Graphene, being an atomically thin conducting sheet, is a candidate material for gate electrodes in vacuum electronic devices, as it may be traversed by low-energy electrons. The transparency of graphene to electrons with energies between 2 and 40 eV has been measured by using an optimized vacuum-triode setup. The measured graphene transparency equals ∼60% in most of this energy range. Based on these results, nano-patterned sheets of graphene or of related two-dimensional materials are proposed as gate electrodes for ambipolar vacuum devices.
Transparency of graphene for low-energy electrons measured in a vacuum-triode setup APL Materials 3, 076106 (2015) Mobile energy converters require, in addition to high conversion efficiency and low cost, a low mass. We propose to utilize thermoelectronic converters that use 2D-materials such as graphene for their gate electrodes. Deriving the ultimate limit for their specific energy output, we show that the positive energy output is likely close to the fundamental limit for any conversion of heat into electric power. These converters may be valuable as electric power sources of spacecraft, and with the addition of vacuum enclosures, for power generation in electric planes and cars.
Energy storage is particularly essential for renewable energy sources. Here we present the concept of high‐temperature latent‐heat storage coupled with thermoelectronic energy conversion. We analyze this concept and its potential for storing large quantities of energy for several days. We investigate the efficiency of electricity generation and storage by using a single thermoelectronic energy converter and a bottoming cycle with a steam turbine. For storage temperatures above 1400 °C and large amounts of stored energy (>100 MWh), the maximum energy conversion efficiencies of such systems are high. Thus the proposed systems are attractive storage solutions for excessive heat storage and heat‐on‐demand delivery of large‐scale thermal solar power plants.
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