Simultaneous impregnation and microencapsulation of CaCl2 using silica gel and methyl cellulose for thermal energy storage applications

Thermal energy storage utilizing the adsorption of moisture from air is a promising energy storage technology due to its high energy density and minimum heat losses. Salt hydrates and salt hydrate composites, such as calcium chloride (CaCl2) and CaCl2-based composites, have shown favourable energy storage properties in this area of research. However, these materials have shown issues with stability due to swelling and deliquescence. In this work, CaCl2 was stabilized using three methods: impregnation into silica gel, encapsulation in methyl cellulose, and both impregnation and encapsulation stabilization techniques used simultaneously. Therefore, three CaCl2-based composites were synthesized. For the first composite, silica gel was impregnated with CaCl2. For the second composite, CaCl2 was encapsulated by methyl cellulose. For the third composite, silica gel was impregnated with CaCl2 and the CaCl2 was encapsulated with methyl cellulose. These samples were structurally characterized using scanning electron microscopy as well as Brunauer-Emmett-Teller (BET) to  determine surface area, pore size distribution and nitrogen adsorption isotherms at 77 K. Water vapour adsorption isotherms were also determined at 25 °C for different relative humidities by dynamic vapor sorption (DVS). Similarly, LiCl-based composites were also synthesized and examined in this work, but issues of deliquescence, swelling, and agglomeration made the materials impractical to work with. To determine the prepared materials' thermal energy storage performance, 2-6 g of each sample was tested in a lab-scale apparatus. This process uses the exothermic adsorption of moisture from ambient air in an open thermal energy storage system. The CaCl2 impregnated silica gel that was encapsulated in methyl cellulose showed reasonably high stability and energy storage performance after 3 hydration and dehydration cycles with minimum agglomeration. An energy storage density of 241 kWh/m3 (0.87 GJ/m3) and specific energy of 630 Wh/kg (2268 kJ/kg) was achieved with this material for 90% inlet relative humidity after a regeneration at 90 °C.

Triggered Nanoexplosions of Pd Hollow Spheres

Gas filled Pd nanocontainers can serve as model nanochambers for reaction and phase equilibria studies. In the current study, palladium hollow spheres (PdHS) filled with oxygen are brought in intimate contact with hydrogen filled PdHS at room temperature (with internal pressure in both the spheres at 20 bar). The molecular hydrogen gets chemisorbed in the Pd shell and further diffuses into the oxygen filled sphere. The rapid reaction of hydrogen with oxygen in the inner wall of the oxygen filled sphere leads to a nanoexplosion, with the formation of water. This explosion results in either the complete breakage of the nanoshell or the formation of connected shells via the rupture of the internal wall connecting the shells. Transmission electron microscopy and Raman spectroscopy have been used to establish the sequence of processes. Further, the water in the nanochambers is cooled below sub-zero temperature to crystallize ice. This phenomenon is observed for the first time at room temperature.