Electrode materials for aqueous asymmetric supercapacitors

Wang, Faxing; Xiao, S.Y.; Hou, Yuyang; Hu, Chenglin; Liu, Huan; Wu, Yuping

doi:10.1039/c3ra23466e

Cited by 497 publications

(269 citation statements)

References 224 publications

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“…In terms of cost and safety, aqueous asymmetric supercapacitors (ASCs) are a suitable choice for commercial SCs [11]. Aqueous ASCs usually consist of a battery-type Faradic electrode for the energy source and a capacitor-type electrode for the power source, and employ aqueous electrolytes, which can increase cell voltage (up to 2 V) and hence improve both energy and power densities [11,12].Polyoxometalates (POMs) are attractive Faradic electrode materials because of their remarkable redox activity, structural integrity, and low cost [13][14][15]. However, POM-based electrodes are electrochemically unstable in aqueous solution due to the dissociation of ionic aggregates [13], which leads to unnecessary loss of specific capacitance.…”

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High-performance asymmetric supercapacitors based on polyoxometalate-graphene nanohybrids

Yang¹,

Choi²

2016

Carbon letters

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Supercapacitors (SCs) have attracted much attention as energy storage devices capable of accumulating electricity from renewable sources, as well as deliver high power to smart and portable electronic devices due to their fast dynamic response, high power density, and long cycle-life [1,2]. So far, nanostructured electrodes with pseudocapacitive materials have been widely utilized to enhance the specific capacitance and energy density of supercapcitors [3,4]. However, such materials typically have low electrical conductivity (10) [5,6], degrade structurally under rigorous reaction conditions [7], and have a narrow electrochemical window (<1 V) [8,9] which can lead to high internal resistance, large irreversible capacitance loss, and poor rate capability and, consequently, result in supercapacitors with limited power density. A promising strategy to increase power density has been to extend operating cell voltage by taking advantage of an organic electrolyte, or an asymmetric cell configuration [10]. In terms of cost and safety, aqueous asymmetric supercapacitors (ASCs) are a suitable choice for commercial SCs [11]. Aqueous ASCs usually consist of a battery-type Faradic electrode for the energy source and a capacitor-type electrode for the power source, and employ aqueous electrolytes, which can increase cell voltage (up to 2 V) and hence improve both energy and power densities [11,12].Polyoxometalates (POMs) are attractive Faradic electrode materials because of their remarkable redox activity, structural integrity, and low cost [13][14][15]. However, POM-based electrodes are electrochemically unstable in aqueous solution due to the dissociation of ionic aggregates [13], which leads to unnecessary loss of specific capacitance. In addition, POM powders have low specific surface areas (<10 m 2 g −1) [16]. Therefore, POMs need to be anchored on an insoluble solid matrix with a high specific surface area to achieve high specific capacitance and stable cycle performance. In this respects, nanocarbons (e.g., carbon nanotubes [17][18][19][20] and graphene [21][22][23]) are good candidates for anchoring POMs. Moreover, their superior electrical conductivity and electrochemical/mechanical stability enable improvement in supercapacitor performance [20,22,23]. However, there has been limited success in utilizing POMs in SCs with satisfactory high specific capacitance and cycle performance, due to limited binding sites and difficulty dispersing the nanocarbons, as well as the weak interaction between POMs and nanocarbons, which still remain a challenge.Herein, we demonstrate aqueous ASCs based on a POM-graphene nanohybrid with polymeric ionic liquid (POM/PIL/G) as a positive elctrode and activated carbon (AC) as a negative electrode in an aqueous electrolyte of H 2 SO 4 . The polymeric ionic liquid (PIL) was selected as the surface functionality because of its high binding affinity for the graphene surface, and high ionic conductivity, as well as sufficient binding sites to produce a high density of POMs on the graphene surf...

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High-performance asymmetric supercapacitors based on polyoxometalate-graphene nanohybrids

Yang¹,

Choi²

2016

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“…최근에는 루테늄 산화물에 비해서 저가이면서도 친환경적인 여러 금속산화물(망간, 철, 코발트, 니켈 산화물 등)들이 PC용 전극물질로 개발되고 있다 [13,14]. 이 중에서도 망간산화물 (MnO2)은 높은 이론용량(1100 F/g), 친환경성 및 낮은 단가로 인하여 차세대 슈퍼커패시터용 전극 소재로 각광받고 있다 [16].…”

Section: 서 론unclassified

“…이 중에서도 망간산화물 (MnO2)은 높은 이론용량(1100 F/g), 친환경성 및 낮은 단가로 인하여 차세대 슈퍼커패시터용 전극 소재로 각광받고 있다 [16]. 대부분의 산 화/환원 반응을 수반하는 금속산화물 기반의 전극 물질들은 금속산화 물의 낮은 전기전도도로 인하여 출력 및 수명 특성이 EDLC에 비해서 떨어지는 단점이 있다 [13,14]. …”

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Development of High-performance Supercapacitors Based on MnO₂/Functionalized Graphene Nanocomposites

Choi¹

2016

Applied Chemistry for Engineering

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In this report, MnO2 nanoparticle-deposited functionalized graphene sheets were prepared and their superior electrochemical performances were demonstrated by cyclic voltammetry, galvanostatic charge-discharge, and impedance analysis. Ionic liquids were employed to functionalize the surface of reduced graphene oxides (RGOs), leading to prevention of the aggregation of RGO sheets and abundant growth sites for deposition of MnO2 nanoparticles. As-prepared MnO2/RGO nanocomposites were characterized using scanning electron microscope, transition electron microscope, X-ray photoelectron spectroscopy, and X-ray diffraction. Electrochemical properties of MnO2/RGO electrode were evaluated using Na2SO4 electrolyte under a three-electrode system. The MnO2/RGO electrode showed a high specific capacitance (251 F/g), a high rate capability (80.5% retention), and long-term stability (93.6% retention).

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“…[1][2][3][4] Because pseudocapacitance involves electrontransfer reactions, the quantity of charge-storage per mass or volume often surpasses that achieved with double-layer capacitance alone. The enhanced charge-storage capacity provided by pseudocapacitive metal oxides compensates for the voltage limitations of aqueous-electrolyte ECs, resulting in asymmetric aqueous EC designs [5][6][7] that provide competitive performance and safer operation compared to conventional symmetric carbon-carbon ECs that use organic electrolytes.…”

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Extending Electrochemical Quartz Crystal Microbalance Techniques to Macroscale Electrodes: Insights on Pseudocapacitance Mechanisms in MnOx-Coated Carbon Nanofoams

Beasley¹,

Sassin

Long

2015

J. Electrochem. Soc.

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Electrochemical quartz crystal microbalance studies of MnOx-coated carbon nanofoams reveal that charge-compensation mechanisms associated with MnOx pseudocapacitance in mild aqueous electrolytes are dominated by anion insertion rather than more commonly reported cation ejection. Specific charge-compensation behavior depends on such factors as electrolyte composition, nanofoam pore size, and polarization amplitude. For example, MnOx-carbon nanofoams with average pore sizes of 5-20 nm, cycled in 2.5 M LiNO 3 , reveal a kinetically-hindered, mixed anion-cation charge-compensation mechanism, whereas the same nanofoam cycled in 2.5 M NaNO 3 shows only anion association. Nanofoams with larger pores (10-200 nm) Transition metal oxides that exhibit "pseudocapacitance", capacitor-like behavior that arises from faradaic reactions, are challenging high-surface-area carbons, which rely primarily on doublelayer capacitance, as active materials in next-generation electrochemical capacitors (ECs).1-4 Because pseudocapacitance involves electrontransfer reactions, the quantity of charge-storage per mass or volume often surpasses that achieved with double-layer capacitance alone. The enhanced charge-storage capacity provided by pseudocapacitive metal oxides compensates for the voltage limitations of aqueous-electrolyte ECs, resulting in asymmetric aqueous EC designs 5-7 that provide competitive performance and safer operation compared to conventional symmetric carbon-carbon ECs that use organic electrolytes.Manganese oxides (MnOx) have emerged as one of the most important classes of pseudocapacitive materials due to their low cost, competitive specific capacitance, availability in a wide range of compositions and crystal habits, and adaptability to a variety of electrode architectures. [8][9][10][11] The electrochemical characteristics of MnOx have been extensively demonstrated, yet the underlying mechanisms responsible for pseudocapacitance are still a subject of debate. Spectroscopic methods have been used to confirm that pseudocapacitive charge storage is supported by reversible toggling of the Mn oxidation state (ranging between +3 and +4, but typically <1 e -per Mn site) during electrochemical cycling in aqueous electrolytes. [12][13][14] Changes in Mn oxidation state must be accompanied by insertion or adsorption of charge-balancing ions from the contacting electrolyte. In the case of mild aqueous electrolytes, charge compensation typically occurs via cation-insertion/association mechanisms where the cations are supplied by either the electrolyte salt (e.g., Li + , Na + , or K + ), the H 2 O solvent (in the form of H + or H 3 O + ), or combinations thereof.14-20 Because of the prospective participation of multiple types of ions (in varying degrees of solvation), deconvolution of MnOx pseudocapacitance mechanisms has proven difficult. The ability to draw broader conclusions regarding MnOx pseudocapacitance mechanisms has been further complicated by the wide range of materials that are broadly identified in the literature a...

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Electrode materials for aqueous asymmetric supercapacitors

Cited by 497 publications

References 224 publications

High-performance asymmetric supercapacitors based on polyoxometalate-graphene nanohybrids

High-performance asymmetric supercapacitors based on polyoxometalate-graphene nanohybrids

Development of High-performance Supercapacitors Based on MnO₂/Functionalized Graphene Nanocomposites

Extending Electrochemical Quartz Crystal Microbalance Techniques to Macroscale Electrodes: Insights on Pseudocapacitance Mechanisms in MnOx-Coated Carbon Nanofoams

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Electrode materials for aqueous asymmetric supercapacitors

Cited by 497 publications

References 224 publications

High-performance asymmetric supercapacitors based on polyoxometalate-graphene nanohybrids

High-performance asymmetric supercapacitors based on polyoxometalate-graphene nanohybrids

Development of High-performance Supercapacitors Based on MnO2/Functionalized Graphene Nanocomposites

Extending Electrochemical Quartz Crystal Microbalance Techniques to Macroscale Electrodes: Insights on Pseudocapacitance Mechanisms in MnOx-Coated Carbon Nanofoams

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Development of High-performance Supercapacitors Based on MnO₂/Functionalized Graphene Nanocomposites