Near-field enhanced thermionic energy conversion for renewable energy recycling

Abstract

This article proposes a new energy harvesting concept that greatly enhances thermionic power generation with high efficiency by exploiting the nearfield 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.

Precision Measurement of Phonon-Polaritonic Near-Field Energy Transfer between Macroscale Planar Structures Under Large Thermal Gradients

“…When two objects are separated by a nanoscale vacuum gap, thermal radiation can exceed the blackbody limit by several orders of magnitude due to photon tunneling of thermal evanescent electromagnetic (EM) waves, along with other near-field effects such as interferences and surface polaritons [1]. Such remarkable enhancement of thermal radiation can be beneficially used in many energy applications, including thermophotovoltaic [2][3][4][5][6][7][8] and thermionic [9] solid-state heat engines, thermal extraction [10], thermotronics [11][12][13][14][15], and dynamic thermal modulation [16]. However, experimental demonstration of such emerging energy applications has not been fully explored to date due to technical difficulties in precisely measuring near-field thermal radiation between large planar structures under a substantial temperature difference.…”

Selected methods of converting solar energy into electricity - comparative analysis

“…In the case of NETEC system, its energy conversion efficiency should be defined as the ratio of the electrical power output, P NETEC , to the heat input to the NETEC system, or nearfield thermal radiation absorbed by the cathode, Q E → C [9]: For NETEC system, maximum efficiency is about 44% (cathode electron affinity χ C ≈ 1.4 eV, emitter temperature T E = 2,000 K, anode temperature T A = 300 K, anode work function φ A = 0.7 eV, the vacuum gap distance between emitter and cathode d g = 100 nm, thickness of the cathode d c = 1.5 μm, doping concentration of the cathode: 2.4 ×10 18 cm −3 , cathode material: p-doped In 0,53 Ga 0,47 As) [9]. The above results do not take into account the impact of space charges between the cathode and anode of NETEC system, which cause the repelling between the electrons traversing the gap [10,11,12].…”

“…The above results do not take into account the impact of space charges between the cathode and anode of NETEC system, which cause the repelling between the electrons traversing the gap [10,11,12]. Based on results obtained in papers [5,9], the dependences of efficiency on temperature for PETE and NETEC have been elaborated (Fig.5 -Fig.7). For cathode electron affinity χ C = 0.6 eV, the conversion efficiency of NETEC is higher than PETE in full analysed range.…”

“…The above plots show that the conversion efficiency increases as the cathode electron affinity rises. Table 1 presents the features of each method [5,9]. …”

A Review of Tunable Wavelength Selectivity of Metamaterials in Near-Field and Far-Field Radiative Thermal Transport

“…Thus, the artificial metamaterials show an extensive emission spectrum, while emissive properties of nanostructured materials are remarkably different from those of natural bulk materials. Thermal metamaterials show great potential in the development of selective thermal emitters or absorbers which play a major role in the progression of solar cells and thermophotovoltaics (TPVs) and infrared thermal sensing applications [ 3 , 4 , 5 , 6 , 7 , 8 , 9 ], thermal diodes [ 10 , 11 ], radiation cooling [ 12 , 13 , 14 , 15 ], thermal rectification [ 16 , 17 ], biosensors, and chemical sensors [ 18 , 19 ]. Nanomaterials/nanostructures have become the topic of many articles, which focus on energy conversion and thermal management, such as one or two dimensional metal-dielectric periodic structures [ 20 ], multi-layered structures of thin films [ 21 ], nanoparticle-embedded thin films [ 22 , 23 ], hyperbolic metamaterials [ 24 , 25 ] and phase changing metamaterials [ 26 ].…”