First-principles Calculation Of Hydrogen Storage Performance Of Metal-supported Carbon-based Materials

Exploring efficient,safe and reversible hydrogen storage materials is an important link to promote the practical application of hydrogen.Carbon-based materials are widely used in the field of solid-state hydrogen storage for research due to their good hydrogen absorption and desorption kinetics,large specific surface area,and high hydrogen storage mass density.Increasing the surface activity of carbon-based materials can be achieved by adding substrates,doping or substituting metal atom modifications,etc.However,high-density metal atoms tend to form clusters during the diffusion of carbon-based materials,making their hydrogen storage capacity lower.Therefore,research and innovation should focus on the adsorption mechanism of hydrogen on carbon-based materials,the hydrogen storage mechanism of metal-loaded carbon-based materials,and the enhancement of the adsorption performance of metals on carbon-based materials to improve hydrogen storage capacity.In this paper,the adsorption behavior of graphene to hydrogen under interlayer coupling,g-CN through the combination of graphene to form a heterojunction method for the adsorption of transition metal atoms,and the hydroxyl-modified defect-containing g-C₃N₄photocatalytic performance was studied.The main findings are summarized as follows:1.The hydrogen adsorption performance of graphene（Gr）surface under the coupling effect of cubic boron nitride（c BN）was studied.It was found that the hydrogen adsorption behavior of Gr surface can be achieved by adding the c BN（111）surface with N atom as the terminal atom as a substrate Regulation.First,three possible stacking forms of the Gr/N-c BN（111）composite structure were constructed,and the sub-lattice symmetry of Gr was broken to cause a small band gap.Secondly,we found that the adsorption energy of a single hydrogen atom on the carbon atoms of different sublattices of the heterostructured Gr is different from the range of the generated magnetic moment.In the AA configuration,atαsite,the adsorption energy can reach-4.046 e V.In addition,the formation energy between two adsorbed hydrogens was studied as a function of the interatomic distance.The calculation results show thatααis the most stable adsorption form in the AA and ABN configurations,which is different from theαβsite adsorption in the ABB configuration.This shows that adding a substrate to Gr is an effective method to regulate the adsorption behavior of small molecules.2.The adsorption properties of 3d transition metals on the surface of g-CN were studied by constructing a heterostructure with Gr.It was found that the adsorption energy of metal atoms in g-CN/Gr system was enhanced.g-CN is a direct band gap semiconductor with a band gap of 1.52 e V,and Gr is a zero band gap semiconductor.The energy band structure and differential charge density of g-CN/Gr are calculated:the system can stably exist with an adsorption energy of-0.7 e V,the charge of the Gr layer is transferred to the g-CN layer,and Gr is a band gap of 0.12 e V appears at the high symmetry pointΓ.The optimal metal atom adsorption position of g-CN/Gr system is the position of the hole center on the side of g-CN,and the adsorption energy is enhanced compared with pure g-CN.Charge layout analysis shows that metal atoms lose more charge in the g-CN/Gr system.3.The photocatalytic performance of the g-C₃N₄system co-doped with hydroxyl groups（-OH）and non-metal atoms（O,B,F）or atomic vacancies（V_N,V_C）was studied.It was found that under the synergistic effect of-OH and V_N（OH-V_N/g-C₃N₄）,the band gap of g-C₃N₄decreased from 2.59 e V to 1.96 e V,and its conduction band edge was closer to the water reduction potential.By analyzing the edge-side charge density,it was found that the recombination of photogenerated electron-hole pairs was suppressed in the co-doped system.The calculated light absorption range of the OH-V_N/g-C₃N₄system was increased to 497 nm,and it was theoretically verified that the synergistic effect of OH-surface modification and V_Ncan enhance the photocatalytic hydrogen production performance of g-C₃N₄.