Functionalization of nanocomposites for alternative energy
According to the scientific report at the meeting of the Presidium of the NAS of Ukraine, March 31, 2021
DOI:
https://doi.org/10.15407/visn2021.05.054Keywords:
concentrated solar energy, low-temperature thermionic converters, metal–nanostructured carbon compositesAbstract
The electrical conductive properties of the titanium (Ti) powder - multi-walled carbon nanotubes (MWCNTs) system in the processes of appearance electrical contacts between its components under compression deformations are studied. There is the formation of composites, which is accompanied by an increase in the electrical conductivity of the material more than 5 times compared to the original components when the concentration of MWCNTs approaches 15 wt. %. This effect is due to the transfer of electrons from metal particles to MWCNTs. It is shown that the use of metal–carbon nanostructure composites opens the way to the creation of ‘cold’ cathodes for thermionic energy converters (TECs) that can operate from low-temperature energy sources. The Ti–thermoexpanded graphite (TEG) composite cathode under the irradiation of TEC with concentrated sunlight allowed for the first time to observe voltage and direct current at temperatures of 170–350°C. These values are up to 9 times lower than the operating temperatures of traditional TECs made of refractory metals. Furthermore, the current was observed in a closed electrical circuit without the application of additional external potential difference. Changes in the composite sample surface morphology under the action of concentrated solar radiation at the stage of preliminary annealing of samples at temperatures above 270–310°C play a significant role. During annealing on the metal particles surface of the composite, the carbon nanostructures (from TEG component) are formed in the form of separately located cylindrical outgrowths with a diameter of 20–80 nm, which can provide a significant increase in the contribution from autoelectron emission based on temperature-independent tunneling mechanism. The established mechanisms of current and voltage generation in TECs with composite cathodes allowed formulating the physical principles of ‘cold’ electrodes construction for direct emission converters of concentrated solar energy into electricity.
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