Molecular Dynamics Investigation on Thermal Conductivity and Photon Behaviors of Graphene With Sierpinski Carpet Fractal Defects

The thermal conductivity (TC) of graphene with Sierpinski carpet fractal (SCF) and regular carpet (RC) defects is numerically studied by the non-equilibrium molecular dynamics (NEMD) method. The influences of porosity, fractal levels, and types of defects on the TC of graphene are clarified, and the underlying mechanisms of phonon behaviors are uncovered. The numerical results indicate that the defects in graphene induce the atoms that have the heat transfer blockage effect, and thus, the TC of defective graphene decreases with increasing porosity. With the increase in fractal levels, more atoms have the heat transfer blockage effect, which induces the TC of graphene with SCF defects to sharply decrease. Moreover, compared with the graphene with RC defects, more atoms participate in the heat transfer blockage under the graphene with SCF defects, which leads to the lower TC of graphene with SCF defects.

Theoretical Study on V Atom Supported on N and P-Doped Defective Graphene for Electrocatalytic Nitrogen Reduction

Ammonia (NH3) is one of the most extensively produced chemicals worldwide, and it plays an important and indispensable role in the global economy. At present NH3 is mainly produced by the traditional Haber-Bosch process operated at high pressure and temperature, which results in massive energy consumption and carbon dioxide emissions. The electrochemical nitrogen reduction reaction (NRR) can allow the production of NH3 from nitrogen and water under ambient conditions and is regarded as a sustainable alternative to the Haber–Bosch process because of its low energy consumption and limited environmental impact. In this study, using density functional theory calculations, we designed a monovacancy defective graphene (MVG) doped with various nitrogen and phosphorus atoms and a single vanadium atom (VN1–3@MVG and VP1–3@MVG) to be used as electrocatalysts. The results revealed that N- and P-doping are beneficial for N2 adsorption and activation and can effectively reduce the energy barrier of the NRR, especially for P-doping. Among the synthesized electrocatalysts, double P-doped V@MVG demonstrated the best catalytic activity with a low free energy barrier of 0.43 eV. This paper reports the development of an efficient catalyst for electrochemical NH3 synthesis and provides valuable insights on the design of electrocatalysts with high activity and stability.