The unique structural characteristics make the 2D materials potential candidates for designing negative electrodes for rechargeable energy storage devices. Here, by employing density functional theory (DFT) calculations, we study the precise viability of using Si 2 BN, a graphene-like 2D material, as a high-capacity anode material for Mg-ion battery (MIB) application. The favorable Mg-adsorption sites with maximum possible coverage effect are explored in detail. It is found that the Si 2 BN sheet can be adsorbed to a configuration of Mg 8 Si 16 B 8 N 8 , which proposes a theoretical capacity of 647.896 mA h g −1 for divalent Mg 2+ -ion battery applications. The average open-circuit voltage of 0.6−0.7 V and intercalation migration energy barrier in the range of 0.08−0.35 eV make Si 2 BN one of the most promising anode materials for MIB applications. The porous Si 2 BN with high structural stability and metallic electronic structures along with the low Mg 2+ -ion migration barrier energies predict high electron and Mg-ion conductivity, ensuring fast charge/discharge cyclic performance. The above-mentioned findings validate that the Si 2 BN sheet can work as an excellent high-performance anode material for MIBs.

Identifying a suitable cathode material for aluminum dual-ion batteries (ADIBs) with an enhanced specific capacity, cyclic durability, and open circuit voltage is among the major challenges in its commercialization. This study presents a graphdiyne (GDY) monolayer, a recently synthesized carbon allotrope, as a promising cathode material to host the diffusing AlCl4 –, which is responsible for the charging/discharging process in ADIBs. Density functional theory calculations are performed to reveal the mechanism of adsorption of AlCl4 on GDY, while thermodynamical stability and diffusion dynamics are examined through ab initio molecular dynamics simulations. The theoretical specific capacity of this room-temperature stable system is calculated to be 186 mA h/g, which is 3 times higher compared to the case in which graphite is used as the cathode. The cyclic durability of this system is established as the GDY regains its equilibrium structure after releasing AlCl4 during discharge. The activation barriera measure of ease with which the diffusion occursis calculated with the aid of the climbing image-nudged elastic band method and found to be 0.08 and 0.05 eV for monolayer and bilayer GDY, respectively. Hence, with GDY as the cathode material, we can achieve an ultralow diffusion energy barrier. Furthermore, due to charge transfer between Cl and C sites, the semiconducting GDY becomes metallic upon AlCl4 adsorption, which is an added advantage in improving the electronic conductivity.

Understanding the mechanism of NO 2 interaction on semiconductor surfaces such as TiO 2 is a key step in designing the catalytic processes for conversion of NO 2 to useful products. In the present work, through density functional theory calculations and NEB simulations, we have performed a comprehensive electronic structure study and established the reaction steps for efficient conversion of NO 2 to HONO on TiO 2 surface in the presence of water vapor. We predict the dimerization of NO 2 to form a metastable N 2 O 4 . The latter's dissociation to NO δ+ and NO 3 δ− complexes occurs in two pathways: (i) direct disproportionation reaction and (ii) through formation of NO 2 δ+ and NO 2 δ− intermediates followed by O transfer. The introduction of H 2 O on a NO 2 chemisorbed surface leads to the formation of nitrous acid through the interaction of NO δ+ with the water. The reaction pathways leading to formation of nitrous and nitric acids are formulated.

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Adsorption of CO 2 on a semiconductor surface is a prerequisite for its photocatalytic reduction. Owing to superior photocorrosion resistance, nontoxicity and suitable band edge positions, TiO 2 is considered to be the most efficient photocatalyst for facilitating redox reactions. However, due to the absence of adequate understanding of the mechanism of adsorption, the CO 2 conversion efficiency on TiO 2 surfaces has not been maximized. While anatase TiO 2 (101) is the most stable facet, the (001) surface is more reactive and it has been experimentally shown that the stability can be reversed and a larger percentage (up to ~ 89%) of the (001) facet can be synthesized in the presence fluorine ions. Therefore, through density functional calculations we have investigated the CO 2 adsorption on TiO 2 (001) surface. We have developed a three-state quantum-mechanical model that explains the mechanism of chemisorption, leading to the formation of a tridentate carbonate complex. The electronic structure analysis reveals that the CO 2 -TiO 2 interaction at the surface is uniaxial and long ranged, which gives rise to anisotropy in binding energy (BE). It negates the widely perceived one-to-one correspondence between coverage and BE and infers that the spatial distribution of CO 2 primarily determines the BE. A conceptual experiment is devised where the CO 2 concentration and flow direction can be controlled to tune the BE within a large window of ~1.5 eV. The experiment also reveals that a maximum of 50% coverage can be achieved for chemisorption. In the presence of water, the activated carbonate complex forms a bicarbonate complex by overcoming a potential barrier of ~0.9 eV. * Electronic address: nandab@iitm.ac.in 2 I.