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  • Low-temperature heat storage in porous materials : structure-property relationship
    Zabukovec Logar, Nataša
    Large-scale utilization of solar thermal energy for heating and cooling applications, which represent almost half of the final energy demand in developed countries, depends on effective heat storage ... systems. A new and very promising concept of heat storage consists of systems that utilize reversible physicochemical sorption phenomena (mostly water adsorption on solid sorbents) to store energy. Under the influence of a heat supply, water is desorbed from the material, and is then stored separately (an endothermic phenomenon referred to as the charging or activation of material). When water and sorbent are put into contact, there is a heat release (an exothermic phenomenon referred to as a material's discharge or deactivation). Energy can therefore be stored with negligible thermal loss, as long as the water and sorbent are kept separately. Despite the great importance of heat storage in enabling a low-carbon society, there have been no systematic studies of the possible mechanisms for heat storage enhancement concerning materials optimization. The crucial questions that remain to be answered are whether and how we can further increase the materials storage performance by controlling their structural features to a higher degree. In this contribution, a study of the structure/sorption-behavior relationship of three microporous aluminophosphate structures with the aim of improving the design of storage materials is highlighted. The performance of the three materials in heat storage applications is first determined by a comparative thermogravimetric and calorimetric study of the materials (SAPO-34, AlPO4-18 and APO-Tric all with pore window diameters of 0.38 nm) and is later correlated with their structural features. The maximum water sorption capacityis similar for all three samples and reaches a water uptake of 381 g/kg and an energy density of 240 kWh/m3 (in a temperature range from 40 to 140 °C). The elemental composition influences the gradual (silicoaluminophosphate SAPO-34) or sudden (aluminophosphates AlPO4-18 and APO-Tric) water uptake. The latter is favourable in storage systems and is more pronounced in APO-Tric. Close examination of the crystal structures of hydrated AlPO4-18 and APO-Tric reveals that the driving force for the determined water sorption process is the formation of highly ordered water clusters in the pores, which is enabled by rapid and reversible changes in theAl coordination and optimal pore diameters. The ease with which changes in the Al coordination can occur in APO-Tric is related to the use of the fluoride route in the synthesis. The understanding of these fundamental structure/sorption relationships forms an excellent basis for predicting the storage potential of numerous known or new microporous aluminophosphates and other porous materials from their crystal structures.
    Vir: Book of abstracts (Str. 46)
    Vrsta gradiva - prispevek na konferenci
    Leto - 2012
    Jezik - angleški
    COBISS.SI-ID - 5116442

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