High-performance Electrochemical Capacitors Research Articles

Application of metal oxide/porous carbon nanocomposites in electrochemical capacitors: A review

In the past decade, electrochemical capacitors (ECs) have emerged as innovative energy storage devices, attracting considerable interest from both industrial and academic sectors due to their prolonged cyclic stability and impressive power density. Recently, there has been a focus on advancing high-performance ECs by developing electrode material composed of metal oxide incorporated with porous carbon. Integrating metal oxides into a porous carbon structure enhances capacitance, charge storage, and cyclic stability. Furthermore, the porous structure inherent in carbon materials offers efficient ion diffusion and large surface area, thereby augmenting the overall effectiveness of the nanocomposites. Efficient electron and ion transport within the electrode's bulk is achieved through the interaction between electrodes and electrolytes occurring at the electrode-electrolyte interface, subsequently increasing the capacitance. This paper summarizes the latest developments in ECs, focusing on key performance metrics such as cyclic stability and capacitance. It also summarizes the recent advancements made in electrode materials, emphasizing the utilization of sustainable feedstocks. As the research landscape shifts towards more environmentally friendly solutions, the incorporation bio-materials into electrode design has gained significant attention. It particularly highlights underlying mechanisms governing the performance of metal oxides/porous carbon nanocomposites in ECs and outlines future research directions aimed at maximizing their potential for next-generation energy storage devices. Additionally, the paper delves into the possibilities and challenges associated with the preparation, and optimization of the structure of metal oxide electrodes incorporating porous carbon to improve energy storage performance in ECs.

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.

Enhancing Interfacial Capacitance by Boron Doping in Vertically Porous Carbon Toward High-Performance AC Filtering Electrochemical Capacitors.

Electrochemical capacitors (ECs) show great perspective in alternate current (AC)filtering once they simultaneously reach ultra-fast response and high capacitance density. Nevertheless, the structure-design criteria of the two key properties are often mutually incompatible in electrode construction. Herein, it is proposed that combining vertically oriented porous carbon with enhanced interfacial capacitance (Ci) can efficiently solve this issue. Theoretically, the density function theory calculation shows that the Ci of a carbon electrode can be enhanced by boron doping due to the corresponding compact induced charge layer. Experimentally, the vertical-oriented boron-doped graphene nanowalls (BGNWs) electrodes, whose Ci is enhanced from 4.20 to 10.16µFcm-2 upon boron doping, are prepared on a large scale (480 cm2) using a hot-filament chemical vapor deposition technique (HFCVD). Owing to the high Ci and vertically oriented porous structure, BGNWs-based EC has a high capacitance density of 996µFcm-2 with a phase angle of - 79.4° at 120Hz in aqueous electrolyte and a high energy density of 1953µFV2cm-2 in organic electrolyte. As a result, the EC is capable of smoothing 120Hz ripples for 60Hz AC filtering. These results provide enlightening insights on designing high-performance ECs for high-frequency applications.

Hierarchical Porous Carbon Aerogel Derived from Sodium Alginate for High Performance Electrochemical Capacitor Electrode

To improve the performance of electrochemical capacitors, there is a notable focus on carbon materials characterized by a large surface area, reasonable pore size, pore size distribution, appropriate electronic conductivity, and excellent chemical durability. Herein, the hierarchical porous carbon aerogel originating from sodium alginate (SA) with well-defined porosity are proposed. The resultant hierarchical porous carbon aerogel shows a substantial specific surface area of 2050.6 m2 g−1 with macropores, mesopores and micropores confirmed by techniques such as TEM, SEM, BET, etc., resulting from a sequence of aerogel formation-carbonization-activation. By electrochemical measurement, the hierarchical porous carbon aerogel exhibits a specific capacitance of 204 F g−1 at an operating current density of 0.2 A g−1 employing 6 M KOH aqueous solution. The hierarchical carbon aerogel displays outstanding cycling stability with a 96.2% capacity maintenance for 10,000 cycles at an operating current density of 1 A g−1. This study presents a viable method for for preparing hierarchical porous carbon aerogel derived from biopolymer for electrochemical capacitors.

High utilization efficiency of tetramethylbenzoquinone hybridized in the pores of activated carbon for high-performance electrochemical capacitor electrodes

High utilization efficiency of tetramethylbenzoquinone hybridized in the pores of activated carbon for high-performance electrochemical capacitor electrodes

Choline chloride-based deep eutectic solvents as electrolytes for wide temperature range supercapacitors

Deep eutectic solvents (DESs) are a promising new class of environmentally friendly versatile solvent systems. In this work, a new approach for applying choline chloride-based DESs as cost-effective, and anti-corrosion electrolytes for activated carbon-based electrochemical capacitors (ECs) is proposed for the first time. In this regard, DESs of choline chloride/glycerol and choline chloride/propionic acid were prepared with molar ratios of 1:2. Important properties such as viscosity, electrical conductivity, and electrochemical measurements were studied in the range of room temperature up to 373 K. With the rising temperature, the viscosity of DESs decreased and their electrical conductivity increased. High energy is provided by the symmetric ECs in the choline chloride-based electrolytes, which exhibit excellent electrochemical stability at a maximum voltage up to 2.5 V. The electrolyte with DES ChCl/PA under 373 K has a specific capacitance of 198 F g−1 (with an energy density of 110 Wh kg−1), which can be reduced to 145 F g−1 (with an energy density of 16.3 Wh kg−1) at room temperature. In addition, 93 % capacity retention was achieved in the supercapacitor prepared based on DES ChCl/PA up to 5000 cycles at 373 K. According to the results, important implications are presented for expanding the application of green, non-toxic and cheap electrolytes for high-performance ECs with wide voltage windows and superior lifetime.

N-Doped Carbon Fibers Derived from Porous Wood Fibers Encapsulated in a Zeolitic Imidazolate Framework as an Electrode Material for Supercapacitors

Developing highly porous and conductive carbon electrodes is crucial for high-performance electrochemical double-layer capacitors. We provide a method for preparing supercapacitor electrode materials using zeolitic imidazolate framework-8 (ZIF-8)-coated wood fibers. The material has high nitrogen (N)-doping content and a specific surface area of 593.52 m2 g-1. When used as a supercapacitor electrode, the composite exhibits a high specific capacitance of 270.74 F g-1, with an excellent capacitance retention rate of 98.4% after 10,000 cycles. The symmetrical supercapacitors (SSCs) with two carbon fiber electrodes (CWFZ2) showed a high power density of 2272.73 W kg-1 (at an energy density of 2.46 W h kg-1) and an energy density of 4.15 Wh kg-1 (at a power density of 113.64 W kg-1). Moreover, the SSCs maintained 81.21% of the initial capacitance after 10,000 cycles at a current density of 10 A g-1, which proves that the SSCs have good cycle stability. The excellent capacitance performance is primarily attributed to the high conductivity and N source provided by the zeolite imidazole framework. Because of this carbon material's unique structural features and N-doping, our obtained CWFZ2 electrode material could be a candidate for high-performance supercapacitor electrode materials.

Brewery waste derived activated carbon for high performance electrochemical capacitors and lithium-ion capacitors

In this study we report about the synthesis and characterization of an activated carbon (AC) displaying very large surface area (∼3600 m2 g−1) obtained from a cheap and abundant brewery waste product (Brewer's spent grains, BSG). AC based electrodes prepared from BSG demonstrated a very high specific capacitance (46 F g−1) and capacitance retention when evaluated in symmetric Electrical Double Layer Capacitors (EDLCs) devices with organic electrolytes. We showed that these electrodes can be successfully utilized for the realization of lab scale EDLCs and Lithium-ion Capacitors exhibiting very high energy and power densities as well excellent cycling stability (85% capacitance retention after 200 h of float test). Considering these results, the BSG-derived AC can be certainly considered as very promising material, which can contribute to the development of high performance, cost effective and eco-friendly high-power devices.

Fabrication of ternary NiCoMoOx with yolk-shell hollow structure as a positive electrode material for high-performance electrochemical capacitor applications.

Although the fabrication of hollow nanostructures from single and binary transition metal oxides has been accomplished effectively, there still exists a significant challenge in creating advanced hollow morphologies comprising mixed transition metal oxides such as ternary and quaternary compositions. In this context, we have adopted an alternative approach by employing a straightforward self-templating method to synthesize ternary metal molybdate nanomaterials. These materials possess the chemical composition of NiCoMoOx and exhibit a unique nanoporous yolk-shell hollow structure. Commencing with mixed metal-glycerate solid spheres, we have successfully guided the formation of this chemical composition and distinctive yolk-shell hollow sphere architecture through meticulous thermal treatment control. The consistency of our results is confirmed through SEM images. Thanks to their robust structural integrity, advanced internal morphology, and increased surface area, these hierarchical hollow spheres demonstrate remarkable electrochemical performance when utilized as advanced electrode materials for supercapacitors. When serving as electrode materials in supercapacitors, these nanoporous NiCoMoOx yolk-shell hollow spheres deliver a specific capacitance of 1125 F g-1 at a current density of 0.5 A g-1, maintaining an impressive cycling stability of 91.48% even after 5000 cycles. In a hybrid device configuration wherein activated carbon (AC) functions as the negative electrode and NiCoMoOx yolk-shell hollow spheres serve as the positive electrode, exceptional performance is observed. This configuration achieves a substantial specific energy density of 44.67 W h kg-1, alongside a maximum power density of 8000 W kg-1, and exceptional cycling stability of 93.03% even after 5000 cycles.

Facile syntheses of Fe2O3-rGO and NiCo-LDH-rGO nanocomposites for high-performance electrochemical capacitors

Faraday-type electrode materials and devices for electrochemical capacitors have been widely investigated. However, their applications are severely limited by the preparation method and cost of electrode materials. In this work, high-performance electrochemical capacitors were successfully assembled using Fe2O3-decorated reduced graphene oxide (rGO) nanocomposites and NiCo-Layered Double Hydroxides (LDH) as the anode and cathode, respectively. An easy and efficient approach (the modified precipitation method) for the large-scale fabrication was used to prepare Fe2O3 and NiCo-LDH, supported by rGO sheets, respectively. The anode material, Fe2O3-rGO, exhibited an excellent specific capacitance (Csp) of 1073 F g−1 at a current density of 1 A g−1 and a retention rate of 92 % at 10 A g−1, while the NiCo-LDH-rGO cathode material provided a Csp of 1850 F g−1 at 1 A g−1 and maintained 84 % at 10 A g−1. The effective combination of these electrodes for the NiCo-LDH-rGO//Fe2O3-rGO electrochemical capacitors resulted in an excellent energy density of 108 Wh/kg at a power density of 884 W/kg, with remarkable cycling stability (80 % after 1000 cycles at 10 A g−1). We believe that this work, including the proposed method and electrode materials, will advance the further development and commercialization of electrochemical capacitors.

MXene (Ti3C2T x ) modified α-Co(OH)2 battery-type cathode and highly capacitive binder-free Ti3C2T x anode for high-performance electrochemical hybrid capacitor

The layered nanostructure of cobalt hydroxide has received great attention in the field of the electrochemical hybrid capacitor (EHC). However, the poor electrical conductivity and cyclic stability hinder its practical applicability. Surface modification of electrodes is considered one of the effective strategies to improve these properties. In this work, the surface of α-Co(OH)2 is modified via Ti3C2T x MXene using a simple drop-casting method with different mass loadings and corresponding electrochemical performance is evaluated. The α-Co(OH)2 surface modified with 0.05 mg cm−2 Ti3C2T x MXene (CM0.05) shows the maximum specific capacity of 403 C g−1 at the current density of 3 A g−1. The aqueous EHC fabricated with CM0.05 as a positive electrode and two-dimensional (2D) Ti3C2T x MXene nanosheets as a negative electrode outperforms the EHC fabricated with the activated carbon as a negative electrode. The CM0.05//MXene EHC shows the maximum energy density of 44.5 Wh kg−1 at the power density of 2762 W kg−1. This also shows appreciable stability of 72% even after 5000 cycles. The flexible EHC fabricated using polyvinyl alcohol: KOH gel electrolyte demonstrates a superior energy density of 1.17 mWh cm−2 at the power density of 11.9 mW cm−2 with a wide operating potential of 1.6 V. Therefore, MXene (Ti3C2T x ) modified α-Co(OH)2 can be considered as a promising electrode material for flexible EHCs.

Flexible supercapacitor electrodes based on modified binary metal phosphites on three dimensional graphene sponge

In this paper, two flexible graphene-based materials were prepared by electrochemically depositing FeCoP and FeZnP on graphene sponges (GS) as self-standing electrodes for high-performance electrochemical capacitors. The structural and morphological properties of FeCoP/GS and FeZnP/GS electrodes were characterized using different spectroscopic techniques. As a result, the FeCoP/GS and FeZnP/GS electrodes demonstrated a high specific capacitance of 2100 and 1100 F/g at 1.0 A/g, great cycling stability after 10,000 cycles maintaining 80 % and 74 % of its initial capacitance, respectively, which showed better performance than GS electrode. Moreover, two asymmetric supercapacitors were fabricated with FeCoP/GS and FeZnP/GS electrodes and GS; FeCoP/GS//GS and FeZnP/GS//GS circuits displayed a specific capacitance of 1100 and 780 F/g at 1.0 A/g and an outstanding energy density of 185 and 98 Wh/kg at a high power density of 5.6 and 3.8 kW/kg, respectively. Therefore, the as-fabricated electrodes hold great potential in the field of energy storage.

Metal-Free Homocoupling of Pyrene inside the Pores of Mesoporous Carbons via Electrochemical Oxidation: Application for Electrochemical Capacitors.

A pyrene dimer (PYD) is synthesized by electrochemical oxidation via homocoupling of pyrene (PY) inside the pores of MgO-templated mesoporous carbons without any metal catalysts or organic solvents. The resulting MgO-C/PYD hybrids can be used as high-performance aqueous electrochemical capacitor electrodes due to the reversible redox property of PYD and large contact area between the hybridized PYD and conductive carbon surfaces, which enable rapid charge transfer at the large contact interface. In our previous study, PY was considered to polymerize through electrochemical oxidation, and activated carbon with the pore sizes of ∼4 nm was used as a porous carbon substrate. In this study, the MgO-templated carbons have the average pore sizes of 5, 10, and 30 nm, and their large mesopore volumes can accommodate a large amount of PYD for enhancing the capacitance. To develop high-performance electrochemical capacitors, the dependence of the capacitance enhancement and the capacitance retention on the amount of PY and the pore sizes of MgO-templated carbons are studied. It is found that mesopores are necessary for fast charging/discharging, but the capacitance retention and capacitance enhancement decrease with increasing the mesopore sizes and the amount of PY due to the decreased utilization ratio of PY.

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.

Tubular carbon nanofibers decorated with RuO2 nanorods toward flexible electrochemical capacitors

RuO2 nanorod-decorated tubular carbon nanofibers(CNFs) are carefully fabricated by adjusting the recrystallization temperature for use in high-performance electrochemical capacitors. The tubular structured CNFs/RuO2 electrodes provide a short diffusion path for the ion transport through the inner hollow channel that allowed the maximum utilization of the active sites of the amorphous RuO2 nanomaterials at the electrode/electrolyte interface. The optimized the tubular structured CNFs/RuO2 electrodes exhibit good rate capability with a high surface capacitance, energy density, and good long-term cycling stability of 190 Fg−1, 22 Whkg−1, and 94% after 10,000 cycles, respectively, in an aqueous solution. The asymmetric cell presents a wide and stable operating voltage window, which greatly improves the energy density stored in the asymmetric device. In addition, there is no noticeable difference in the electrochemical properties under bent states, making it a flexible energy storage device for wearable applications. Hence, flexible supercapacitors using CNFs/RuO2 electrodes with the tubular structure show low resistance, high capacitance, good rate retention, and excellent cycle stability, making it a promising material for energy storage applications.

Performance evaluation of electrochemical capacitors with activated carbon spheres as electrode material and aqueous electrolyte

The model activated carbon spheres (ACSs) were optimized to be used as negative electrode in asymmetric electrochemical capacitors (ECs). A microporous commercial activated carbon was used as positive electrode.Carbon spheres (CSs) were synthesized by precipitation polymerization at room temperature followed by pyrolysis and activation. By enhancing the carbon:KOH ratio from 1:2 to 1:4, an increase in the specific surface area from 380 m2 g−1 to 2835 m2 g−1 (1:4) was achieved along with an increase in pore volume/size. Consequently, the electrochemical performance in the aqueous electrolyte was improved. After activation, low-temperature-pyrolyzed polymer spheres (400 °C) result in random-like particles with macroporous structure, while intermediate- and high-temperature-pyrolyzed materials (550 °C and 700 °C) lead to partially and totally conserved spheres.The interaction between the electrode material and electrolyte is important and is related to the texture, morphology, and surface chemistry of ACS. In 1 mol L−1 H2SO4, capacitance and rate handling are mostly affected by electrode morphology and wettability with the electrolyte. In 1 mol L−1 Li2SO4 electrolyte solution, texture and surface chemistry of the electrode material are crucial to obtain high-performance EC. Regardless of morphology, poor wetting properties of synthesized materials were found in Li2SO4, compared to the H2SO4 solution.

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.

Engineering a Novel AgMn2O4@Na0.55Mn2O4 Nanosheet toward High-Performance Electrochemical Capacitors

Manganese oxides, as a type of two-dimensional (2D) material with high specific area and low cost, are considered promising energy storage materials. Here, we report novel AgMn2O4/Na0.55Mn2O4 nanosheets created by a popular liquid precipitation method with different AgNO3 contents, and their corresponding physical and electrochemical characterizations are performed. The results show that the ultra-thin Na0.55Mn2O4 nanosheets were combined with the AgMn2O4 nanoparticles and an enhancement in their specific capacity was observed compared to the pristine sheets. This electrode material displays a peak specific capacitance of 335.94 F g−1 at 1 A g−1. Using an asymmetric supercapacitor (ASC) assembled using a positive electrode made of AgMn2O4/Na0.55Mn2O4 nanosheets and a reduced graphene oxide (rGO) negative electrode, a high energy density of 65.5 Wh kg−1 was achieved for a power density of 775 W kg−1. The ASC showed good cycling stability with a capacitance value maintained at 90.2% after 10,000 charge/discharge cycles. The excellent electrochemical performance of the device was ascribed to the heterostructures and the open space formed by the interconnected manganese oxide nanosheets, which resulted in a rapid and reversible faraday reaction in the interface and further enhanced its electrochemical kinetics.

Synthesis of hydrous RuO2 anchored on seaweed-derived porous carbon for high-performance electrochemical capacitors

Supercapacitors (SCs) have attracted widespread attention due to the fast development of electronics and electrical vehicles. As a potential pseudocapacitive electrode material for SCs, RuO2 is promising for fast energy storage, but its performance is severely restricted by the spontaneous agglomeration and high cost. Here, we prepared seaweed-derived porous carbon (SDC) as a conductive substrate of hydrous RuO2 nanoparticles for electrochemical SCs, and the as-prepared hybrid exhibits high specific capacitance of 807 F g−1 at 2 mV s−1, excellent high-rate (988.1 F g−1 at 0.1 A g−1 and 635.9 F g−1 at 5 A g−1) and cycling performances (93.8% retention after 1000 cycles at 1 A g−1) in 1 M H2SO4. The outstanding performance of the hybrid can be attributed to the interconnected three-dimensional mesoporous structure of the SDC and the uniform dispersion of hydrous RuO2 nanoparticles. This work demonstrates that the hierarchical porous SDC can be used as an excellent conductive substrate to further enhance the electrochemical performance of other easily agglomerated nanoparticles.

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.