Theoretical investigation on [Formula: see text] monolayer for an efficient bifunctional water splitting catalyst.

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 [Formula: see text] 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 [Formula: see text] 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 [Formula: see text] monolayer is an efficient bifunctional water-splitting catalyst, without the need for any co-catalyst.

Potential hydrogen storage materials from metal decorated 2D-C2N: an ab initio study.

Two dimensional nitrogenated holey graphene (2D-C2N) is often considered as an ideal material for hydrogen storage applications owing to its lower mass density and high surface-to-volume ratio. As the interaction between H2 and pristine 2D-C2N is very weak with an adsorption energy of only 0.10 eV per H2, it is important to improve it through appropriate materials design. Using density functional theory calculations, we investigated the hydrogen storage properties of metal (M = Mg, Ca, Ti, V, Mn, Fe, Co, Ni, Cu, and Zn) decorated 2D-C2N. From this study, we found that M binding energy on 2D-C2N is greater than the cohesive energy of the respective bulk metals, indicating that the metal is strongly bonded with the 2D-C2N, which rules out the metal clustering issue. In particular, 2D-C2N with Mg decoration leads to 6.79 wt% hydrogen storage capacity with a desirable adsorption energy which is above the Department of Energy's target. The electronic structure analyses show that the Mg decoration leads to a semiconductor-to-metallic transition in 2D-C2N. Our chemical bonding analyses through partial density of states, charge density, electron localization function, charge transfer, and Bader effective charge confirm the presence of an iono-covalent character for Mg decorated 2D-C2N. This indicates that the H2 molecules are adsorbed by a polarization mechanism. Overall, our results suggest that Mg decorated 2D-C2N is a promising candidate for potential hydrogen storage applications.