Thermally treated pristine and BaTiO3 coated stainless steel as an efficient spectrally selective absorber for photothermal application

Abstract

Spectrally selective absorbers advance rapidly, yet achieving lower emittance at higher temperatures is still a challenge. The present study examined the absorptance and emittance performance of thermally treated stainless steel (Annealed/SS) and stainless steel coated with barium titanate oxide (BTO/SS) as efficient solar selective absorbers and their robustness. The absorptance values for Annealed/SS and BTO/SS in the UV–Vis range (0.2 to 0.8 µm) are 90 and 88 %, respectively, whereas the emittance values in the infrared range (2.5 to 25 µm) are 3 % and 9 %. The solar selective coating maintains its absorptance of ∼ 88 - 90 % and emittance of 2 - 9 % for BTO/SS and annealed/SS for 60 h after annealing at 500 °C. In addition, at a scan rate of 50 mV/s, the corrosion measurement indicates that the pristine SS substrate has a greater rate of corrosion (0.097 mm/yr) compared to BTO/SS (∼0.057 mm/yr) and Annealed/SS (∼0.0001 mm/yr) suggesting the long span stability of Annealed/SS in a harsh environment, as also evident from the electrochemical impedance spectroscopy (EIS) measurements. The annealed stainless steel (SS) exhibits higher charge transfer resistance (1000 k$\Omega$) compared to BTO/SS and bare SS. Thus, the thermally annealed SS can be used an efficient solar selective absorber with enhanced durability, thermal stability, and corrosion resistance. It, in turn, allows to realize the spectrally selective absorber coatings without any additional processing, offering a low-cost, scalable alternative to traditional methods for creating solar selective coatings on a large scale.