Investigation of Mg2XH6 (X = Cu, Zn, Cd) hydrides for practical hydrogen storage applications with moderate desorption temperature and high capacity: DFT perspectives

초록

Hydrogen is a clean energy carrier in the modern energy landscape as it provides high gravimetric energy density and is eco-friendly. However, the development of safe and efficient hydrogen storage materials is one of the great technical challenges. This work studies the vacancy-ordered Mg2XH6 (X = Cd, Cu, Zn) perovskites within the density functional theory framework, employing the WIEN2k code. Structural stability, electronic structure, mechanical behavior, thermodynamics, and hydrogen storage properties are analyzed to understand their capability as solid-state storage materials. The predicted structural configurations are optimized, and formation energies are evaluated, which verify the stability of the hydrides. The various mechanical properties, such as elastic constants, elastic moduli, Pugh's ratio, anisotropy, and hardness of the hydrides Mg2XH6 (X = Cu, Zn, Cd), were evaluated to assess the stability, brittleness, and toughness of the materials. The examination of rates of elastic waves, Debye temperature, and melting temperature is also the prediction of thermodynamic behavior. The electronic band structure shows that Mg2CuH6 and Mg2CdH6 have a metallic nature, while Mg2ZnH6 is found to have a semiconductor nature with a direct band gap of 0.46eV. In contrast to semiconductor Mg2ZnH6, metallic Mg2CuH6 and Mg2CdH6 may provide enhanced charge separation, which makes them more suitable for hydrogen release applications. Finally, we investigate the hydrogen storage characteristics. This is to assess the hydrogen storage capacities and release temperature. The storage capacities have been observed to be 5.12, 5.04, and 3.62wt.% for Mg2CuH6, Mg2ZnH6, and Mg2CdH6, respectively. The obtained desorption temperatures of 376.51, 334.65, and 307.59K suggest that the hydrogen desorption temperature is closely matched to the optimal range. As such, this study can significantly advance hydrogen storage technology and prompt researchers to carry out probable experimental validation.

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