Recent path to ultrafine Mg/MgH2 synthesis for sustainable hydrogen storage

Scientific efforts in search of renewable energy to replace fossil fuels have increased over the last few decades. Exploring natural energy sources such as the sun and the wind offers viable alternatives for energy production other than burning carbon-based fuels. Although these natural energy sources are seasonally regulated, hydrogen provides a huge platform for storing these energies to ensure their continued application; hence, the implementation of a hydrogen economy consisting of hydrogen production, storage, and conversion, in which hydrogen storage plays a vital role. One of its promising playgrounds is solid-state hydrogen storage in magnesium hydride (MgH2), which offers the benefit of hydrogen reversibility with a high capacity of 7.6 wt%. However, it operates at temperatures above 350 °C, unsuitable for storing hydrogen for fuel cells operating near ambient temperatures. Among several methods used to disrupt the thermodynamic and kinetic stability of the hydride to ensure its operability under ambient conditions, nanostructuring offers a broad approach with great benefits. In this review, the recent advances in Mg/MgH2 nanoengineering that cut across nanoconfinement using scaffolds, nanoconfinement with in-situ catalysis, and non-confinement via chemical reduction of Mg/Mg-salts are summarized. The hydrogen storage implications of these emerging techniques are also correlated to unravel the challenges and provide insights for future developments.