First-Principles Calculation of Optimizing the Performance of Germanene-Based Supercapacitors by Vacancies and Metal Atoms

Germanene with folded atomic layers has double surfaces and high surface/volume ratio, similar to carbon nanomaterials, and is expected to be used in supercapacitors and field effect transistors. By the first-principle calculations, it is found that the introduction of various defects can improve the quantum capacitance of germanene. The enhancement of quantum capacitance is attributed to the existence of localized states near the Fermi level. By introducing the metal atoms into the lattice, such as Ag, Au, Al, Cu, and Ti, germanene can be modulated to have quasi-metallic properties, accompanied by electron transfer and localized states formed near the Fermi level. While the quantum capacitance of pristine germanene is limited by the low density of states near the Fermi level, its quantum capacitance can be significantly improved by introducing the complex of single vacancy and metal atoms, especially Cu and Ti.