Co-adsorption of hydrogen and methane can improve the energy storage capacity of Mn-modified graphene. (July 2023)

• Record Type: Journal Article
• Authors: Sun, Jialin; Ju, Jiaming; Chen, Yuhong; Chen, Li; Chen, Zhiwei; Chen, Chenghui
• Is Part Of: Journal of energy storage. Volume 63(2023)
• Publication Date: 2023-07
• Subjects: Graphene -- Modification -- CH4 -- H2 -- Absorption; Energy storage -- Periodicals; Energy storage -- Research -- Periodicals; 621.3126
• DOI: 10.1016/j.est.2023.106973
• Languages: English
• ISSNs: 2352-152X

Abstract

Abstract: First principles and density functional theory (DFT) are used to investigate the role of H2 molecules in the process of adsorbing CH4 molecules on Mn-modified graphene. The results show that in the 2Mn-modified graphene substrate, the best modification sites of two Mn atoms are the two centrosymmetric benzene ring pore sites, and the substrate can adsorb 7 CH4 molecules and 2 H2 molecules on each side. The average adsorption energy of the CH4 molecules is −0.344 eV, and the adsorption capacity of the CH4 molecules can reach 40.2 wt%. If H2 molecules adsorbed on the substrate are converted into CH4 molecules with the same energy, the adsorption capacity can reach 43.91 wt%. According to the charge density analysis, the polarization of H2 molecular makes the H atom in H2 molecular which has a farther distance with the substrate become negatively charged, and the charge transfer occurs between it and the CH4 molecules in the outer layer, which can reduce the positivity of H atoms on the surface of the outer layer CH4 molecules and weaken the intermolecular repulsion of these CH4 molecules, thus improving the adsorption performance of the outer layer CH4 molecules. In addition, the mechanism of the negatively charged H2 molecules between the two layers of CH4 molecules is similar to the negative center formed on the Mn-modified graphene substrate, which can enhance the adsorption properties of CH4 molecules. Highlights: By converting adsorbed H2 molecules into same energy CH4 molecules, the adsorption capacity can reach 43.91 wt%. The adsorption of the two layers of CH4 molecules appears zipper-like distribution. The polarization of H2 molecules can reduce the intermolecular repulsive force of CH4 molecules. The absorbed H2 molecules act as a bridge between the CH4 molecules in the inner and outer layers.