Mg decoration enhanced H2 binding energy in 2D-C2N and found to be a promising H2 storage medium for mobile applications.

Alkaline-earth hydrides (AH2) are considered as potential hydrogen storage material. Due to high decomposition temperature and slow sorption kinetics, these hydrides cannot be used for energy storage applications. As fluorine is more electronegative than hydrogen, substitution of hydrogen by fluorine will bring anisotropic bonding interaction, and hence, it may improve the hydrogen storage properties. Hence, the structural stability, electronic structure, and chemical bonding of AH2 and fluorinated AH2 (AH2–x F x ) are delineated using ab initio calculations. From the calculated enthalpy of formation we have predicted that AH2–x F x are relatively more stable than the corresponding pure hydrides. The positive and very low value of enthalpy of mixing for AH2–x F x imply that single-phase of AH2–x F x may form at reasonable temperatures. The band structure and density of states (DOS) calculations reveal that AH2–x F x are insulators. Partial DOS, charge density, electron localization function, and crystal orbital Hamiltonian population analyses conclude that these compounds are governed mainly by ionic bonding. The calculated H site energy increases as the fluorination increases and thus fluorination bring extra stability in the lattice. The present results suggest that hydrogen closer to fluorine can be removed more easily than that far away from fluorine. Hence, the fluorination brings disproportionation in the bonding between the constituents.

The search for an active, stable, and abundant semiconductor-based bifunctional catalysts for solar hydrogen production will make a substantial impact on the sustainable development of the society that does not rely on fossil reserves. The photocatalytic water splitting mechanism on a $$\hbox {BeN}_{{2}}$$ BeN 2 monolayer has here been investigated by using state-of-the-art density functional theory calculations. For all possible reaction intermediates, the calculated changes in Gibbs free energy showed that the oxygen evolution reaction will occur at, and above, the potential of 2.06 V (against the NHE) as all elementary steps are exergonic. In the case of the hydrogen evolution reaction, a potential of 0.52 V, or above, was required to make the reaction take place spontaneously. Interestingly, the calculated valence band edge and conduction band edge positions for a $$\hbox {BeN}_{{2}}$$ BeN 2 monolayer are located at the potential of 2.60 V and 0.56 V, respectively. This indicates that the photo-generated holes in the valence band can oxidize water to oxygen, and the photo-generated electrons in the conduction band can spontaneously reduce water to hydrogen. Hence, the results from the present theoretical investigation show that the $$\hbox {BeN}_{{2}}$$ BeN 2 monolayer is an efficient bifunctional water-splitting catalyst, without the need for any co-catalyst.

In order to overcome the disadvantages of MgH2 towards its applications in on-board hydrogen storage, first principle calculations have been performed for Ti (2+, 3+, and 4+) substituted MgH2. Our calculated enthalpy of formation and H site energy implies that Ti substitution in Mg site reduces the stability of MgH2 which improve the hydrogen storage properties and Ti prefers to be in +4 oxidation state in MgH2. The bonding analyses through partial density of states, electron localization function and Bader charge of these systems confirm the existence of iono-covalent bonding. Electronic structure obtained from hybrid functional calculations show that intermediate bands (IB) are formed in Ti 4+ substituted MgH2 which could improve the solar cell efficiencies due to multiple photon absorption from valence band to conduction band via IBs and converts low energy photons in the solar spectrum also into electricity. Further, our calculated carrier effective masses and optical absorption spectra show that Ti 4+ substituted MgH2 is suitable for higher efficiency photovoltaic applications. Our results suggest that Ti 4+ substituted MgH2 can be considered as a promising material for hydrogen storage as well as photovoltaic applications.