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6. Introduction

Author

Agarwal, Akanksha, Sankapal, Babasaheb R., Sankapal, Babasaheb R., editor, Ennaoui, Ahmed, editor, Gupta, Ram B., editor, and Lokhande, Chandrakant D., editor

Published
2023
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28. In-depth understanding of electrochemical energy storage efficiency in a series of new 3d–4d mixed metal polyoxometalates: experimental and theoretical investigations.

Author

Morla, Kalyankumar S., Thakre, Dewendra, Deshmukh, Tushar Balasaheb, Malo, Sunanda, Ahamed, Subuhan, Aparna, Ravari Kandy, Sahoo, Subham, Sarma, Debajit, Mondal, Kartik Chandra, Sankapal, Babasaheb R., and Banerjee, Abhishek

Abstract

Transition-metal complexes, with their reversible redox properties, are the basis for electrochemical energy storage devices, such as rechargeable batteries and supercapacitors. In order to comprehend the variation in the electronic properties and electrochemical activity of concurrent transition elements existing in identical coordination environments, we have pursued extensive multi-method spectroscopic and electrochemical studies of three new isostructural 3d–4d mixed metal polyoxometalate complexes, viz. the vanado-molybdate Na2(NH4)5[(Mo VI2 O5)2(VIIIO2){O3P-C(O)(CH2-4-C5NH4)-PO3}2]·10H2O (1a), the chromo-molybdate (NH4)5[H2(Mo VI2 O5)2(CrIIIO2){O3P-C(O)(CH2-4-C5NH4)-PO3}2]·10H2O (2a) and the mangano-molybdate Na(NH4)6[H(Mo VI2 O5)2(MnIIIO2){O3P-C(O)(CH2-4-C5NH4)-PO3}2]·9H2O (3a). The structures of the polyanions have been determined using single-crystal X-ray diffraction studies, with all three polyanionic complexes having identical connectivity and arrangement in the solid state. The electronic properties of the complexes have been analyzed thoroughly with electronic paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS) methods. EPR measurements for all three complexes are characterized by Δms = ±2 signals (forbidden half-field transition) at 77 K in the solid state, confirming the existence of VIII, S = 1 for 1a; CrIII, S = 3/2 for 2a; MnIII, S = 2 for 3a. Using our original and novel binder-free approach to prepare supercapacitor electrodes, thorough comparative electrochemical energy storage studies have been performed on the three compounds using cyclic voltammetry, galvanostatic charge–discharge, electrochemical impedance spectroscopy, and cycling stability tests. The oxo-vanado-molybdate complex has shown superior electrochemical performance, with respect to specific capacitances, energy density, power density, and electrochemical stability, followed by the oxo-chromo-molybdate and the oxo-mangano-molybdate complexes. The electrochemical performance trend has been corroborated by DFT calculations at the B3LYP-D3(BJ)/Def2-SVP level of theory in a polar medium, with the same order of promptness of undergoing oxidation of the polyanionic species [M2+ to M3+; M = V (1′) > Cr (2′) > Mn (3′); ΔG(M3+–M2+) = +48 (1′), +58 (2′), +81 (3′) kcal mol−1], corroborating the experimental observations. The oxidation of these anionic species from 8-(MII) to 7-(MIII) has thus been computed to be highly favourable in the gas phase [∼−328 (1′), −311 (2′), and −309 (3′) kcal mol−1]. The studies on the HOMO–LUMO structures of the complexes also corroborate the trend of the electrochemical behavior. [ABSTRACT FROM AUTHOR]

Published
2024
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43. Conducting Polymers–Metal Chalcogenides Hybrid Composite: Current Trends and Future Prospects Toward Supercapacitor Applications.

Author

Agarwal, Akanksha, Tolani, Raunak, and Sankapal, Babasaheb R.

Subjects
CONDUCTING polymer composites, HYBRID materials, COMPOSITE materials, SUPERCAPACITORS
Abstract

Conducting polymers have grown in popularity as electrode materials in supercapacitors due to their polymeric mechanical structure and outstanding conductivity. Nanostructured conducting polymers, in particular, have been the focus due to unique properties such as higher surface area, shorter diffusion lengths for ion transport, and a high electrochemical nature. Nonetheless, the volumetric expansion of conducting polymer electrodes after long charge–discharge cycles reduces capacitance retention. Metal chalcogenides, on the other hand, are distinguished from other metallic compounds by their distinctive 2D structure, large theoretical capacities, abundant electrochemical active sites, and tunable shape, enabling them as a potential candidature when combined with conducting polymers to produce a composite material taking "material mutualism" to enhance the properties. Hence, the review focuses on recent advancement in the field of creating conducting polymers–metal chalcogenides composite for supercapacitors. It especially covers how nanoarchitecture, composition, and doping affect the electrochemical characteristics of these composites. A brief introduction of several synthesis procedures is also offered, which includes chemical approaches with and without templates or binder additives. Furthermore, noteworthy works on the fabrication of symmetric and asymmetric devices are highlighted. [ABSTRACT FROM AUTHOR]

Published
2024
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