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Environmentally sustainable electroplating of selective cobalt-chromium coating on stainless steel for efficient solar collectors
Umeå University, Faculty of Science and Technology, Department of Physics. Absolicon Solar Collector AB, Härnösand, Sweden.
Umeå University, Faculty of Science and Technology, Department of Physics.ORCID iD: 0000-0002-8438-2581
RISE Research Institutes of Sweden, Materials and Surface Design, Stockholm, Sweden.
Absolicon Solar Collector AB, Härnösand, Sweden.
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2022 (English)In: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 245, article id 111821Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Elsevier, 2022. Vol. 245, article id 111821
Keywords [en]
Cobalt-chromium coating, Deep eutectic solvent, Electroplating, Selective surface, Solar absorber, Trivalent chromium
National Category
Energy Engineering Subatomic Physics Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:umu:diva-197729DOI: 10.1016/j.solmat.2022.111821ISI: 000826692500002Scopus ID: 2-s2.0-85132515771OAI: oai:DiVA.org:umu-197729DiVA, id: diva2:1680388
Available from: 2022-07-04 Created: 2022-07-04 Last updated: 2025-04-25Bibliographically approved
In thesis
1. Heating a sustainable future: optical coatings for solar collectors
Open this publication in new window or tab >>Heating a sustainable future: optical coatings for solar collectors
2025 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Uppvärmning av en hållbar framtid : optiska beläggningar för solfångare
Abstract [en]

The green transition is the great undertaking of our time, and it will require significant ingenuity and change in all areas of society. Most urgently, perhaps, regarding energy, where the demand for transport, electricity and heat must be met by renewables instead of fossil fuels. Solar thermal is one alternative with the potential to contribute substantially to sustainable heat production. To realize this potential, the availability of competitive, sustainable and cost effective optical coatings for solar collectors is a prerequisite. The coatings used today are primarily produced with expensive vacuum-based deposition techniques, transferring a hampering cost to the collectors, which impede the deployment of solar thermal as an energy source. Herein, we show that by leveraging scalable deposition techniques, with elaborate material choices and innovative nanoscale designs, it is possible to produce sustainable coatings that are highly competitive with regards to cost and performance.Using a scalable aerosol-based deposition technique, an antireflective mesoporous silica coating, commonly implemented in advanced solar technologies, is produced with an ordered hexagonal pore structure. The attention to optical thickness and pore structure facilitates a superior performance and an increased durability, making it especially suitable for arid climates. Moreover, we present several methods to achieve solar selectivity for the receiver. We leverage the large potential window of a deep eutectic solvent to facilitate electrodeposition of a texture-based cobalt-chromium coating, making an otherwise unsustainable technique viable today. High selectivity is also achieved by manipulating interference effects in coatings produced through precise control of thermal annealing of steel and ultrasonic spray coating of carbon nanotube composites. Such optical effects are only achieved for selective coatings deposited with more advanced and expensive techniques.Science is an iterative process of small incremental advances, often seemingly insignificant in the moment, which over time accumulate to surprisingly quick change. Here we present examples of sustainable, scalable, durable and cost competitive antireflective and solar selective coatings, thereby hopefully contributing to an accelerated implementation of solar thermal technologies.

Place, publisher, year, edition, pages
Umeå: Umeå University, 2025. p. 64
Keywords
Solar thermal collectors, optical coatings, solar selective coatings, antireflective coatings
National Category
Nanotechnology for Energy Applications
Research subject
Physics; Materials Science; nanomaterials
Identifiers
urn:nbn:se:umu:diva-238174 (URN)978-91-8070-654-4 (ISBN)978-91-8070-655-1 (ISBN)
Public defence
2025-05-23, KB301-Lilla hörsalen, Linnaeus väg 6, 907 36 Umeå, Umeå, 09:00 (English)
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Supervisors
Note

In thesis listed paper "Solar selective carbon nanotube composite coatings on optically tunable undercoating" is in the printed thesis published with title "Towards Solar Selective Carbon Nanotube Composites on Optically Tunable Undercoatings". 

Available from: 2025-04-30 Created: 2025-04-25 Last updated: 2025-04-28Bibliographically approved

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Zäll, ErikNordenström, AndreasWågberg, Thomas

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