Modification of organic substrates with inorganic polyoxometalate (POM) clusters can be used to engineer nanocomposite materials with improved properties and diverse functionalities. This review will outline concepts and methodologies for fabricating POM based inorganic–organic composite materials with a special focus on the electrochemical functionality of these composites for energy storage applications. The strengths and limitations of three different fabrication techniques, chemisorption to a carbon surface, immobilization in a polymer matrix, and layer-by-layer self-assembly will be assessed. Furthermore, the latest developments in the use of POM nanocomposite materials in energy storage applications like electrochemical capacitors (ECs) and lithium ion batteries will be presented. This review will highlight the issues and challenges that need to be addressed to achieve inorganic–organic POM nanocomposites able to support high performance energy storage applications.

Polyoxometalate modified inorganic–organic nanocomposite materials for energy storage applications: A review

. Fourier transform infrared spectra showed the presence of both 1-butyl-3-methylimidazolium cations and the Keggin anion. Cyclic voltammetry illustrated that the reduction peak potentials of the Keggin anion in the hybrid materials shift toward negative values. The hybrid materials can be suspended in ultrapure water to form true suspensions. Alternating current electro- phoretic deposition was used to obtain thick homogeneous films of the hybrid materials in few minutes over stainless steel SS wires from aqueous suspensions at 30 Hz and 200 Vp-p. BMIM4SiW12O40/SS and BMIM3PMo12O40/SS previously treated at 370°C for 15 min were subjected to cyclic voltammetry and galvanostatic charge-discharge cycling in 0.5 M Na2SO4 p H7 and observed to exhibit capacitance behavior between 0 and �0.6 V vs AgCl/Ag. In 0.5 M Na2SO4 p H7 and in this range of potentials, the hybrid BMIM4SiW12O40 material had an ideal behavior with a stable specific capacitance close to 172 F g �1

Ionic Liquid–Heteropolyacid: Synthesis, Characterization, and Supercapacitor Study of Films Deposited by Electrophoresis

In this work, we show a comparative study based on the effects of specific chemical functional groups (–OH, –NH2), grafted on Vulcan carbon (VC) with the incorporation of a specific polyoxometalate (POM), PMo12 (H3PMo12O40), to improve electrochemical performance. We observed a decrease in the specific surface area of the grafted matrices (VC-OH and VC-NH2) [1], and the same trend was observed for PMo12 (POM) incorporation. Our electrochemical studies showed low concentrations of POM in unmodified VCs and higher POM concentrations for grafted matrices (VC-OH and VC-NH2) after 500 voltammetric cycles, especially for the VC grafted with –OH groups (VC-OH-POM). Mechanisms have been proposed for POM interaction with the grafted groups in carbon, emphasizing the role of aqueous medium and redox activity of POM. Cyclic voltammograms suggested the POM anchoring through –OH groups with a strong interaction as a covalent bond, resulting in a surface coverage of 1.66 × 10−11 mol cm−2. Surface modifications could be extrapolated to other carbons, and the materials could be employed for different potential applications such as photocatalysis, amperometric sensors, fuel cells, and supercapacitors.

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Electrochemical study of H3PMo12 retention on Vulcan carbon grafted with NH2 and OH groups

Understanding bond formation and its impact on the capacitive properties of SiW12 polyoxometalates adsorbed on functionalized carbon nanotubes

Carbon has shown to give excellent performance in electrodes of energy storage devices, such as Li-ion batteries and supercapacitors. The grafting of polyoxometalates (POM) at carbon has scarcely been explored at the theoretical and experimental level, and the mechanism behind the chemical bonding between POM and carbon has not been fully understood. In order to give insights into these issues, an electronic structure study was carried out on the following POM systems adsorbed on carbon: PdMo12, RuNb12, SiMo12, PMo12 and SiW12. The prediction of the existence and chemical stability of PdMo12 and RuNb12 systems is reported for the first time. All systems were fully optimized with the nominal charges and also neutralized with counterions, as a benchmark to elucidate an optimal scheme that models the interaction in these nanocomposite systems. The POM/carbon attraction lies at about 250 pm in average, which may be addressed to a non-covalent bonding of the electrostatic-type, where the van der Waals contribution may also play a role. The density of states is evidently increased around the Fermi level in all POM/carbon systems. This may be due to the rising of new trajectories that ions may follow at the electrode of a solid-state device, such as a supercapacitor, giving as a result the strengthening of density current values and pseudocapacitive properties than those observed in pristine carbon systems. It was found that the SiWO12 and RuNb12 POM systems may be more feasible to be adsorbed on carbon substrates and may not require functional groups to allow POM retention. These systems represent potential candidates to be considered in nanohybrid electrodes for solid-state applications.

First principles study on the electronic structure properties of Keggin polyoxometalates on Carbon substrates for solid-state devices

Resumen en: We prepared nanocomposite hybrid materials based on previously oxidized carbon nanofibers (fCNFs) and polyoxometalates (POM). We analyzed fCNFs by XRD an...

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M. Gonzales-Toledo

Papers

Nanocomposite hybrid material based on carbon nanofibers and polyoxometalates