Integrated DFT and experimental study on Co3O4/CeO2 catalyst for direct synthesis of dimethyl carbonate from CO2
The oxygen deficient site on the catalyst has a strong impact on the activation of CO2 for the synthesis of dimethyl carbonate (DMC). The Co3O4/CeO2 catalyst exhibits multiple reduction behavior as cobalt metal species differ in the strength of their interaction with CeO2. This causes the surface reduction from Ce4+ to Ce3+ in solid solution Co-O-Ce. The dispersion of Co3O4 enhanced the formation of oxygen deficient site as revealed by XPS, CO2-chemisorption and TPR. The non-precious Co3O4/CeO2 nanorod was recognized as a potential catalyst for promoting Ce4+ to Ce3+ for CO2 activation and dimethyl carbonate synthesis (81.5% of yield). Energetics of oxygen vacancy formation of low index surfaces of CeO2 was determined with first-principles calculations based on DFT. Results disclosed the Ce4+ to Ce3+ formation energy of CeO2 due to Co substitution and corroborated the experimental results. Further, calculations provide the details of the effect of Co substitution on the electronic structure of reduced CeO2 surfaces. Estimated CO2 adsorption energy indicates (110) as the most active surface for activation of CO2.
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Universal Ligands for Dispersion of Two-Dimensional MXene in Organic Solvents
Tae Yun Ko, Daesin Kim, Seon Joon Kim, Hyerim Kim, Arun Nissimagoudar, Seung-Cheol Lee, Xiaobo Lin, Peter T. Cummings, Sehyun Doo, Seongmin Park, Tufail Hassan, Taegon Oh, Ari Chae, Jihoon Lee, Yury Gogotsi, Insik In, and Chong Min Koo
ACS Nano
Abstract
Universal Ligands for Dispersion of Two-Dimensional MXene in Organic Solvents
Ligands can control the surface chemistry, physicochemical properties, processing, and applications of nanomaterials. MXenes are the fastest growing family of two-dimensional (2D) nanomaterials, showing promise for energy, electronic, and environmental applications. However, complex oxidation states, surface terminal groups, and interaction with the environment have hindered the development of organic ligands suitable for MXenes. Here, we demonstrate a simple, fast, scalable, and universally applicable ligand chemistry for MXenes using alkylated 3,4-dihydroxy-l-phenylalanine (ADOPA). Due to the strong hydrogen-bonding and π-electron interactions between the catechol head and surface terminal groups of MXenes and the presence of a hydrophobic fluorinated alkyl tail compatible with organic solvents, the ADOPA ligands functionalize MXene surfaces under mild reaction conditions without sacrificing their properties. Stable colloidal solutions and highly concentrated liquid crystals of various MXenes, including Ti2CTx, Nb2CTx, V2CTx, Mo2CTx, Ti3C2Tx, Ti3CNTx, Mo2TiC2Tx, Mo2Ti2C3Tx, and Ti4N3Tx, have been produced in various organic solvents. Such products offer excellent electrical conductivity, improved oxidation stability, and excellent processability, enabling applications in flexible electrodes and electromagnetic interference shielding.
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Surface Oxygen Passivation-Driven Large Anomalous Hall Conductivity in Early Transition Metal-Based Nitride MXenes: Can AHC Be a Tool to Determine Functional Groups in 2D Ferro(i)magnets?
Ajit Jena, Seung-Cheol Lee, and Satadeep Bhattacharjee
The Journal of Physical Chemistry C
Abstract
Surface Oxygen Passivation-Driven Large Anomalous Hall Conductivity in Early Transition Metal-Based Nitride MXenes: Can AHC Be a Tool to Determine Functional Groups in 2D Ferro(i)magnets?
Identifying the existence of specific functional groups in MXenes is a difficult topic that has perplexed researchers for a long time. At the same time, the realization of intrinsic ferromagnetism, which is important for two-dimensional (2D) materials’ families, is one of the fascinating properties that MXenes offer. Here, using first-principle calculations, we have examined the actual magneto-transport phenomena in transition metals and nitride-based-functionalized MXenes. We demonstrate that intrinsic anomalous Hall conductivity (AHC) can be used to identify the presence of more probable functional groups. The maximum AHC at Fermi energy, EF, is found in the case of Mn2NO2 (470 S/cm), which is attributed to the presence of avoided band crossing and a larger density of states. Together, when considering all the studied systems, the AHC can be above 2500 S/cm within EF± 0.25 eV. Our findings could be useful not only in guiding the experimentalists by considering AHC as a possible tool in determining the most probable functional groups in 2D ferro(i)magnets but also in designing memory devices with negligible stray fields.
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Effective Formation of a Mn-ZIF-67 Nanofibrous Network via Electrospinning: An Active Electrocatalyst for OER in Alkaline Medium
Sam Sankar Selvasundarasekar, T. K. Bijoy, Sangeetha Kumaravel, Arun Karmakar, Ragunath Madhu, Krishnendu bera, Sreenivasan Nagappan, Hariharan N. Dhandapani, Gaber A. M. Mersal, Mohamed M. Ibrahim, Debashish Sarkar, Seikh Mohammad Yusuf, Seung-Cheol Lee,
ACS Applied Materials and Interfaces
Abstract
Effective Formation of a Mn-ZIF-67 Nanofibrous Network via Electrospinning: An Active Electrocatalyst for OER in Alkaline Medium
Finding the active center in a bimetallic zeolite imidazolate framework (ZIF) is highly crucial for the electrocatalytic oxygen evolution reaction (OER). In the present study, we constructed a bimetallic ZIF system with cobalt and manganese metal ions and subjected it to an electrospinning technique for feasible fiber formation. The obtained nanofibers delivered a lower overpotential value of 302 mV at a benchmarking current density of 10 mA cm–2 in an electrocatalytic OER study under alkaline conditions. The obtained Tafel slope and charge-transfer resistance values were 125 mV dec–1 and 4 Ω, respectively. The kinetics of the reaction is mainly attributed from the ratio of metals (Co and Mn) present in the catalyst. Jahn–Teller distortion reveals that the electrocatalytic active center on the Mn-incorporated ZIF-67 nanofibers (Mn-ZIF-67-NFs) was found to be Mn3+ along with the Mn2+ and Co2+ ions on the octahedral and tetrahedral sites, respectively, where Co2+ ions tend to suppress the distortion, which is well supported by density functional theory analysis, molecular orbital study, and magnetic studies.
66
A general rule for predicting the magnetic moment of Cobalt-based Heusler compounds using compressed sensing and density functional theory
Satadeep Bhattacharjee, Seung-Cheol Lee
Journal of Magnetism and Magnetic Materials
Abstract
A general rule for predicting the magnetic moment of Cobalt-based Heusler compounds using compressed sensing and density functional theory
We propose a general rule for estimating the magnetic moments of Co2(cobalt)-based Heusler alloys, especially when doped with late transition metals. We come up with a descriptor that can characterise both pure Co2YZ compounds and the doped ones with the chemical formula Co2Y1−xMxZ (M is the dopant) using online data for magnetic moments of Heusler alloys with Co2YZ structure and compressive sensing approach. The newly proposed descriptor not only depends on the number of valence electrons of the compound also it depends on the number of unoccupied d-electrons in the doping site. A comparison of the performance of the proposed descriptor and the Slater-Pauling rule is made. Unlike the Slater-Pauling rule, which is only effective for half-metallic Heusler compounds, our machine-learning approach is more generic since it applies to any Co2YZ Heusler compounds, regardless of whether they are half-metals or not. We use this new rule to estimate the magnetic moments of a few yet-to-be-discovered Heusler compounds and compare the results to density functional theory (DFT) based calculations. Finally, we use DFT and machine learning investigations to prove their stability.
Silicene: An excellent material for flexible electronics
Swastik Sahoo, Abhinaba Sinha, Namitha Anna Koshi, Seung-Cheol Lee, Satadeep Bhattacharjee and Bhaskaran Muralidharan
Journal of Physics D: Applied Physics
Abstract
Silicene: An excellent material for flexible electronics
The outstanding properties of graphene have laid the foundation for exploring graphene-like 2D systems, commonly referred to as 2D-Xenes. Among them, silicene is a front-runner due to its compatibility with current silicon fabrication technologies. Recent works on silicene have unveiled its useful electronic and mechanical properties. The rapid miniaturization of silicon devices and the useful electro-mechanical properties of silicene necessitate the exploration of potential applications of silicene flexible electronics in nano electro-mechanical systems. Using a theoretical model derived from the integration of ab initio density-functional theory and quantum transport theory, we investigate the piezoresistance effect of silicene in the nanoscale regime. As with graphene, we obtain a small value of the piezoresistance gauge factor (GF) of silicene, which is sinusoidally dependent on the transport angle. The small GF of silicene is attributed to its robust Dirac cone and strain-independent valley degeneracy. Based on the obtained results, we propose to use silicene as an interconnect in flexible electronic devices and as a reference piezoresistor in strain sensors. This work will hence pave the way for exploring flexible electronics applications in other 2D-Xene materials.
Temperature-dependent bandgap of (In,Ga)As via P5Grand: A Python Package for Property Prediction of Pseudobinary systems using Grand canonical ensemble
Gyuseung Han, In Won Yeu, Kun Hee Ye, Seungjae Yoon, Taeyoung Jeong, Seung-Cheol Lee, Cheol Seong Hwang, Jung-Hae Choi
Chemical Physics Letters
Abstract
Temperature-dependent bandgap of (In,Ga)As via P5Grand: A Python Package for Property Prediction of Pseudobinary systems using Grand canonical ensemble
We introduce introduces an open-source program for calculating the properties of solid solutions, “Python Package for Property Prediction of Pseudobinary systems using Grand canonical ensemble” (P5Grand). P5Grand uses two main strategies to improve calculation efficiency: random configuration sampling and separate calculations of the strain energy induced by local compositional fluctuations within the grand canonical ensemble. P5Grand can efficiently calculate thermodynamic properties and any properties of interest for arbitrary solid solution as a function of temperature and composition using two input files. The efficiency of P5Grand is demonstrated by the bandgap prediction of (In,Ga)As.
63
Constructing electrospun spinel NiFe2O4 nanofibers decorated with palladium ions as nanosheets heterostructure: boosting electrocatalytic activity of HER in alkaline water electrolysis
Sam Sankar Selvasundarasekar, T. K. Bijoy, Sangeetha Kumaravel, Arun Karmakar, Ragunath Madhu, Krishnendu Bera, Sreenivasan Nagappan, Hariharan N. Dhandapani, Seung-Cheol Lee and Subrata Kundu
Nanoscale
Abstract
Constructing electrospun spinel NiFe2O4 nanofibers decorated with palladium ions as nanosheets heterostructure: boosting electrocatalytic activity of HER in alkaline water electrolysis
The development of efficient electrocatalysts for the water splitting process and understanding their fundamental catalytic mechanisms are highly essential to achieving high performance in energy conversion technologies. Herein, we have synthesised spinel nickel ferrite nanofibers (NiFe2O4-NFs) via an electrospinning (ES) method followed by a carbonization process. The resultant fiber was subjected to electrocatalytic water splitting reactions in alkaline medium. The catalytic efficiency of the NiFe2O4-NFs in OER was highly satisfactory. But it is not high enough to catalyse the HER process. Hence, palladium ions were decorated as nanosheets on NiFe2O4-NFs as a heterostructure to improve the catalytic efficiency for HER. Density functional theory (DFT) confirms that the addition of palladium to NiFe2O4-NFs helps to reduce the effect of catalyst poisoning and improve the efficiency of the catalyst. In an alkaline hybrid electrolyser, the required cell voltage was observed as 1.51 V at a fixed current density of 10 mA cm−2.
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Electrical and magneto-transport in the 2D semiconducting MXene Ti2CO2
Anup Kumar Mandia, Namitha Anna Koshi, Bhaskaran Muralidharan, Seung-Cheol Lee, and Satadeep Bhattacharjee
Journal of Materials Chemistry C
Abstract
Electrical and magneto-transport in the 2D semiconducting MXene Ti2CO2
The Hall scattering factor is formulated using Rode's iterative approach to solving the Boltzmann transport equation in such a way that it may be easily computed within the scope of ab initio calculations. Using this method in conjunction with density functional theory based calculations, we demonstrate that the Hall scattering factor in electron-doped Ti2CO2 varies greatly with temperature and concentration, ranging from 0.2 to around 1.3 for weak magnetic fields. The electrical transport was modelled primarily using three scattering mechanisms: piezoelectric scattering, acoustic scattering, and polar optical phonons. Even though the mobility in this material is primarily limited by acoustic phonons, piezoelectric scattering also plays an important role which was not highlighted earlier.
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Pressure-Induced Isostructural Phase Transition in Biskyrmion Host Hexagonal MnNiGa
Anupam K. Singh, Parul Devi, Ajit K. Jena, Ujjawal Modanwal, Seung-Cheol Lee, Satadeep Bhattacharjee, Boby Joseph, Sanjay Singh
Physica Status Solidi (Rapid Research Letters)
Abstract
Pressure-Induced Isostructural Phase Transition in Biskyrmion Host Hexagonal MnNiGa
Magnetic skyrmions are vortex-like spin textures, which can be manipulated by external stress or pressure via magnetoelastic effects. Herein, the observation of isostructural phase transition in a biskyrmion host hexagonal MnNiGa at pressure P ≈4 GPa using pressure-dependent synchrotron X-Ray powder diffraction (XRD) data analysis is presented. The XRD data reveals anisotropic compression behavior with pressure with different compression rates of the a-axis in the basal plane and the c-axis in the prismatic plane. However, the hexagonal symmetry remains unchanged for pressure up to 14 GPa. Fitting of unit cell volume with pressure using a second-order Birch–Murnaghan equation of state reveals that the data fall into two distinct curves for those above and below 4 GPa. Herein, the understanding of crystal structure with the application of hydrostatic pressure in the biskyrmion host MnNiGa is contributed to, wherein the skyrmion textures can be manipulated by pressure due to their magnetoelastic character.