Parametric Optimum Design of a Graphene-Based Thermionic Energy Converter

Zhang, Xin; Pan, Yuzhuo; Chen, Jincan

doi:10.1109/ted.2017.2747586

Cited by 32 publications

(14 citation statements)

References 29 publications

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“…4 is aimed to illustrate the discrepancy between the Dirac cone approximation and the full-band model. Realistic modeling of graphene-based thermionic energy device should include important effects, such as image potential lowering [20], blackbody radiation [17], space charge [47][48][49][50], electric-field-induced Fermi level shifting [51], secondary electron emission [52,53], and carrier scattering effects [26,27,29,30]. Such detailed modeling is beyond the scope of this work and shall form the subjects of future works.…”

Section: Resultsmentioning

confidence: 99%

“…This exceedingly large ratios of J RD /J FB 1 suggests that the RD model can severely overestimate the thermionic emission current densities in graphene. Thus, the generalized model proposed here, which rigorously captures the detailed high-energy features of the band structure and the two-dimensionality of graphene, shall be more advantageous than both the classic RD model and the simplified model based on Dirac cone approximation, especially for purposes where the magnitude of thermionic emission current density is important, such as the modelling, computational design and parametric optimization of graphene-based thermionic devices [10,[15][16][17][18]58].…”

Section: Resultsmentioning

confidence: 99%

“…Previous theoretical models [14][15][16][17][18][19][20][21][22] describes the outof-plane thermionic electron emission from the surface of graphene via two key assumptions: (i) electron wavevector component lying in the plane of graphene, denoted as k , is conserved during the out-of-plane emission process [20]; and (ii) electrons undergoing thermionic emission are described by a conic energy band structure, commonly known as the Dirac cone approximation [19,20,[23][24][25]. These assumptions break down in the case of thermionic emission of high-energy electrons due to the following reasons.…”

Section: Introductionmentioning

confidence: 99%

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Generalized High-Energy Thermionic Electron Injection at Graphene Interface

et al. 2019

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Graphene thermionic electron emission across high-interface-barrier involves energetic electrons residing far away from the Dirac point where the Dirac cone approximation of the band structure breaks down. Here we construct a full-band model beyond the simple Dirac cone approximation for the thermionic injection of high-energy electrons in graphene. We show that the thermionic emission model based on the Dirac cone approximation is valid only in the graphene/semiconductor Schottky interface operating near room temperature, but breaks down in the cases involving highenergy electrons, such as graphene/vacuum interface or heterojunction in the presence of photon absorption, where the full-band model is required to account for the band structure nonlinearity at high electron energy. We identify a critical barrier height, Φ (c) B ≈ 3.5 eV, beyond which the Dirac cone approximation crosses over from underestimation to overestimation. In the high-temperature thermionic emission regime at graphene/vacuum interface, the Dirac cone approximation severely overestimates the electrical and heat current densities by more than 50% compared to the more accurate full-band model. The large discrepancies between the two models are demonstrated using a graphene-based thermionic cooler. These findings reveal the fallacy of Dirac cone approximation in the thermionic injection of high-energy electrons in graphene. The full-band model developed here can be readily generalized to other 2D materials, and shall provide an improved theoretical avenue for the accurate analysis, modeling and design of graphene-based thermionic energy devices.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Generalized High-Energy Thermionic Electron Injection at Graphene Interface

et al. 2019

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“…However, recent analytical derivations have asserted that graphene sheets and other select materials such as 3D Dirac semimetals may exhibit a pre-factor temperature dependence of J ≈ T 3 . [122][123][124][125][126][127][128][129] Several researchers have proposed that this enhanced temperature dependence could prove advantageous if such materials were used as emitters in TECs. [122,126,128,129] However, we are aware of only a single dataset [130] that has been used to experimentally validate this enhanced temperature dependence, [122,124] and we are unaware of any TEC prototypes that have been created to demonstrate this concept.…”

Section: Suspended Graphene Cathodesmentioning

confidence: 99%

Progress Toward High Power Output in Thermionic Energy Converters

Campbell

Celenza

Schmitt³

et al. 2021

Advanced Science

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Thermionic energy converters are solid‐state heat engines that have the potential to produce electricity with efficiencies of over 30% and area‐specific power densities of 100 Wcm−2. Despite this prospect, no prototypes reported in the literature have achieved true efficiencies close to this target, and many of the most recent investigations report power densities on the order of mWcm−2 or less. These discrepancies stem in part from the low‐temperature (<1300 K) test conditions used to evaluate these devices, the large vacuum gap distances (25–100 µm) employed by these devices, and material challenges related to these devices' electrodes. This review will argue that, for feasible electrode work functions available today, efficient performance requires generating output power densities of >1 Wcm−2 and employing emitter temperatures of 1300 K or higher. With this result in mind, this review provides an overview of historical and current design architectures and comments on their capacity to realize the efficiency and power potential of thermionic energy converters. Also emphasized is the importance of using standardized efficiency metrics to report thermionic energy converter performance data.

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“…Based on thermionic emission processes, two kinds of devices, namely thermionic generators and thermionic coolers, have been proposed 3,20,21 . Thermionic generators show promising applications in harvesting thermal energy 22,23 . In addition, they have been used to convert solar energy to electricity 24 .…”

Section: Introductionmentioning

confidence: 99%

Thermionic enhanced heat transfer in electronic devices based on 3D Dirac materials

Huang

Lewis

Zhang

2019

Journal of Applied Physics

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We calculate the heat transfer from electronic devices based on three-dimensional Dirac materials without and with thermionic cooling. Without thermionic cooling, the internal temperature of the devices is at best equal to and usually higher than the temperature of the surrounding environment. However, when thermionic cooling is employed to transport heat, the internal temperature can be considerably lower than the environmental temperature. In the proposed thermionic cooling process, the energy efficiency can be as high as 75% of the Carnot efficiency.

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Parametric Optimum Design of a Graphene-Based Thermionic Energy Converter

Cited by 32 publications

References 29 publications

Generalized High-Energy Thermionic Electron Injection at Graphene Interface

Generalized High-Energy Thermionic Electron Injection at Graphene Interface

Progress Toward High Power Output in Thermionic Energy Converters

Thermionic enhanced heat transfer in electronic devices based on 3D Dirac materials

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