Theoretical Considerations of 2D Materials in Energy Applications

Two-dimensional materials are potential candidates for various applications such as piezoelectric energy conversion from mechanical energy, photovoltaic, and photoelectrochemical cells for hydrogen evolution. In this work, we introduce a tool based on density functional theory (Quantum ESPRESSO) and finite difference time domain technique for efficient energy applications of two-dimensional materials. To understand the electronic properties of transition metal dichalcogenides, like WSe₂ both bulk and monolayer, we discuss the density functional theory or the first-principle approach. We show how density functional theory can be used to predict properties like electronic band structure, bandgap, work function, etc., of TMDC from the first principle. We show that the monolayer form of WSe₂ has a direct bandgap of 1.63 eV. We then discuss the Finite-Difference Time-Domain method (FDTD) or Yee's method. The FDTD is simple yet conceptually elegant and frequently used full-wave techniques to solve problems in electromagnetics. We then discuss the piezoelectric output due to externally applied strain. In the end, we review the mechanism of hydrogen evolution through water splitting. We also review the key parameters like active sites, intrinsic catalytic properties, and conductivity. These parameters are tunable for efficient hydrogen evolution from two-dimensional materials when used as photocatalysts in the photoelectrochemical cell.