Electrodeposited black cobalt selective coatings for application in solar thermal collectors: Fabrication, characterization, and stability.

• Selective black cobalt coatings (BC) are viable for solar thermal collectors. • Electrodeposition is a robust and scalable BC fabrication method. • BC films on Pt are stable to 750 °C; on stainless steel – nickel to 300 °C. • The BC selective film is hydrophobic and stable under weathering. • The BC coating has been demonstrated in solar thermal collectors. We report on the electrodeposition of nickel/black cobalt selective coatings, and evaluate the performance stability as a function of the substrate material, the temperature of heat treatments, and under accelerated weathering conditions. The black cobalt absorber material is shown to be stable up to 750 °C, and the performance stability for a stainless steel substrate with a nickel/black cobalt selective coating after 200 h at 300 °C is demonstrated, with a solar absorptance of 95% and thermal emittance of 7% (at 100 °C). The galvanostatic electrodeposition process has been scaled up to collector size, and is demonstrated both for a flat plate and a tubular substrate. A copper flat plate of 193 cm × 12 cm connected to a riser tube was coated, and a single-fin solar thermal collector was evaluated under realistic outdoor conditions. The collector produced essentially the same amount of heat as an identical reference collector with a commercial TiNOX selective coating. In addition, the coating was applied to a copper tube for a 3 m parabolic trough collector. The selective coating is hydrophobic and withstands an accelerated weathering test, illustrating the viability of black cobalt electrodeposition for the fabrication of solar collectors for low and high temperature applications. [ABSTRACT FROM AUTHOR]