Spontaneous heat current and ultra-high thermal rectification in asymmetric graphene: a molecular dynamics simulation

Non-equilibrium molecular dynamics (NEMD) simulations reveal the existence of a spontaneous heat current (SHC) in the absence of a temperature gradient and demonstrate ultra-high thermal rectification in asymmetric trapezoid-shaped graphene. These unique properties have potential applications in power generation and thermal circuits, functioning as thermal diodes. Our findings also show the presence of negative and zero thermal conductivity in this system. The negative thermal conductivity could enable the design of a conductive heat machine that pumps heat from the cold side to the hot side without additional energy consumption, functioning as a "full-free refrigerator." Meanwhile, zero thermal conductivity paves the way for the development of high-efficiency thermoelectric devices. Simulations were performed in two scenarios: with hydrogenated edges and without them. To ensure the reliability of the results, Reactive Empirical Bond Order and Tersoff potentials were employed. Finally, we examined how the SHC and the temperature difference at which the heat current is zero depend on the sample length, system width, and system temperature.