Materials For Electrochemical Capacitors Research Articles

Carbon nanospheres-induced enhanced capacitive dynamics in C/WS2/WO3 nanocomposites for high-performance electrochemical capacitors

This work investigates the impact of carbon nanospheres on the electrochemical performance of C/WS2/WO3 nanocomposites for electrochemical supercapacitors. The nanocomposites have been synthesized and characterized by various techniques like XRD, UV–vis spectroscopy, SEM, TEM and FTIR. The electrochemical properties of the nanocomposites have been analysed in order to study the charge transport, reaction kinetics, impedimetric properties and specific capacitance by using cyclic voltammetry (CV) and potentio electrochemical impedance spectroscopy (PEIS). The capacitive performance of the samples has been investigated by the obtained specific capacitance values and Nyquist plots. The specific capacitance of the samples has been found in a range of 0.8–2.8F/g at 20 mV/s. The sample with the least amount of carbon showed maximum specific capacitance. The electrochemical insights, combined with comprehensive material characterizations, provide valuable knowledge for tailoring the capacitive performance of C/WS2/WO3 nanocomposites through controlled carbon nanospheres and thus the suitability of materials for electrochemical capacitors.

A Highly Robust and Conducting Ultramicroporous 3D Fe(II)-Based Metal-Organic Framework for Efficient Energy Storage.

Exploitation of metal-organic framework (MOF) materials as active electrodes for energy storage or conversion is reasonably challenging owing to their poor robustness against various acidic/basic conditions and conventionally low electric conductivity. Keeping this in perspective, herein, a 3D ultramicroporous triazolate Fe-MOF (abbreviated as Fe-MET) is judiciously employed using cheap and commercially available starting materials. Fe-MET possesses ultra-stability against various chemical environments (pH-1 to pH-14 with varied organic solvents) and is highly electrically conductive (σ=0.19Sm-1) in one fell swoop. By taking advantage of the properties mentioned above, Fe-MET electrodes give prominence to electrochemical capacitor (EC) performance by delivering an astounding gravimetric (304Fg-1) and areal (181mFcm-2) capacitance at 0.5Ag-1 current density with exceptionally high cycling stability. Implementation of Fe-MET as an exclusive (by not using any conductive additives) EC electrode in solid-state energy storage devices outperforms most of the reported MOF-based EC materials and even surpasses certain porous carbon and graphene materials, showcasing superior capabilities and great promise compared to various other alternatives as energy storage materials.

Electrochemical Capacitance Traces with Interlayer Spacing in Two‐dimensional Conductive Metal–Organic Frameworks

AbstractElectrically conductive metal–organic frameworks (MOFs) are promising candidates for electrochemical capacitors (EC) for fast energy storage due to their high specific surface areas and potential for redox activity. To maximize energy density, traditional inorganic pseudocapacitors have utilized faradaic processes in addition to double‐layer capacitance. Although conductive MOFs are usually comprised of redox active ligands which allow faradaic reactions upon electrochemical polarization, systematic studies providing deeper understanding of the charge storage processes and structure‐function relationships have been scarce. Here, we investigate the charge storage mechanisms of a series of triazatruxene‐based 2D layered conductive MOFs with variable alkyl functional groups, Ni3(HIR3‐TAT)2 (TAT=triazatruxene; R=H, Et, n‐Bu, n‐Pent). Functionalization of the triazatruxene core allows for systematic variation of structural parameters while maintaining in‐plane conjugation between ligands and metals. Specifically, R groups modulate interlayer spacing, which in turn shifts the charge storage mechanism from double‐layer capacitance towards pseudocapacitance, leading to an increase in molar specific capacitance from Ni3(HIH3‐TAT)2 to Ni3(HIBu3‐TAT)2. Partial exfoliation of Ni3(HIBu3‐TAT)2 renders redox active ligand moieties more accessible, and thus increases the dominance of faradaic processes. Our strategy of controlling charge storage mechanism through tuning the accessibility of redox‐active sites may motivate further design and engineering of electrode materials for EC.

Electrochemical Capacitance Traces with Interlayer Spacing in Two-dimensional Conductive Metal-Organic Frameworks.

Electrically conductive metal-organic frameworks (MOFs) are promising candidates for electrochemical capacitors (EC) for fast energy storage due to their high specific surface areas and potential for redox activity. To maximize energy density, traditional inorganic pseudocapacitors have utilized faradaic processes in addition to double-layer capacitance. Although conductive MOFs are usually comprised of redox active ligands which allow faradaic reactions upon electrochemical polarization, systematic studies providing deeper understanding of the charge storage processes and structure-function relationships have been scarce. Here, we investigate the charge storage mechanisms of a series of triazatruxene-based 2D layered conductive MOFs with variable alkyl functional groups, Ni3(HIR3-TAT)2 (TAT=triazatruxene; R=H, Et, n-Bu, n-Pent). Functionalization of the triazatruxene core allows for systematic variation of structural parameters while maintaining in-plane conjugation between ligands and metals. Specifically, R groups modulate interlayer spacing, which in turn shifts the charge storage mechanism from double-layer capacitance towards pseudocapacitance, leading to an increase in molar specific capacitance from Ni3(HIH3-TAT)2 to Ni3(HIBu3-TAT)2. Partial exfoliation of Ni3(HIBu3-TAT)2 renders redox active ligand moieties more accessible, and thus increases the dominance of faradaic processes. Our strategy of controlling charge storage mechanism through tuning the accessibility of redox-active sites may motivate further design and engineering of electrode materials for EC.

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.

Electrochemical Performance of Activated Graphene-Based Materials for Electrodes of Double-Layer Supercapacitors

Activated graphene oxide seems to be a promising electrode material for electrochemical double-layer capacitors, also known as supercapacitors or ultracapacitors, and other energy storage purposes. This article summarizes the results of our research about the effect of graphene oxide KOH-catalyzed activation on their specific surface area (SSA) and their capacitance, both strongly related to their electrochemical performance. KOH-catalyzed activation increased the SSA values of the reduced graphene oxide (rGO) from ∼783 m2 g−1 to ∼2144 m2 g−1; it is important to note that the SSA and oxygen-containing groups are two important factors determining electrochemical performance. Moreover, the highest capacitance value was 50.08 F g−1, using 1.0 M H2SO4 as an aqueous electrolyte. Activated graphene-based materials with high SSA support conductive networks decorated with oxygen groups synergistically improve charge storage capability in EDLCs.

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.

Utilization of biomass wastes: coconut and Pangium edule shells as activated carbon for energy storage device material

In this research, activated carbon (AC) was synthesized from biomass wastes of coconut and Pangium edule shells and utilized as a material for electrochemical double-layer capacitors (EDLC), which are eco-friendly energy storage devices. This research was intended to bridge the need for greenhouse gas-free energy storage device and the handling of abundant biomass wastes. These efforts would undoubtedly contribute to mitigating climate change. To begin the research, the coconut and Pangium edule shells underwent carbonization at varying temperatures of 600°C and 700°C for 2 hours. Subsequently, they were subjected to chemical activation using KOH and physical activation at varying temperatures of 110°C and 600°C. Some characterization techniques, including SEM, XRD, TGA/DSC, BET, Iodine number, and proximate analysis, were employed to analyze the materials. The capacitive properties of EDLC electrodes were assessed through cyclic voltammetry (CV). After carbonization at 700°C and subsequent physical activation at 600°C, the coconut and Pangium edule shells exhibited the highest active surface area of 548.542 m2g-1 and 333.4 m2g-1, respectively. Notably, the EDLC demonstrated a maximum specific capacitance of 364.5 Fg-1 at 2 mVs-1 scan rate. These findings indicate the viability of utilizing AC from biomass waste as a promising material for EDLC applications.

Controllable Preparation of Cu NPs/CNTs@PANI Composites as Electrode Materials for Electrochemical Double-Layer Capacitors

Controllable Preparation of Cu NPs/CNTs@PANI Composites as Electrode Materials for Electrochemical Double-Layer Capacitors

Development of activated carbon/bimetallic transition metal phosphide composite materials for electrochemical capacitors and oxygen evolution reaction catalysis

Development of activated carbon/bimetallic transition metal phosphide composite materials for electrochemical capacitors and oxygen evolution reaction catalysis

Cost effective, metal free reduced graphene oxide sheet for high performance electrochemical capacitor application

A simple, cost-effective, and large-scale production of metal-free self-assembled graphene oxide sheets (GOS) with an area of 15 × 15 cm is synthesized using a modified Hummer's method. The reduced graphene oxide sheet (rGOS) was prepared by heat-treating GOS at a range of 300 °C in a hydrogen atmosphere. The XRD results show that GOS has an interlayer distance of 0.79 nm and the rGOS has an interlayer distance of 0.34 nm. The electrochemical analysis of rGOS and GOS was investigated. The porous structure, large-size sheet, and fast transit kinetics of electrochemical analysis and electrons on the interface of electrolyte/electrode contributed to the rGOS showing the high performance of an electrochemical capacitor. The GOS has a specific capacitance value of 54 F/g at 1 A/g, while the reduced GOS has a higher specific capacitance value (469 F/g at 1 A/g), which is 8.6-fold higher than the GOS and has excellent cycle stability. Heat-treated rGOS is regarded as a strong, cost-effective, and scalable electrochemical capacitor material.

Porous hierarchical Ni2P nanosheet arrays combined with Cu3P layers on copper foam as a binder-free battery-type cathode for high-energy-density asymmetrical all-solid-state electrochemical capacitors

Transition metal phosphides with a satisfying theoretical electrochemical characteristics are the promising environmentally friendly energy storage materials for high-performance electrochemical capacitors. The possession of high specific surface area, numerous active sites and stable structure is helpful for the electrochemical energy storage process. In this study, porous hierarchical Ni2P nanosheet arrays combined with Cu3P layers on copper foam (Ni2P/C@Cu3P-CF) is fabricated via hydrothermal-reduction/carbonization-phosphorization process using the 2D Ni-based metal organic framework nanosheets as the precursor. Benefit from this rational design and super-hydrophilic property, the Ni2P/C@Cu3P-CF electrode possess a satisfying capacity of 1105.0 mC cm−2 at a current density of 5 mA cm−2 and good rate performance (61.5% capacity retention at a high current density of 50 mA cm−2). In addition, asymmetrical all-solid-state electrochemical capacitors assembled with our Ni2P/C@Cu3P-CF electrode can deliver a high areal energy density of 1.6 mWh cm−2 at a power density of 0.16 mW cm−2. Moreover, this electrochemical capacitors display the robust cycling stability with a 91.2% capacity retention after 5000 cycles at a rate of 10 mA cm−2. These results demonstrate a great potential for the Ni2P/C@Cu3P-CF electrode in the commercial application of the advanced aqueous electrochemical energy storage device.

Ultrasonically decorated zinc cobaltate on nanocellulose interface for supercapacitors

The strategic design of energy storage materials from renewable sources has been a keen interest for researchers, especially for energy storage applications. In the present study, ZnCo2O4 and its nanostructures were fabricated along with cellulose nanocrystals (ZnCo2O4@CNC) using the green ultrasonication technique. Structural and morphological examination of composite materials have been investigated by the aid of Field-emission transmission electron microscopy (FE-TEM), X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), and Surface Brunauer-Emmett-Teller (BET) analysis revealing the existence of spherical particles arranged in a controlled nanoscale range (i.e., < 10 nm). The electrochemical properties of ZnCo2O4 and ZnCo2O4@CNC nanocomposites were performed by CV, GCD, and EIS measurements. The ZnCo2O4@CNC electrode reveals a higher specific capacitance value of 346 F/g than its pristine ZnCo2O4 (236 F/g) at 0.5 A/g (current density) in a three-electrode cell assembly. The ZnCo2O4@CNC nanocomposite electrode shows exceptional capacitance with 97% cyclic retention straight after 5000 cycles at 0.5 A/g with an energy density of 15.8 Wh kg−1 at a power density of 138.4 W kg−1, significantly superior to its pristine ZnCo2O4 composite. The increased specific capacitance of nanocomposite materials manifested by the improved surface and morphological properties convince it as capable materials for high-performance electrochemical capacitors.

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.