Germanomolybdate (GeMo12O404−) Modified Carbon Nanotube Composites for Electrochemical Capacitors

Genovese, Matthew; Foong, Yee Wei; Lian, Keryn

doi:10.1016/j.electacta.2013.11.114

Cited by 20 publications

(12 citation statements)

References 21 publications

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“…These multilayer electrodes require even larger amounts of the poorly conductive PDDA, further inhibiting their high power capabilities. 19,30,37 Ionic liquids (ILs), particularly their imidazolium based cation units, could serve as effective LbL electrostatic linkers to engineer POM composites for high power applications. ILs have demonstrated a strong affinity for POM anions, 38,39 and some IL POMs have even been reported.…”

Section: Introductionmentioning

confidence: 99%

Ionic Liquid-Derived Imidazolium Cation Linkers for the Layer-by-Layer Assembly of Polyoxometalate-MWCNT Composite Electrodes with High Power Capability

Genovese

Lian

2016

ACS Appl. Mater. Interfaces

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Imidazolium cations derived from ionic liquids were demonstrated as effective linker molecules for the layer-by-layer (LbL) deposition of polyoxometalates (POMs) to increase the charge storage of multi-walled carbon nanotube (MWCNT) electrodes. MWCNTs modified with GeMo12O40(4-) (GeMo12) via an imidazolium cation linker demonstrated highly reversible redox reactions and a capacitance of 84 F cm(-3), close to 4 times larger than bare CNT. Compared to CNT-GeMo12 composites fabricated with a conventional polyelectrolyte linker poly(diallyldimethylammonium chloride), (PDDA), the imidazolium cations resulted in lower POM loading, but higher conductivity and in turn superior performance at fast charge-discharge conditions. A polymerized imidazolium linker (PIL) was also synthesized based on the ethyl-vinyl-imidazolium monomer. CNT-GeMo12 composites fabricated with this PIL achieved high POM loading comparable to PDDA, while still maintaining the good conductivity and high rate capabilities shown by the monomer imidazolium units. The high conductivity imparted by the PIL is especially valuable for the fabrication of multilayer POM composites. Dual-layer GeMo12 O40(4-)-SiMo12O40(4-) (GeMo12-SiMo12) electrodes built with this PIL demonstrated a combined contribution of the individual POMs resulting in a capacitance of 191 F cm(-3), over nine times larger than bare MWCNT. The PIL dual layer composites also maintained 72% of this capacitance at a fast rate of 2 V s(-1), compared to just over 50% retention for similar electrodes fabricated with PDDA.

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Section: Introductionmentioning

confidence: 99%

Ionic Liquid-Derived Imidazolium Cation Linkers for the Layer-by-Layer Assembly of Polyoxometalate-MWCNT Composite Electrodes with High Power Capability

Genovese

Lian

2016

ACS Appl. Mater. Interfaces

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“…Our previous results have shown that the CVs of multi-layer POM electrodes demonstrate an additive combination of constituent layers. 26 To predict the CV shape of a dual-layer electrode with a PMo layer superimposed on a GeMo 12 -SiMo 12 layer, a simple model showing the direct addition of the GeMo 12 -SiMo 12 and PMo 12 CV curves is plotted along with the experimental data in Figure 5B (gray line). The charge storage of these constituent layers is not complementary; rather the redox peaks of PMo 12 almost directly overlay those of the GeMo 12 -SiMo 12 electrode.…”

Section: Multi-layer Polyoxometalate Electrodesmentioning

confidence: 99%

“…12,23 Most recently, reports of high performance graphene-POM nanocomposite EC electrodes have also emerged. [24][25] These studies demonstrate the potential for POMs as effective pseudocapacitive materials; however, these studies only explored a few commercially available POM chemistries like PMo 12 or PW 12 22,26 In order to overcome this limitation, we have shown that the LbL technique can be used to superimpose different POM molecules on the same electrode. With this method, multiple POM chemistries with different redox peak potentials can be combined to achieve overlapping redox features and a more ideally capacitive CV profile.…”

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confidence: 99%

“…Instead, the CVs of Keggin molecules display narrow redox features with little overlap, resulting in current densities that can vary dramatically with voltage. 22,26 In order to overcome this limitation, we have shown that the LbL technique can be used to superimpose different POM molecules on the same electrode. With this method, multiple POM chemistries with different redox peak potentials can be combined to achieve overlapping redox features and a more ideally capacitive CV profile.…”

mentioning

confidence: 99%

“…With this method, multiple POM chemistries with different redox peak potentials can be combined to achieve overlapping redox features and a more ideally capacitive CV profile. 22,26 In addition to the multi-layer technique, a mixed layer coating approach can also be used to combine the effects of multiple POMs. For this method, different POM molecules are combined in an aqueous solution and coated on the electrode simultaneously in a single active layer.…”

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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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Redox Chemistry of Heteropolyacid Microemulsions

et al. 2014

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Insight from electroanalysis studies of dense fluid phases (known as “third” phases) in the Keggin heteropolyacid tri‐n‐butyl phosphate (TBP) system is provided. The differences between the H3PW12O40 and H4SiW12O40 redox chemistry in the third phases and in bulk aqueous electrolytes reflect the differences in the formal charge of the protonated acid solvates of TBP in the low dielectric organic media and the deprotonated anions in the high dielectric aqueous media. The faradaic W‐based redox activity leading to heteropoly blue entities drives concerted proton transfer across the organic‐analyte–aqueous‐electrolyte phase boundary in both the heteropolyacid microemulsions (formed by solvent extraction) and the molecular liquids (formed by dissolution) to maintain charge neutrality in the organic phases. This study of heteropolyacid third phases complements the emerging field of mesoscale sciences with polyoxometalates and their electrochemical properties.

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Germanomolybdate (GeMo12O404−) Modified Carbon Nanotube Composites for Electrochemical Capacitors

Cited by 20 publications

References 21 publications

Ionic Liquid-Derived Imidazolium Cation Linkers for the Layer-by-Layer Assembly of Polyoxometalate-MWCNT Composite Electrodes with High Power Capability

Ionic Liquid-Derived Imidazolium Cation Linkers for the Layer-by-Layer Assembly of Polyoxometalate-MWCNT Composite Electrodes with High Power Capability

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

Redox Chemistry of Heteropolyacid Microemulsions

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