Switchable spin crossover material for passive control of temperature fluctuations in buildings Esther Resines-Urien 1 , Miguel Ángel García García-Tuñón 2 , Mar García-Hernández 3 , Jose Alberto Rodríguez-Velamazán 4 , Ana Espinosa *1 and Jose Sánchez Costa *1 1 IMDEA Nanociencia, C/ Faraday 9, Madrid 28049, Spain, Tel: 912998888. 2 Instituto de Cerámica y Vidrio, CSIC, C/Kelsen s/n, Madrid 28240, Spain. 3 Instituto de Ciencia de Materiales de Madrid, CSIC, C/Sor Juana Inés de la Cruz, 3, 28049, Madrid, Spain. 4 Institut Laue-Langevin, 71 avenue des Martyrs, BP 156, 38042, Grenoble Cedex 9, France. Nowadays, building thermalization is a widespread human necessity, accounting for 28% of energy-related carbon dioxide (CO2) worldwide emissions.1 These CO2 emissions are a major contributor to climate change, which has become one of the biggest concerns of humankind.2 Thus, the growing energy-saving and environmental protection demand have prompted the development and implementation of more energy efficient and environmentally friendly thermalization technology. In this regard, remarkable efforts have been focused on the implementation of passive thermal regulation systems, that can be incorporated directly into windows,3 roofs, or walls of buildings and operate without the need for electricity.4 Here, it is demonstrated that the heat generated by the sun is sufficient to produce a partial spin transition in an spin crossover (SCO) material. SCO materials exhibit a reversible transition, between the high spin and low spin electronic states through the application of external stimuli such as temperature.5 This SCO leads to a cooling effect with respect to other materials, due to an increase in light reflection resulting from the color change (from pink to white) and the energy absorption associated with the spin transition. In addition, when the material is cooled, a dampening of the temperature decrease is produced due to the energy release associated with the spin transition. Therefore, these materials can be used to reduce temperature fluctuations, and could potentially be implemented for passive temperature control in buildings. Interestingly, SCO molecule-based materials are remarkably stable upon cycling and highly versatile, allowing for the design of compounds adapting the intended properties (transition temperature and hysteresis) for the desired climatic conditions and comfort temperature.
References 1. International Energy Agency “The Critical Role of Buildings, Perspectives for the Clean Energy Transition – Analysis”, https:// www.iea.org/reports/the-critical-role of-buildings (accessed: November 2020). 2. Crowley, T. J.; Berner, R. A.; Science 2001, 292, 870-872. 3. Wang, S.; Zhou, Y.; Jiang, T.; Yang, R.; Tan, G.; Long, Y.; Nano Energy 2021, 89, 106440. 4. Granqvist, C. G.; Mater. 2003, 15, 1789-1803. 5. Vallone, S.P.; Tantillo, A.N.; dos Santos, A.M.; Molaison, J.J.; Kulmaczewski, R.; Chapoy, A.; Ahmadi, P.; Halcrow, M.A.; Sandeman, K.G.; Chem. Rev. 2017, 346, 176-205.
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