Tang Chunmei, Zhang Xue, Zhou Xiaofeng
College of Science, Hohai University, Nanjing, Jiangsu 210098, P. R. China.
Phys Chem Chem Phys. 2017 Feb 15;19(7):5570-5578. doi: 10.1039/c6cp07433b.
Density functional calculations were used to investigate the hydrogen storage abilities of Na-atoms-decorated BN sheets under both external biaxial strain and a vertical electric field. The Na atom generally has the weakest binding strength to a given substrate compared with the other elements in the periodic table [PANS, 2016, 113, 3735]. Consequently, it is understudied in comparison to other elements and there are few reports about the hydrogen storage abilities of Na-decorated nanomaterials. We calculated that the average binding energy (E) of Na atoms to the pure BN sheet is 1.08 eV, which is smaller than the cohesive energy of bulk Na (1.11 eV). However, the E can be increased to 1.15 eV under 15% biaxial strain, and further up to 1.53 eV with the control of both 15% biaxial strain and a 5.14 V nm electric field (E-field). Therefore, the application of biaxial strain and an external upward E-field can prevent clustering of the Na atoms on the surface of a BN sheet, which is crucial for the hydrogen storage. Each Na atom on the surface of a BN sheet can adsorb only one H molecule when no strain or E-field is applied; however, the absorption increases to five H molecules under 15% biaxial strain and six H molecules under both 15% biaxial strain combined with a 5.14 V nmE-field. The average adsorption energies for H of BN-(Na-mH) (m = 1-6) are within the range of practical applications (0.2-0.6 eV). The hydrogen gravimetric density of the periodic BN-(Na-6H) structure is 9 wt%, which exceeds the 5.5 wt% value that should be met by 2017 as specified by the US Department of Energy. On the other side, removal of the biaxial strain and E-field can help to desorb the H molecule. These findings suggest a new route to design hydrogen storage materials under near-ambient conditions.
采用密度泛函计算方法，研究了在外部双轴应变和垂直电场作用下，钠原子修饰的氮化硼片层的储氢能力。与元素周期表中的其他元素相比，钠原子对给定基底的结合强度通常最弱[《美国国家科学院院刊》，2016年，第113卷，第3735页]。因此，与其他元素相比，对其研究较少，关于钠修饰的纳米材料储氢能力的报道也很少。我们计算得出，钠原子与纯氮化硼片层的平均结合能（E）为1.08电子伏特，小于块状钠的内聚能（1.11电子伏特）。然而，在15%双轴应变下，E可增加到1.15电子伏特，在15%双轴应变和5.14伏纳米电场（E场）共同作用下，E进一步增加到1.53电子伏特。因此，双轴应变和外部向上的E场的应用可以防止钠原子在氮化硼片层表面聚集，这对储氢至关重要。当不施加应变或E场时，氮化硼片层表面的每个钠原子只能吸附一个氢分子；然而，在15%双轴应变下，吸附量增加到五个氢分子，在15%双轴应变与5.14伏纳米E场共同作用下，吸附量增加到六个氢分子。BN-(Na-mH)（m = 1-6）中氢的平均吸附能在实际应用范围内（0.2-0.6电子伏特）。周期性BN-(Na-6H)结构的氢重量密度为9重量%，超过了美国能源部规定的到2017年应达到的5.5重量%的值。另一方面，去除双轴应变和E场有助于氢分子解吸。这些发现为在近环境条件下设计储氢材料提供了一条新途径。
