Surfactant-enabled strategy for molecular solar thermal energy storage systems in water

Molecular solar thermal energy storage (MOST) systems, which absorb sunlight, store this energy in chemical bonds, and release it as heat, are receiving increasing attention in renewable energy storage applications. Among the norbornadiene/quadricyclane (NBD/QC) couples developed for MOST, the 2,3-difunctionalized cyano- and p-aryl-substituted NBD/QC couples have received greater attention for their promising properties. However, their application in solution requires the use of hazardous solvents, which limits their potential for large-scale implementation. Here, new greener systems consisting of cyano- and p-alkoxyphenyl-substituted NBD/QC derivatives dissolved in non-ionic surfactants and water were investigated. Concentrations of NBD up to 1.6 M were achieved by tuning the water/surfactant ratio, meeting the solubilization properties of organic solvents. The most promising system was further characterized, and its properties in water-based solutions were compared with those observed in toluene. Integration into a solar energy-harvesting liquid device led to the full conversion of the NBD to QC. The evaluation of the heat release performance upon catalytic trigger resulted in a temperature increase of 4.7 °C in ambient conditions. This demonstrates that promising NBDs/QCs can be used for MOST in aqueous media without compromising key performance parameters such as energy density, photoconversion, and catalyzed heat release.

• Lorette Fernandez¹
• Helen Hölzel^1,2
• Pedro Ferreira¹
• Nicolò Baggi¹
• Kévin Moreno¹
• Zhihang Wang^3,4
• Kasper Moth-Poulsen^1,5,6,7

•   ¹Department of Chemical Engineering, Universitat Politècnica de Catalunya, EEBE, Eduard Maristany 10-14, 08019 Barcelona, Spain
• ²Institute of Organic Chemistry, Justus-Liebig-University Giessen, Heinrich-Buff-Ring 17, 35392 Giessen, Germany
• ³School of Engineering, College of Science and Engineering, University of Derby, Markeaton Street, Derby DE22 3AW, UK
• ⁴Department of Materials Science and Metallurgy, University of Cambridge, Cambridge, UK
• ⁵Department of Chemistry and Chemical Engineering, Chalmers University of Technology, 41296 Gothenburg, Sweden
• ⁶The Institute of Materials Science of Barcelona, ICMAB-CSIC, Bellaterra, 08193 Barcelona, Spain
• ⁷Catalan Institution for Research & Advanced Studies, ICREA, Pg. Lluìs Companys 23, 08010 Barcelona, Spain

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