Hierarchical nested-network nanostructure by dealloying.

Applications of porous microstructures in functional materials often impose conflicting requirements on the pore size, which may be met by hierarchical structures that combine porosity on distinctly different length scales. Here we report an electrochemical dealloying strategy that yields bulk samples of porous gold with a hierarchical microstructure. A nanoscale network of solid ligaments forms the lower hierarchy level, which is nested within the geometrically similar, but much larger, network of the upper hierarchy level. Starting from a dilute solid solution of Au in Ag, controlled electrochemical corrosion yields nanoporous Ag-Au alloy as an intermediate product. Coarsening of the porous alloy creates the large ligaments of the upper hierarchy level. Those are then again dealloyed, which creates the fine ligaments of the lower hierarchy level. We show that the material exhibits enhanced charge transport kinetics while maintaining a large specific surface area.