Tachikawa Hiroto, Izumi Yoshiki, Iyama Tetsuji, Azumi Kazuhisa
Division of Applied Chemistry, Faculty of Engineering, Hokkaido University, Sapporo 060-8628, Japan.
ACS Omega. 2021 Mar 10;6(11):7778-7785. doi: 10.1021/acsomega.1c00243. eCollection 2021 Mar 23.
Carbon materials such as graphene nanoflakes (GRs), carbon nanotubes, and fullerene can be widely used for hydrogen storage. In general, metal doping of these materials leads to an increase in their H storage density. In the present study, the binding energies of H to Mg species on GRs, GR-Mg ( = 0-2), were calculated using density functional theory calculations. Mg has a wide range of atomic charges. In the case of GR-Mg ( = 0, Mg atom), the binding energy of one H molecule is close to 0, whereas those for = 1 (Mg) and 2 (Mg) are 0.23 and 13.2 kcal/mol ( = 1), respectively. These features suggest that GR-Mg has a strong binding affinity toward H, whereas GR-Mg has a weak binding energy. In addition, it was found that the first coordination shell is saturated by four H molecules, GR-Mg-(H) ( = 4). Next, direct ab initio molecular dynamics calculations were carried out for the electron-capture process of GR-Mg-(H) and a hole-capture process of GR-Mg-(H) ( = 4). After electron capture, the H molecules left and dissociated from GR-Mg: GR-Mg-(H) + e → GR-Mg + (H) (H is released into the gas phase). In contrast, the H molecules were bound again to GR-Mg after the hole capture of GR-Mg: GR-Mg + (H) (gas phase) + hole → GR-Mg-(H) . On the basis of these calculations, a model device with reversible H adsorption-desorption properties was designed. These results strongly suggest that the GR-Mg system is capable of H adsorption-desorption reversible storage.
诸如石墨烯纳米片（GRs）、碳纳米管和富勒烯等碳材料可广泛用于储氢。一般来说，这些材料的金属掺杂会导致其储氢密度增加。在本研究中，使用密度泛函理论计算来计算H与GRs上Mg物种（GR-Mg，(n = 0 - 2)）的结合能。Mg具有广泛的原子电荷范围。在GR-Mg（(n = 0)，Mg原子）的情况下，一个H分子的结合能接近0，而对于(n = 1)（Mg(^+)）和(n = 2)（Mg(^{2 + })），结合能分别为0.23和13.2千卡/摩尔（(n = 1)）。这些特征表明GR-Mg对H具有很强的结合亲和力，而GR-Mg(^0)的结合能较弱。此外，发现第一配位壳层被四个H分子饱和，即GR-Mg-(H)(_4)（(n = 4)）。接下来，对GR-Mg-(H)(_4)的电子俘获过程和GR-Mg-(H)(_4)（(n = 4)）的空穴俘获过程进行了直接的从头算分子动力学计算。电子俘获后，H分子离开并从GR-Mg解离：GR-Mg-(H)(_4) + e → GR-Mg + 4(H)（H释放到气相中）。相反，GR-Mg的空穴俘获后，H分子再次与GR-Mg结合：GR-Mg + 4(H)（气相）+空穴 → GR-Mg-(H)(_4) 。基于这些计算，设计了一种具有可逆H吸附-解吸特性的模型装置。这些结果有力地表明GR-Mg系统能够进行H吸附-解吸可逆存储。
