Formation of Magnesium and Nickel Coatings on Al2O3 Granules by Plasma Spraying and Investigation of Their Hydrogenation Properties

Hydrogen storage remains a key challenge in the transition toward sustainable energy systems, particularly for applications requiring high energy density and safe operation. Among various solid-state storage materials, magnesium hydride (MgH2) is considered highly promising due to its high hydrogen capacity, low cost, and good reversibility; however, its practical application is hindered by slow kinetics and high thermodynamic stability. In this study, Mg and Ni coatings were deposited on Al2O3 based substrates using a direct current plasma spraying technique to develop a composite system for enhanced hydrogen storage performance. The influence of plasma torch parameters on coating characteristics was investigated, and the hydrogenation behavior was analyzed under controlled conditions (350 °C & 200 °C, 5 atm H2). The structural, morphological, and compositional evolution of the coatings before and after hydrogenation was examined using SEM, EDS, XRD, and FTIR techniques. Results demonstrate that plasma-sprayed Mg coatings undergo significant morphological transformation after hydrogenation, including surface cracking, increased porosity, and phase conversion to MgH2, confirming effective hydrogen uptake. In contrast, Ni coatings exhibit limited hydride formation but play a catalytic role by facilitating hydrogen dissociation and improving surface reactions. The influence of plasma power on coating quality and hydrogenation efficiency was also identified, with higher power leading to improved coating uniformity and enhanced MgH2 formation. Additionally, a reaction–diffusion model was developed to evaluate the effect of temperature and hydrogen pressure on hydride layer growth. The model predicts an optimal temperature range (~300–330 °C) for MgH2 formation, beyond which thermodynamic instability limits hydride stability. Overall, the study demonstrates that plasma-sprayed Mg/Ni coatings on granular substrates represent a promising approach for developing efficient hydrogen storage systems, combining improved kinetics, structural stability, and scalable processing.