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    Environmentally sustainable electroplating of selective cobalt-chromium coating on stainless steel for efficient solar collectors

    Year: 2022

    Journal: Sol. Energy Mater. Sol. Cells, Volume 245, SEP 15

    Authors: Zall, Erik; Nordenstrom, Andreas; Jarn, Mikael; Mossegard, Jonatan; Wagberg, Thomas

    Organizations: Absolicon Solar Collector AB

    Keywords: Electroplating; Selective surface; Solar absorber; Trivalent chromium; Deep eutectic solvent; Cobalt-chromium coating

    Half of today's global energy consumption is in the form of heating and cooling. Solar collectors are the most promising sustainable alternative to fossil fuels in this sector. The most important component in a solar collector is the receiver, which by use of a selective surface absorbs and converts solar irradiance to thermal energy. Herein, a novel selective surface for low-to mid-temperature solar collectors is developed, studied and presented. The surface is produced by electroplating a cobalt-chromium coating on a stainless steel substrate using an electrolyte based on a deep eutectic solvent. Our method makes use of trivalent instead of traditionally used hexavalent chromium, which significantly reduces health-related issues and makes it more environmentally benign. We obtain a coating of chromium doped cobalt where the surface exhibits an absorptance and emittance of 0.96 and 0.14, respectively, giving it a solar-to-thermal efficiency of 0.95. An observed loss in optical efficiency, is shown to correlate to an oxidation of the metallic cobalt to Co3O4 at elevated temperatures. We further show that this oxidation can be mitigated by dip-coating a protective silica top coating, which concurrently improves the optical selectivity of the surface. The present selective surface is efficient, cheap, scalable, and easy to produce sustainably, making it competitive to industry standards. We foresee that our method will have impact on the advancement of improved low-to mid-temperature solar collectors, assisting a faster transition towards a sustainable society.
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