SUMMARY

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 strength. Due to these properties, NP metals have demonstrated great potential in many applications. At the same time, a deep understanding of their mechanical properties is lacking, especially for hiearachical metals where individual struts and joints that make up open cell 3D network are nanocrystalline. The aim of this work is to provide such understanding through a dedicated experimental campaign. Towards this goal, a variety of hierarchical NP metal systems have been synthesize, such as nanocrystalline NP Pt and nanotwinned NP Cu. The mechanical properties of these systems are investigated via ex-situ and in-situ nanoindentation experiments to infer scalings of modulus and strength with crucial parameters such as relative density and characteristic dimensions of struts. Both NP Pt and NP Cu are found to have highly elevated properties comparable to single-crystal systems and far exceeding expectations based in simplified dimensional arguments. The origin of this enhancement is traced back to a combination of material effects arising from small dimensions of the struts/joints and the geometrical features of NP metals. Selected applications of the systems synthesized during this work in electrochemistry and catalysis are demonstrated, typically with the performance comparable to or exceeding the best available alternative systems.