The unusual electronic properties of 3-D topological Dirac semimetals have led to intensive research efforts focusing on their potential applications in high-performance electronic, photonic, and optoelectronic devices. In this work, we propose a conceptual design of thermionic energy converters (TECs) based on a Cd3As2 anode with significantly improved performance. Using the electronic properties of Cd3As2—an air-stable topological Dirac semimetal—from first-principle density functional theory (DFT) calculation, such a device can achieve a maximum output power density and conversion efficiency of 10.96 W/cm2 and 57.29% at 1800 K, respectively. The advantages of topological Dirac anode over conventional metal- and graphene-based TECs are revealed. This work opens an exciting route toward high-performance energy converters via the union of topological material and thermionic devices. [ABSTRACT FROM AUTHOR]