Effects of Compact Integrity and Microstructural Coarsening on Hydrogen Evolution in an Al–Zn Alloy

The use of compacted machining chips as feedstock for hydrogen production offers a promising route for both metallic waste valorization and sustainable energy generation. Although microstructural refinement is known to enhance hydrogen evolution in Al‐based alloys, its influence on the behavior of compacted metallic waste remains unclear. In this work, hydrogen evolution from compacted chips produced from a rapidly solidified Al–10 wt.% Zn alloy with a dendritic spacing of 17 μm was investigated in 5 mol L ⁻¹ NaOH at 25 and 45 °C. The results were analyzed in the context of previously reported data for coarser microstructures (39.7 and 215 μm). The refined bulk alloy exhibited enhanced hydrogen evolution at 25 °C due to the higher density of Zn‐rich microgalvanic sites, whereas temperature became the dominant kinetic parameter at 45 °C. In contrast, the compacted chips displayed behavior strongly influenced by electrolyte penetration and compact integrity. Despite its intrinsically higher reactivity, the compact produced from the finest microstructure exhibited a more linear response and lower hydrogen production than expected, indicating restricted electrolyte access within the compact structure. At 45 °C, hydrogen generation increased substantially, although the compact remained structurally stable throughout the reaction. These findings demonstrate that, in compacted Al–Zn waste, hydrogen evolution is governed not only by microstructural refinement but also by the physical characteristics of the compact, highlighting compact integrity as a critical design parameter for recycling‐based hydrogen production routes.