Tandem selective solar absorbers based on carbon nanotubes/Pt/Si

TOQUER, GUILLAUME; COMEDI, DAVID; ALASTUEY, PATRICIO; TIRADO, MONICA

Parque Tecnológico Miguelete, Buenos Aires

Encuentro; XIX Encuentro de Superficies y Materiales Nanoestructurados: NANO 2019; 2019

Centro Atómico Constituyentes

Solar thermal energy presents the most obvious technology used to harness solar energy for domestic applications such as water heating. The basic principle of solar thermal conversion is transform from solar energy into caloric energy by heating a transfer fluid through an absorber. To minimize optical losses, selective absorbers are required to have a high absorptivity over the spectral range of solar emission (0.5-2 µm) and a low emittance in the mid and far infrared spectral region (2-20µm) [1-3].This work investigates the application of carbon nanotubes (CNT) as selective solar absorbers (SSA) by using the technique of anodic electrophoretic deposition (EPD). The CNT?s were stabilized by ultrasound in a solution of Pyrocatechol Violet (99% Sigma Aldrich) in water (mQ) for two hours. Zeta potentials up to -36 mV were measured using a Malvern zeta sizer nanoseries (ZS90) equipment. The EPD process was made using a Solartrón Modulab and the substrate used was a Sillicon wafer coated with 100nm of Pt. The obtained samples were spectrally characterized by UV-Vis-NIR spectroscopy and Fourier Transform Spectroscopy obtaining values of efficiency of 0.90 for the SWCNT. SEM micrographs were taken in order to have a measurement of the thickness (cross-section) and morphology (top view). Using multi-walled CNT (MWCNT) it is easy to have a good absorbance (~0.95) but the efficiency is not so high (~0.8) due to the emissivity [3-6]. So in order to be more selective, we used semiconductive single walled CNT (SWCNT) (99% Sigma Aldrich) with an optical band-gap of ~0.5 eV, and we measured values of solar absorptance of 0.92 and thermal emittance of 0.04 for a working temperature of 100°C wich is almost the exact same value that Chen et al. predicted in 2014 by simulating using the software Setfos 3.4 from FLUXiM [7] under similar conditions.References:[1] Shehayeb et al., Surface and coating technology 322 (2017) 38-45.[2] F. Cao et al., Energ. Environ. Sci. 7 (2014) 1615-1627.[3] W.F. Bogaerts, C.M. Lampert, J. Mater. Sci. 18 (1983) 2847-2875.[4] Fraczek-Szczypta et al., Journal of Molecular Structure 1040 (2013) 238-245.[5] Chen et al., Proceedings of the EuroSun 2014 Conference 1 (2014) 16-19.[6] Chen and Boström et al., Solar Energy Materials and Solar Cells 144 (2012) 678-683.[7] Chen et al., Solar Energy Procedia 58 (2014) 179-184.