Photothermal emissivity of carbon nanotubes coatings for enhanced thermal waste management

• Photothermal properties of annealed CNTs arrays are numerically analyzed. • Higher annealing temperatures reduce CNTs photothermal activity. • Photo-thermionic effect was used to evaluate CNTs thermal stability. High-optical-absorbance coatings are key contributors to the conversion of photons into heat for industrial applications, particularly in thermophotovoltaic (TPV) systems. Carbon nanotubes (CNTs) remain a promising material for these applications due to their exceptional melting point, superior optical absorbance, and efficient thermal emittance properties. Here we present CNTs arrays subjected to an annealing process, evaluating both experimental samples and numerical models based on properties reported in the literature, to proposed as absorb/emitter coatings in a TPV system. The thermal stability of the experimental samples was evaluated using a photo-thermionic emission experiment, which revealed the direct impact of the annealing temperature on their stability. The photothermal transient characteristics were analyzed considering a laser beam to simulate irradiances levels comparable to the solar radiation. The heat equation was employed to predict the behavior of the induced effects associated with optical energy transference. The optical properties of the coatings were analyzed considering differences in the dimensionality of the nanostructures to determine the thermal emittance spectrum. Based on the results of the CNTs coating, we propose a TPV cell designed to hardness thermal radiation and generate electrical power. Under ideal conditions, the proposed TPV system demonstrates efficiency ranging from 7 % to 11 %, at temperatures from 700 K to 1500 K, respectively. The enhanced CNTs coatings were shown to significantly improve photothermal activity and offer a means to manage thermal waste for applications in different industry sectors.