| Abstract Scope |
Thermochemical hydrogen storage using the H2-H2O redox cycle of iron offers a safe, compact, and low-cost alternative to hydrogen compression or liquefaction. However, Fe-based hydrogen storage has been hindered by rapid sintering of iron powder beds during high-temperature-cycling, causing irreversible capacity loss. Here, we demonstrate that adding redox-active tungsten overcomes this decades-old limitation. In a custom automated reactor, a kilogram-scale Fe-W powder bed reversibly stores 43.8 g of H2 and sustains 93±3% capacity utilization over 30 redox cycles. Using temperature-resolved in-situ X-ray diffraction, we uncover a dual sintering-inhibition mechanism: a chemical-vapor-transport-mediated self-foaming process that dynamically refines the microstructure and generates nano-porosity during cycling, complemented by static contact barriers that prevent particle coarsening during high-temperature holds. This sintering resistance persists even under partial-capacity cycling, a practical operational mode. By integrating intrinsic safety, high volumetric energy density, and robust cycle life, Fe-W powder beds establish a scalable platform for stationary hydrogen storage. |