In-situ GISAXS-Revealed Interplay Among Dealloying, Ostwald Ripening and Coalescence of PtXNi100-X Bimetallic Alloy Under PEMFC Simulated Operational Conditions

Platinum-based bimetallic alloys demonstrated to be a promising and cheaper alternative to bare Pt as catalysts for the cathode electrode of Proton Exchange Membranes Fuel Cells (PEMFCs). Among them, PtNi was found to have a very good mass activity and a competitive catalytic activity1,2. The main drawback in applying Pt-based bimetallic alloys relies in their reduced stability, which is still under investigation. Being able to clearly describe Pt-based bimetallic alloy at a fundamental level is essential to shed light on the entire chain of interconnected degradation mechanisms taking place in catalyst model systems, which would help in interpreting catalyst degradation in real complex fuel cells. Here (Figure 1), we have combined in situ Inductively Coupled Plasma Mass Spectroscopy, in situ Grazing-Incidence Small-Angle X-ray Scattering, and ex situ Scanning Electron Microscopy, we have studied the morphological evolution of PtXNi100–X model catalysts with different Ni contents (ranging from 0 to 75%) undergoing potentiodynamic cycling to two different upper potentials (1.0 and 1.3 V), selected to mime different operational conditions of a PEMFC. Data analysis allowed to develop a methodology for distinguishing among Ni dissolution, particle coalescence, and Ostwald ripening and their effects on both particle size distribution and interparticle distance. Finally, time-dependent interplay maps were realized to highlight the timeframe in which the aforementioned phenomena are prevailing or coexisting.