitors.

Recent Advancements of Polyaniline/Metal Organic Framework (PANI/MOF) Composite Electrodes for Supercapacitor Applications: A Critical Review

Supercapacitors (SCs), also known as ultracapacitors, should be one of the most promising contenders for meeting the needs of human viable growth owing to their advantages: for example, excellent capacitance and rate efficiency, extended durability, and cheap materials price. Supercapacitor research on electrode materials is significant because it plays a vital part in the performance of SCs. Polyaniline (PANI) is an exceptional candidate for energy-storage applications owing to its tunable structure, multiple oxidation/reduction reactions, cheap price, environmental stability, and ease of handling. With their exceptional morphology, suitable functional linkers, metal sites, and high specific surface area, metal–organic frameworks (MOFs) are outstanding materials for electrodes fabrication in electrochemical energy storage systems. The combination of PANI and MOF (PANI/MOF composites) as electrode materials demonstrates additional benefits, which are worthy of exploration. The positive impacts of the two various electrode materials can improve the resultant electrochemical performances. Recently, these kinds of conducting polymers with MOFs composites are predicted to become the next-generation electrode materials for the development of efficient and well-organized SCs. The recent achievements in the use of PANI/MOFs-based electrode materials for supercapacitor applications are critically reviewed in this paper. Furthermore, we discuss the existing issues with PANI/MOF composites and their analogues in the field of supercapacitor electrodes in addition to potential future improvements.

Material Nanoarchitectonics of Functional Polymers and Inorganic Nanomaterials for Smart Supercapacitors

Smart supercapacitors are a promising energy storage solution due to their high power density, long cycle life, and low-maintenance requirements. Functional polymers (FPs) and inorganic nanomaterials are used in smart supercapacitors because of the favorable mechanical properties (flexibility and stretchability) of FPs and the energy storage properties of inorganic materials. The complementary properties of these materials facilitate commercial applications of smart supercapacitors in flexible smart wearables, displays, and self-generation, as well as energy storage. Here, an overview of strategies for the development of suitable materials for smart supercapacitors is presented, based on recent literature reports. A range of synthetic techniques are discussed and it is concluded that a combination of organic and inorganic hybrid materials is the best option for realizing smart supercapacitors. This perspective facilitates new strategies for the synthesis of hybrid materials, and the development of material technologies for smart energy storage applications.

Hydrogenation of phenol to cyclohexanol using carbon encapsulated Ni–Co alloy nanoparticles

Highly active NiCo alloy nanoparticles for phenol hydrogenation to cyclohexanol were developed.

In Situ-Grown Heterostructured Co3S4/CNTs/C Nanocomposites with a Bridged Structure for High-Performance Supercapacitors

As one of the most competitive candidates for energy storage devices, supercapacitors have attracted extensive research interest due to their incomparable power density and ultralong cycling stability. However, the large surface area required for charge storage is an irreconcilable contradiction with the requirement of energy density. Therefore, a high energy density is a major challenge for supercapacitors. To solve the contradiction, Co₃S₄/CNTs/C with a bridged structure is designed, where CNTs generated in situ serve as a bridge to connect a porous carbon matrix and a Co₃S₄ nanoparticle, and Co₃S₄ nanoparticles are anchored on the topmost of CNTs. The porous carbon and Co₃S₄ are used for electrochemical double-layer capacitors and pseudocapacitors, respectively. This bridged structure can efficiently utilize the surface of Co₃S₄ nanoparticles to increase the overall energy storage capacity and provide more electrochemically active sites for charge storage and delivery. The materials show an energy density of 41.3 Wh kg^-1 at 691.9 W kg^-1 power density and a retaining energy density of 33.1 Wh kg^-1 at a high power density of 3199.9 W kg^-1 in an asymmetrical supercapacitor. The synthetic technique provides a simple method to obtain heterostructured nanocomposites with a high energy density by maximizing the effect of pseudocapacitor electrode active materials.

A novel zinc sulfide impregnated carbon composite derived from zeolitic imidazolate framework-8 for sodium-ion hybrid solid-state flexible capacitors

The pyrolysis of metal-organic frameworks (MOFs) is an easy approach to prepare metal oxides as well as nanoporous carbon with high specific surface area. In the present work, for the first time, ZIF-8 (zeolitic imidazolate framework-8) has been pyrolyzed under different conditions to derive two products, i.e., highly porous carbon (C) and zinc sulfide (ZnS) infused carbon (ZnS@C). These two materials, i.e., nanoporous C and ZnS@C, have been investigated as a negative and a positive electrode, respectively, for potential application in a hybrid asymmetrical solid-state supercapacitor device (HASD). The controlled pyrolysis approach for the preparation of ZnS@C has yielded uniformly distributed ZnS nanoparticles inside the carbon structure. A 1.8 V HASD has been assembled, which delivered an excellent energy density of 38.3 W h kg^-1 (power density of 0.92 kW kg^-1) along with the greatly desirable feature of cycling stability. The proposed selection of materials as electrodes is promising to develop futuristic hybrid capacitors.

High electrochemical performance of Ni-foam supported Ti3C2TxMXene/rGO nanocomposite

Two-dimensional (2D) materials have attracted extensive attention owing to their unique electronic/physiochemical properties, and wide application potential in energy storage and conversion. However, 2D materials are often tendency to aggregate due to the strong van der Waals interactions, leading to gradually decrease of an efficient mass transfer pathway and accessible surface area for the electrolyte. Here, we demonstrate an efficient approach for large-scale production of a hybrid nanostructures (Ti₃C₂T_x/rGO) based on ultrathin MXene nanosheets anchored on layered reduced graphene (rGO) supported by porous Ni-foam via a plain chemical dipping method followed by high temperature annealing process. Ti₃C₂T_x/rGO electrode exhibits a porous structure, excellent ionic and electrical conductivities, and remarkable specific capacitance. Furthermore, it shows ultra-high cycle stability, for example, 88.70% of its specific capacity can be maintained through 3000 cycles. This kind of porous nanostructure and integrated design idea is significant to design other energy storage modules.

Metal organic framework derived porous carbon materials excel as an excellent platform for high-performance packaged supercapacitors

Designing and synthesizing new materials with special physical and chemical properties are the key steps to assembling high performance supercapacitors. Metal organic framework (MOF) derived porous carbon materials have drawn great attention in supercapacitors because of their large specific surface area, high chemical/thermal stability and tunable pore structure. Thus, the recent development of porous carbon as an electrode material for supercapacitors is reviewed. The types, design and synthesis strategies of porous carbon are systematically summarized. This review will be divided into three main parts: (1) the design and synthesis of MOF precursors and templates for MOF-derived porous carbon materials; (2) the application of different types of MOF-derived carbon in supercapacitors; and (3) the design of typical structures of porous carbon composites for supercapacitors. Finally, the problems and challenges confronted when using porous carbon are assessed and elaborated, and some suggestions on future research directions are proposed.

Zeolitic imidazolate framework (ZIF)-derived porous carbon materials for supercapacitors: an overview

The present analysis focuses on the synthetic methods used for the application of supercapacitors with various mysterious architectures derived from zeolitic imidazolate frameworks (ZIFs). ZIFs represent an emerging and unique class of metal–organic frameworks with structures similar to conventional aluminosilicate zeolites, consisting of imidazolate linkers and metal ions. Their intrinsic porous properties, robust functionalities, and excellent thermal and chemical stabilities have resulted in a wide range of potential applications for various ZIF materials. In this rapidly expanding area, energetic research activities have emerged in the past few years, ranging from synthesis approaches to attractive applications of ZIFs. In this analysis, the development of high-performance supercapacitor electrodes and recent strategies to produce them, including the synthesis of various heterostructures and nanostructures, are analyzed and summarized. This analysis goes via the ingenuity of modern science when it comes to these nanoarchitecture electrodes. Despite these significant achievements, it is still difficult to accurately monitor the morphologies of materials derived from metal–organic frameworks (MOFs) because the induction force during structural transformations at elevated temperatures is in high demand. It is also desirable to achieve the direct synthesis of highly functionalized nanosized materials derived from zeolitic imidazolate frameworks (ZIFs) and the growth of nanoporous structures based on ZIFs encoded in specific substrates for the construction of active materials with a high surface area suitable for electrochemical applications. The latest improvements in this field of supercapacitors with materials formed from ZIFs as electrodes using ZIFs as templates or precursors are discussed in this review. Also, the possibility of usable materials derived from ZIFs for both existing and emerging energy storage technologies is discussed.

The present analysis focuses on the synthetic methods used for the application of supercapacitors with various mysterious architectures derived from zeolitic imidazolate frameworks (ZIFs).

Porous Carbon-Based Supercapacitors Directly Derived from Metal-Organic Frameworks

Numerously different porous carbons have been prepared and used in a wide range of practical applications. Porous carbons are also ideal electrode materials for efficient energy storage devices due to their large surface areas, capacious pore spaces, and superior chemical stability compared to other porous materials. Not only the electrical double-layer capacitance (EDLC)-based charge storage but also the pseudocapacitance driven by various dopants in the carbon matrix plays a significant role in enhancing the electrochemical supercapacitive performance of porous carbons. Since the electrochemical capacitive activities are primarily based on EDLC and further enhanced by pseudocapacitance, high-surface carbons are desirable for these applications. The porosity of carbons plays a crucial role in enhancing the performance as well. We have recently witnessed that metal-organic frameworks (MOFs) could be very effective self-sacrificing templates, or precursors, for new high-surface carbons for supercapacitors, or ultracapacitors. Many MOFs can be self-sacrificing precursors for carbonaceous porous materials in a simple yet effective direct carbonization to produce porous carbons. The constituent metal ions can be either completely removed during the carbonization or transformed into valuable redox-active centers for additional faradaic reactions to enhance the electrochemical performance of carbon electrodes. Some heteroatoms of the bridging ligands and solvate molecules can be easily incorporated into carbon matrices to generate heteroatom-doped carbons with pseudocapacitive behavior and good surface wettability. We categorized these MOF-derived porous carbons into three main types: (i) pure and heteroatom-doped carbons, (ii) metallic nanoparticle-containing carbons, and (iii) carbon-based composites with other carbon-based materials or redox-active metal species. Based on these cases summarized in this review, new MOF-derived porous carbons with much enhanced capacitive performance and stability will be envisioned.

Assembling well-arranged covalent organic frameworks on MOF-derived graphitic carbon for remarkable formaldehyde sensing

Constructing heterostructures with advanced architectures is an effective strategy for enhancing the crystallinity and functional performance of covalent organic frameworks (COFs). Herein, a novel core-shell heterostructure integrating a metal-organic framework (MOF)-derived graphitic carbon core (GC) and a well-arranged COF shell, termed MOF-GC@COF, is reported. ZIF-67 dodecahedra are first chemically etched with a weak organic acid and further converted to MOF-GC via thermal pyrolysis. In the subsequent step, β-ketoenamine-linked COF nanofibers are vertically assembled on the surface of the MOF-GC cores to generate the MOF-GC@COF heterostructure. As a proof-of-concept application, the as-prepared MOF-GC@COF heterostructure is used as an effective quartz crystal microbalance (QCM) sensor for the adsorption of formaldehyde. Benefiting from the synergistic effect of the hybrid composition and the advantages of the core-shell heterostructure, the newly prepared MOF-GC@COF heterostructure exhibits excellent sensing performance toward formaldehyde with rapid adsorption kinetics, high sensitivity, and superior selectivity.

One-step preparation and characterization of a nanostructured hybrid electrode material via a microwave energy-based approach

Nanostructured hybrid electrode materials are prepared in one-step via a MW energy-based approach with promising electrochemical energy storage application performance.

Rationally engineered 3D-dendritic cell-like morphologies of LDH nanostructures using graphene-based core-shell structures

Functionalization of graphene-based materials using chemical moieties not only modify the electronic structure of the underlying graphene but also enable in limited enhancement of targeted properties. Surface modification of graphene-based materials using other nanostructures enhances the effective properties by minimally modifying the properties of pristine graphene backbone. In this pursuit, we have synthesized bio-inspired hierarchical nanostructures based on Ni-Co layered double hydroxide on reduced graphene oxide core-shells using template based wet chemical approach. The material synthesized have been characterized structurally and electrochemically. The fabricated dendritic morphology of the composite delivers a high specific capacity of 1056 Cg^-1. A cost effective solid state hybrid supercapacitor device was also fabricated using the synthesized electrode material which shows excellent performance with high energy density and fast charging capability.

Ultrastable tetraphenyl-p-phenylenediamine-based covalent organic frameworks as platforms for high-performance electrochemical supercapacitors

In this study we synthesized two tetraphenyl-p-phenylenediamine-based covalent organic frameworks (TPPDA-TPPyr and TPPDA-TPTPE COFs) for potential use in high-performance electrochemical supercapacitors. This excellent performance arose from their structures containing redox-active triphenylamine derivatives and their high surface areas.

Size-Related Electrochemical Performance in Active Carbon Nanostructures: A MOFs-Derived Carbons Case Study

Metal-organic framework-derived carbon nanostructures have generated significant interest in electrochemical capacitors and oxygen/hydrogen catalysis reactions. However, they appear to show considerably varied structural properties, and thus exhibit complex electrochemical-activity relationships. Herein, a series of carbon polyhedrons of different sizes, between 50 nm and µm, are synthesized from zeolitic imidazolate frameworks, ZIF-8 (ZIF-derived carbon polyhedrons, ZDCPs) and their activity is studied for capacitance and the oxygen reduction reaction (ORR). Interestingly, a well-correlated performance relationship with respect to the particle size of ZDCPs is evidenced. Here, the identical structural features, such as specific surface area (SSA), microporosity, and its distribution, nitrogen doping, and graphitization are all strictly maintained in the ZDCPs, thus allowing identification of the effect of particle size on electrochemical performance. Supercapacitors show a capacity enhancement of 50 F g-1 when the ZDCPs size is reduced from micrometers to ≤200 nm. The carbonization further shows a considerable effect on rate capacitance-ZDCPs of increased particle size lead to drastically reduced charge transportability and thus inhibit their performance for both the charge storage and the ORR. Guidelines for the capacitance variation with respect to the particle size and SSA in such carbon nanostructures from literature are presented.

Ni(OH)2 Nanoflakes Supported on 3D Ni3 Se2 Nanowire Array as Highly Efficient Electrodes for Asymmetric Supercapacitor and Ni/MH Battery

Porous Ni(OH)₂ nanoflakes are directly grown on the surface of nickel foam supported Ni₃ Se₂ nanowire arrays using an in situ growth procedure to form 3D Ni₃ Se₂ @Ni(OH)₂ hybrid material. Owing to good conductivity of Ni₃ Se₂ , high specific capacitance of Ni(OH)₂ and its unique architecture, the obtained Ni₃ Se₂ @Ni(OH)₂ exhibits a high specific capacitance of 1689 µAh cm^-2 (281.5 mAh g^-1 ) at a discharge current of 3 mA cm^-2 and a superior rate capability. Both the high energy density of 59.47 Wh kg^-1 at a power density of 100.54 W kg^-1 and remarkable cycling stability with only a 16.4% capacity loss after 10 000 cycles are demonstrated in an asymmetric supercapacitor cell comprising Ni₃ Se₂ @Ni(OH)₂ as a positive electrode and activated carbon as a negative electrode. Furthermore, the cell achieved a high energy density of 50.9 Wh L^-1 at a power density of 83.62 W L^-1 in combination with an extraordinary coulombic efficiency of 97% and an energy efficiency of 88.36% at 5 mA cm^-2 when activated carbon is replaced by metal hydride from a commercial NiMH battery. Excellent electrochemical performance indicates that Ni₃ Se₂ @Ni(OH)₂ composite can become a promising electrode material for energy storage applications.

Fabrication of Highly Conductive Porous Cellulose/PEDOT:PSS Nanocomposite Paper via Post-Treatment

In this paper, we report the fabrication of highly conductive poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS)/cellulose nanofiber (CNF) nanocomposite paper with excellent flexibility through post-treatment with an organic solvent. The post-treated PEDOT:PSS/CNF porous nanocomposite papers showed a lower sulfur content, indicating the removal of residual PSS. The electrical conductivity of PEDOT:PSS/CNF porous nanocomposite paper was increased from 1.05 S/cm to 123.37 S/cm and 106.6 S/cm by post-treatment with dimethyl sulfoxide (DMSO) and ethylene glycol (EG), respectively. These values are outstanding in the development of electrically conductive CNF composites. Additionally, the highly conductive nanocomposite papers showed excellent bending stability during bending tests. Cyclic voltammetry (CV) showed a Faradaic redox reaction and non-Faradaic capacitance due to the redox activity of PEDOT:PSS and large surface area, respectively. Electrochemical energy storage ability was evaluated and results showed that capacitance improved after post-treatment. We believe that the highly conductive PEDOT:PSS/CNF porous nanocomposite papers with excellent flexibility described here are potential candidates for application in porous paper electrodes, flexible energy storage devices, and bioengineering sensors.

Temperature-Dependent Morphologies of Precursors: Metal-Organic Framework-Derived Porous Carbon for High-Performance Electrochemical Double-Layer Capacitors

In this work, three Cu metal-organic framework samples with tunable rhombic, squama, and trucated bipyramid morphologies have been synthesized at 0, 25, and 60 °C, respectively, and further employed as precursors to initially prepare Cu@C composites by the calcination-thermolysis procedure. Then Cu@C composites have been etched with HCl and subsequently activated with KOH to obtain activated porous carbon (APC-0, -25, and -60). Interestingly, APC-25 presents a loose multilevel morphology of cabbage and possesses the largest specific surface area (1880.4 m² g^-1) and pore volume (0.81 cm³ g^-1) among these APC materials. Consequently, APC-25 also exhibits the highest specific capacitance of 196 F g^-1 at 0.5 A g^-1, and the corresponding symmetric supercapacitor cell (SSC) achieves a remarkable energy density of 11.8 Wh kg^-1 at a power density of 350 W kg^-1. Furthermore, APC-25 shows excellent cycling stability, and the loss of capacitance is only 7.7% even after 10000 cycles at 1 A g^-1. Significantly, five light-emitting diodes can be lit by six SSCs, which proves that APC-25 can be used in energy storage devices.

Rapid synthesis of Ni(OH)2/graphene nanosheets and NiO@Ni(OH)2/graphene nanosheets for supercapacitor applications

β-Ni(OH)₂ or NiO@Ni(OH)₂ grew on commercial graphene nanosheets with high specific capacitance and excellent rate capability.

High-Performance Symmetrical Supercapacitor with a Combination of a ZIF-67/rGO Composite Electrode and a Redox Additive Electrolyte

The synthesis of a highly porous composite of ZIF-67 and reduced graphene oxide (rGO) using a simple stirring approach is reported. The composite has been investigated as an electrode to be assembled in a supercapacitor. In the presence of an optimized redox additive electrolyte (RAE), that is, 0.2 M K3[Fe(CN)6] in 1 M Na2SO4, the ZIF-67/rGO composite electrode has combined the properties of improved conductivity, high specific surface area, and low resistance. The proposed composite electrode in the three-electrode system shows an ultrahigh specific capacitance of 1453 F g-1 at a current density of 4.5 A g-1 within a potential window of -0.1 to 0.5 V. Further, the ZIF-67/rGO composite electrode was used to fabricate a symmetrical supercapacitor whose operation in the presence of the RAE has delivered high values of specific capacitance (326 F g-1 at a current density of 3 A g-1) and energy density (25.5 W h kg-1 at a power density of 2.7 kW kg-1). The device could retain about 88% of its initial specific capacitance after 1000 repeated charge-discharge cycles. The practical usefulness of the device was also verified by combining two symmetrical supercapacitors in series and then lighting a white light-emitting diode (illumination for 3 min). This study, for the first time, reports the application of a ZIF-based composite (ZIF-67/rGO) in the presence of an RAE to design an efficient supercapacitor electrode. This proposed design is also scalable to a flexible symmetric device delivering high values of specific capacitance and energy density.

Engineering hydrogenated manganese dioxide nanostructures for high-performance supercapacitors

Improving the rate capability of transition metal oxides is of great important for the development of high-performance electrodes for supercapacitors. Here, a novel strategy of hydrogenation to enhance the electron transfer rate of manganese dioxide (MnO₂) is proposed. Detailed preparative parameters (i.e. hydrogenation temperature and time) are systematically investigated. The hydrogenated MnO₂ (H-MnO_x) exhibits modified crystal phase/surface structures and increased electrical conductivity. The prepared H-MnO_x exhibits high specific capacitance (640 mF cm^-2 at current density of 1 mA cm^-2), good rate capability (89.6% of capacitance retained from 1 to 10 mA cm^-2), and good cycling stability (84.6% retention after 1000 cycles). The high specific capacitance is ascribed to the unique interconnected ultrathin nanosheets structure, which could not only provide porous channels for electrolyte infiltration to offer sufficient electrode/electrolyte interface, but also shorten the ions diffusion distance inside the active material. The good rate capability could be attributed to the good conductivity of the H-MnO_x nanosheets, which was confirmed by the DFT calculation. These results highlight the importance of hydrogenation as a facile yet effective strategy to improve the rate capability of transition metal oxides for supercapacitors.