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Hydrogen is considered as one of the most important clean and renewable energy resources to get rid of carbon-based fuels and to solve the problem of environmental hazzards caused for using fossil fuels. Hence, the large-scale production of hydrogen by water splitting through Hydrogen Evolution Reaction (HER) demands inexpensive and efficient electrocatalysts to replace the scarce and expensive noble metal-based catalysts. In this work, using the density functional theory (DFT)-based computations, we have considered a family of one dimensional (1D) metal organic frameworks (MOFs), namely TM-dithiolene (TM-BTT), and TM-bis(iminothiolato) (TM-BIT), consisting of benzene-1,2,4,5-tetrathiolate (BTT) and benzene-bis(iminothiolato) (BIT) organic ligands, respectively and a family of first row transition metals (TM = Fe, Co, and Ni), to find their catalytic activity towards HER. Using the Gibbs free energy for the adsorption of atomic hydrogen ( $\mathrm{\Delta G_{H^{*}}}$) as the key descriptor, we reached to the conclusion that Ni-bis(iminothiolato) MOF exhibit better catalytic activity towards HER over all other investigated 1D-MOFs.

With the urgent need for efficient energy storage devices, enormous attention has been paid to researching and developing promising anode materials for metal-ion batteries. Through density functional study, we have successfully predicted the electrochemical performance of the P3S and C3S monolayers for the first time, which could be used in alkali metal (Li, Na, and K)-ion batteries. Our study examines the pristine monolayers' energetical, dynamical, and thermal stability. The electronic structures of the pristine nanosheets exhibit wide-gap semiconductors. After single metalation on the monolayers, the composite systems become metallic. Charge density difference (CDD) analysis indicates that charge transfer occurs from the alkali metal atoms to the P3S and C3S monolayers, and Bader charge analysis quantifies the amount of charge transfer. We have analyzed how readily a single adatom diffuses within the 2D structures. One example is the diffusion of K on C3S, which has a low barrier value of 0.06 eV and seems practically barrierless. Furthermore, our predicted composite systems report considerable theoretical storage capacity (C); for example, hexalayer K-adsorbed C3S shows a storage capacity of 1182.79 mA h g−1. The estimated open-circuit voltage (OCV) values imply that the C3S monolayer is promising anode material for Li-, Na-, and K-ion batteries, while the P3S monolayer is suitable as cathode material for Li-, Na-, and K-ion batteries.

Unsupported and oxygen deficient TiO2 surface supported small Rux/Rhx nanoclusters can efficiently and selectively convert CO2 into formic acid.

Nowadays, great attention is being directed towards the development of promising electrode materials for non-lithium rechargeable batteries such as sodium and calcium ion batteries (SIBs and CIBs), due to their large abundance, storage capacity and charge/discharge rate. Using density functional theory (DFT) based computations we have predicted that the recently synthesized bilayer

Searching for an alternative nonhazardous catalyst for direct urea synthesis that avoids the traditional route of NH3 synthesis followed by CO2 addition is a challenging field of research nowadays. Based on first-principles calculations, we herein propose a novel electrocatalyst comprising of totally nonmetal earth abundant elements (dual-Si doped g-C6N6 sheet) which is capable of activating N2 and making it susceptible toward direct insertion of CO into the N-N bond, producing *NCON* which is the precursor for urea production by direct coupling of N2 and CO2 followed by multiple proton coupled electron transfer processes. Remarkably, the calculated onset potential for urea production is much less than that of NH3 synthesis and hydrogen evolution reactions, and also the faradaic efficiency is nearly 100% for production urea over ammonia, which promotes exclusive electrocatalytic urea synthesis by suppressing the NH3 synthesis as well as hydrogen evolution reactions.

Recently, two-dimensional organic-inorganic hybrid perovskites have attracted great attention for their outstanding performances in solar energy conversion devices. By using first principles calculations, we explored the structural, electronic and optical properties of recently synthesized (PEA)2 PbI4 and (PEA)2 SnI4 organic-inorganic hybrid perovskites to understand the photovoltaic performances of these systems. Our study reveals that both the perovskites are direct band gap semiconductors and possess desirable band gap for solar energy absorption. We have further extended our study to fluoro-, chloro-, and bromo-functionalized phenethylammonium (PEA) cations based [X(X = F, Cl, Br)PEA]2 A(A = Pb, Sn)I4 perovskite materials. The halogenated benzene moiety confers an ultrahydrophobic character and protects the perovskites from ambient moisture. The halogen functionalized perovskites remain direct band gap semiconductors and all the perovskites show very strong optical absorption (∼7 × 105 cm-1 ) across UV-visible region. We have further calculated the photo-conversion efficiency (PCE) of both arene and functionalized arene based perovskites. The halogen-functionalized PEA-based perovskites also exhibit high PCE as like pristine ones and finally achieve high PCE of up to 24.30%, making them competitive with other previously reported perovskite-based photovoltaic devices.

We synthesized two types of donor-acceptor Stenhouse adducts (DASAs), a new type of photochromic molecules showing dual color in two different isomeric forms in solution phase, using Meldrum acid (DASA-Mel) and barbituric acid (DASA-Bar), along with a naphthalimide derivative to obtain interesting fluorescence properties. DASA-Mel was found to have fast photochromic conversion in comparison to DASA-Bar, evident from ultraviolet-visible (UV-vis) and fluorescence spectroscopic studies. The colored form of DASA-Mel was encapsulated inside the water-soluble Stoddart's blue box and became soluble in water much faster than DASA-Bar. Interestingly, the competitive encapsulation experiment showed that DASA-Mel was selectively encapsulated inside the blue box in water whereas DASA-Bar was mostly separated out from the solution after centrifugation, and this phenomenon was confirmed by 1H and DOSY NMR and mass spectroscopies. Moreover, we found through density functional theory (DFT) optimization that the open form of DASA-Mel was more stable during the encapsulation reaction in a water medium in comparison to DASA-Bar. The calculated binding energies of encapsulated DASA-Mel and DASA-Bar are -10.2 and -9.9 kcal/mol, respectively, clearly showing that the former is more stable by 0.3 kcal. Consequently, the organic macrocycle selectively separating one kind of DASA from a mixture by encapsulation in water is reported for the first time with experimental and theoretical support in the literature.

Carbon nanotubes (CNTs) are appealing candidates for solar and optoelectronic applications. Traditionally used as electron sinks, CNTs can also perform as electron donors, as exemplified by coupling with perylenediimide (PDI). To achieve high efficiencies, electron transfer (ET) should be fast, while subsequent charge recombination should be slow. Typically, defects are considered detrimental to material performance because they accelerate charge and energy losses. We demonstrate that, surprisingly, common CNT defects improve rather than deteriorate the performance. CNTs and other low dimensional materials accommodate moderate defects without creating deep traps. At the same time, charge redistribution caused by CNT defects creates an additional electrostatic potential that increases the CNT work function and lowers CNT energy levels relative to those of the acceptor species. Hence, the energy gap for the ET is decreased, while the gap for the charge recombination is increased. The effect is particularly important because charge acceptors tend to bind near defects due to enhanced chemical interactions. The time-domain simulation of the excited-state dynamics provides an atomistic picture of the observed phenomenon and characterizes in detail the electronic states, vibrational motions, inelastic and elastic electron-phonon interactions, and time scales of the charge separation and recombination processes. The findings should apply generally to low-dimensional materials, because they dissipate defect strain better than bulk semiconductors. Our calculations reveal that CNT performance is robust to common defects and that moderate defects are essential rather than detrimental for CNT application in energy, electronics, and related fields.

Designing metal-free photocatalysts for oxygen reduction reaction (ORR) is an important step toward the development of sustainable and alternative energy resources because ORR plays a key role in fuel cell reactions. An efficient photocatalyst for ORR must possess suitable band positions with respect to electrochemical potentials of ORR, minimize energy losses due to charge transport and electron-hole recombination, and have kinetically suitable electron transfer properties. Using first-principles theoretical studies, we herein demonstrate that a single Si atom doped on the alternative pores of the porous graphitic carbon nitride (g-C

Rechargeable zinc ion batteries (ZIBs) have received significant attention from the scientific community as an alternative to lithium ion batteries (LIBs) for large-scale energy storage systems owing to their high safety and low cost. However, the lack of a suitable cathode material limits their practical implementation. By using density functional theory (DFT)-based computations, we have herein investigated the electronic structure of a very recently synthesized phenanthroline-based covalent organic framework (PACOF) to lend support for its applicability as a promising cathode material for ZIBs. We have analyzed the diffusion barriers, open-circuit voltages (OCVs), and storage capacity of this COF. Thereafter, inspired by some very recent experimental research works, we have predicted a new framework based on quinone and phenanthroline (QPACOF), which is found to exhibit better electrochemical performance as a cathode material for ZIBs compared with PACOF. Our predicted framework (QPACOF) exhibits almost twice the storage capacity shown by PACOF. Moreover, the OCVs of QPACOF are higher than that of PACOF, ensuring a larger cell voltage for QPACOF. Finally, we have proposed a possible synthetic route to experimentally synthesize our predicted model system (QPACOF).

Half metallic materials with intrinsic ferromagnetism are identified as the pillar of next generation spintronic devices. In search of new low-dimensional materials with these excellent properties, herein we systematically study the electronic and magnetic properties of edge dependent (armchair (ac) and zigzag (zz)) vanadium nitride nanoribbons (VNNRs) using density functional theory (DFT) based calculations. Both the ac and zz VNNRs show robust ferromagnetism and extensive half-metallicity with large band gaps (3.9-4.3 eV for ac and 2.5-3.0 eV for zz VNNRs) for the down spin channel. Interestingly, even with the application of uniaxial strain (both tensile and compressive) along the axis of the ribbons, VNNRs retain their extensive half metallicity with a large spin band gap and robust ferromagnetic behavior. Spin dependent electronic transport reveals the 100% spin filtering efficiency of nanoribbons, in both the free state and under applied strain, which support the robust half metallicity of VNNRs. Our study of VNNRs on a MoS2 substrate also shows half metallicity along with high stability, indicating the usage of MoS2 as a substrate for the synthesis of VNNRs. All these results guide the potential application of VNNRs in spintronic devices.

H2O driven N2 fixation is known as the best alternative pathway to synthesise NH3 under ambient conditions. The thermodynamic non-spontaneous reaction can be accomplished by a photocatalytic water splitting reaction over a TiO2 supported surface with oxygen vacancies. Previous experiments have also shown N2 activation over a neutral Ru cluster whose catalytic activity was remarkably enhanced by TiO2 doping. In this article, we have investigated the detailed mechanism and kinetics of the H2O catalyzed nitrogen reduction reaction (NRR) over bare and TiO2 doped Ru5 clusters in conjunction with DFT and TST calculations. The lack of photochemical activity of the small model cluster provoked us to explore an alternative route of NH3 formation via H2O catalysis. For this, we have considered H2 as co-reactant. The partial reduction of N2 into NH3 or N2H4 could be achieved by a H2O oxidation reaction, however, catalytic regeneration requires additional H2 which effectively makes the overall reaction catalyzed by H2O. Above all, the present investigation suggests that NH3 is most favorably produced through the distal mechanism. Analysis of the rate constants demonstrates that the doping with TiO2 accelerates the kinetics of NRR by a few orders of magnitude. Furthermore, an increase of the size of the metal cluster would not significantly enhance the overall performance of NRR.

Recently, inorganic–organic hybrid perovskites have gained immense attention in view of its outstanding performance in solar cell devices. Due to the toxicity of lead, lead-free perovskites are hig...

Two dimensional (2D) van der Waals heterostructures formed by stacking two different 2D materials have gained immense attention as they have the promise of showing interesting properties. Herein we...

Because of the low cost and plentiful resources of sodium as compared to lithium, sodium-ion batteries (SIBs) are becoming promising alternatives to lithium-ion batteries for large-scale electroche...

Until now, reactions between methane photolysis products (CH3•, CH2) and active N atom or reactive NO radical are proposed as routes of HCN formation in the prebiotic Earth. Scientists think that the reducing atmosphere of primitive Earth was made of H2, He, N2, NO, CH4, H2O, CO2, etc., and there was no molecular oxygen. However, it has been evident from experiments that the vacuum ultraviolet (VUV) photolysis of CO2 can produce atomic oxygen. Therefore, it can be presumed that atomic oxygen was likely present in early Earth's atmosphere. Was there any impact of atomic oxygen in production of early atmospheric HCN for the emergence of life? To hunt for the answer, we have employed computational methods to study the mechanism and kinetics of CH3NO + O(1D) and CH2NO• + O(3P) addition reactions. Current study suggests that the addition of O(1D) into nitrosomethane (CH3NO) and the addition of O(3P) into nitrosomethylene radical (CH2NO•) can efficiently produce HCN through an effectively barrierless pathway. At STP, Bartis-Widom phenomenological loss rate coefficients of O(1D) and O(3P) are obtained as 2.47 × 10-12 and 4.67 × 10-11 cm3 molecule-1 s-1, respectively. We propose that addition reactions of atomic oxygen with CH3NO and CH2NO• might act as a potential source for early atmospheric HCN.

Designing the efficient inorganic/organic hybrid light harvesting systems through understanding of charge generation, separation, and recombination dynamics is an important pathway for improvement ...

Conceptualisation of geo-hydrological characteristic of a drainage basin quantitative measurement of morphometric parameters has been required. Assessment and understanding the hydrological characteristics of Nagar River Basin morphometric analysis has been carried out. Remote sensing and ArcGIS techniques have been used for measuring and calculating the morphometric characteristics of the Nagar River Basin. Total area of Nagar River Basin is 2381.69 sq.km with dendritic drainage pattern. This stream frequency of the Nagar River Basin is 0.09 km/sq.km. Probability of flooding is quite high with intense rainfall in dendritic type of drainage system. Monsoonal rainfall is the main cause for the formation of stream segment. Very coarse drainage texture has been found in this Nagar River Basin with T value 0.04. This river basin is highly elongated in nature. The presence of a large number of stream segments exhibits the soil erosion in this study area by surface runoff, and the eroded materials deposited into the river bed aggregated channel depth causing flooding in rainy season. Flood is one of the major natural hazards having massive damage every year all over the world. For constructing flood vulnerability mapping of Nagar River Basin, AHP method has been used by compiling some morphometric parameters with other flood-influencing factors of Nagar River Basin. It can be concluded that the lower portion of the Nagar River Basin is highly vulnerable to flooding.

For π-conjugated systems, polaron formation has a major impact on their optoelectronic properties. In fact, for such systems, an exquisite interplay between electron delocalization and the steric effect determines their ground state properties. However, an excess charge (positive or negative) injection causes structural reorientation because of extended conjugation. Herein, we investigate the effect of such an excess charge in an individual polyphenylene on its quantum conductance behavior. By combining the DFT and NEGF formalisms, we characterize both structural and electronic changes occurring upon electron and hole injection. We demonstrate that for both the cationic and anionic radicals, the excess charge is observed to be localized, inducing a partial planarization of the molecule and forming cationic and anionic polarons, respectively. The calculated low-bias conductance values determine the polaronic effect and could be implemented for easy determination and measurement of polaron formation. In fact, cationic and anionic polarons induce a large degree of conductance switching, involving a decrease and increase of conductance, respectively.

On the basis of first-principle calculations, we have studied the electronic and magnetic properties of a series of one-dimensional metal–organic frameworks (MOFs), labeled as MIT. These are coordi...

Presently, great attention is focused on the search for promising anode materials due to the rapid development of electronic products. In this study, by means of density functional calculations, we...

Using the density functional method, we demonstrate that edge-modified phosphorene antidot nanoflakes (PANFs) and their van der Waals heterojunctions are the new entity for novel light–electricity ...