Verification of hydrothermal stability of adsorbent materials for thermal energy storage

This paper presents an experimental protocol for the cycling stability of adsorbent materials for thermal energy storage (TES) applications under hydrothermal conditions. Two different aging conditions were identified, namely, cycle and shelf test. The former one mimicking the cycling between desorption and adsorption conditions, while the latter one keeping a constant temperature for long time under constant water vapor pressure. A flexible experimental setup was then designed and realized to contemporarily perform both aging condition under selectable operating conditions. The protocol defines different characterization methods to compare the fresh and the aged samples. The measurement of the water vapor adsorption equilibrium isobars represents the main parameter to directly highlight possible degradation phenomena. Subsequently, X-ray diffraction patterns (XRD), nitrogen physisorption, and scanning electron microscopy coupled to energy dispersive x-ray (SEM-EDX), are used to evaluate structural, textural, morphological, and elemental composition variation that can help in identifying the causes of possible degradation. The proposed protocol was employed to validate the stability of a commercial adsorbent, AQSOA Z02, that proved a quite stable behavior both under cycle and shelf investigated conditions.