Selective decoration of nitrogenated holey graphene (C2N) with titanium clusters for enhanced hydrogen storage application

Abstract

For an envisioned hydrogen (H2) economy, the design of new multifunctional two-dimensional (2D) materials have been a subject of intense research for the last several decades. Here, we report the thriving H2 storage capacity of 2D nitrogenated holey graphene (C2N), functionalized with Tin (n = 1–5) clusters. By using spin polarized density functional theory (DFT) calculations implemented with the van der Waals corrections, the most favourable adsorption site for the Tin clusters on C2N has been revealed. With the monomer Ti, the functionalization was evenly covered on C2N having 5% doping concentration (C2N–Ti). For C2N–Ti sheet, Ti binds to C2N with a strong binding energy of ~6 eV per Ti which is robust enough to hinder any Ti–Ti clustering. Bader charge analysis reveals that the Tin clusters donate significant charges to C2N sheet and become cationic to polarize the H2 molecules, thus act as efficient anchoring agents to adhere multiple H2 molecules. Each Ti in C2N–Ti could adsorb a maximum of 10H2 molecules, with the adsorption energies in the range of −0.2 to −0.4 eV per H2 molecule, resulting into a high H2 storage capacity of 6.8 wt%, which is promising for practical H2 storage applications at room temperature. Furthermore, Tim (m = 2, 3, 4, 5) clusters have been selectively decorated over C2N. However, with Tim functionalization H2 storage capacities fall short of the desirable range due to large molecular weights of the systems. In addition, the H2 desorption mechanism at different conditions of pressure and temperature were also studied by means of thermodynamic analysis that further reinforce the potential of C2N–Ti as an efficient H2 storage material.