Rapid Synthesis of\nNanoporous Zn Powder by Selective\nEtching of Al from Micrometer-Sized Zn–Al Powder Particles\nProduced by Gas Atomization and Its Application in Hydrogen Generation

The scalable synthesis of non-precious nanoporous metals,\nsuch\nas nanoporous zinc (NP-Zn), nanoporous iron (NP-Fe), and nanoporous\naluminum (NP-Al), is crucial for large-scale production of hydrogen\nthrough the reaction between non-precious metals and water. The fabrication\nof bulk NP-Zn by selective removal of Al from sub-centimeter-sized\narc-melted Zn–Al parent alloys through free corrosion dealloying\nusually takes a few days. Here, we demonstrate that this free corrosion\ndealloying process can be reduced from a few days to 4 min simply\nusing micrometer-sized Zn–Al powder particles with nominal\ncomposition Zn<sub>40</sub>Al<sub>60</sub> atomic % produced by gas\natomization as the parent alloy. Reducing the size of the parent alloy\nsignificantly enhances the dealloying rate. Furthermore, Al and Zn\nare phase-separated in Zn–Al powder particles due to the gas\natomization process, making removing the sacrificial Al phase easy.\nWe used various techniques, including X-ray diffraction, Xe<sup>+</sup> plasma focused ion beam/scanning electron microscopy (FIB/SEM),\nenergy-dispersive spectroscopy (EDS), and inductively coupled plasma\noptical emission spectroscopy (ICP–OES) to thoroughly characterize\nthese materials before and after free corrosion dealloying. The fabricated\nNP-Zn powder exhibits a hierarchical ligament/pore morphology, with\ntiny structures with a size of ≈10 nm coming from Zn nanoparticle\naggregation during dealloying and large structures in the range of\n≈50–200 nm coming from the removal of the sacrificial\nAl phase. We demonstrate that this NP-Zn can spontaneously react with\nwater at near-neutral pH to produce hydrogen and zinc oxide solid\nbyproducts with a hydrogen generation yield of ≈52% within\n60 min.