Interplay Among Dealloying, Ostwald Ripening, and Coalescence in Pt_XNi_100–X Bimetallic Alloys under Fuel-Cell-Related Conditions

Abstract

Platinum-based bimetallic alloys have been largely investigated during the last few years as a valid alternative to bare Pt cathode catalysts for proton-exchange membrane fuel cells (PEMFCs) to improve their cost-efficiency. Nonetheless, Pt bimetallic alloys are characterized by a reduced stability, which is poorly understood at a fundamental level. It is thus essential to describe the entire chain of interconnected degradation mechanisms to formulate a comprehensive model of catalyst degradation that will help interpret bimetallic alloy behavior in real complex fuel cell systems. By combining 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 Pt X Ni100–X model catalysts with different Ni contents (ranging from 0 to 75%) undergoing potentiodynamic cycling to two different upper potentials mimicking the different operational conditions of a PEMFC: 1.0 and 1.3 VRHE. Data analysis allowed us to develop a methodology to distinguish the influence of Ni dissolution, particle coalescence, and Ostwald ripening on particle size distribution and interparticle distance and to realize time-dependent interplay maps to highlight the timeframe in which the aforementioned phenomena are prevailing or coexisting. Results show that Ni dissolution is the only phenomenon inducing morphological evolution when the lower upper potential is chosen. On the contrary, at 1.3 VRHE, Ni dissolution is rapidly overcome by particle coalescence at first and by Ostwald ripening in the later stages of the investigated time range. The onset of every phenomenon was found to occur earlier in time for larger values of Ni concentrations.

On the electrocatalytical oxygen reduction reaction activity and stability of quaternary RhMo-doped PtNi/C octahedral nanocrystals

“…The total amount of dissolved Ni is in the ballpark of what was reported in precedent studies. 40 The dissolved amount of the other three metals is at least two orders of magnitude smaller. The amount of dissolved Rh is the smallest, which is followed by Pt.…”

Atomic spectrometry update: review of advances in the analysis of metals, chemicals and materials

“…In recent years platinum-based bimetallic alloys have been investigated as an alternative to bare platinum cathode catalysts for proton-exchange membrane fuel cells to improve their cost-effectiveness. 128 However, they have a reduced stability, which is poorly understood at a fundamental level. It is necessary to elucidate the entire chain of interconnected degradation mechanisms to formulate a comprehensive model of catalyst degradation that will help interpret bimetallic alloy behaviour.…”

Monitoring of Pore Orientation by in Operando Grazing Incidence Small-Angle X-ray Scattering during Templated Electrodeposition of Mesoporous Pt Films

“…Being applicable for in situ investigations, SAXS has been used to study Ag nanoparticle formation during multipulse electrodeposition . In our previous work, we investigated electrochemical aging by in situ GISAXS and observed changes in the morphology of fuel cell electrodes during simulated operation. – A limited number of in situ SAXS studies during templated electrodeposition have been reported in literature. Richardson et al studied the templated electrodeposition of Pt films using phytantriol in inverse bicontinuous lipid cubic phases.…”