Tuning Stability of AB 3 -Type Alloys by Suppressing Magnetism

High Resolution Image Download MS PowerPoint Slide Hydrogen is a promising clean energy carrier, yet effective and reversible storage remains a major challenge. AB 3 -type intermetallic alloys have emerged as promising candidates for solid-state hydrogen storage owing to their intermediate thermodynamic stability and rapid hydrogen uptake. However, optimizing both stability and gravimetric density has been hindered by competing thermodynamic and magnetic effects. Here, we present a systematic analysis of AB 3 compounds (A = Ca, Y, Mg; B = Co, Ni) and their ternary alloys Ca x Y y Mg 1– x – y B 3 (B = Co, Ni), combining first-principles calculations with Monte Carlo simulations. Strikingly, we uncover a direct correlation between formation energy and total magnetic moment that dictates alloy stability, thereby explaining the observed trade-off in hydrogen storage optimization. In Co-based systems with large lattice volumes, such as Ca-rich and Y-rich compositions, formation energy increases monotonically with magnetization, exhibiting a near one-to-one correlation and establishing magnetism as the dominant factor governing alloy stability. While Mg-rich compositions achieve high gravimetric densities, strong magnetism destabilizes the system, necessitating Y substitution to suppress magnetic moments and stabilize a low-spin state–thereby limiting optimization when heavy Y is introduced. In contrast, replacing Co with Ni dramatically weakens the magnetism: YNi 3 is nonmagnetic, while CaNi 3 and MgNi 3 display only weak spin polarization, enabling thermodynamic stability across the entire compositional range. Notably, the experimentally known CaMg 2 Ni 9 combines high theoretical capacity (∼3.32 wt %) with good reversibility, and our calculations further identify the Mg-rich Ni-based region as an unexplored compositional domain that couples negative formation energies with the highest gravimetric densities (up to ∼3.40 wt %). These findings establish magnetism as a fundamental thermodynamic variable controlling alloy stability and reveal magnetic suppression via transition-metal substitution as the key to overcoming the stability–capacity trade-off in AB 3 -type hydrogen storage materials.