Back-gated graphene anode for more efficient thermionic energy converters

Yuan, Hongyuan; Riley, Daniel C.; Shen, Zhi‐Xun; Pianetta, P.; Melosh, Nicholas A.; Howe, Roger T.

doi:10.1016/j.nanoen.2016.12.027

Cited by 61 publications

(37 citation statements)

References 21 publications

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“…Collection of these emitted electrons at the anode forms an electricity through an external load, thus achieving thermionic-based heatto-electricity conversion. Recent experiment has demonstrated graphene monolayer as a highly efficient anode for direct heat-to-electricity energy conversion with high conversion efficiency reaching 9.8%, which can be further optimized by electrostatic gating and cathode-anode gap reduction [1]. Thermionic emission of electrons over an insulating barrier can also be harnessed to achieve electronic cooling effect [3][4][5][6].…”

Section: Introductionmentioning

confidence: 99%

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: Introductionmentioning

confidence: 99%

Generalized High-Energy Thermionic Electron Injection at Graphene Interface

et al. 2019

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“…Yuan et al 48 studied TEC using a barium dispenser cathode as an emitter and a back-gated graphene as a collector (anode) with a 20-nm-thick HfO dielectric layer as the gate. They were able to observe TEC of 9.8% at a cathode temperature of 1000°C.…”

Section: Back-gated Graphene Thermionic Energy Conversionmentioning

confidence: 99%

Theoretical studies of thermionic conversion of solar energy with graphene as emitter and collector

Olawole

2018

J. Photon. Energy

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, "Theoretical studies of thermionic conversion of solar energy with graphene as emitter and collector," J. Photon. Energy 8(1), 018001 (2018), doi: 10.1117/1.JPE.8.018001. Abstract. Thermionic energy conversion (TEC) using nanomaterials is an emerging field of research. It is known that graphene can withstand temperatures as high as 4600 K in vacuum, and it has been shown that its work function can be engineered from a high value (for monolayer/ bilayer) of 4.6 eV to as low as 0.7 eV. Such attractive electronic properties (e.g., good electrical conductivity and high dielectric constant) make engineered graphene a good candidate as an emitter and collector in a thermionic energy converter for harnessing solar energy efficiently. We have used a modified Richardson-Dushman equation and have adopted a model where the collector temperature could be controlled through heat extraction in a calculated amount and a magnet can be attached on the back surface of the collector for future control of the spacecharge effect. Our work shows that the efficiency of solar energy conversion also depends on power density falling on the emitter surface, and that a power conversion efficiency of graphenebased solar TEC as high as 55% can be easily achieved (in the absence of the space-charge effect) through proper choice of work functions, collector temperature, and emissivity of emitter surfaces. Such solar energy conversion would reduce our dependence on silicon solar panels and offers great potential for future renewable energy utilization. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

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“…The latter quantities are primarily controlled by temperature and work functions of emitter and collector T T W and W , , , e c e c the emitter collector configuration (i.e., the space between them), and arrangements that control space charge. Recently Yuan et al (2017) discussed new method of controlling space charge using magnetic field and gate voltage [34]. To model a TEC, specially, with graphene as an emitter, it is very important to obtain the accurate model of temperature dependence of W W I and I , , .…”

Section: Introductionmentioning

confidence: 99%

“…In a TEC [31][32][33][34] with the work function of the emitter, > W W e c of the anode (collector) and when the emitter and collector is connected through a load, the output power is = -…”

Section: Introductionmentioning

confidence: 99%

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A three-dimensional model for thermionic emission from graphene and carbon nanotube

De¹,

Olawole²

2019

J. Phys. Commun.

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Graphene and carbon nanotube (CNT) have been proposed to be good materials for thermionic energy converter (TEC). For accurate simulation of performance of TEC, it is important to know the correct equation for temperature dependence of thermionic emission current density (J) from graphene and carbon nanotube. In this paper we first consider the existing theory of electron energy dispersion relation in graphene to reconsider the relations between Fermi energy and Fermi velocity in relation to some form of electron mass in graphene. We then consider existing various models of temperature dependence of J versus T (J(T)) and their applicability to nano-materials. We find that no model exists to date that fully conforms to the available experimental data on J(T) of nano materials. By providing justifications for three components of electron momentum vector during thermionic emission from graphene, we then find a three-dimensional model that fits the experimental thermionic emission data from graphene and carbon nanotube far better than any existing model. We present a detailed comparison of our model with existing models of thermionic emission. The work function determined using our model also agrees very well with independent experimental results. This model is expected to be very effective in modelling TEC with graphene or CNT.

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Back-gated graphene anode for more efficient thermionic energy converters

Cited by 61 publications

References 21 publications

Generalized High-Energy Thermionic Electron Injection at Graphene Interface

Generalized High-Energy Thermionic Electron Injection at Graphene Interface

Theoretical studies of thermionic conversion of solar energy with graphene as emitter and collector

A three-dimensional model for thermionic emission from graphene and carbon nanotube

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