Modulating the Energetics of C-H Bond Activation in Methane by Utilizing Metalated Porphyrinic Metal-Organic Frameworks.

In recent years, much effort has been directed toward utilizing metal-organic frameworks (MOFs) for activating C-H bonds of light alkanes. The energy demanding steps involved in the catalytic pathway are the formation of metal-oxo species and the subsequent cleavage of the C-H bonds of alkanes. With the intention of exploring the tunability of the activation barriers involved in the catalytic pathway of methane hydroxylation, we have employed density functional theory to model metalated porphyrinic MOFs (MOF-525(M)). We find that the heavier congeners down a particular group have high exothermic oxo-formation enthalpies ΔHO and hence are associated with low N2O activation barriers. Independent analyses of activation barriers and structure-activity relationship leads to the conclusion that MOF-525(Ru) and MOF-525(Ir) can act as an effective catalysts for methane hydroxylation. Hence, ΔHO has been found to act as a guide, in the first place, in choosing the optimum catalyst for methane hydroxylation from a large set of available systems.

Theoretical investigation of a tetrazine based covalent organic framework as a promising anode material for sodium/calcium ion batteries.

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 s-tetrazine based covalent organic framework (bilayer TZACOF) may be a promising anode material for sodium and calcium ion batteries. The electronic band structure calculations suggest that the bilayer TZACOF is an indirect band gap semiconductor with a band gap of 0.95 eV. The sodium and calcium atoms are adsorbed on the bilayer TZACOF at the most energetically favorable adsorption sites with adsorption energies of -1.37 eV and -2.27 eV, respectively. Moreover, the diffusion energy barriers for the migration of sodium and calcium atoms on the bilayer TZACOF are 0.19 eV and 0.63 eV, respectively, which indicates the fast ion mobility and charge/discharge rate. The theoretical specific capacity (TSC) of the bilayer TZACOF as the electrode material for SIBs and CIBs is 618.69 and 412.46 mA h g-1, respectively. Furthermore, the average voltage of the bilayer TZACOF as the electrode material for SIBs and CIBs is found to be 0.96 and 1.13 V, respectively. Based on the results of rich electronic properties, low diffusion barriers, high storage capacity, and low average voltage, we can reach at the conclusion that the bilayer TZACOF may be a suitable candidate for use as an anode material for sodium and calcium ion batteries (SIBs and CIBs).

Ultrafast Charge Transfer and Delayed Recombination in Graphitic-CN/WTe2 van der Waals Heterostructure: A Time Domain Ab Initio Study.

In search of an efficient solar energy harvester, we herein performed a time domain density functional study coupled with nonadiabatic molecular dynamics (NAMD) simulation to gain atomistic insight into the charge carrier dynamics of a graphitic carbon nitride (g-CN)-tungsten telluride (WTe2) van der Waals heterostructure. Our NAMD study predicted ultrafast electron (589 fs) and hole-transfer (807 fs) dynamics in g-CN/WTe2 heterostructure and a delayed electron-hole recombination process (2.404 ns) as compared to that of the individual g-CN (3 ps) and WTe2 (0.55 ps) monolayer. The ultrafast charge transfer is due to strong electron-phonon coupling during the charge-transfer process while comparatively weak electron-phonon coupling, sufficient band gap, comparatively lower nonadiabatic coupling (NAC), and fast decoherence time slow down the electron-hole recombination process. The NAMD results of exciton relaxation dynamics are valuable for insightful understanding of charge carrier dynamics and in designing photovoltaic devices based on organic-inorganic 2D van der Waals heterostructures.

Tuning the structural skeleton of a phenanthroline-based covalent organic framework for better electrochemical performance as a cathode material for Zn-ion batteries: a theoretical exploration.

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).

Silicon and Phosphorus Co-doped Bipyridine-Linked Covalent Triazine Framework as a Promising Metal-Free Catalyst for Hydrogen Evolution Reaction: A Theoretical Investigation.

Electrocatalytic water spliting is the most attractive route for hydrogen production, but the development of nonprecious, stable, and high-performance catalysts for hydrogen evolution reaction (HER) to replace the scarce platinum group metal-based electrocatalysts is still a challenging task for the scientific community. In this work, within the framework of density functional theory computations, we have predicted that a silicon and phosphorus co-doped bipyridine-linked covalent triazine framework, followed by substitution of bipyridine hydrogens at the P-site with fluorine atoms, may be a potential catalyst for HER. Our predicted model system (SiPF-Bpy-CTF) exhibits a very low band gap (7 meV), which may exhibit facile charge transfer kinetics during HER. Using the Gibbs free energy for the adsorption of atomic hydrogen ([Formula: see text]) as the key descriptor, we have found that our proposed model system (SiPF-Bpy-CTF) exhibits superior HER catalytic activity, with its [Formula: see text] being close to the ideal value (0 eV).

Computational Investigation on the Electronic Structure and Functionalities of a Thiophene-Based Covalent Triazine Framework.

Using the state-of-the-art theoretical method, we have investigated the electronic and optical properties of a thiophene-based covalent triazine framework (TBCTF). We have found that TBCTF is a direct band gap semiconductor. Our calculations reveal that constitutional isomerism is a tool for band gap tuning. The variation of band gap can be achieved by the bilayer TBCTF formation and further can be tuned by the z-axial strain. We have designed a new two-dimensional van der Waals heterostructure g-ZnO/TBCTF, which shows type-II band alignment, ensuring effective separation of photogenerated electron-hole pairs. This composite system also exhibits enhanced absorption in the visible range compared to that of individual g-ZnO and TBCTF monolayers. Therefore, this composite system may find potential application in photovoltaic devices. We have also investigated the hydrogen adsorption ability of TBCTF through Li atom doping. Our results indicate that the calculated hydrogen adsorption energies lie in the range, which is suitable for reversible hydrogen storage under ambient conditions. Therefore, the lithium-doped TBCTF may be a potential candidate for the hydrogen storage material.