The electrochemical behavior of nanoporous gold (NPG) obtained by dealloying a AgAu alloy has been investigated by means of cyclic voltammetry (CV) in 0.1 M H2SO4 and 0.1 M KOH solutions supplemented by X‐ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) in order to understand different effects of the electrochemical treatment on the development of the surface structure of NPG. In order to reduce the IR drop caused by the high surface area of the bicontinuous network of pores and ligaments in NPG, NPG was transformed to a powder, from which a small portion was filled into a cavity microelectrode (CME). Additionally, this avoided sample‐to‐sample variation from the dealloying process because many fillings could be made from one NPG monolith. The cycling in 0.1 M H2SO4 led to restructuring of the surface to a more faceted one, only after the residual silver on the surface had been removed in the initial scan. The same cycling program in 0.1 M KOH did not cause restructuring. However, a transfer of the sample to 0.1 M H2SO4 could start the process. The ligament size did not change during restructuring. Additionally, it was found that residual Ag in NPG stabilizes the highly curved surfaces of the ligaments containing a high density of surface defects. The dissolution of the residual Ag in acid electrolytes lifts the blockage towards surface restructuring. These findings form a basis for understanding the electrochemical behavior of NPG and to devise appropriate treatments, for instance for their use in electrocatalysis.

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) obtained by dealloying Ag75Au25 with an overall residual Ag content of less than 1% was investigated as an electrocatalyst for the oxidation of methanol, formaldehyde, and formate in aqueous 0.1 M NaOH solution. The NPG was used to fill cavity microelectrodes, which allowed the recording of well-resolved voltammetry from the porous material. NPG differs from polycrystalline Au (Au­(poly)) by its microstructure and its residual Ag content and also behaves distinctly different than Au­(poly). The residual Ag content is higher at the surface of the ligaments than in the bulk. By cycling the NPG electrodes in 0.1 M H2SO4, the surface concentration of Ag could be decreased. It could then be set to a defined value by underpotential deposition (UPD) of Ag. The surface structure, and specifically its evolution upon the removal of Ag from the surface, was analyzed by the characteristic voltammetric features of Pb UPD. The effect of Ag on the electrocatalytic methanol oxidation reaction (MOR) is different in different potential regions. Ag coverage shifts the onset of the methanol oxidation current to less positive potentials. In the range of the peak current density, only a defined low Ag concentration enhanced the MOR current density compared to the Ag-free NPG. The {1 0 0} and {1 1 1} facets contributed the largest current, as concluded from selective poisoning experiments. At a potential of 1.63 V vs RHE, Ag2O at the surface is oxidized to AgO. Those layers can oxidize methanol and formate to CO2. The oxidation of formaldehyde proceeds at a much higher reaction rate than the MOR and formate oxidation; the reaction leads to CO and CO2 depending on the applied potential. Given the high oxidation rate of formaldehyde, it would be immediately further oxidized should it be formed as an intermediate of MOR. This is an important difference to the methanol oxidation at Pt. The water oxidation that occurs at the same potential range in the methanol-free solution was suppressed during CO2 formation.

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