Pseudocapacitive Performance Research Articles

Graphene quantum dot inlaid carbon nanofibers: Revealing the edge activity for ultrahigh rate pseudocapacitive energy storage

The edge sites of carbon show high electrochemical activity because of the unique electronic structure and functionalization. But revealing their energy storage ability and the underlying mechanism are still challenging. Herein, we prepare a novel edge-enriched carbon nanofiber fabric by exposing the embedded graphene quantum dots (GQDs) through partial hydrolysis of the electrospun GQDs/polyacrylonitrile fabric. The edges of inlaid GQDs are mainly terminated by various oxygen-bearing functional groups even after high temperature treatment, simultaneously contributing to abundant surface redox active sites and good electrolyte wettability. Further facilitated by the entire conductive networks, the edge sites are proved to show an ultrafast pseudocapacitive performance (200 F g−1 at 1 A g−1, 130 F g−1 at 100 A g−1) because of the robust electrochemical kinetics. Moreover, at an ultra-high mass loading of 25.5 mg cm−2 (thickness: 1.4 mm), the multilayer-folded fabric performs a remarkable areal capacitance (3.95 F cm−2 at 25.5 mA cm−2), outstanding rate performance (2.04 F cm−2 at 510 mA cm−2), and good cycle stability (98% capacitance retention after 10,000 times), demonstrating the great potential of edge structure design for high power devices.

Solvothermal synthesis of MnCo2O4 microspheres for high-performance electrochemical supercapacitors

MnCo2O4 microspheres were synthesized via the solvothermal method by employing ethylene glycol as a solvent and these synthesized materials were characterized by Field Emission Scanning Electron Microscope (FESEM), Energy Dispersive Analysis of X-rays (EDAX), X-ray Diffraction spectroscopy (XRD), X-ray Photoelectron Spectroscopy (XPS). The morphology and structural conformation of MnCo2O4 microspheres were confirmed by FESEM and XRD. The electrochemical performance of MnCo2O4 @ 18 h electrode material was analyzed by cyclic voltammetry, Galvanostatic charge discharge, and electrochemical impedance spectroscopy techniques. Impressively, the MnCo2O4 @ 18 h microspheres achieved remarkable results in pseudocapacitive performance with a high specific capacitance of 439 Fg−1 at 1 Ag−1 and exhibits excellent cyclic stability of 80.6% capacitance retention after 10,000 cycles at 1 Ag−1.

Mn doped graphene aerogels for high capacity and long-life supercapacitor

The pure graphene aerogel material is a double-layer capacitor material which provides capacitance by the surface area. Its conductivity and specific capacitance require further improvement. In this work, manganese doped graphene aerogels were synthesized by hydrothermal method using manganese chloride as a source of manganese. The effect of manganese content on the structure and properties of the material was studied. It is found that the specific surface area and pore volume of aerogels decrease with the increase of Mn content. The Mn doped graphene aerogel prepared at the current density of 0.1 A/g shows a capacitance of 180 F/g and exhibits pseudo capacitance performance in the three-electrode test. After assembling the button capacitor, the capacity retention rate is 93% after 1000 cycles at a current density of 0.5 A/g.

Enhanced pseudo-capacitance and rate performance of amorphous MnO2 for supercapacitor by high Na doping and structural water content

Owing to the advantages of high theoretical capacitance, low cost, and environmental friendliness, MnO2 shows a great potential as the electrode material for supercapacitors. However, its low conductivity and sluggish ion migration lead to the unsatisfied electrochemical performance especially at high rates. In this work, amorphous MnO2 with both high Na doping and structural water content (nw-MnO2) is synthesized via a simple redox reaction in the saturated sodium chloride solution. On the one hand, high Na doping can effectively improve the conductivity of MnO2; on the other hand, the charge shielding effect enabled by structural water facilitates the rapid ion migration in MnO2 lattice. In addition, the amorphous feature also provides more active sites and decreases the ion diffusion length. Benefitting from the above merits, the prepared nw-MnO2 electrode delivers superior rate performance (324.7 F g−1 at 0.5 A g−1 and 182.6 F g−1 even at an ultrahigh rate of 50 A g−1) and excellent cycle stability with 91% of capacitance retention over 10,000 cycles. Moreover, the assembled nw-MnO2//activated carbon asymmetric supercapacitor delivers a high energy density of 81.1 Wh kg−1 and superior capacity retention of 101% after 7000 cycles.

2D Conjugated Covalent Organic Frameworks: Defined Synthesis and Tailor-Made Functions

ConspectusCovalent organic frameworks (COFs) are an emerging class of crystalline porous polymers and have received tremendous attention and research interest. COFs can be classified into two-dimensional (2D) and three-dimensional (3D) analogues. Resembling the architectures of porous graphene, 2D conjugated COFs have exhibited promising prospects in many fields, such as gas storage and separation, heterogeneous catalysis, sensing, photocatalysis, environmental remediation, drug delivery, energy storage and conversion, and so forth. However, efficient structural design for high-throughput production of crystalline 2D COFs remains challenging.In this Account, we summarize our recent contributions to the design, synthesis, and application exploration of 2D conjugated COFs. First, we raised an efficient "two-in-one" strategy for the facile synthesis of 2D imine COFs with good reproducibility and solvent adaptability. Thanks to this elaborate molecular design strategy, we could easily modulate the topology of COFs and fabricate COF films. In addition, we developed two approaches to stabilize the 2D conjugated COFs by using planar building blocks and donor-acceptor structures. We also proposed a skeleton engineering strategy to design COFs as electrode materials, through which redox-active orthoquinone moieties were stepwise-incorporated in the skeletons of isostructural 2D imine-linked COFs. This strategy enabled systematic investigations on a series of 2D conjugated COFs with analogous structures but different numbers of active sites for energy storage, which provides a good platform to unveil the underlying structure-property relationships. In addition, we recently developed a new kind of arylamine-linked 2D conjugated COFs. The electroactive diphenylamine linkages endowed these 2D conjugated COFs with extended conjugation and improved stability, which also conferred these COFs with excellent pseudocapacitive energy storage performance. Moreover, tailor-made sulfur-rich COFs were introduced that were synthesized by selective introduction of polysulfide or sulfonyl groups on the COF skeletons and were used for Li storage and proton conduction. At the end, the key challenges of 2D conjugated COFs toward practical applications and their future prospects are suggested. We hope that this Account will evoke new inspirations and innovative work in the field of 2D conjugated COFs in the near future, especially in some burgeoning and interdisciplinary research areas.

Pyrazine-based organic electrode material for high-performance supercapacitor applications

Pseudocapacitors (PCs) exhibit high capacitance and high energy density, which renders incredible execution in energy storage gadgets. PCs bridge the gap between batteries and electrostatic double-layer capacitors (EDLCs). Herein, we designed novel electrode material i.e. naphtho[2,3-h]naphtho[2′,3′:5,6]quinoxalino[2,3-a]naphtho[2′,3′:5,6]quinoxaline [2,3-c]phenazine-5,12,17,22, 27,30-hexaone (Pyz-ANQ) composed of hexaketocyclohexane (HKCH) and 2,3-diaminoanthraquione (ANQ) subunits. The Pyz-ANQ electrode has been fabricated on a Toray carbon paper (CP) and used as a pseudocapacitor electrode which showed efficient pseudocapacitor performance in a three-electrode configuration. The specific capacitance (Csp) by cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) analysis are 85.2 F g−1 at a scan rate of 5 mV s−1 and 43.1 F g−1 at current density 0.5 A g−1 in 1 M H2SO4, respectively. The PCs behavior is attributed to the reversible redox chemistry of Pyz-ANQ. Furthermore, we fused the material into a symmetric solid-state two-electrode supercapacitor (SSSC) device for practical demonstration of its potential in future energy storage applications and it shows the Csp value by two methods CV and GCD such as 52.5 F g−1 @ 5 mV s−1 and 36.6 F g−1 @ 0.5 A g−1, as well as it shows excellent cyclic performance in three-electrode and two-electrode system in the percentage of 78.8% and 75.9% for 2000 GCD cycles. Significantly, Pyz-ANQ/CP electrode has an energy density of 2.6 Wh kg−1 at 4.7 kW kg−1 of power density, respectively. In this way, by utilizing HKCH and ANQ in the redox system, Pyz-ANQ/CP results in pseudocapacitive energy storage, bringing a new dimension to improve the chemistry of organic supercapacitors.

Pseudocapacitive Conjugated Polyelectrolyte/2D Electrolyte Hydrogels with Enhanced Physico‐Electrochemical Properties

AbstractConducting polymer hydrogels (CPHs) are an attractive class of materials that synergize the electrical properties of organic semiconductors with the physical properties of hydrogels. Of particular interest is the implementation of CPHs as electrode materials for electrochemical energy storage by taking advantage of redox‐tunable conjugated backbones and the large electroactive surface area. Herein, the use of 2D electrolytes as an effective post‐polymerization additive to enhance the pseudocapacitive performance of CPHs, is demonstrated. By using the self‐doped conjugated polyelectrolyte CPE‐K hydrogel as a model system, improvements in cycling stability, specific capacitance and working voltage window upon addition of the 2D electrolytes, are shown. Furthermore, positively charged 2D electrolytes to be more effective than their negatively charged counterparts are revealed. Rheology measurements and SEM imaging indicate that the 2D electrolytes serve as non‐covalent cross‐linkers that help in forming a mechanically more robust and highly percolated conducting network. These results provide a new and simple to execute post‐polymerization strategy to optimize the electrochemical performance of CPH‐based pseudocapacitors.

Enhanced Pseudocapacitive Performance of Chemically Deposited β-Ni(OH)2 Nanoflakes on 3D Graphene Oxide Framework

Enhanced Pseudocapacitive Performance of Chemically Deposited β-Ni(OH)2 Nanoflakes on 3D Graphene Oxide Framework

Intercalation pseudocapacitance of hollow carbon bubbles with multilayered shells for boosting K-ion storage

A novel carbon skeleton constructed by hollow carbon boxes with a unique multilayered shell and an impressive large interlayer spacing of 0.76 nm, inducing the production of intercalation pseudocapacitance and high performance of K-ion storage.

Layered tungsten-based composites and their pseudocapacitive and electrocatalytic performance

The WS2–g-C3N4 composite was synthesized for pseudocapacitive and hydrogen evolution reaction measurements.

Mixed-valence manganese oxide/reduced graphene oxide composites with enhanced pseudocapacitive performance

Mixed-valence manganese oxide/reduced graphene oxide composites with enhanced pseudocapacitive performance

Mechanistic insights into the pseudocapacitive performance of bronze-type vanadium dioxide with mono/multi-valent cations intercalation

Mechanistic understanding of mono/multi-valent cations' behaviors upon intercalation into solvothermally prepared VO2(B), which enables rational design of layered oxides with excellent charge storage performance.

Influence of Co on the Microstructure, Electrochemical and Pseudocapacitive Properties of Amorphous Manganese Dioxide

Manganese dioxide is a cathode material for zinc-ion batteries which is low in cost and high in performance, whereas, traditional manganese dioxide materials have poor cycle stability and poor conductivity. In response to this problem, many researchers have carried out related research, such as the preparation of various crystal forms of manganese dioxide, element doping (Co, Sn, V, etc.) and so on. However, the research on doping amorphous materials to solve the above problems is in scarcity. In this paper, amorphous manganese oxide and Co doping were combined for the first time, and Co-doped amorphous manganese dioxide was prepared by in-situ liquid phase dispersion coprecipitation method. The influence of Co doping on the microstructure and electrochemical properties of amorphous manganese dioxide were also investigated for the first time. As can be observed from the results, despite that Co doping preserves the abundant structural defects in amorphous manganese dioxide, it transforms the amorphous manganese dioxide particles from spherical to nano-sheet shape, significantly increases the particular area of surface and pore size of amorphous manganese dioxide, and stabilizes its crystal structure. Furthermore, Co doping can not only reduce the impedance of the amorphous manganese dioxide cathode, but also extremely boost the pseudocapacitive performance of amorphous manganese dioxide, thereby greatly improving its discharge specific capacity, the rate performance and the cycle stability. The prepared Co-doped amorphous manganese dioxide cathode has a maximum discharge specific capacity of 325 mAh g−1, and a capacity retention rate of 64% at 600 cycles under a current density of 1 A g−1.

Facile stepwise hydrothermal synthesis of hierarchical CoMoO4/CoMoO4 core/shell dandelion-like nanoarrays: A promising binder-free positive electrode for high-performance asymmetric supercapacitors

In this study, we have fabricated a flexible supercapacitor with outstanding pseudocapacitive performance using hierarchical CoMoO4/CoMoO4 core/shell dandelion-like nanoarrays. The dandelion-like CoMoO4/CoMoO4 nanostructure electrode yields a high specific capacitance (1548 F g−1 at a current density of 1 A g−1) and superior cycling stability performance (94% capability retention after 5000 cycles at 8 A g−1) in the 3 mol L–1 KOH solution. Furthermore, a flexible asymmetric supercapacitor device was assembled based on nickel foam/CoMoO4/CoMoO4 dandelion-like as positive electrode and activated carbon (AC) as negative electrode. The CoMoO4/CoMoO4 nanostructure//AC asymmetric supercapacitor device represents remarkable electrochemical performance such as good specific capacitance of 152 F g−1 and maximum energy and power densities of 54.04 Wh kg−1 and 8.83 kW kg−1, respectively. These encouraging results depict great potential in developing energy storage devices by making heterostructure nanomaterials.

Tungsten disulfide nanoparticles embedded in gelatin-derived honeycomb-like nitrogen-doped carbon networks with reinforced electrochemical pseudocapacitance performance

In this paper, we demonstrated a hierarchical honeycomb-like tungsten disulfide (WS2) composite nanostructure comprised of WS2 nanoparticles dispersed and embedded in gelatin-derived carbon networks with well-developed porous structures and high surface areas. In this composite, open porous architecture was favorable to easy access of electrolyte, efficient ion diffusion and relief of mechanical stress from volume variation. The unique inlaid configuration of WS2 nanoparticles in carbon matrix greatly inhibited aggregation of particles, improved structural stability and increased electrical conductivity. Profiting from these structural advantages, the optimized WS2 composite electrode demonstrated tremendously enhanced electrochemical properties. As an electrode material for pseudocapacitor, it exhibited a high capacitive value of 1305.5 Fg−1 under a current density of 0.2 A g−1. Even measured at 10 A g−1, the optimized WS2 composite still kept a high capacity of 482.6 Fg−1 and demonstrated a stable cycling performance during a long-period test. Moreover, an asymmetric capacitor based on assembly of WS2 composite cathode and activated carbon anode was fabricated. As tested under a current density of 0.1 A g−1, it could deliver a high capacitance of ∼135.9 Fg−1 and achieved an energy density of 27.2 Wh kg−1 along with a power density of 59.9 W kg−1.

Development of Binder Free Interconnected 3D Flower of NiZn2O4 as an Advanced Electrode Materials for Supercapacitor Applications

The design and development of electrode materials for energy-storage applications is an area of prime focus around the globe because of the shortage of natural resources. In this study, we developed a method for preparing a novel three-dimensional binder-free pseudocapacitive NiZn2O4 active material, which was grown directly over nickel foam (NiZn2O4@3D-NF), using a simple one-step hydrothermal process. The material was characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Cyclic voltammetry, galvanostatic charge–discharge, and electrochemical impedance spectroscopy techniques were employed to evaluate the pseudocapacitive performance of the NiZn2O4 active material in a three-electrode assembly cell. The prepared NiZn2O4@3D-NF electrode exhibited an excellent specific capacitance, of 1706.25 F/g, compared to that of the NiO@3D-NF (1050 F/g) electrode because it has the bimetallic characteristics of both zinc and nickel. The NiZn2O4@3D-NF electrode showed better cyclic stability (87.5% retention) compared to the NiO@3D-NF electrode (80% retention) after 5000 cycles at a fixed current density, which also supports the durability of the NiZn2O4@3D-NF electrode. The characteristics of NiZn2O4@3D-NF include corrosion resistance, high conductivity, an abundance of active sites for electrochemical reaction, a high surface area, and synergism between the bimetallic oxides, which make it a suitable candidate for potential application in the field of energy storage.

Superior pseudocapacitive performance and mechanism of self-assembled MnO2/MXene films as positive electrodes for flexible supercapacitors

Two-dimensional (2D) MXene materials have significant potential applications in electrochemical energy storage. A Ti3C2Tx MXene film can be used as a high-performance electrode for a flexible supercapacitor owing to its flexibility and excellent rate capability. However, Ti3C2Tx is usually only used as a negative electrode material because it can be easily oxidized under positive (anodic) potential. Herein, we report a simple filtration method to fabricate a hybrid cathode by mixing a colloidal solution of 2D Ti3C2Tx nanosheets and 1D MnO2 nanobelts to form an alternating MnO2/Ti3C2Tx stacked structure. Compared with pure Ti3C2Tx, the hybrid cathode has higher electrochemical stability toward anodic oxidation. The MnO2/Ti3C2Tx hybrid cathode delivers a high gravimetric capacitance of 315 F g−1 at 10 mV s−1 and a good rate capability of 166 F g−1 at 100 mV s−1. The high stability of the MnO2/Ti3C2Tx hybrid cathode is mainly attributed to the charge transfer-induced work function enlargement at the Ti3C2Tx and MnO2 heterointerface. Furthermore, a flexible asymmetric supercapacitor assembled using MnO2/Ti3C2Tx as the cathode and alkalized Ti3C2Tx as the anode delivers a high-voltage window up to 1.9 V. This work provides new insights for designing high-performance MXene-based cathode materials and devices for wearable electronics.

Binder-free CoMn2O4/carbon nanotubes composite electrodes for high-performance asymmetric supercapacitor

This study presents the fabrication of supercapacitor electrodes composed of CoMn2O4 (CMO) nanosheets coated onto carbon nanotubes which are grown on a stainless-steel mesh (SSM). The synthesis includes chemical vapor deposition of carbon nanotubes (CNTs) on the SSM followed by annealing at 450 °C in air for 2 h in order to generate defects for further electrodeposition of CMO nanosheets. The electrodeposited CMO exhibits excellent pseudocapacitive performance owing to high oxidation potential of cobalt as well as the fast electron transportation ability of manganese. By controlling the deposition time of CMO, favorable morphology and excellent capacitance can be achieved. Furthermore, the direct growth of CMO on CNTs/SSM prevents the use of binders or additives and avoids undesired resistances. The binder-free CMO/CNT electrode exhibits a superior specific capacitance of 732 F/g at a scan rate of 2 mV/s. Furthermore, an asymmetric supercapacitor was fabricated by paring the CMO/CNT electrode with activated carbon as an anode. The asymmetric supercapacitor exhibits an energy density of 47.39 W/kg with a power density of 400 Wh/kg together with good stability of 77% capacitance retention after 5000 cycles, which suggest that the composite electrode is of great significance for practical energy storage devices.

Pseudocapacitive TiNb2O7/reduced graphene oxide nanocomposite for high–rate lithium ion hybrid capacitors

Lithium ion hybrid capacitors (LIHCs) have a capacitor-type cathode and a battery-type anode and are a prospective energy storage device that delivers high energy/power density. However, the kinetic imbalance between the cathode and the anode is a key obstacle to their further development and application. Herein, we prepared TiNb2O7 nanoparticles through a facile solvothermal method and annealing treatment. Then a homogeneous three-dimensional (3D) self-supported reduced graphene oxide (rGO)-coated TiNb2O7 (TiNb2O7/rGO) nanocomposite was constructed by freeze-drying, followed by a high-temperature reduction, which demonstrates an enhanced pseudocapacitive lithium ions storage performance. Benefiting from the improved electrical conductivity, ultrashort ions diffusion paths, and 3D architecture, the TiNb2O7/rGO nanocomposite exhibits a high specific capacity of 285.0 mA h g−1, excellent rate capability (73.6% capacity retention at 8 A g−1), and superior cycling stability. More importantly, quantitative kinetics analysis reflects that the capacity of TiNb2O7/rGO is mainly dominated by capacitive behavior, making it perfectly match with the capacitor-type activated carbon (AC) cathode. By using pre-lithiated TiNb2O7/rGO as anode material and AC as cathode material, a high-rate TiNb2O7/rGO//AC LIHC device can be fabricated, which delivers an ultrahigh energy density of 127 Wh kg−1 at the power density of 200 W kg−1, a maximum power density of 10 kW kg−1 at the energy density of 56.4 Wh kg−1, and durable service life.

Toward understanded the electrochemical capacitance mechanism of MXene by intercalation of inorganic ions and organic macromolecular ions

Interlayer ion modification of MXene is one of the effective ways to improve the pseudocapacitance performance. However, the origin of electrochemical capacitance mechanism still remains elusive due to the effect of different kinds of ion interlayer modification. In this work, interlayer modification of MXene (Ti3C2Cl2) with inorganic ions (NaCl) and organic macromolecular ions (cetyl trimethyl ammonium bromide cation, CTAB) were carried out by ion ultrasonic intercalation and the electrochemical capacitance mechanism was investigated. It was found that MXene- CTAB has higher specific capacitance (258.28F g−1 Vs 225.55F g−1) and better cycle stability (93% retention Vs 85% retention after 3000 cycles) than MXene-NaCl. Such a large difference in electrochemical energy storage performance is mainly due to two points : (1) Organic macromolecular CTAB can effectively expand the layer spacing of MXene, which is conducive to the storage of electrolyte ions. (2) Compared with inorganic ions, organic macromolecular ions not only have redox reaction with interlayer ions of MXene, but also can adsorb counter ions in the electrolyte, thus providing additional pseudocapacitance. This work opens up a new way for the development of high-performance MXene based electrode materials.