Cobalt diselenide nanobelts grafted on carbon fiber felt: an efficient and robust 3D cathode for hydrogen production

Design and fabrication of low-cost, highly efficient and robust three-dimensional (3D) hierarchical structure materials for electrochemical reduction of water to make molecular hydrogen is of paramount importance for real water splitting applications. Herein, a 3D hydrogen evolution cathode constructed by in situ growing of cobalt diselenide nanobelts on the surface of commercial carbon fiber felt shows exceptionally high catalytic activity with 141 mV overpotential to afford a current density of 10 mA cm^–2, and a high exchange current density of 5.9 × 10^–2 mA cm^–2. Remarkably, it also exhibits excellent catalytic stability, and could be used for more than 30 000 potential cycles with no decrease in the current density in 0.5 M H₂SO₄. This easily prepared 3D material with excellent electrocatalytic performance is promising as a realistic hydrogen evolution electrode.     

Electroorganic synthesis of 6-aminonicotinic acid from 2-amino-5-chloropyridine

A synthesis of 6-aminonicotinic acid by electrochemical hydrogenation of 5-chloro-2-nitropyridine and electrochemical carboxylation of 2-amino-5-chloropyridine at a cathode surface in the presence of sulphuric acid and carbon dioxide in a dimethylformamide (DMF) solution at an apparent current density of 10 mA/cm² using an undivided cell with good yields is reported.     

Metal framework as a novel approach for the fabrication of electric double layer capacitor device with high energy density using plasticized Poly(vinyl alcohol): Ammonium thiocyanate based polymer electrolyte

High performance electric double-layer capacitors (EDLCs) based on poly (vinyl alcohol) (PVA): ammonium thiocyanate (NH₄SCN):Cu(II)-complex plasticized with glycerol (GLY) have been fabricated. The maximum DC ionic conductivity (σ_DC) of 2.25 × 10^-3 S cm⁻¹ is achieved at ambient temperature. The X-ray diffraction (XRD) patterns confirmed that the addition of both Cu(II)–complex and GLY enhanced the amorphous region within the samples. Through the Fourier transform infrared (FTIR) the interactions between the host polymer and other components of the prepared electrolyte are observed. The FESEM images reveal that the surface morphology of the samples showed a uniform smooth surface at high GLY concentration. This is in good agreement with the XRD and FTIR results. Transference numbers of ion (t_ion) and electron (t_el) for the highest conducting composite polymer electrolyte (CPE) are recognized to be 0.971 and 0.029, respectively. The linear sweep voltammetry (LSV) revealed that the electrochemical stability window for the CPE is 2.15 V. These high values of t_ion and potential stability established the suitability of the synthesized systems for EDLC application. Cyclic voltammetry (CV) offered nearly rectangular shape with the lack of Faradaic peak. The specific capacitance and energy density of the EDLC are nearly constant within 1000 cycles at a current density of 0.5 mA/cm² with average of 155.322F/g and 17.473 Wh/Kg, respectively. The energy density of the EDLC in the current work is in the range of battery specific energy. The EDLC performance was found to be stable over 1000 cycles. The low value of equivalent series resistance reveals that the EDLC has good electrolyte-electrode contact. The EDLC exhibited the initial high power density of 4.960 × 10³ W/Kg.     

Fabrication of Vertical-Standing Co-MOF Nanoarrays with 2D Parallelogram-like Morphology for Aqueous Asymmetric Electrochemical Capacitors

Metal organic frameworks (MOFs) have been considered as one of the most promising electrode materials for electrochemical capacitors due to their large specific surface area and abundant pore structure. Herein, we report a Co-MOF electrode with a vertical-standing 2D parallelogram-like nanoarray structure on a Ni foam substrate via a one-step solvothermal method. The as-prepared Co-MOF on a Ni foam electrode delivered a high area-specific capacitance of 582.0 mC cm⁻² at a current density of 2 mA cm⁻² and a good performance rate of 350.0 mC cm⁻² at 50 mA cm⁻². Moreover, an asymmetric electrochemical capacitor (AEC) device (Co-MOF on Ni foam//AC) was assembled by using the as-prepared Co-MOF on a Ni foam as the cathode and a active carbon-coated Ni foam as the anode to achieve a maximum energy density of 0.082 mW cm⁻² at a power density of 0.8 mW cm⁻², which still maintained 0.065 mW cm⁻² at a high power density of 11.94 mW cm⁻². Meanwhile, our assembled device exhibited an excellent cycling stability with a capacitance retention of nearly 100% after 1000 cycles. Therefore, this work provides a simple method to prepare MOF-based material for the application of energy storage and conversion.     

Preparation and electrochemical performance of activated carbon thin films with polyethylene oxide-salt addition for electrochemical capacitor applications

The effect of polymer–salt addition in the activated carbon electrode for electric double-layer capacitor (EDLC) has been investigated. A series of composite thin film electrode consisting of activated carbon, carbon black, polytetrafluoroethylene and polymer–salt complex (polyethyleneoxide–LiClO₄) with an appropriate weight ratio were prepared and examined their performance for EDLCs using 1 mol L⁻¹ LiClO₄ in ethylene carbonate:diethylcarbonate electrolyte solution. The electrochemical capacitance performances of these electrodes with different compositions were characterized by cyclic voltammetry, galvanostatic charge–discharge cycling, and AC impedance measurements. By comparison, the best results were obtained with a composite electrode rich in polymer–salt additive (132 F g⁻¹ at 100 mA g⁻¹ of galvanostatic experiment). In general, the polymer–salt-containing electrode had shown improved performance over activated carbon electrodes without polymer–salt at high current density.     

Highly stable performance of supercapacitors using microporous carbon derived from phenol–melamine–formaldehyde resin

A series of microporous carbons were prepared by simple carbonization and activation of phenol–melamine–formaldehyde resin. The morphology, surface area, and elemental composition of the samples were investigated by scanning electron microscope, Brunauer–Emmett–Teller measurement, Raman spectra, and elemental analysis, respectively. Electrochemical characteristics were evaluated by cyclic voltammograms, galvanostatic charge/discharge, and electrochemical impedance spectroscopy measurements in 6.0?mol?L^?1 KOH. The microporous carbon activated by KOH presented a high specific capacitance of 202?F?g^?1 at a scan rate of 2?mV?s^?1. Furthermore, the KOH-activated microporous carbon electrode exhibited durable operation, the total loss of capacitance after 20,000 cycles is 2% at a current density of 500?mA?g^?1. The good electrochemical performance of the activated carbon was ascribed to well-developed micropores, high surface area, larger pore volume as well as oxygen groups.     

The production of activated carbon from cation exchange resin for high-performance supercapacitor

High-performance activated carbon for electrochemical double-layer capacitors (EDLC) has been prepared from cation exchange resin by carbonization and subsequent activation with KOH. The activation temperature has a key role in the determination of porous carbon possessing high surface areas, and large pore structures. The porous carbon activated at 700 °C (carbon-700-1:4) has high surface area (2236 m²?g^?1) and large total pore volume (1.15 cm³?g^?1), which also displays best capacitive performances due to its well-balanced micro- or mesoporosity distribution. In details, specific capacitances of the carbon-700-1:4 sample are 336.5 F?g^?1 at a current density of 1 A?g^?1 and 331.8 F?g^?1 at 2 A?g^?1. At high current density as 20 A?g^?1, the retention of its specific capacitance is 68.4 %. The carbon-700-1:4 sample also exhibits high performance of energy density (46.7 Wh?kg^?1) and long cycle stability (～8.9 % loss after 3,000 cycles). More importantly, due to the amount of waste ion-exchange resins increasing all over the world, the present synthetic method might be adopted to dispose them, producing high-performance porous carbons for EDLC electrode materials.     

Nanosized Fe3O4-modified activated carbon for supercapacitor electrodes

Nanosized Fe₃O₄-modified activated carbon composites for supercapacitor electrodes have been investigated. Structural and morphological characterizations of activated materials are carried out using X-ray diffraction and scanning electron microscopy, respectively. The electrochemical performances of the composite electrodes are evaluated by cyclic voltammetry, chronopotentiometry and electrochemical impedance spectroscopy. The experimental results show that the specific capacitances of the 10 wt % Fe₃O₄-modified activated carbon composite electrode (154.3 F g^?1) is highly improved compared with that of Fe₃O₄ (78.5 F g^?1) and AC (79.2 F g^?1) at the current density of 5 mA cm^?2, respectively. The charge/discharge tests show that it could retain 79.6% of its initial capacitance over 1000 cycles, suggesting its potential application for the fabrication of high-quality supercapacitors.     

A high-performance asymmetric supercapacitor achieved by surface-regulated MnO2 and organic-framework–derived N-doped carbon cloth

It is possible to achieve high energy density and power density simultaneously for asymmetric supercapacitors by using pseudocapacitive materials with abundant ion intercalation/de-intercalation sites on the surface. Herein, a positive electrode based on feather-like MnO₂ anchored on the activated carbon cloth is prepared, in which oxygen-enriched MnO₂ nanorods with a radial sheet-like structure (OMO@AC) further form via electrochemical oxidation. Because of the large contact area with electrolyte and abundant oxidation functional groups on its surface, the OMO@AC displays excellent capacitance of 3,160 mF/cm² at 1 mA/cm². For the nitrogen-doped active carbon negative electrode, the capacitance is up to 1,875 mF/cm² at 4 mA/cm² due to the increase in disorder and defect on the carbon surface by N-doping. Furthermore, we verify the good electrochemical activity on the OMO@AC electrode surface by first-principles calculations and confirm the good matching degree between the positive and negative electrodes by CV testes. The aqueous oxygen-enriched MnO₂// nitrogen-doped active carbon asymmetric supercapacitor exhibits an ultrahigh energy density of 8.723 mWh/cm³ at a power density of 14.248 mW/cm³ and display excellent cycle stability maintaining 95.5% after 10,000 cycles. The facile synthesis method and excellent performance provide a feasible way for the preparation of high-performance electrode materials for energy storage devices.     

Polymer-Supported Liquid Layer Electrolyzer Enabled Electrochemical CO2 Reduction to CO with High Energy Efficiency

The electrochemical conversion of carbon dioxide (CO₂) to carbon monoxide (CO) is a favorable approach to reduce CO₂ emission while converting excess sustainable energy to important chemical feedstocks. At high current density (>100 mA cm⁻²), low energy efficiency (EE) and unaffordable cell cost limit the industrial application of conventional CO₂ electrolyzers. Thus, a crucial and urgent task is to design a new type of CO₂ electrolyzer that can work efficiently at high current density. Here we report a polymer-supported liquid layer (PSL) electrolyzer using polypropylene non-woven fabric as a separator between anode and cathode. Ag based cathode was fed with humid CO₂ and potassium hydroxide was fed to earth-abundant NiFe-based anode. In this configuration, the PSL provided high-pH condition for the cathode reaction and reduced the cell resistance, achieving a high full cell EE over 66 % at 100 mA cm⁻².     

Amorphous cobalt silicate nanobelts@carbon composites as a stable anode material for lithium ion batteries

During the past decade, tremendous attention has been given to the development of new electrode materials with high capacity to meet the requirements of electrode materials with high energy density in lithium ion batteries. Very recently, cobalt silicate has been proposed as a new type of high capacity anode material for lithium ion batteries. However, the bulky cobalt silicate demonstrates limited electrochemical performance. Nanostructure engineering and carbon coating represent two promising strategies to improve the electrochemical performance of electrode materials. Herein, we developed a template method for the synthesis of amorphous cobalt silicate nanobelts which can be coated with carbon through the deposition and thermal decomposition of phenol formaldehyde resin. Tested as an anode material, the amorphous cobalt silicate nanobelts@carbon composites exhibit a reversible high capacity of 745 mA h g^–1 at a current density of 100 mA g^–1, and a long life span of up to 1000 cycles with a stable capacity retention of 480 mA h g^–1 at a current density of 500 mA g^–1. The outstanding electrochemical performance of the composites indicates their high potential as an anode material for lithium ion batteries. The results here are expected to stimulate further research into transition metal silicate nanostructures for lithium ion battery applications.     

Porous carbon nanotubes improved sulfur composite cathode for lithium-sulfur battery

Porous multi-walled carbon nanotubes (PCNTs) with multiple mesopores structure are synthesized through activation of multi-walled carbon nanotubes (MWCNTs) by potassium hydroxide. The potassium hydroxide activation process results in a significantly enhanced specific surface area with numerous small pores. The as-obtained PCNTs are employed as the conductive matrix for sulfur in the sulfur cathode. Compared with the composite sulfur cathode based on the original MWCNTs, the sulfur-PCNTs cathode shows a significantly improved cycle performance and columbic efficiency. The reversible capacity is 530 mAh?g^?1 and columbic efficiency is 90 % after 100 cycles at a current density of 100 mA?g^?1. The improvement in the electrochemical performance for S-PCNT is mainly attributed to the enlarged surface area and the porous structure of the unique mesopores carbon nanotube host, which cannot only facilitate transport of electrons and Li⁺ ions, but also trap polysulfides, retard the shuttle effect during charge/discharge process.     

The Use of High Surface Area Mesoporous-Activated Carbon from Longan Seed Biomass for Increasing Capacity and Kinetics of Methylene Blue Adsorption from Aqueous Solution

Microporous- and mesoporous-activated carbons were produced from longan seed biomass through physical activation with CO₂ under the same activation conditions of time and temperature. The specially prepared mesoporous carbon showed the maximum porous properties with the specific surface area of 1773 m²/g and mesopore volume of 0.474 cm³/g which accounts for 44.1% of the total pore volume. These activated carbons were utilized as porous adsorbents for the removal of methylene blue (MB) from an aqueous solution and their effectiveness was evaluated for both the adsorption kinetics and capacity. The adsorption kinetic data of MB were analyzed by the pseudo-first-order model, the pseudo-second-order model, and the pore-diffusion model equations. It was found that the adsorption kinetic behavior for all carbons tested was best described by the pseudo-second-order model. The effective pore diffusivity (D_e) derived from the pore-diffusion model had the values of 4.657 × 10⁻⁷–6.014 × 10⁻⁷ cm²/s and 4.668 × 10⁻⁷–19.920 × 10⁻⁷ cm²/s for the microporous- and mesoporous-activated carbons, respectively. Three well-known adsorption models, namely the Langmuir, Freundlich and Redlich–Peterson equations were tested with the experimental MB adsorption isotherms, and the results showed that the Redlich–Peterson model provided the overall best fitting of the isotherm data. In addition, the maximum capacity for MB adsorption of 1000 mg/g was achieved with the mesoporous carbon having the largest surface area and pore volume. The initial pH of MB solution had virtually no effect on the adsorption capacity and removal efficiency of the methylene blue dye. Increasing temperature over the range from 35 to 55 °C increased the adsorption of methylene blue, presumably caused by the increase in the diffusion rate of methylene blue to the adsorption sites that could promote the interaction frequency between the adsorbent surface and the adsorbate molecules. Overall, the high surface area mesoporous carbon was superior to the microporous carbon in view of the adsorption kinetics and capacity, when both carbons were used for the removal of MB from an aqueous solution.     

Mesoporous Carbons Templated by PEO-PCL Block Copolymers as Electrode Materials for Supercapacitors

In this study, samples of activated mesoporous carbon are fabricated with pore structures with cylinder and gyroid nanostructures through the templating effect of amphiphilic poly(ethylene oxide-block-caprolactone) (PEO-PCL) and by using specific resol/PEO-PCL weight ratios (e.g., 60:40 for cylinders; 55:45 for gyroids). After carbonization and KOH activation, the activated mesoporous carbons were tested as electrode materials for electric double-layer capacitor (EDLC) supercapacitors. The electrochemical properties were examined by using three-electrode (6 m KOH_(aq) as electrolyte) and CR2032 coin-cell (1 m tetraethylammonium tetrafluoroborate (TEABF₄)/CN as the electrolyte) systems. The gyroid carbon samples provided specific capacitances higher than those of the cylinder carbon samples in both aqueous and organic systems: 155 F g⁻¹ compared with 135 F g⁻¹ in 6 m KOH_(aq), and 105.6 compared with 96 F g⁻¹ in 1 m TEABF₄/MeCN, after 100 charge/discharge cycles. It is suspected that the bi-continuous mesochannels of the gyroid-type activated mesoporous carbons provided a relatively higher effective adsorption surface area; in other words, the greater surface area for energy storage originated from a moderate pore size and an interconnected pore structure.     

Surface Modification and Performance of Activated Carbon Electrode Material

A commercial activated carbon was modified by surface treatment using three chemicals, nitric acid, hydrogen peroxide, and ammonia, respectively. The modified carbons were characterized by N₂ adsorption-desorption isotherms and FTIR spectroscopy. The resultant carbon electrode-based electric double-layer capacitors (EDLCs) were assembled with 6 mol·L⁻¹ KOH as the electrolyte. The influence of surface modification on the performance of EDLCs was studied by galvanostatic charge-discharge, cyclic voltammetry, and alternating current impedance. The surface modification resulted in no big decrease in specific surface area and little decrease in average pore size, and introduced functional groups, such as hydroxyl, carbonyl, and amidogen, on the carbon surface. These functional groups significantly improved the wettability and reduced the resistance of the activated carbon. As a result, the specific capacitance of the carbon modified with 65% HNO₃ reached 250 F·g⁻¹, 72.4% higher than that of original carbon. The leakage current of testing EDLCs decreased unexpectedly to 3-18 μA, only 0.8%-4.9% that of the original carbon electrode-based EDLC (371 μA).     

In Situ Growth of Hierarchical Ni-Mn-O Solid Solution on a Flexible and Porous Ni Electrode for High-Performance All-Solid-State Asymmetric Supercapacitors

To endow all-solid-state asymmetric supercapacitors with high energy density, cycling stability, and flexibility, we design a binder-free supercapacitor electrode by in situ growth of well-distributed broccoli-like Ni_0.75Mn_0.25O/C solid solution arrays on a flexible and three-dimensional Ni current collector (3D-Ni). The electrode consists of a bottom layer of compressed but still porous Ni foam with excellent flexibility and high electrical conductivity, an intermediate layer of interconnected Ni nanoparticles providing a large specific surface area for loading of active substances, and a top layer of vertically aligned mesoporous nanosheets of a Ni_0.75Mn_0.25O/C solid solution. The resultant 3D-Ni/Ni_0.75Mn_0.25O/C cathode exhibits a specific capacitance of 1657.6 mF cm⁻² at 1 mA cm⁻² and shows no degradation of the capacitance after 10 000 cycles at 3 mA cm⁻². The assembled 3D-Ni/Ni_0.75Mn_0.25O/C//activated carbon asymmetric supercapacitor has a high specific capacitance of 797.7 mF cm⁻² at 2 mA cm⁻² and an excellent cycling stability with 85.3 % of capacitance retention after 10 000 cycles at a current density of 3 mA cm⁻². The energy density and power density of the asymmetric supercapacitor are up to 6.6 mW h cm⁻³ and 40.8 mW cm⁻³, respectively, indicating a fairly promising future of the flexible 3D-Ni/Ni_0.75Mn_0.25O/C electrode for efficient energy storage applications.     

Enhanced Electrochemical Performance of Supercapacitors via Atomic Layer Deposition of ZnO on the Activated Carbon Electrode Material

Fabricating electrical double-layer capacitors (EDLCs) with high energy density for various applications has been of great interest in recent years. However, activated carbon (AC) electrodes are restricted to a lower operating voltage because they suffer from instability above a threshold potential window. Thus, they are limited in their energy storage. The deposition of inorganic compounds’ atomic layer deposition (ALD) aiming to enhance cycling performance of supercapacitors and battery electrodes can be applied to the AC electrode materials. Here, we report on the investigation of zinc oxide (ZnO) coating strategy in terms of different pulse times of precursors, ALD cycles, and deposition temperatures to ensure high electrical conductivity and capacitance retention without blocking the micropores of the AC electrode. Crystalline ZnO phase with its optimal forming condition is obtained preferably using a longer precursor pulse time. Supercapacitors comprising AC electrodes coated with 20 cycles of ALD ZnO at 70 °C and operated in TEABF₄/acetonitrile organic electrolyte show a specific capacitance of 23.13 F g⁻¹ at 5 mA cm⁻² and enhanced capacitance retention at 3.2 V, which well exceeds the normal working voltage of a commercial EDLC product (2.7 V). This work delivers an additional feasible approach of using ZnO ALD modification of AC materials, enhancing and promoting stable EDLC cells under high working voltages.     

Module-Designed Carbon-Coated Separators for High-Loading,High-Sulfur-Utilization Cathodes in Lithium–Sulfur Batteries

Lithium–sulfur batteries have great potential as next-generation energy-storage devices because of their high theoretical charge-storage capacity and the low cost of the sulfur cathode. To accelerate the development of lithium–sulfur technology, it is necessary to address the intrinsic material and extrinsic technological challenges brought about by the insulating active solid-state materials and the soluble active liquid-state materials. Herein, we report a systematic investigation of module-designed carbon-coated separators, where the carbon coating layer on the polypropylene membrane decreases the irreversible loss of dissolved polysulfides and increases the reaction kinetics of the high-loading sulfur cathode. Eight different conductive carbon coatings were considered to investigate how the materials’ characteristics contribute to the lithium–sulfur cell’s cathode performance. The cell with a nonporous-carbon-coated separator delivered an optimized peak capacity of 1112 mA∙h g⁻¹ at a cycling rate of C/10 and retained a high reversible capacity of 710 mA∙h g⁻¹ after 200 cycles under lean-electrolyte conditions. Moreover, we demonstrate the practical high specific capacity of the cathode and its commercial potential, achieving high sulfur loading and content of 4.0 mg cm⁻² and 70 wt%, respectively, and attaining high areal and gravimetric capacities of 4.45 mA∙h cm⁻² and 778 mA∙h g⁻¹, respectively.     

Laser-Induced Interdigital Structured Graphene Electrodes Based Flexible Micro-Supercapacitor for Efficient Peak Energy Storage

The rapidly developing demand for lightweight portable electronics has accelerated advanced research on self-powered microsystems (SPMs) for peak power energy storage (ESs). In recent years, there has been, in this regard, a huge research interest in micro-supercapacitors for microelectronics application over micro-batteries due to their advantages of fast charge–discharge rate, high power density and long cycle-life. In this work, the optimization and fabrication of micro-supercapacitors (MSCs) by means of laser-induced interdigital structured graphene electrodes (LIG) has been reported. The flexible and scalable MSCs are fabricated by CO₂-laser structuring of polyimide-based Kapton ^® HN foils at ambient temperature yielding interdigital LIG-electrodes and using polymer gel electrolyte (PGE) produced by polypropylene carbonate (PPC) embedded ionic liquid of 1-ethyl-3-methyl-imidazolium-trifluoromethansulphonate [EMIM][OTf]. This MSC exhibits a wide stable potential window up to 2.0 V, offering an areal capacitance of 1.75 mF/cm² at a scan rate of 5.0 mV/s resulting in an energy density (E_a) of 0.256 µWh/cm² @ 0.03 mA/cm² and power density (P_a) of 0.11 mW/cm² @0.1 mA/cm². Overall electrochemical performance of this LIG/PGE-MSC is rounded with a good cyclic stability up to 10,000 cycles demonstrating its potential in terms of peak energy storage ability compared to the current thin film micro-supercapacitors.     

The superior electrochemical performance of oxygen-rich activated carbons prepared from bituminous coal

Oxygen-rich activated carbons (OAC) were prepared from bituminous coal through a quick KOH activation. OAC exhibited a moderately large surface area of 1950 m²/g, a relative wide pore size distribution, good conductivity and very high oxygen content (up to 12 wt.%). Compared with high surface area activated carbons prepared by the conventional KOH activation, OAC have superior capacitive behavior, power output and high energy density in electrochemical double layer capacitors (EDLC). OAC presented a high specific capacitance of 370 F/g in 3 M KOH electrolyte at a low current density of 50 mA/g and still remained 270 F/g even at a high current density of 20 A/g.