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

[Display omitted] •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.