Charge-induced electromechanical actuation of two-dimensional hexagonal and pentagonal materials

Using first-principles calculations, we investigate electromechanical properties of two-dimensional (2D) hexagonal and pentagonal materials as a function of electron and hole dopings, in which 2D materials including graphene, chair-like graphane, table-like graphane, penta-graphene (PG), hydrogenated penta-graphene (HPG), and penta-CN₂ are considered. We find that the actuation responses such as actuation strain, stress generated, and work area-density per cycle of the 2D materials in the case of hole doping are substantially larger than those of electron doping. Moreover, the electromechanical properties of the 2D materials can be improved by hydrogenation. In particular, the actuation strain and work area-density per cycle of graphane and HPG are much larger than those of graphene and PG for hole doping, respectively. Interestingly, both the 2D hexagonal and pentagonal materials show an asymmetric dependence of theoretical strength (a maximum value of the stress that the materials can achieve by applying the strain) on the electron and hole dopings. These results provide an important insight into the electromechanical properties of the 2D hexagonal and pentagonal materials, which are useful for artificial muscle applications.