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.