Nanoporous gold (Au) films are self-supported structures that possess a large surface area and extraordinary catalytic activity. Generally, nanoporous gold is obtained by solution-based dealloying where the less noble metal, often silver (Ag), is etched out. However, the residual amounts of the sacrificial metal are not well controlled, the impure samples show restructuring, and the residual metal prevents the study of the catalytic role of Au alone. Here, we fabricate impurity-free nanoporous gold films by a plasma-enabled dry synthetic route. The scheme does not include sacrificial metals or solution processing and is much more general. It is used to obtain self-supported ultra-pure nanoporous gold films with controllable pore sizes. The impurity-free nanoporous gold films possess highly curved ligaments, are remarkably robust, and stable over hundreds of electrochemical cycles. Furthermore, they contain many catalytically active sites, which is highly promising for electrocatalytic applications.
American Chemical Society ACS catalysis Washington, DC : ACS, 2011 13(2023), 17, Seite 11656-11665 Online-Ressource
Sonstige Körperschaft: Technische Universität Hamburg ; Sonstige Körperschaft: Technische Universität Hamburg, Institut für Werkstoffphysik und Werkstofftechnologie
Electrocatalysis; Methanol oxidation; Nanoporous gold; Surface structure; Under potential deposition
Nanoporous gold (NPG) obtained by potentiostatic dealloying of an AuAg master alloy was pulverized, filled into a cavity microelectrode and its surface electrochemistry was investigated in NaOH and KOH solutions. This method yielded highly resolved undistorted voltammograms of this polycrystalline material with clear evidences for surface segregation of Ag during storage in air. One cycle in 0.1 M H SO can remove most of the residual Ag from the surface as evidenced by voltammetry after back transfer to alkaline solution and by X-ray photoelectron spectroscopy (XPS). After removal of residual Ag from the surface, the surface undergoes rephasing forming wider 111 and 110 terraces as evidenced by Pb underpotential deposition (UPD). By adjustment of the bulk concentration of Pb species, a selective partial coverage of the high internal surface area of NPG could be intentionally adjusted. Lead species remain attached to the NPG surface at potentials positive of the UPD regions either as plumbates or Pb species as evidenced by XPS. Those tools enable to disentangle effects on the electrocatalysis of the methanol oxidation reaction (MOR) in different potential regions for 1 M methanol in different concentrations of NaOH and KOH. The MOR commences at lower potentials in the presence of residual Ag. At very high potential, the presence of Ag species promotes the oxidation to CO /CO . Tafel analysis after selective blocking of specific facets shows that the 110 terraces promote especially the first step of MOR while the 111 terraces enhance the rate of further steps that are rate-limiting at higher potentials. While high coverages by Pb UPD layers or adsorbed plumbate anions inhibit electrooxidation, the behavior of NPG electrodes with low coverages of Pb species is reminiscent to NPG electrodes with residual Ag. This could be caused by promoting the methoxide and/or OH adsorption at low overpotentials and catalyzing complete oxidation by a surface bound Pb species at higher potentials. The catalytic currents increase with base concentration and are higher for KOH compared to NaOH. Comparable effects of base concentration on the parameters of the Tafel lines suggest that this effect is a result of slightly stronger deprotonation of methanol in bulk KOH solutions. 2 4 2 3 II IV 2- - IV
Electrochimica acta New York, NY [u.a.] : Elsevier, 1959 383(2021), Artikel-ID 138348, Seite 1-15 Online-Ressource
