Enhancement of the quantum capacitances of group-14 elemental two-dimensional materials by Ti-doping: A first principles study

Abstract Group-14 elemental two-dimensional materials are a key material for future supercapacitors because of their various advantages compared to activated carbon. However, the lack of density of states (DOS) near the Fermi level (EF) of these materials is one of the limiting factors for the performance of supercapacitors, especially for electric double-layer capacitors (EDLCs). In this study, Ti-doping was investigated as a strategy for providing a large amount of DOS near the EF. By using density functional theory calculations, it was confirmed that the d band of the Ti atom provides additional DOS to the materials. The calculated quantum capacitances and the surface charge densities of the doped systems were enhanced overall in both their gravimetric and specific aspects thanks to the increased DOS near the EF. In addition, it was revealed that Ti-doped silicene has superior characteristics at the low voltage range compared to other materials. These findings may provide practical guidelines for improving the performance of EDLCs.