Rapid Synthesis of Nanoporous Zn Powder by Selective Etching of Al from Micrometer-Sized Zn-Al Powder Particles...

The scalable synthesis of non-precious nanoporous metals, such as nanoporous zinc (NP-Zn), nanoporous iron (NP-Fe), and nanoporous aluminum (NP-Al), is crucial for large-scale production of hydrogen through the reaction between non-precious metals and water. The fabrication of bulk NP-Zn by selective removal of Al from sub-centimeter-sized arc-melted Zn-Al parent alloys through free corrosion dealloying usually takes a few days. Here, we demonstrate that this free corrosion dealloying process can be reduced from a few days to 4 min simply using micrometer-sized Zn-Al powder particles with nominal composition Zn₄₀Al₆₀ atomic % produced by gas atomization as the parent alloy. Reducing the size of the parent alloy significantly enhances the dealloying rate. Furthermore, Al and Zn are phase-separated in Zn-Al powder particles due to the gas atomization process, making removing the sacrificial Al phase easy. We used various techniques, including X-ray diffraction, Xe⁺ plasma focused ion beam/scanning electron microscopy (FIB/SEM), energy-dispersive spectroscopy (EDS), and inductively coupled plasma optical emission spectroscopy (ICP-OES) to thoroughly characterize these materials before and after free corrosion dealloying. The fabricated NP-Zn powder exhibits a hierarchical ligament/pore morphology, with tiny structures with a size of ≈10 nm coming from Zn nanoparticle aggregation during dealloying and large structures in the range of ≈50-200 nm coming from the removal of the sacrificial Al phase. We demonstrate that this NP-Zn can spontaneously react with water at near-neutral pH to produce hydrogen and zinc oxide solid byproducts with a hydrogen generation yield of ≈52% within 60 min.