Concept for Realizing High Output Power Density Thermionic Energy Convertor by Field-Assisted Thermionic Emission Using a Direct-Tunneling Metal–Insulator–Graphene Cathode

The usage of waste heat is an effective way to satisfy the great demand for energy in modern human society. A thermionic energy convertor (TEC) can directly produce electricity from thermal energy with high efficiency. However, high working temperature is one of the major challenges in TEC. In this work, a concept based on field-assisted thermionic emission (FTE) has been proposed to solve this problem. Basically, the field-assisted thermionic energy convertor (FTEC) uses a metal-insulator-graphene (MIG) structure as the cathode to produce direct-tunneling FTE current for the conversion. The fundamental performance of FTEC has been theoretically studied. The penetration field within the MIG structure that controls both the FTE current and the hot electron energy is the key for the performance optimization. By engineering the MIG cathode band structure to balance the above mentioned effects of the penetration field, the ideal efficiency of ~10% and the corresponding output power density of ~5 W/cm
²
can be obtained simultaneously under 700 K. Further comparison between FTEC and conventional TEC indicates that the output power density can be improved by at least four orders of magnitude under a mild temperature (600-700 K). These results provide a universal approach for realizing compact high output power density TEC and its combined system.