School Of Basic And Applied Sciences
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Item Theoretical investigation of quantum capacitance of Co-doped ?-MnO2 for supercapacitor applications using density functional theory(Royal Society of Chemistry, 2023-09-07T00:00:00) Vijayan, Ariya K.; Sreehari, M.S.; Kour, Simran; Dastider, Saptarshi Ghosh; Mondal, Krishnakanta; Sharma, A.L.The rapid depletion of fossil fuels and ever-growing energy demand have led to a search for renewable clean energy sources. The storage of renewable energy calls for immediate attention to the fabrication of efficient energy storage devices like supercapacitors (SCs). As an electrode material for SCs, MnO2 has gained wide research interest because of its high theoretical capacitance, variable oxidation state, vast abundance, and low cost. However, the low electric conductivity of MnO2 limits its practical application. The conductivity of MnO2 can be enhanced by tuning the electronic states through substitution doping with cobalt. In the present work, first principles analysis based on density functional theory (DFT) has been used to examine the quantum capacitance (CQC) and surface charge (Q) of Co-doped MnO2. Doping enhanced the structural stability, electrical conductivity, potential window, and quantum capacitance of ?-MnO2. The shortened band gap and localized states near the Fermi level improve the CQC of ?-MnO2. For the narrow potential range (?0.4 to 0.4 V), the CQC is observed to increase with doping concentration. The highest CQC value at +0.4 V is observed to be 2412.59 ?F cm?2 for Mn6Co2O16 (25% doping), five times higher than that of pristine MnO2 (471.18 ?F cm?2). Mn6Co2O16 also exhibits better CQC and �Q� at higher positive bias. Hence, it can be used as an anode material for asymmetric supercapacitors. All these results suggest better capacitive performance of Co-doped ?-MnO2 for aqueous SCs and as an anode material for asymmetric supercapacitors. � 2023 The Royal Society of Chemistry.Item Ab Initio Modeling of the ZnO-Cu(111) Interface(American Chemical Society, 2021-12-31T00:00:00) Mondal, Krishnakanta; Megha; Banerjee, Arup; Fortunelli, Alessandro; Walter, Michael; Moseler, MichaelThe morphology at the catalytically active interfacial site of ZnO/Cu in the commercial ZnO/Cu/Al2O3 catalyst for CO2 hydrogenation to methanol is still an open question. In the present study, we employ ab initio density functional theory based methods to gain insight into the structure of the ZnO-Cu interface by investigating the morphology of supported ZnO nano-ribbons at the interface with the Cu(111) surface in the presence of hydrogen and water molecules. We find that the stabilities of free-standing ZnO nano-ribbons get enhanced when they are supported on the Cu(111) surface. These supported nano-ribbons are further stabilized by the adsorption of hydrogen atoms on the top of O atoms of the nano-ribbons. Interestingly, the hydrogenated nano-ribbons are found to be equally stable and they appear to be an array of independent chains of ZnOH motifs, suggesting that the hydrogenated nano-ribbons are structurally fluxional. The edge of these fluxional nano-ribbons is stabilized via a triangular reconstruction with a basic composition of Zn6O7H7 in the presence of water molecules. Such a triangular structure gets further stabilized when it is attached to a bulk-like part of the ZnO/Cu(111) system. Furthermore, we find that the triangular reconstruction is energetically favorable even at the methanol synthesis conditions. Therefore, we propose that, under methanol synthesis conditions, the motif Zn6O7H7 represents a stable form at the interface between the bulk-like part of ZnO and the Cu(111) surface in the ZnO/Cu/Al2O3 based commercial catalyst. � 2021 American Chemical SocietyItem Adsorption and Activation of CO2on Small-Sized Cu-Zr Bimetallic Clusters(American Chemical Society, 2021-03-17T00:00:00) Megha; Mondal, Krishnakanta; Ghanty, Tapan K.; Banerjee, ArupAdsorption and activation of CO2 is a key step in any chemical reaction, which aims to convert it to other useful chemicals. Therefore, it is important to understand the factors that drive the activation process and also search for materials that promote the process. We employ the density functional theory to explore the possibility of using small-sized bimetallic Cu-Zr clusters, Cu4-nZrn, with n = 1-3 for the above-mentioned key step. Our results suggest that after adsorption, a CO2 molecule preferably resides on Zr atoms or at the bridge and triangular faces formed by Zr atoms in bimetallic Cu-Zr clusters accompanied with its high degree of activation. Importantly, maximum activation occurs when CO2 is adsorbed on the CuZr3 cluster. Interestingly, we find that the adsorption energy of CO2 can be tuned by varying the extent of the Zr atom in Cu-Zr clusters. We rationalize the high adsorption of CO2 with the increase in the number of Zr atoms using the d-band center model and the concept of chemical hardness. The strong chemisorption and high activation of CO2 are ascribed to charge migration between Cu-Zr clusters and the CO2 molecule. We find an additional band in the infrared vibrational spectra of CO2 chemisorbed on all of the clusters, which is absent in the case of free CO2. We also observe that the energy barriers for the direct dissociation of the CO2 molecule to CO and O decrease significantly on bimetallic Cu-Zr clusters as compared to that on pure Cu4. In particular, the barrier heights are considerably small for Cu3Zr and CuZr3 clusters. This study demonstrates that Cu3Zr and CuZr3 clusters may serve as good candidates for activation and dissociation of the CO2 molecule. � 2021 American Chemical Society.Item Does Water Play a Crucial Role in the Growth of ZnO Nanoclusters in ZnO/Cu Catalyst?(American Chemical Society, 2023-05-04T00:00:00) Dastider, Saptarshi Ghosh; Panigrahi, Abhishek Ramachandra; Banerjee, Arup; Haldar, Krishna Kanta; Fortunelli, Alessandro; Mondal, KrishnakantaThe catalytically active configuration of ZnO/Cu in the commercial ZnO/Cu/Al2O3 catalyst for methanol synthesis from CO2 is still not clear. In this study, we employ density functional theory based methods to shed light on the structure and stoichiometry of ZnO clusters both free in the gas phase and also deposited on the Cu(111) surface under methanol synthesis conditions. Specifically, we investigate the structural evolution of ZnO clusters in the presence of hydrogen and water. We find that the stability of ZnO clusters increases with the concentration of water until the ratio of Zn and OH in the clusters reaches 1:2, with a morphological transition from planar to 3D configurations for clusters containing more than 4 Zn atoms. These clusters exhibit weak interaction with CO2, and water is predicted to block the active center. The Cu(111) surface plays an important role in enhancing the adsorption of CO2 on the ZnO/Cu(111) systems. We infer that ZnO nanostructures covered with OH species may be the morphology of the ZnO during the methanol synthesis from the hydrogenation of CO2 on the industrial catalyst. � 2023 American Chemical Society.Item Ag-S Type Quantum Dots versus Superatom Nanocatalyst: A Single Sulfur Atom Modulated Decarboxylative Radical Cascade Reaction(American Chemical Society, 2023-04-06T00:00:00) Meena, Sangeeta; Dastider, Saptarshi G.; Nishad, Chandra Shekhar; Jangid, Dilip Kumar; Kumar, Pankaj; Khirid, Samreet; Bose, Shubhankar Kumar; Mondal, Krishnakanta; Banerjee, Biplab; Dhayal, Rajendra S.The preparation of high-nuclearity silver nanoclusters in quantitative yield remains exclusive and their potential applications in the catalysis of organic reactions are still undeveloped. Here, we have synthesized a quantum dot (QD)-based catalyst, [Ag62S13(SBut)32](PF6)4 (denoted as Ag62S12-S) in excellent yield that enables the direct synthesis of pharmaceutically precious 3,4-dihydroquinolinone in 92% via a decarboxylative radical cascade reaction of cinnamamide with ?-oxocarboxylic acid under mild reaction conditions. In comparison, a superatom [Ag62S12(SBut)32](PF6)2 (denoted as Ag62S12) with identical surface anatomy and size, but without a central S2- atom in the core, gives an improved yield (95%) in a short time and exhibits higher reactivity. Multiple characterization techniques (single-crystal X-ray diffraction, nuclear magnetic resonance (1H and 31P), electrospray ionization mass spectrometry, energy dispersive X-ray spectroscopy, Brunauer-Emmett-Teller (BET), Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, and thermogravimetric analysis) confirm the formation of Ag62S12-S. The BET results expose the total active surface area in supporting a single e- transfer reaction mechanism. Density functional theory reveals that leaving the central S atom of Ag62S12-S leads to higher charge transfer from Ag62S12 to the reactant, accelerates the decarboxylation process, and correlates the catalytic properties with the structure of the nanocatalyst. � 2023 American Chemical Society.Item Mechanism of Iron Integration into LiMn1.5Ni0.5O4for the Electrocatalytic Oxygen Evolution Reaction(American Chemical Society, 2022-09-14T00:00:00) Ahmed, Imtiaz; Biswas, Rathindranath; Dastider, Saptarshi Ghosh; Singh, Harjinder; Mete, Shouvik; Patil, Ranjit A.; Saha, Monochura; Yadav, Ashok Kumar; Jha, Sambhu Nath; Mondal, Krishnakanta; Singh, Harishchandra; Ma, Yuan-Ron; Haldar, Krishna KantaSpinel-type LiMn1.5Ni0.5O4 has been paid temendrous consideration as an electrode material because of its low cost, high voltage, and stabilized electrochemical performance. Here, we demonstrate the mechanism of iron (Fe) integration into LiMn1.5Ni0.5O4 via solution methods followed by calcination at a high temparature, as an efficient electrocatalyst for water splitting. Various microscopic and structural characterizations of the crystal structure affirmed the integration of Fe into the LiMn1.5Ni0.5O4 lattice and the constitution of the cubic LiMn1.38Fe0.12Ni0.5O4 crystal. Local structure analysis around Fe by extended X-ray absorption fine structure (EXAFS) showed Fe3+ ions in a six-coordinated octahedral environment, demonstrating incorporation of Fe as a substitute at the Mn site in the LiMn1.5Ni0.5O4 host. EXAFS also confirmed that the perfectly ordered LiMn1.5Ni0.5O4 spinel structure becomes disturbed by the fractional cationic substitution and also stabilizes the LiMn1.5Ni0.5O4 structure with structural disorder of the Ni2+ and Mn4+ ions in the 16d octahedral sites by Fe2+ and Fe3+ ions. However, we have found that Mn3+ ion production from the redox reaction between Mn4+ and Fe2+ influences the electronic conductivity significantly, resulting in improved electrochemical oxygen evolution reaction (OER) activity for the LiMn1.38Fe0.12Ni0.5O4 structure. Surface-enhanced Fe in LiMn1.38Fe0.12Ni0.5O4 serves as the electrocatalytic active site for OER, which was verified by the density functional theory study. � 2022 American Chemical Society.Item Dithiophosphonate Anchored Heterometallic (Ag(I)/Fe(II)) Molecular Catalysts for Electrochemical Hydrogen Evolution Reaction(American Chemical Society, 2022-08-12T00:00:00) Jangid, Dilip Kumar; Dastider, Saptarshi G.; Biswas, Rathindranath; Khirid, Samreet; Meena, Sangeeta; Kumar, Pankaj; Sahoo, Subash C.; Verma, Ved Prakash; Makde, Ravindra D.; Kumar, Ashwani; Jangir, Ravindra; Mondal, Krishnakanta; Haldar, Krishna Kanta; Dhayal, Rajendra S.The dichalcogenide ligated molecules in catalysis to produce molecular hydrogen through electroreduction of water are rarely explored. Here, a series of heterometallic [Ag4(S2PFc(OR)4] [where Fc = Fe(?5-C5H4)(?5-C5H5), R = Me, 1; Et, 2; nPr, 3; isoAmyl, 4] clusters were synthesized and characterized by IR, absorption spectroscopy, NMR (1H, 31P), and electrospray ionization mass spectrometry. The molecular structures of 1, 2, and 3 clusters were established by single-crystal X-ray crystallographic analysis. The structural elucidation shows that each triangular face of a tetrahedral silver(I) core is capped by a ferrocenyl dithiophosphonate ligand in a trimetallic triconnective (?3 ?2, ?1) pattern. A comparative electrocatalytic hydrogen evolution reaction of 1-5 (R = iPr, 5) was studied in order to demonstrate the potential of these clusters in water splitting activity. The experimental results reveal that catalytic performance decreases with increases in the length of the carbon chain and branching within the alkoxy (-OR) group of these clusters. Catalytic durability was found effective even after 8 h of a chronoamperometric stability test along with 1500 cycles of linear sweep voltammetry performance, and only 15 mV overpotential was increased at 5 mA/cm2 current density for cluster 1. A catalytic mechanism was proposed by applying density functional theory (DFT) on clusters 1 and 2 as a representative. Here, a ?1 coordinated S-site between Ag4 core and ligand was found a reaction center. The experimental results are also in good accordance with the DFT analysis. � 2022 American Chemical Society.