Self-foaming Fe–Sn powder beds for durable hydrogen storage and release

Hydrogen storage and release via redox cycling of oxide-metal powders offers advantages in safety and scalability as compared to pressurized tanks, but long-term storage capacity loss due to sintering and densification of powder beds remains a major challenge. In this work, we demonstrate that a transient liquid-phase swelling effect, triggered by the addition of a low-melting element to a high-melting powder bed, can effectively preserve powder-bed porosity and reactive surface area during extended redox cycling. By incorporating up to 40 at. % Sn into Fe powder beds, we induce a self-foaming behavior that counteracts powder densification and enables stable hydrogen storage/release performance over 50 redox cycles at 650 ºC. In situ X-ray diffraction and thermodynamic analysis reveal that both the added Sn and the resulting Fe-Sn intermetallic phase undergo reversible transformations throughout cycling, helping maintain high hydrogen storage/release capacity. Microstructural analysis shows that the continuous formation of “liquid-depletion porosity” at former Sn powder sites and the volumetric expansion of solid particles from imbalanced diffusion contribute to the retention of a porous architecture. This strategy achieves a hydrogen capacity of up to 261 mL/g, which is 22 times higher than that of pure Fe after 50 redox cycles. It provides a new materials design approach for durable metal/oxide systems in hydrogen storage, with other potential applications in solar thermochemical water splitting, carbon dioxide utilization,and chemical looping technologies.