Multiscale Analysis of Electrochemical Dealloying of Bimetallic Nanoparticles to Tune Catalytic Activity

Electrochemical dealloying is a promising technique to tune the activity and material utilization of electrocatalysts. Studying this process in bimetallic nanoparticles remains challenging since their synthesis yields ensembles with varied properties. To understand the dealloying behavior of individual nanoparticles, we present a combined characterization method that provides statistical distributions in composition, morphology, and catalytic activity. AgxAuy alloy nanoparticles synthesized via reverse micelles were dealloyed, by potential cycling, to tune their activity for the hydrogen evolution reaction. In a multiscale approach, we performed macroscale measurements on a glassy carbon electrode and scanning electrochemical cell microscopy (SECCM) on small groups of particles/aggregates within the confines of the scanned droplet. The SECCM pipet was used to create different states of dealloying within a single sample, followed by higher-resolution SECCM activity mapping. The faster mass transport in the SECCM tip, compared to the macroelectrode configuration, led to accelerated Ag dissolution from the AgxAuy nanoparticles. While the particles showed the highest activity and largest Ag content decrease after only 0.5 cycles, heterogeneous behavior was still evident among individual particle groups. Further, using a boron-doped diamond electrode, identical-location scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy studies allowed Ag leaching and particle shrinking to be followed at the single-particle level, as a function of cycle number, for a statistically relevant sample number (n > 70). Increased cycling induced particle deactivation, shrinking, and coalescence. Overall, our results showcase an efficient and versatile route to combine systematic tuning and high-throughput screening of nanocatalyst property-activity relationships.