Electrode Materials For Electrochemical Capacitors Research Articles

Effect of Aggregation Structure on Capacitive Energy Storage in Conducting Polymer Films.

Conducting polymers (CPs), a significant class of electrochemical capacitor electrode materials, exhibit exceptional capacitive energy storage performance in aqueous electrolytes. Current research primarily concentrates on enhancing the electrical conductivity and capacitive performance of CPs via molecular design and structural control. However, the absence of a comprehensive understanding of the impact of molecular chain spatial order on ion/electron transport and capacitive performance impedes the development and optimization of advanced electrode materials. Here, a solvent treatment strategy is employed to modulate the molecular chain spatial order of PEDOT:PSS films. The results of electrochemical performance tests and Grazing Incidence Wide Angle X-ray Scattering (GIWAXS) show that PEDOT:PSS films with both face-on and edge-on orientations exhibit exceptional electronic conductivity and ion diffusion efficiency, with capacitive performance 1.33 times higher than that of PEDOT:PSS films with only edge-on orientation. Consequently, molecular chain orientations conducive to charge transport not only enhance inter-chain coupling, but also effectively reduce ion transport resistance, enabling efficient capacitive energy storage. This research provides novel insights for the design and development of higher performance CPs-based electrode materials.

Nanofeather ruthenium nitride electrodes for electrochemical capacitors.

Fast charging is a critical concern for the next generation of electrochemical energy storage devices, driving extensive research on new electrode materials for electrochemical capacitors and micro-supercapacitors. Here we introduce a significant advance in producing thick ruthenium nitride pseudocapacitive films fabricated using a sputter deposition method. These films deliver over 0.8 F cm-2 (~500 F cm-3) with a time constant below 6 s. By utilizing an original electrochemical oxidation process, the volumetric capacitance doubles (1,200 F cm-3) without sacrificing cycling stability. This enables an extended operating potential window up to 0.85 V versus Hg/HgO, resulting in a boost to 3.2 F cm-2 (3,200 F cm-3). Operando X-ray absorption spectroscopy and transmission electron microscopy analyses reveal novel insights into the electrochemical oxidation process. The charge storage mechanism takes advantage of the high electrical conductivity and the morphology of cubic ruthenium nitride and Ru phases in the feather-like core, leading to high electrical conductivity in combination with high capacity. Accordingly, we have developed an analysis that relates capacity to time constant as a means of identifying materials capable of retaining high capacity at high charge/discharge rates.

Analysis of voltametric data from electrochemical capacitor electrode materials: Method refinement for improved outcomes

A revised model is proposed to improve analysis outcomes from the voltametric analysis of electrochemical capacitor materials and electrodes at different sweep rates (v). Conventional analysis involves breaking down the voltametric current (i) into contributions from capacitive processes (i∝v) and diffusional processes (i∝v1/2). The proposed model introduces a resistance or residual current term, improving the goodness of fit and the quality of data interpretation. This is demonstrated by application of the revised model to artificial voltametric data, electrical double layer capacitor data, as well as pseudo-capacitive electrode data. Analysis with this model also demonstrates the importance of understanding resistive processes in electrode systems, in particular differentiating resistance in the act of charge storage (double layer and redox processes), and ohmic electrode resistance.

MnCo2O4/activated carbon wheat husk (ACWH) as a novel electrode material for electrochemical capacitors

Supercapacitors are very suitable devices for energy storage in the coming years. Researches on the introduction of efficient, cost-effective, and environmentally friendly electrodes are still ongoing. In this investigation, we used wheat husk, which is an agricultural waste, for the preparation of carbon with excellent specific surface area to be used in supercapacitors' electrodes. The results of BET analysis showed a specific surface area of 339.04 m2 g−1. In addition to this efficient carbon electrode introduction, we reached the specific capacity of 1392 F/g at current density 1 A/g by the addition of MnCo2O4 composite to the activated carbon wheat husk (ACWH), hence, increasing the conductivity and decreasing the resistance. Also, the results of EIS analysis showed that the resistance due to charge transfer for the wheat husk electrode decreased from about 22 Ω to 3.8 Ω after adding the composite. Comparative investigations were done on the three-electrode system with wheat husk, MnCo2O4, and MnCo2O4/ACWH carbon electrodes. Results indicated that the synergistic effect of the synthesized carbon (with the excellent surface area) along with MnCo2O4 increases the number of active sites and, thus, the specific capacity. Furthermore, using a ACWH improved MnCo2O4 electrode stability so that the synthesized hybrid showed 90.8 % stability after 5000 consecutive cycles.

Novel favorably interconnected N-doped porous carbon hybrid electrode materials for high energy density supercapacitors

A strategy to prepare facile electrode materials for electrochemical capacitors with high conductivity, high surface area and hierarchical pore structure along with nitrogen functional groups to enhance the electrochemical performance, is presented in this work. Partially unravelled carbon nanotubes (PURNTs) are interconnected to the wrinkled few layered graphene nanosheets (WfG), which act as quick ion and charge transportation channels. Here, PURNTs acts as a spacer to the WfG to avoid the restacking. Though WfG-PURNTs exhibit good results, to further improve the electrochemical performance we developed an electrode material by designing nitrogen-doped porous carbon covered favorably interconnected WfG-PURNTs with interconnected pore structure. The WfG-PURNTs serve as the conductive matrix, which plays a key role in enhancing the N-PC (WfG-PURNTs) electrode material's electrochemical performance. And the nitrogen functional groups, through faradaic red-ox reactions, contribute to the pseudocapacitance in addition to the electric double layer capacitance, thereby enhancing overall supercapacitive performance. The developed N-PC (WfG-PURNTs)-700 shows a high nitrogen amount of 6.8 at %, with a high active surface area of 2418 m2 g−1. The synergistic effect of the WfG-PURNTs and N-doped porous carbon results in high supercapacitive performance and better cyclic stability. It shows an excellent specific capacitance (Cp) of 954 F g−1 at high current density of 2 A g−1. Also, the assembled symmetric supercapacitors show high energy densities of 61.1, 119.4, and 195.4 Wh kg−1 in acidic, neutral and ionic liquid electrolytes, respectively. We also designed asymmetric solid-state flexible supercapacitor which exhibits a high specific capacitance of 209.4 F g−1 at 2 A g−1 and an excellent energy density of 29.15 Wh kg−1. Furthermore, the assembled three such flexible supercapacitors in series connection, could able to light up red colored LED for 30 min once charged for 60 s.

Progress in Conducting Polymer‐Based Electrospun fibers for Supercapacitor Applications: A Review

AbstractThe ever‐growing need for energy storage has been at the forefront of research for the past few decades. A supercapacitor is an attractive candidate for storage needs with widespread applications in electronic gadgets, electric vehicles and hybrid vehicles, especially in space and the military. The significant role of electrodes in the performance of supercapacitors has led to the development of materials endowed with exceptional electrochemical performance and mechanical stability. Conducting polymers with intriguing properties like tuneable electronic conductivity, broad voltage window, tuneable redox activity etc., are excellent candidates as electrode materials for electrochemical capacitors with superior performance parameters. Electrospun conducting polymer nanofibers exhibit unique characteristics and favourable morphologies that have the potential to enhance the performance of supercapacitors. The review covers the fundamentals of electrochemical capacitors and introduces electrospinning as a versatile method to fabricate nanofibers using conducting polymers and their composites. The application of these nanofibers as electrodes in supercapacitors is discussed in detail and the performance parameters are compared. The article also discusses the challenges and prospects in using these electrospun nanofibers as effective supercapacitor electrodes.

BƯỚC ĐẦU NGHIÊN CỨU TỔNG HỢP NICKEL SULFIDE DÙNG LÀM VẬT LIỆU ĐIỆN CỰC CHO TỤ ĐIỆN HÓA

NiS as an electrode material for electrochemical capacitors has been synthesized by chemical and hydrothermal methods. The results show that the synthesized NiS is in amorphous form, increasing the reaction temperature or hydrothermal time tends to reduce the porosity of the materials. NiS synthesized by hydrothermal method exhibits better electrochemical properties than those synthesized by chemical method. NiS synthesized at the optimal condition of a hydrothermal temperature of 140 oC in 5h has a specific capacitance of 1592 F\g (265 mAh\g) and 1567 F\g (261 mAh\g) at a scan rate of 5 mV\s and a current density of 5 A\g, respectively. This value is about 88% of the theoretical value of NiS and is maintained after 25 continuous charge-discharge cycles at different current densities ranging from 5 to 40 A\g.

Optimized mesopores enable enhanced capacitance of electrochemical capacitors using ultrahigh surface area carbon derived from waste feathers.

Porous carbons with high specific surface area are critical engineering materials for current electrochemical capacitors (ECs) technology. Controlling the pore size distribution of porous carbons remains a significant challenge as it is a key aspect in many applications. Herein, we synthesized porous carbon as the electrode material of ECs by means of a two-step synthesis procedure using abandoned feathers as carbon precursor and potassium hydroxide as activating agent. The optimal sample (AFHPC-800-1:3) exhibited an ultra-high specific surface area (SBET) of 3474m2/g and a huge total pore volume (VT) of 1.82m3 g-1 as well as abundant small mesopores ranging from 2 to 5nm in size. The ECs based on the AFHPC-800-1:3 electrode exhibited an ultra-high specific capacitance (Csp) of up to 709F g-1 at 0.5 A g-1. More interestingly, a capacitance of 212F g-1 was retained even at 100 A g-1, demonstrating excellent high-rate capacitive performance. Furthermore, the symmetrical capacitor yielded an excellent energy density of 35.1 Wh kg-1 when the specific power density was 625Wkg-1, substantiating the potential of the small mesopores in promoting the overall capacitance and energy density of electrode materials.

Optimization of porous carbon nanofiber/MnO2 electrode-based supercapacitor performance using γ‑cyclodextrin: Effects of graphene and MnCl2 contents

• Graphene and MnCl 2 content is optimized for supercapacitor performance of PCM(5)G(3). • PCM(5)G(3) has high surface area and active material of MnO 2 embedded in the fiber. • PCM(5)G(3) maximize the synergistic effect of the pseudocapacity and EDLC. • PCM(5)G(3) have great potential in electrochemical capacitor electrode materials. We systematically evaluate the influence of graphene and MnCl 2 contents on the structure and capacity of γ-cyclodextrin/graphene-based carbon nanofibers and MnO 2 (PCMG). The PCMG electrodes are stable long-term and had good capacitances, e.g., up to 236Fg -1 at 1mAcm -2 and 25.5Whkg -1 at 400Wkg -1 . The electrochemical performance is maximized by the synergistic effect between the pseudocapacity of MnO 2 well-embedded in the fiber and the electric double layer capacity induced by the well-developed surface pores.

Vanadium dioxide sulphur-doped reduced graphene oxide composite as novel electrode material for electrochemical capacitor

In this study, vanadium dioxide (VO2) combined with sulphur-doped reduced graphene oxide (S-rGO) as a composite material is reported. Vanadium dioxide sulphur-doped reduced graphene oxide (VO2@S-rGO) composite was successfully synthesized via a rapid solvothermal technique by varying the S-rGO concentration on VO2. The structural, morphological, and textural properties revealed the successful integration of S into the rGO matrix, leading to a good interaction between S-rGO and VO2 in the composite materials. The optimized composite (VO2@S-rGO-1) presented better electrochemical performance and exhibits a specific capacitance of 204.2 F g−1 in 0.5 M K2SO4 electrolyte at a specific current of 0.5 A g−1 within a large stable potential window of 0.8 V vs Ag/AgCl. VO2@S-rGO-1 and cocoa-derived activated carbon (Cocoa-AC) were used as positive and negative electrodes, respectively, to fabricate an asymmetric supercapacitor device (VO2@S-rGO-1//Cocoa-AC). The device displayed excellent specific energy of 32.6 W h kg−1 with a corresponding specific power of 426.0 W kg−1 at 0.5 A g−1 in an operating cell voltage of 1.7 V. The stability test exhibited an excellent columbic efficiency of 99.9 % and capacitance retention of 75 % up to 10,000 galvanostatic charge/discharge at 10 A g−1. Overall, VO2@S-rGO-1//Cocoa-AC asymmetric device demonstrated excellent electrochemical properties and is thus a promising candidate for wide use in energy storage systems.

Heteroatom-doped reduced graphene oxide integrated with nickel-cobalt phosphide for high-performance asymmetric hybrid supercapacitors

The increasing energy demand and lack of sustainable energy storage systems have attracted considerable attention towards electrochemical capacitors. Transition metal phosphides have emerged as excellent electrode materials for electrochemical capacitors because of their highly metalloid characteristics and low cost. This paper reports the synthesis of binder-free nickel-cobalt phosphide nano horns wrapped with phosphorus-doped reduced graphene oxide by a hydrothermal reaction followed by phosphorization. The nickel-cobalt phosphide nano horns are formed by the Kirkendall effect due to differences in the diffusion rates of phosphorus ions and metal sources. The as-prepared electrode delivers a high specific capacity of 264.9 mAh g−1 (2384 F g−1) at 1 A g−1 and a high rate capability of 72 % at 15 A g−1. The asymmetric hybrid supercapacitor consisted of nickel-cobalt phosphide wrapped with phosphorus-doped reduced graphene as the anode, and activated carbon as the cathode yields a good energy density of 39.7 Wh kg−1 and a high power-density of 8.82 kW kg−1 with high cycling stability of 90 % after 10,000 charge–discharge cycles. The excellent pseudocapacitive properties of the as-prepared binary metal phosphide confirms its value for widespread practical applications in electrochemical supercapacitors.

Reduced Graphene Oxide—Polycarbonate Electrodes on Different Supports for Symmetric Supercapacitors

Electrode materials for electrochemical capacitors or supercapacitors (SCs) are widely studied, as they are needed for the development of energy storage devices in electrical vehicles and flexible electronics. In the current work, a self-supported paper of reduced graphene oxide (rGO) with polycarbonate (PC) (as rGO-PC composite) was prepared by simple vacuum filtration and low-temperature annealing. rGO-PC as a freestanding single electrode was studied in a three-electrode system and presented a capacitive energy storage mechanism. To fabricate SCs based on rGO-PC, flexible polyethylene terephthalate (PET) with layers of both Cu tape (Cu tape) and carbon tape (C tape) (PET/Cu/C), as well as PET covered by graphene ink (PET/GrI), were used as supports. Fabricated flexible symmetric SCs have shown similar behavior with a higher areal capacitance value than that on PET/Cu/C substrate.

Bridged Carbon Fabric Membrane with Boosted Performance in AC Line-Filtering Capacitors.

High‐frequency responsive capacitors with lightweight, flexibility, and miniaturization are among the most vital circuit components because they can be readily incorporated into various portable devices to smooth out the ripples for circuits. Electrode materials no doubt are at the heart of such devices. Despite tremendous efforts and recent advances, the development of flexible and scalable high‐frequency responsive capacitor electrodes with superior performance remains a great challenge. Herein, a straightforward and technologically relevant method is reported to manufacture a carbon fabric membrane “glued” by nitrogen‐doped nanoporous carbons produced through a polyelectrolyte complexation‐induced phase separation strategy. The as‐obtained flexible carbon fabric bearing a unique hierarchical porous structure, and high conductivity as well as robust mechanical properties, serves as the free‐standing electrode materials of electrochemical capacitors. It delivers an ultrahigh specific areal capacitance of 2632 µF cm−2 at 120 Hz with an excellent alternating current line filtering performance, fairly higher than the state‐of‐the‐art commercial ones. Together, this system offers the potential electrode material to be scaled up for AC line‐filtering capacitors at industrial levels.

Nanostructured V2O5 and its nanohybrid with MXene as an efficient electrode material for electrochemical capacitor applications

Vanadium pentoxide (V 2 O 5 ) is an excellent electrode material for electrochemical capacitor (ECCs) applications, but its lower electrical conductivity is the primary obstacle that restricts its practical applications. This obstacle can be eliminated by forming its nanohybrid (NCs) with a highly capacitive and conductive matrix such as MXene. MXene is a new two-dimensional (2D) material with good electronic conductivity and a larger specific surface area, making it a very suitable substrate for composite formation. Unfortunately, the two-dimensional MXene sheets stacked quickly, limiting their specific surface area and charge/mass transport properties. Here we used the hydrothermal approach to fabricate V 2 O 5 nanowires (NWs) and form their nanohybrid with MXene via the ultrasound route. To assess electrochemical suitability, the fabricated samples were loaded onto a carbon cloth (CC) and used as a working electrode in the half-cell configuration. The nanohybrid (V 2 O 5 /MXene) sample showed a good specific capacity (C sp ) of 768 F/g (at 1 A/g) because of its greater surface area, hybrid composition, excellent electrical conductivity, and passive nanostructure. It also showed superior cyclic, electrochemical and mechanical capability and maintained a specific capacity of 93.3%, even after completion of 6000 GCD tests. In addition, the nanohybrid sample electrode also exhibits superb rate performance and lost only 14.4% of its initial specific capacity on increasing the applied current density from 1 to 5 A/g. There is no doubt that V 2 O 5 NWs inter-stack between MXene nanosheets to develop effective interface interaction and suppress their stacking.

Nanoparticles of Nickel Hexacyanoferrate Derivatives as the Components of Electrode Materials for Electrochemical Capacitors

Nanoparticles of Nickel Hexacyanoferrate Derivatives as the Components of Electrode Materials for Electrochemical Capacitors

Theoretical investigation of capacitances in functionalised MXene supercapacitors M n+1C n O2, M = Ti, V, Nb, Mo

MXene, the class of two-dimensional materials, has been found to be useful as potential electrode materials for electrochemical capacitors. Although experimental investigation on the electrochemical performances of a few MXenes have been carried out with exciting results, a complete understanding of their atomic scale behaviour is yet to be done. Using first-principles electronic structure methods, we perform a systematic investigation of the capacitances in pristine and functionalised MXenes where M = Ti, V, Nb and Mo. We provide results on each of the three sources of the capacitance and analyse them in detail for a complete understanding of their behaviour. The interpretation of the experimental results, wherever available, in the light of our computations, provides useful insights.

Effect of dye-adsorption on Fe3O4-polypyrrole nanocomposite as electrode material in electrochemical capacitors

In this study, we have analyzed the effect of adsorption of organic dyes like methylene blue (MB) and methyl orange (MO) on the electrochemical performance of Fe3O4-polypyrrole (Fe3O4-PPy) nanocomposite as electrode material in supercapacitors. We have performed cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy for electrochemical measurements. The results of this work reveal that the nanocomposite shows higher specific capacitance than that of the dye adsorbed forms. But in terms of cyclic stability the dye modified nanocomposites show superior performance than the Fe3O4-PPy nanocomposite. Among all the three electrode materials Fe3O4-PPy-MO shows highest cyclic stability retaining 85% of initial capacitance after 1000 cycles along with a good specific power. The results of this work reveal that adsorption of organic dyes significantly improves cyclic stability of the nanocomposite as electrode material.

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.

Layered Vanadium Phosphates as Electrodes for Electrochemical Capacitors Part II: The Case of VOPO4•CTAB and K0.5VOPO4•1.5H2O

In the present work two layered vanadium phosphates were prepared, VOPO4 • CTAB and K0.5VOPO4 • 1.5H2O as electrode materials for electrochemical capacitors. These materials contain different molecular species in their interlayer space leading to an electrochemical behavior that drastically differs from the crystalline phase VOPO4 • 2H2O, with water molecules in the interlayer space. In the case of VOPO4 • CTAB, it was found that CTAB molecules block the pathway of electrolyte ions into the crystalline structure avoiding an intercalation/deintercalation process. In the case of K0.5VOPO4• 1.5H2O, the K+ ions from the crystalline structure hinder the intercalation/deintercalation process leading around 73 and 71 percent of the charge arise from a capacitive process in 3 M LiOH and 3 M KOH, respectively.

Role of morphological features and oxygen vacancies on electrocatalytic oxygen evolution reaction (OER) activity and pseudocapacitance performance of BiVO4 structures

In the present study, bismuth vanadate nanostructures have been synthesized by hydrothermal route. The final calcination has been carried out in an open atmosphere and also inside the closed system (autoclave). The role of morphology, defects, and oxygen vacancies generated during the synthesis in the open air and in limited supply of oxygen on electrochemical oxygen evolution reaction and capacitor performance has been studied. The samples synthesized in open air exhibit fine size and uniform distribution of particles. However, the samples synthesized in autoclave reveal larger size particles, a greater number of defect states, and oxygen vacancies. The sample synthesized in open air elucidates a lower water oxidation overpotential of 170 mV to retrieve current density of 10 mA cm−2. The results predict that morphological features play a vital role in electrocatalytic activity compared to defect states and vacancies. To avoid the prevailing confusion regarding the electrode materials for electrochemical capacitors and batteries, the actual pseudocapacitor behavior of the synthesized samples has been studied by cyclic voltammetry (CV) and galvanic charge–discharge characteristics performed at different scan rates and applied currents, respectively. The synthesized samples exhibit higher capacitance retention (>95%) during continuous CV cycling.