Investigations of multilayer polyoxometalates-modified carbon nanotubes for electrochemical capacitors

“…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].…”

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confidence: 99%

“…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.…”

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confidence: 99%

High-performance asymmetric supercapacitors based on polyoxometalate-graphene nanohybrids

Yang¹,

Choi²

2016

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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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confidence: 99%

“…These POM-carbon composites can be prepared by a variety of techniques including electrodeposition, 18 chemisorption, 19 and layer-by-layer (LbL) self assembly. [20][21][22] The improved capacitive properties of MWCNT electrodes modified with PMo 12 O 40 3− (PMo 12 ) through chemisorption have been well documented.3,11 Furthermore, Gomez-Romero has shown that POMs can be effectively immobilized on activated carbon electrodes to achieve enhanced capacitance as well as dramatic * Electrochemical Society Active Member.z E-mail: keryn.lian@utoronto.ca improvements in power density. 12,23 Most recently, reports of high performance graphene-POM nanocomposite EC electrodes have also emerged.…”

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confidence: 99%

Designing Polyoxometalate based Layer-by-Layer Thin Films on Carbon Nanomaterials for Pseudocapacitive Electrodes

Genovese

Foong

Lian

2015

J. Electrochem. Soc.

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Multi-walled carbon nanotube (MWCNT) electrodes modified with mixtures of PMo 12 O 40 3- (PMo 12 ) and PW 12 O 40 3− (PW 12 ) Keggin ions are investigated for electrochemical capacitor (EC) applications. We have discovered that when these polyoxometalate (POM) ions are combined in solution, they do not just mix physically, but instead react to form the PMo 12-x W x mixed addenda chemistries. By simply mixing PMo 12 and PW 12 in different ratios, a variety of mixed addenda ions, each with unique electrochemical properties, can be easily synthesized. This control over POM redox behavior afforded by the novel mixed addenda synthesis is used along with layer-by-layer (LbL) deposition to design molecular coatings that demonstrate desired pseudocapacitive characteristics. The best performance was achieved with a coating that superimposed a 3: Increased demand for reliable high power energy storage devices has led to growing interest in the development of novel electrode materials for electrochemical capacitors (ECs).1-3 One of the most promising approaches in EC electrode design involves the fabrication of nanostructured composites in which pseudocapacitive materials are immobilized on electrochemical double layer capacitive (EDLC) carbon substrates. There is synergy in this combination as the pseudocapacitive material allows for large charge storage capacity due to surface redox reactions, while the carbon substrate imparts mechanical stability, improved conductivity, and physical capacitive effects.4-5 These types of composite materials including RuO 2 -CNT, 6 MnO 2 -graphene, 7 V 2 O 5 -CNT, 8 and conductive organic polymer (COP)-CNT 9 have been investigated extensively for pseudocapacitive EC electrodes.Although there are many pseudocapacitive alternatives, polyoxometalates (POMs), nanoscale transition metal-oxygen clusters, have emerged as promising building blocks for nanocomposite electrodes. [10][11][12][13][14] POMs have an unmatched range of physical and chemical properties which arise from their seemingly endless variety of molecular structures and sizes. 15 One of the most common and widely researched classes of POM molecules is the Keggin cluster which has the general formula [MX 12 O 40 n− ] in which the central heteroatom (i.e. P, Si, or Ge) is surrounded by twelve addenda atoms (i.e. Mo or W) and forty oxygen atoms. [16][17] These molecules demonstrate high stability of their redox states and participate in fast reversible multielectron transfer reactions, making them ideally suited for pseudocapacitive applications. They also offer tremendous versatility as their electrochemical behavior can be tuned with small adjustments to the molecular chemistry. 17The electrochemical activity of POMs can be combined with the stability and high surface area of carbon substrates to create robust nanocomposite EC electrodes. These POM-carbon composites can be prepared by a variety of techniques including electrodeposition, 18 chemisorption, 19 and layer-by-layer (LbL) self assembly. [20][21][22] The improved capa...

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Investigations of multilayer polyoxometalates-modified carbon nanotubes for electrochemical capacitors

Cited by 72 publications

References 20 publications

Wettability of colloid-imprinted carbons by contact angle kinetics and water vapor sorption measurements

Wettability of colloid-imprinted carbons by contact angle kinetics and water vapor sorption measurements

High-performance asymmetric supercapacitors based on polyoxometalate-graphene nanohybrids

Designing Polyoxometalate based Layer-by-Layer Thin Films on Carbon Nanomaterials for Pseudocapacitive Electrodes

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