Thermionic energy conversion based on 3D Dirac semimetals

Abstract

First, we investigate theoretically the thermionic emission from three-dimensional Dirac semimetals (3D DSs), then we explore their practical application as the cathode of a thermionic energy generator (TIEG). Based on the linear energy dispersion around Dirac points, we derive the generalized analytical formula of the thermionic emission from 3D DSs through the Dirac Hamilton, which is significantly different from the Richardson–Dushman (RD) law for metallic materials. The reason for this originates from the fact that electrons behave like massless fermions and follow ultrarelativistic quasiparticle dynamics in 3D DSs, deviating from the nonrelativistic electrons with a parabolic energy dispersion in conventional metal materials. We develop a theoretical model of the solid-state thermionic energy generator using 3D DSs as the cathode and obtain its optimal working regions at different temperatures. For a 3D DS-based cathode at 1400 K, the maximum efficiency of the proposed TIEG can reach 50.0%, where the correspondingly optimal work functions of the cathode and anode are 2.05 eV and 0.612 eV, respectively. The results presented in this work demonstrate that 3D DSs are superior to metallic materials and graphene in thermionic application, and will contribute to the choice of electrode materials, optimal designs, and control operative conditions of practical TIEGs.