Exploring promising KAH3 3 (A = Ca, Sr and Ba) hydrides for solid-state hydrogen storage and thermoelectric applications

The implementation of hydrogen energy as a renewable and ecologically friendly energy carrier has generated significant interest, however, efficient storage remains a formidable obstacle. In order to address the above, scientists switched their focus towards hydride materials, which provide a secure and effective way of storing hydrogen. In this work, we have investigated the structural, mechanical, thermodynamical, thermoelectric and hydrogen storage properties of potassium-based KAH3 3 (A = Ca, Sr and Ba) perovskite-type hydrides using density functional theory (DFT) computations. Structural stability of KAH3 3 hydrides has been assessed by formation enthalpy calculations, which ensure that all the studied hydrides are stable and synthesizable. The most optimal lattice parameters of KCaH3 3 KSrH3 3 and KBaH3 3 are found to be 4.47, 4.78 and 5.14 & Aring;, respectively. Additionally, we have determined the elastic stiffness constants, which confirm the elastic stability of KCaH3 3 hydrides as they fulfill the Born stability criteria. After a detailed study of electronic properties, it is found that KCaH3 3 hydrides possess semiconducting characteristics. Furthermore, we have studied the thermodynamical characteristics, which show that KAH3 3 (A = Ca, Sr, and Ba) hydrides obey Debye's specific heat law and the Dulong-Petit law at high temperatures, indicating their thermodynamical stability. In addition, the appropriateness of the understudy compounds for thermoelectric applications, various thermoelectric parameters such as Seebeck coefficient ( S ), electrical conductivity ( sigma /tau), tau ), electronic thermal conductivity ( kappa /tau) tau ) and thermoelectric power factor ( PF ) has been determined using BoltzTrap2 code and plotted as a function of chemical potential ( mu ). The thermoelectric properties indicate the suitability of KAH3 3 compounds for thermoelectric applications. The calculated values of gravemetric storage capacities of KCaH3, 3 , KSrH3 3 and KBaH3 3 hydrides are 3.68%, 2.33%, and 1.68% respectively. Additionally, the volumetric capacities of KCaH3 3 and KSrH3 3 compounds have achieved the target set by DOE for 2025. Furthermore, the computed desorption temperatures (Td) T d ) for KAH3, 3 , KSrH3 3 and KBaH3 3 are 399, 396 and 393 K, respectively. Interestingly, our computed Td d values of these hydrides are very close to the value (289-399 K) set by DOE for the year of 2025. In short, our findings suggest that the KAH3 3 (A = Ca, Sr, and Ba) hydrides have the potential to be used in hydrogen storage and thermoelectric devices.