Near-field enhanced thermionic energy conversion for renewable energy recycling

•Near-field enhanced thermionic energy conversion (NETEC) is proposed as a new scheme that utilizes near-field thermal radiation for renewable energy recycling.•Fundamental physics of thermionic emission affected by near-field enhanced photoexcitation is discussed.•We have theoretically demonstrated that near-field thermal radiation can greatly enhance the power output and conversion efficiency of the NETEC system.•The electron affinity of the cathode is the key parameter that governs the performance of the NETEC system.

This article proposes a new energy harvesting concept that greatly enhances thermionic power generation with high efficiency by exploiting the near-field enhancement of thermal radiation. The proposed near-field enhanced thermionic energy conversion (NETEC) system is uniquely configured with a low-bandgap semiconductor cathode separated from a thermal emitter with a subwavelength gap distance, such that a significant amount of electrons can be photoexcited by near-field thermal radiation to contribute to the enhancement of thermionic current density. We theoretically demonstrate that the NETEC system can generate electric power at a significantly lower temperature than the standard thermionic generator, and the energy conversion efficiency can exceed 40%. The obtained results reveal that near-field photoexcitation can enhance the thermionic power output by more than 10 times, making this hybrid system attractive for renewable energy recycling.