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Item type:Publication, Access status: without files , Thermally Driven Ag-Au Compositional Changes at the Ligament Surface in Nanoporous Gold: Implications for Electrocatalytic Applications(2020-03-27); ; ; ; Nanoporous gold (NPG) is a versatile, nanoporous bulk material with applications in catalysis, sensors, energy materials, and actuation. NPG obtained from dealloying Ag-rich Au-Ag alloys has interesting applications in electrocatalysis, for which methanol oxidation is an interesting test case. Such materials always contain a content of residual silver which may play a role in activating and binding of reaction intermediates. The residual Ag that is contained in NPG due to the dealloying of a Ag-Au alloy was recently found to be present in silver-rich islands, in contrast to being homogeneously distributed. Because of the importance of residual Ag on the surface science and catalytic properties of NPG, we investigated its distribution and chemical nature with the use of X-ray photoelectron spectroscopy. During the in situ annealing, changes of the near surface content of residual Ag were observed, and they were linked to coarsening of the gold ligaments. In addition, a depth-dependent analysis of synchrotron-based XPS results confirmed the surface segregation in the near surface layers of each ligament. The available data neither confirm nor exclude a further systematic enrichment or depletion of silver in the topmost atomic layer for NPG during electrochemical treatments in KOH solution or during thermal coarsening.Publicationtype: Journal Article97 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Mass Transport in Porous Electrodes Studied by Scanning Electrochemical Microscopy: Example of Nanoporous Gold(2019-06-14); ; ; ; Scanning electrochemical microscopy (SECM) approach curves were measured above different samples of nanoporous gold (NPG) using ascorbic acid as an irreversible redox mediator. Under these circumstances, the microelectrode current is informative in terms of the diffusive mass transport inside the network of pores in the sample, because mediator regeneration at NPG is not possible for an irreversible mediator. The reaction–transport problem was solved by finite element simulation for a wide variety of working distances, film thicknesses, and microelectrode geometries. The Bruggeman equation was used to relate transport properties and porosity. The simulation leads to an analytical expression that allows the determination of porosity values corrected by the tortuosity of insulating and conducting materials. The validity of the approach was demonstrated by applying it to NPG samples for which structural parameters can be varied by the particular dealloying protocol. This procedure is potentially applicable for following coarsening processes in porous electrodes and other materials, because the SECM procedure avoids emersion from electrolyte solution for those determinations.Publicationtype: Journal Article170 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Electrocatalytic methanol oxidation with nanoporous gold: microstructure and selectivity(Royal Society of Chemistry (RSC), 2017-10-17); ; ; ; The properties of Nanoporous Gold (NPG) obtained by the selective dissolution of Ag from an Au–Ag alloy can be tuned by the details of its fabrication, and specifically the residual Ag content is correlated to the ligament size of the material. We link this correlation to methanol electro-oxidation. Specifically, two different NPG types (obtained by potentiostatic dealloying) are compared with one obtained by free corrosion. They show remarkable differences in activity. Quantitative product analysis reveals that NPG shows nearly selective oxidation of CH3OH to HCOO− when NPG is used as an active electrode in contrast to planar Au. This trend can further be enhanced when applying finer nanoporous structures that are linked to a higher Ag content. X-ray photoelectron spectroscopy (XPS) reveals changes in the nature of residual Ag from which we conclude that Ag is not a passive component in the methanol oxidation process.Publicationtype: Journal ArticleScopus© Citations 57 377 336