Thermally-Driven Ag-Au Compositional Changes at the Ligament Surface in Nanoporous Gold: Implications for Electrocatalytic Applications

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 which 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 homogenously distributed. Due to 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. Further, a depth-dependent analysis of synchrotron-based XP...