In Situ Study of Nanoporosity Evolution during Dealloying AgAu and CoPd by Grazing-Incidence Small-Angle X-ray Scattering

Abstract

Electrochemical dealloying has become a standard technique to produce nanoporous network structures of various noble metals, exploiting the selective dissolution of one component from an alloy. While achieving nanoporosity during dealloying has been intensively studied for the prime example of nanoporous Au from a AgAu alloy, dealloying from other noble-metal alloys has been rarely investigated in the scientific literature. Here, we study the evolution of nanoporosity in the electrochemical dealloying process for both CoPd and AgAu alloys using a combination of in situ grazing-incidence small-angle X-ray scattering (GISAXS), kinetic Monte Carlo (KMC) simulations, and scanning transmission electron microscopy (STEM). When comparing dealloying kinetics, we find a more rapid progression of the dealloying front for CoPd and also a considerably slower coarsening of the nanoporous structure for Pd in relation to Au. We argue that our findings are natural consequences of the effectively higher dealloying potential and the higher interatomic binding energy for the CoPd alloy. Our results corroborate the understanding of electrochemical dealloying on the basis of two rate equations for dissolution and surface diffusion and suggest the general applicability of this dealloying mechanism to binary alloys. The present study contributes to the future tailoring of structural size in nanoporous metals for improved chemical surface activity.

In Situ and Operando X-ray Scattering Methods in Electrochemistry and Electrocatalysis

“…Furthermore, both of these studies deduced the presence of directional strain anisotropies in the Au ligaments. More recent studies investigated the influence of temperature on the dealloying process by in situ SAXS , and determined the structural changes in isolated AuAg nanocrystals that were induced by 10 s of dealloying by ex situ BCDI . The latter work provided detailed strain distributions within the nanoparticle that showed the formation of nanopores near the surface induced compressive strain 60–80 nm deep beneath, but weak tensile strain deeper within the particle.…”

Porosity evolution and oxide formation in bulk nanoporous copper dealloyed from a copper–manganese alloy studied by in situ resistometry

“…14,25,25,36 Studies of the dealloying and the electrochemical performance of dealloyed npCu will signicantly contribute to the fundamental understanding of the structural evolution. There are several methods for investigating dealloying processes (including X-ray scattering, [37][38][39] X-ray diffraction, 40 and electron microscopy 41,42 ), but most methods are surface specic and focus on small volumes. One method, which is particularly well suited to investigate the dealloying process on a larger scale is in situ resistometry 43 which enables the monitoring of the entire sample and the study of the evolution of the porous structure in real time.…”