Pseudocapacitive Electrode Materials Research Articles

A high-performance asymmetric supercapacitor device based on CoO@CoAl-LDH hierarchical 3D nanobouquet arrays

3D core–shell CoO@CoAl-LDH nanobouquet arrays on Ni foam are promising active electrode materials for pseudocapacitors.

Construction of CuO/Cu-nanoflowers loaded on chitosan-derived porous carbon for high energy density supercapacitors.

Copper oxide (CuO) and copper (Cu) have been viewed as the prospective pseudocapacitive electrode materials for supercapacitors. Nevertheless, the poor electron transfer capacity, loading amount, and cycling stability limit their wide applications, which can be addressed by developing the CuO based heterojunction on conductive carbons. Here, a CuO/Cu@C comprising CuO/Cu nanoflowers and chitosan-derived N-doped porous carbon was compounded by simple mechanical mixing, freeze-drying, and carbonization. The composite heated at 700°C exhibited a high specific capacitance of 2479F/g at 0.5 A/g and excellent cycling stability with capacitance retention of 82.43% after 10 000 charge-discharge cycles. In addition, the asymmetric supercapacitor (ASC), i.e., CuO/Cu@C-700//AC assembled by CuO/Cu@C (as a positive electrode) and activated carbon (AC, as a negative electrode) displayed a great energy density of 76.87Whkg-1 at 374.5Wkg-1 and kept as high as 25.83Whkg-1 even at 14998Wkg-1. Our work provides a new pathway to preparing transition metal oxide-based electrode materials with distinguished electrochemical performances.

Hierarchical design of NiCo-LDH NFs@Co(OH)2 nanosheets supercapacitor electrode material with boosted electrochemical performance

Layered double hydroxides (LDHs) have been considered as excellent pseudocapacitive electrode materials for supercapacitors because of their controllable layered structures and high theoretical specific capacitances. However, poor conductivity and shortage of effective active sites hinder their applications. Herein, in order to boost the capacitance performance, an electrode material composed of NiCo-LDH nanofibers with cobalt hydroxide (Co(OH)2) nanosheets firmly anchored to or uniformly immobilized onto NiCo-LDH nanofibers surface is constructed. The material architecture takes advantage of superior capacitive activity from Co(OH)2 with good electronic conductivity and dispersibility over the surface of NiCo-LDH nanofibers. The merits based on the elegant synergy between NiCo-LDH nanofibers and Co(OH)2 nanosheets induce an outstanding specific capacitance of 858.9 F/g at a current density of 0.5 A/g. With the current density increasing from 0.5 to 10 A/g, the specific capacitance retention is 67.3%, indicating a good rate capability. Furthermore, the electrode material exhibits a capacitance retention of 83.7% after 2000 cycles at 10 A/g. These excellent electrochemical properties are due to the hierarchically designed structure and the cooperative contributions of NiCo-LDH nanofibers and Co(OH)2 nanosheets, which shows great potential for energy storage applications.

Spiny Spherical Nickel–Cobalt Bimetallic Sulfide Nanocomposite for High-Energy-Density Pseudocapacitor

Multicomponent transition-metal sulfide is a potential electrode material for pseudocapacitors due to its excellent conductivity and high capacitance. Since the morphology and preparation method of electrode materials greatly affect the performance of capacitors, the development of novel structured multimetal sulfide is of great significance. Herein, we prepare Ni,Co–S materials by hydrothermal method and obtain diverse morphologies by changing the ratio of Ni, Co, and thiourea in the precursors. The Ni,Co–S exhibits optimum capacitance performance with a precursor mass ratio of 1:2:2 for Ni, Co, and thiourea. The discharge specific capacitances of Ni,Co–S at 1 and 20 A·g–1 in 6.0 mol·L–1 KOH are 1641 and 1406 F·g–1, respectively. In addition, the assembled asymmetric supercapacitor using Ni,Co–S and NPHTCK as bipolar shows a high energy density of 44.7 Wh·kg–1 at a power density of 800 W·kg–1.

Influence of the Molar Ratio of Co and V in Bimetallic Oxides on Their Pseudocapacitive Properties.

Bimetallic oxides have significant attraction as supercapacitor electrode materials due to their highly reversible redox processes, which are commonly associated with their surface chemistry and morphological features. Here, we report the synthesis, characterization, and electrochemical evaluation of bimetallic oxides with different molar compositions of Co and V (Co0.6V0.4, Co0.64V0.36, Co0.68V0.32, and Co0.7V0.3 denoted as S1, S2, S3, and S4 samples, respectively). The materials were synthesized by a modified solvothermal method using glycerol as a stabilizing agent, characterized by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, scanning electron microscopy-energy-dispersive X-ray spectroscopy, X-ray fluorescence spectroscopy, N2 adsorption isotherms, cyclic voltammetry, and galvanostatic charged/discharged in a three-electrode cell. The role of the CoV oxide compositions on the pseudocapacitive properties was studied through the analysis of the energy storage mechanism following the power law and Dunn's methodology to obtain the b values. An important finding of this work is that CoV oxides exhibited electrochemical characteristics of a pseudocapacitive electrode material even though the charge storage occurs in bulk. This behavior is consistent with the pseudocapacitance generated by redox processes, showing b values of 0.67, 0.53, 0.75, and 0.84, with a capacitive current contribution of 74, 74, 63, and 70% analyzed at a scan rate of 1 mV s-1, for S4, S3, S2, and S1 samples, respectively. Co0.7V0.3 (S4) oxide presented the highest specific capacitance of 299 F g-1 at 0.5 A g-1 with a Coulombic efficiency of 93% tested at 4 A g-1. The better electrochemical performance of this sample was attributed to the synergistic effect of the Co and V atoms since a minimum amount of V in the structure may distort the crystal lattice and improve the electrolyte diffusion, in addition to the formation of several oxidation states due to reduction of V5+, including V3+ and V4+ as well as to the formation of the metastable V4O9.

Mn3P2O8/TiN on Titanium Substrate for Superapacitor Electrode with Long Cycle Stability in KOH and Na2SO4 Aqueous Eletrolytes

The limitation of low-cost and high-safety aqueous manganese-based materials for electrochemical energy storage is largely hampered by their poor cyclic stability, which is usually caused by the manganese dissolution and interfacial kinetics. Here we synthesize a composite electrode which possesses unique structural properties for aqueous supercapacitor application and exhibits higher area specific capacitance. The remarkable long cycle stability of Mn3P2O8/TiN on titanium (Mn3P2O8/TiN@Ti) outperforms that most manganese-based pseudocapacitive electrode materials. The designed unique structure is attractive for quick charge migration, which confirms that the appropriate anodizing of substrate, electrodeposition of active substances and their in situ loading, is an efficient strategy to improve kinetics for high power density pseudocapacitive supercapacitor energy storage application.

Transparent and Multi-Foldable Nanocellulose Paper Microsupercapacitors.

Despite the ever-increasing demand for transparent power sources in wireless optoelectronics, most of them have still relied on synthetic chemicals, thus limiting their versatile applications. Here, a class of transparent nanocellulose paper microsupercapacitors (TNP-MSCs) as a beyond-synthetic-material strategy is demonstrated. Onto semi-interpenetrating polymer network-structured, thiol-modified transparent nanocellulose paper, a thin layer of silver nanowire and a conducting polymer (chosen as a pseudocapacitive electrode material) are consecutively introduced through microscale-patterned masks (which are fabricated by electrohydrodynamic jet printing) to produce a transparent conductive electrode (TNP-TCE) with planar interdigitated structure. This TNP-TCE, in combination with solid-state gel electrolytes, enables on-demand (in-series/in-parallel) cell configurations in a single body of TNP-MSC. Driven by this structural uniqueness and scalable microfabrication, the TNP-MSC exhibits improvements in optical transparency (T = 85%), areal capacitance (0.24 mF cm-2 ), controllable voltage (7.2V per cell), and mechanical flexibility (origami airplane), which exceed those of previously reported transparent MSCs based on synthetic chemicals.

Protic Ionic Liquid Electrolytes to Increase Areal Energy Density of RuO2 Micro-Supercapacitors

The rising growth of smart and autonomous microelectronic devices in the IoT (Internet of Things) era urges the development of advanced microscale energy sources with tailor-made features and customized energy/power requirements [1]. Micro-supercapacitors (MSCs) emerged as potential energy storage devices complementing micro-batteries to power ubiquitous sensor networks needed to foster the development of IoT. However, the low cell voltage and low energy density remain major bottleneck that prevents their application at a large scale in real devices. To mitigate this issue, several studies have been devoted to the engineering of MSC electrode materials and structural architecting of current collectors to enhance the surface area and areal energy density by considering the limited available footprint area [2]. This approach however has associated challenges such as complex synthesis route, the deleterious interfacial and mechanical stability of the electrode, and compatibility issues with the electrolyte and the current collector underneath [3]. Another important challenge to solve for reaching high energy density values in MSCs is the limited electrochemical stability window (ESW) of the electrolytes used as energy stored is directly related to the square of the cell voltage [4]. The electrolytes play a major role in deciding the ESW and liquid-state electrolytes currently employed are troublesome for the microfabrication process due to leakage, evaporation, and safety issues. Therefore, it’s imperative to develop alternative electrolytes including solid-state electrolytes reconcilable to the target application of MSCs. To address the low energy density challenge of current MSCs, we have developed interdigitated MSCs using hydrous ruthenium dioxide (RuO2) electrodes in combination with novel protic ionic liquid (PIL)-based electrolytes able to provide pseudocapacitance while affording a higher ESWs as compared to conventional aqueous electrolytes. As a state-of-the-art pseudocapacitive electrode material, RuO2 owns the key merits of excellent conductivity, high electrochemical reversibility, and cycling stability [5], whereas PILs could help alleviate issues facing currently used electrolytes such as evaporation and encapsulation problems pertaining to aqueous-based and flammability of common organic electrolytes [6], [7], [8]. In the next step, the slow proton transport kinetics of PILs were addressed by the doping of silicotungstic acid (SiWa, H4SiW12O40) with the PIL, which further boosted the pseudocapacitive current response with enlarged cell voltage. The real MSC device was realized by the use of RuO2 deposited on interdigitated porous Au current collectors having a high area enlargement factor (AEF) in combination with triethylammonium bis(trifluoromethanesulfonyl)imide (TEAH-TFSI)-based PIL. The resultant 3D MSC rendered a cell voltage exceeding 2V with areal capacitance as high as 86 mF cm-2 at 5 mV s-1 on par with the performance of 3D MSC tested using 0.5 M H2SO4 (cell voltage of 0.9 V and areal capacitance of 85 mF cm-2 at 5 mV s-1) but higher energy density performance (more than 4 times) using similar number of RuO2 deposition cycles. To demonstrate the potential integration in real on-chip device application, ionogel-based all-solid-state MSC is developed that showed performance comparable to liquid-state electrolyte with superior long-term cycling stability. This study gives a new perspective to develop all-solid-state micro-supercapacitors using pseudocapacitive active materials that can operate in ionic-liquid-based non-aqueous electrolytes compatible with on-chip IoT-based device applications seeking high areal energy/ power performance.

Nanotexturing TiO2 over carbon nanotubes for high-energy and high-power density pseudocapacitors in organic electrolytes

Titanium oxides have been considered potential electrode materials for pseudocapacitors because of their exceptional properties, such as high thermal and chemical stabilities, ready availability and low cost. However, they are not ideal for practical applications due to their poor ionic and electrical conductivity. The electrochemical performance of TiO2 can be greatly improved if the material is nanotextured by reducing the particle size in optimizing the synthesis pathway. Actually, for metallic oxides, the electrochemical performance significantly depends on the particle size/morphology. At relatively low current densities the higher capacity values are exhibited by noncrystalline TiO2 having 2 nm particle size, with values reaching 704 C g−1. However, only thin electrodes are able to operate at a high charge density, limiting the energy density of the final device. Here, we propose a solution to circumvent such a drawback by further nanotexturing TiO2 over multiwalled carbon nanotubes (CNTs). For that purpose, CNTs were introduced during oxide preparation. The synthesis protocol has been optimized for obtaining a uniform coverage of small TiO2 particles on the surface of the CNTs. At low current densities, high mass loading TiO2/CNT composites electrodes are able to deliver capacitances as high as 480 F g−1 and the presence of CNTs allows keeping 70% of the capacitance at high current densities while only 27% is retained when using a regular conductivity agent as carbon black. The results demonstrate that uniform nanotexturation of TiO2 over CNTs allows good rate capabilities to be obtained for thick electrodes having sufficient active material loading to achieve high specific energy and power densities.

Chemical bath deposited Nickel oxide thin film as electrode material for pseudocapacitors

We have synthesized thin films of nickel oxide (NiO) on silver and glass substrates, at very low temperature of 60°C, by chemical bath deposition (CBD) method. The precursor used consists of nickel nitrate and aqueous ammonia. Structural characteristics were studied using x-ray diffraction (XRD) and morphological studies were done using scanning electron microscopy (SEM). Ultraviolet-visible (UV-Vis) spectroscopy was used for optical studies. To investigate electrochemical behaviour of thin film electrode materials, cyclic voltammetry (CV) measurements were conducted. For electrochemical studies the galvanostatic charge/discharge (GCD) tests were also conducted. The formation of face centred cubic NiO structure was confirmed using XRD. The scanning electron microscopy images show uniform distribution of worm-like porous morphology. CV measurements revealed the capacitive behaviour of the films.

Manganese/copper bimetal-decorated biomass porous carbons as advanced electrode materials for high-performance supercapacitors

The development of green and inexpensive carbon materials with high electrochemical performance and good stability as electrode material in supercapacitor applications remains a great challenge. In this work, we report a novel type of Mn/Cu bimetal-decorated biomass porous carbons (AC@MnCu-X) prepared from an agricultural waste (peanut shell) to realize the combination of the double-layer capacitance of porous carbon materials and pseudocapacitance of metal compounds. The obtained carbon samples exhibit unique micro-mesoporous features with large surface area, and Mn/Cu nano strip structures are successfully decorated in the carbon matrix. The Mn/Cu nanostructures are mainly composed of CuO, MnO2 and CuMn2O4, all of which are excellent pseudocapacitor electrode materials. Using as the electrode material, a high specific capacitance of 632 F/g was obtained by AC@MnCu-32 at a current density of 1 A/g in the three-electrode system with an excellent cycle life of 90 % capacitance retention after 10,000 cycles. Besides, AC@MnCu-X samples were also used as electrodes to assemble asymmetric supercapacitors, which successfully lit up a light-emitting diode. AC@MnCu-32//AC exhibited the longest endurance among the three asymmetric capacitors, and its energy density reached 15.62 W h/kg at a power density of 625 W/kg.

Binder-Free Zinc-Iron Oxide as a High-Performance Negative Electrode Material for Pseudocapacitors.

The interaction between cathode and anode materials is critical for developing a high-performance asymmetric supercapacitor (SC). Significant advances have been made for cathode materials, while the anode is comparatively less explored for SC applications. Herein, we proposed a high-performance binder-free anode material composed of two-dimensional ZnFe2O4 nanoflakes supported on carbon cloth (ZFO-NF@CC). The electrochemical performance of ZFO-NF@CC as an anode material for supercapacitor application was examined in a KOH solution via a three-electrode configuration. The ZFO-NF@CC electrode demonstrated a specific capacitance of 509 F g−1 at 1.5 A g−1 and was retained 94.2% after 10,000 GCD cycles. The ZFO-NF@CC electrode showed exceptional charge storage properties by attaining high pseudocapacitive-type storage. Furthermore, an asymmetric SC device was fabricated using ZFO-NF@CC as an anode and activated carbon on CC (AC@CC) as a cathode with a KOH-based aqueous electrolyte (ZFO-NF@CC||AC@CC). The ZFO-NF@CC||AC@CC yielded a high specific capacitance of 122.2 F g−1 at a current density of 2 A g−1, a high energy density of 55.044 Wh kg−1 at a power density of 1801.44 W kg−1, with a remarkable retention rate of 96.5% even after 4000 cycles was attained. Thus, our results showed that the enhanced electrochemical performance of ZFO-NF@CC used as an anode in high-performance SC applications can open new research directions for replacing carbon-based anode materials.

CoMoO4 as Pseudocapacitor Electrode Material and Methanol Electro-Oxidation Catalyst

CoMoO4 as Pseudocapacitor Electrode Material and Methanol Electro-Oxidation Catalyst

High-capacity binderless supercapacitor electrode obtained from sulfidation large interlayer spacing of NiMn-LDH

Layered double hydroxide (LDH) is a promising pseudocapacitive electrode material with adjustable interlayer spacing, good electrochemical properties, and ion exchange ability. However, low conductivity and low exposure of electrochemically active sites limit its application in electrode materials. In the paper, NiMn-LDH nanoarrays with large interlayer spacing were synthesized on nickel foam (NF) by hydrothermal and modified by different degrees of incomplete sulfidation by controlling the times. The results show that NiMn-LDH/Ni3S2 is obtained when the sulfidation time is 3, 5, and 7 h. The best electrochemical performance is obtained at 3 h, with a specific capacity of 682 mA h g–1 at a current density of 5 mA cm–2 and maximum multiplicative performance of 59% (at 100 mA cm–2). The assembled hybrid supercapacitor obtains an energy density of 49 Wh kg–1 at a power density of 815 W kg–1 and capacity retention of 102% after 10,000 cycles (74 F g–1 at 10 A g–1). This is because the expanded interlayer spacing decreases the diffusion resistance between the interlayers, making it easier for OH– to enter the interlayers to improve the interaction with LDH. The sulfidation enhances the interfacial interaction by enhancing the electrical conductivity, while the conductive substrate provides additional electrical conductivity to the electrodes, leading to improved electrochemical performance.

Redox-active conjugated microporous polymers as electron-accepting organic pseudocapacitor electrode materials for flexible energy storage

Redox-active conjugated microporous polymers as electron-accepting organic pseudocapacitor electrode materials for flexible energy storage

Revealing bulk reaction kinetics of battery-like electrode for pseudocapacitor with ultra-high rate performance

Battery-like electrode materials have a high theoretical capacity but suffer from low electrical conductivity and poor structural stability, which are expected to be solved by revealing bulk reaction kinetics of crystal structure to improve the electrochemical performance. Herein, we grow NiCo-LDH single-crystal nanowires along the [003] crystal plane on the surface of amorphous SiO2 hollow spheres. This heterostructured architecture provides a synergistic effect among different components and enlarges the interlayer spacing of the grown NiCo-LDH single-crystal, offering more reactive sites and improving electrical conductivity. The prepared NiCo-LDH@SiO2/C electrode demonstrates ultra-high rate capability with 78.1 % capacitance retention even after a 40-fold increase in the current density. The asymmetric supercapacitors with NiCo-LDH@SiO2/C cathode and active carbon anode could deliver a maximum energy density of 47.6 Wh/g at 1383 W/kg. This work presents a new method to guide the design of NiCo-LDH electrode materials and opens up a new opportunity to develop high-performance battery-type electrode materials for pseudocapacitors.

Metal Phosphides as Promising Electrode Materials for Alkali Metal Ion Batteries and Supercapacitors: A Review

AbstractThe growing demand for mobile electrical devices such as electric vehicles has led to more extensive and in‐depth research on alkali metal ion batteries and supercapacitors. Various metal phosphides have the advantages of large natural reserves of raw materials and low pollution. More importantly, metal phosphides have high theoretical capacity as alkali metal ion batteries and exhibit extremely high capacitance as pseudocapacitive electrode materials, making them potential electrode materials for next‐generation alkali metal ion batteries and supercapacitors. In this paper, the recent research on metal phosphide‐based electrode materials for alkali metal ion batteries and supercapacitors is reviewed. First, the basic principles of alkali metal ion batteries and supercapacitors are introduced. Then, various modification strategies and effects for metal phosphides are summarized. Finally, the problems and prospects of metal phosphide electrode materials are put forward.

The Increasing Number of Electron Reservoirs in Nonporous, High-Conducting Coordination Polymers Cux BHT (x=3, 4, and 5, BHT=Benzenehexathiol) for Improved Faradaic Capacitance.

Although asymmetric supercapacitors (ASCs) can achieve high energy density, the lifespan and power density are severely suppressed due to the low conductivity of using pseudocapacitive or battery-type electrode materials. Recently, nonporous conductive coordination polymers (c-CPs) have sparked interests in supercapacitors. However, their performance is expected to be limited by the nonporous features, low specific surface area and absence of ion-diffusion channels. Here, it is demonstrated that the capacity of nonporous CPs will be significantly enhanced by maximizing the number of faradaic redox sites in their structures through a comparative investigation on three highly conductive nonporous c-CPs, Cux BHT(x=3, 4, 5.5). They show excellent capacitance of 312.1Fg-1 (374.5Cg-1 ) (Cu3 BHT), 186.7Fg-1 (224.0Cg-1 ) (Cu4 BHT) and 89.2Fg-1 (107.0Cg-1 ) (Cu5.5 BHT) at 0.5Ag-1 in a sequence related to the number of electron storage units in structures and outstanding rate performance and cycle stability. Furthermore, the constructed Cu3 BHT//MnO2 ASC device exhibits capacity retention of 92% (after 1500 cycles at 3Ag-1 ) and delivers a high energy density of 39.1Whkg-1 at power density of 549.6Wkg-1 within a large working potential window of 0-2.2V.

Activated Carbon Mediated Hydrothermally Synthesized CuO Thin Films for Electrochemical Supercapacitors

In this paper, we used a simple and fast hydrothermal approach to create copper oxide (CuO) nanostructured thin film electrodes for supercapacitor applications. Nanostructures and material conductivity are critical in ion transport, and short ion and electron diffusion paths give more active sites for electrochemical processes. Activated carbon enhanced the conductivity of the CuO sample (AC). The specific capacitance obtained from CV curve is 333.3 F g−1 at 20 mV s−1 while from GCD curve is 277 F g−1 at 1 mA cm−2. The CuOAC1 electrode preserves more than 66% of capacitance when operated at a high scan rate of 100 mV s−1. Furthermore, the sample performs well, with an energy density of 9.63 Wh kg−1 and a power density of 509.8 W kg−1 at 1 mA cm−2 current density in 1 M acq. KOH electrolyte. The CuOAC1 sample had the lowest series (∼Rs = 0.9 Ω) and charge transfer resistance (∼Rs = 4.0 Ω). Also, the symmetric coin cell was assembled which exhibited areal capacitance of 16.7 mF cm−2 with 2.3 μWh cm−2 energy density at 500 μW cm−2 power density measured at 2 mA cm−2 current density. This paper describes a new platform for increasing the conductivity of pseudocapacitive electrode materials, resulting in a high-performance supercapacitor for future portable electronic devices.

Critical Aspects of Various Techniques for Synthesizing Metal Oxides and Fabricating Their Composite-Based Supercapacitor Electrodes: A Review.

Supercapacitors (SCs) have attracted attention as an important energy source for various applications owing to their high power outputs and outstanding energy densities. The electrochemical performance of an SC device is predominantly determined by electrode materials, and thus, the selection and synthesis of the materials are crucial. Metal oxides (MOs) and their composites are the most widely used pseudocapacitive SC electrode materials. The basic requirements for fabricating high-performance SC electrodes include synthesizing and/or chemically modifying unique conducting nanostructures, optimizing a heterostructure morphology, and generating large-surface-area electroactive sites, all of which predominantly rely on various techniques used for synthesizing MO materials and fabricating MO- and MO-composite-based SC electrodes. Therefore, an SC’s background and critical aspects, the challenges associated with the predominant synthesis techniques (including hydrothermal and microwave-assisted syntheses and chemical-bath and atomic-layer depositions), and resulting electrode electrochemical performances should be summarized in a convenient, accessible report to accelerate the development of materials for industrial SC applications. Therefore, we reviewed the most pertinent studies on these synthesis techniques to provide insight into the most recent advances in synthesizing MOs and fabricating their composite-based SC electrodes as well as to propose research directions for developing MO-based electrodes for applications to next-generation SCs.