Synthesis and mechanical properties of hierarchical nanoporous metals
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Nanoporous (NP) metals are a unique class of materials that are characterized by extremely high surface-to-volume ratios and possess such desirable properties of metals as high electrical conductivity, catalytic activity, and mechanical strength. At the same time, understanding of their physical properties is often lacking, especially for hierarchical NP metals where individual struts and joints that make up open cell 3D network are nanocrystalline. The aim of this work is to employ a dedicated experimental campaign to understand the structure property relation of nanostructured nanoporous metals. Towards this goal, NP Pt and NP Cu have been synthesized for a range of strut sizes and their mechanical properties have been investigated via ex-situ and in-situ nanoindentation experiments. Both NP Pt and NP Cu exhibit relatively high hardness in the range of 0.2 to 1.3 GPa. The relative role of material effects arising from small dimensions of the struts/joints and the geometrical features of NP metals are discussed. Selected applications of the systems synthesized during this work in electrochemistry and catalysis are demonstrated. In the examined applications the NP metals exhibited catalytic activity comparable to or significantly exceeding the best available alternative systems, while offering superior stability.