a b s t r a c tWe explore the elastic and plastic Poisson's ratios, m E and m P , of nanoporous gold, using digital image correlation during compression experiments including load/unload segments. The two coefficients differ significantly, with m E independent of the ligament size, L, and with a trend for m P / L at not too large L. Disorder in the network of ligaments may explain why m E is smaller than predicted by lattice-based models. Finite element simulations, based on the Deshpande-Fleck constitutive law, validate the data analysis. The constitutive law captures work-hardening and transverse flow of nanoporous gold in good agreement with the experiment.

The suggestion, based on atomistic simulation, of a surface-induced tension-compression asymmetry of the strength and flow stress of small metal bodies so far lacks experimental confirmation. Here, we present the missing experimental evidence. We study the transverse plastic flow of nanoporous gold under uniaxial compression. Performing mechanical tests in electrolyte affords control over the surface state. Specifically, the surface tension, γ, can be varied in situ during plastic flow. We find that decreasing γ leads to an increase of the effective macroscopic plastic Poisson ratio, ν. Finite element simulations of a network with surface tension confirm the notion that ν of nanoporous gold provides a signature for a local tension-compression asymmetry of the nanoscale struts that form the network. We show that γ promotes compression while impeding tensile elongation. Because the transverse strain is partly carried by the elongation of ligaments oriented normal to the load axis, the surface-induced tension-compression asymmetry acts to reduce ν. Our experiment confirms a decisive contribution of the surface tension to small-scale plasticity.

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Nanoporous gold (NPG) is characterized by a bicontinuous network of nanometer-sized metallic struts and interconnected pores formed spontaneously by oxidative dissolution of the less noble element from gold alloys. The resulting material exhibits decent catalytic activity for low-temperature, aerobic total as well as partial oxidation reactions, the oxidative coupling of methanol to methyl formate being the prototypical example. This review not only provides a critical discussion of ways to tune the morphology and composition of this material and its implication for catalysis and electrocatalysis, but will also exemplarily review the current mechanistic understanding of the partial oxidation of methanol using information from quantum chemical studies, model studies on single-crystal surfaces, gas phase catalysis, aerobic liquid phase oxidation, and electrocatalysis. In this respect, a particular focus will be on mechanistic aspects not well understood, yet. Apart from the mechanistic aspects of catalysis, best practice examples with respect to material preparation and characterization will be discussed. These can improve the reproducibility of the materials property such as the catalytic activity and selectivity as well as the scope of reactions being identified as the main challenges for a broader application of NPG in target-oriented organic synthesis.

Dealloyed nanoporous gold (np‐Au) has applications as oxygen reduction catalysis in Li‐air batteries and fuel cells, or as actuators to convert electricity into mechanical energy. However, it faces the challenges of coarsening‐induced structure instability, mechanical weakness due to low relative densities, and slow dealloying rates. Here, monolithic np‐Au is dealloyed from a single‐phase Au25Ni75 solid‐solution at a one‐order faster dealloying rate, ultra‐low residual Ni content, and importantly, one‐third more relative density than np‐Au dealloyed from conventional Au25Ag75. The small atomic radius and low dealloying potential of the sacrificing element Ni are intrinsically beneficial to fast produce high relative density np‐Au, as predicted by a general model for dealloying of binary alloys and validated by experiments. Stable, durable, and reversible actuation of np‐Au takes place under cyclic potential triggering in alkaline and acidic electrolytes with negligible coarsening‐induced strain‐shift. The thermal and mechanical robustness of bulk np‐Au is confirmed by two‐order slower ligament coarsening rates during annealing at 300 °C and 45 MPa macroscopic yielding strength distinctive from the typical early onset of plastic yielding. This article opens a rich direction to achieve high relative density np‐Au which is essential for porous network connectivity, mechanical strength, and nanostructure robustness for electrochemical functionality.