Department Of Physics
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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 Unraveling the Role of Orbital Interaction in the Electrochemical HER of the Trimetallic AgAuCu Nanobowl Catalyst(American Chemical Society, 2023-03-24T00:00:00) Biswas, Rathindranath; Dastider, Saptarshi Ghosh; Ahmed, Imtiaz; Barua, Sourabh; Mondal, Krishnakanta; Haldar, Krishna KantaUnraveling the origins of the electrocatalytic activity of composite nanomaterials is crucial but inherently challenging. Here, we present a comprehensive investigation of the influence of different orbitals� interaction in the AuAgCu nanobowl model electrocatalyst during the hydrogen evolution reaction (HER). According to our theoretical study, AgAuCu exhibits a lower energy barrier than AgAu and AgCu bimetallic systems for the HER, suggesting that the trimetallic AgAuCu system interacts optimally with H*, resulting in the most efficient HER catalyst. As we delve deeper into the HER activity of AgAuCu, it was observed that the presence of Cu allows Au to adsorb the H* intermediate through the hybridization of s orbitals of hydrogen and s, dx2-y2, and dz2 orbitals of Au. Such orbital interaction was not present in the cases of AgAu and AgCu bimetallic systems, and as a result, these bimetallic systems exhibit lower HER activities. � 2023 American Chemical Society.Item Gold�Hydrogen Analogy in Small�Sized Hydrogen�Doped Gold Clusters Revisited(John Wiley and Sons Inc, 2022-07-12T00:00:00) Megha; Mondal, Krishnakanta; Ghanty, Tapan K.; Banerjee, ArupThe analogy between gold and hydrogen is a subject of long-standing debate. In the present work, we examine the validity of the gold-hydrogen analogy in a series of small-sized H-doped gold clusters, Aun?1H with n varying between 2 and 10 and also investigate its dependence on the cluster size. Keeping in mind the importance of the role of structures, we make use of the genetic algorithm coupled with a density functional theory based method to exhaustively search and identify the energetically low-lying structures of each of the H-doped gold clusters. These lower energy structures of H-doped and pristine gold clusters are then employed to carry out the calculations of their electronic properties, stability analysis as well as their reactivity towards the adsorption and activation of CO and O2 molecules. Our study shows that in line with the gold-hydrogen analogy, both electronic properties and the adsorption/activation characteristics of H-doped gold clusters remain very similar to those of pristine gold clusters. � 2022 Wiley-VCH GmbH.Item Adsorption and activation of CO2 on a Au19Pt subnanometer cluster in aqueous environment(Elsevier B.V., 2022-04-15T00:00:00) Mondal, Krishnakanta; Megha; Banerjee, Arup; Fortunelli, AlessandroWe employ ab initio density functional theory based method to investigate the ability of a subnanometer bimetallic Au19Pt cluster to adsorb and activate a CO2 molecule in an aqueous electrochemical environment. We find that, in water, Au19Pt gets negatively charged at zero bias and selectively promotes the adsorption and activation of the CO2 molecule via electron transfer and through the hybridization of oxygen p-orbitals and partially filled platinum d-orbitals. Notably, Pt acts as a collector of negative charge and behaves as a CO2-activating single-atom catalyst embedded within a robust Au20-like framework, thus suggesting Au19Pt as a potential candidate for CO2 mitigation. � 2022 Elsevier B.V.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 Topological Insulators: An In-Depth Review of Their Use in Modelocked Fiber Lasers(John Wiley and Sons Inc, 2021-05-03T00:00:00) Mondal, Shyamal; Ganguly, Rounak; Mondal, KrishnakantaTopological insulators (TIs) exhibit exciting optical properties, which open up a new pathway to generate ultrashort pulses from fiber lasers. Layered TIs display distinct saturable absorption properties due to excited state absorption, as compared to their bulk structures. Moreover, the electronic structures of the TI films depend on the thickness of the films due to the quantum confinement of the electrons. By virtue of this, TI nanoparticles play a key role in all-fiber modelocked lasers. By tweaking the crystal structures of TIs, it is possible to generate ultrashort pulses across the visible, near-infrared, and mid-infrared wavelengths. Starting from the crystal structures and density of states calculations, how different topological insulators can be fabricated and integrated as an efficient passive saturable absorber in all-fiber modelocked lasers with the capability of producing fundamental to high-harmonic pulse generation are described clearly in this review report. Moreover, this report reviews the current state-of-art of TI-based saturable absorbers and their applications in different regimes of modelocked fiber�lasers. � 2021 Wiley-VCH GmbHItem 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.