Enhancement effects of hydrolysable/soluble Al-type dopants on the efficiency of CaO/CaCO3 thermochemical energy storage

Modification of CaO-based materials using Al -type dopants has been considered a promising method to enhance energy storage performance. The synergistic multi -doping effects of different Al -type dopants (soluble, hydrolysable and insoluble) on the energy storage performances, thermophysical and mechanical properties of CaObased materials have never been reported. The hydrolysable/soluble Al -type supports co -doped CaO-based pellets were prepared, which exhibited superior energy storage density, multi -cycle stability, reaction rate, thermal conductivity and crushing strength compared to undoped CaO pellets. The regulation mechanisms of hydrolysable/soluble Al -type dopants (AlN/Al(NO 3 ) 3 ) on the reaction kinetics, multi -cycle stability, thermophysical properties and mechanical properties of CaO-based pellets were revealed. The addition of different Altype dopants results in different dispersions of the formed Ca 12 Al 14 O 33 , which leads to different micromorphologies and pore structures of CaO-based pellets. Hydrolysable Al -type dopants exhibit a more concentrated distribution in CaO-based pellets and the pellets have smaller crystallite sizes of CaO and predominantly microporous pores, which results in the high CO 2 reactivity. Soluble Al -type dopants exhibit a more uniform dispersion in CaO-based pellets and the pellets have larger crystallite sizes of CaO and obvious pore channels, which results in the improved cyclic stability and decomposition kinetics. The optimized CaO-based pellets combine the advantages of the two Al -type dopants and present an increasing trend of energy storage density during the cyclic process. Its energy storage density remains 1571 kJ/kg after 50 cycles, and the value for CaO is only 569 kJ/kg. In addition, the optimal synthesized material has excellent thermal conductivity and crushing strength, which are 1.36 and 9.75 times those of CaO, respectively.