Nanoscale Morphological and Structural Transformations of PtCu Alloy Electrocatalysts during Potentiodynamic Cycling

Abstract

PtCu bimetallic alloys are known to provide better activity than pure platinum in proton exchange membrane fuel cells. However, such catalysts undergo complex degradation processes during fuel cell operation, resulting in deterioration of their activity. By using in situ electrochemical (EC) atomic force microscopy combined with in situ EC infrared reflection absorption spectroscopy, we provide a comprehensive investigation of morphological and structural transformations of PtCu model thin film catalysts during accelerated degradation tests (ADTs). The ADTs consist of potentiodynamic cycling to three different upper potentials relevant for different modes of fuel cell operation. The results show that, depending on the upper potential limit, PtCu alloy electrocatalysts are subject to drastic changes in the surface composition, morphology, and structure.

Evolution of the PtNi Bimetallic Alloy Fuel Cell Catalyst under Simulated Operational Conditions

“…The oxide reduction charge is decreasing when going to a large number of cycles, which is due to the surface area decrease as particles become larger. Moreover, there is a shift in the oxide reduction peak to higher potentials (highlighted by arrows in CVs, Figure ), apparently due to the lower oxophilicity of larger Pt nanoparticles. − These observations are in good agreement with literature and our previous studies and correspond to the dealloying and platinum coarsening. ,,− …”

Stability of Bimetallic PtxRuy – From Model Surfaces to Nanoparticulate Electrocatalysts

“…The shape of the whole dissolution feature changes from a straight line to a sudden increase, followed by a slow decay of the dissolution rate to a steady-state value. Unlike in the case of, for example, PtCu or AgAu bimetallic systems, − no parting limit (a specific amount of the less noble constituent in the alloy below which no dealloying occurs, irrespective of the UPL applied) can be defined for PtRu. We speculate that this is because the nobility (i.e., redox potentials) of Pt and Ru does not differ significantly.…”

“…These surface pits appeared as cracks in the case of Ni-and Cu-rich PtNi and PtCu samples. 54,57,58 Crack formation was always accompanied by an increase in the grain sizes. The size of the cracks and the development of the overall surface morphology highly depended on two aspects: the amount of the less noble component in the alloy and the applied electrochemical protocol (number of cycles and upper potential limit).…”

Electroactive Area from Porous Oxide Films Loaded with Silver Nanoparticles: Electrochemical and Electron Tomography Observations

“…In the domain of catalysis and electrocatalysts, the evolution of NPs is still a major industrial issue as it has been proven that properties are usually strongly affected by the fact that particles evolve during the catalytic process, inducing migration and size and shape evolution, 13,14 also known as catalysis leaching. 15,16 This usually leads to a significant reduction in material properties and is therefore a major drawback for most industrial applications. Catalysts are extremely small particles embedded in a solid matrix and are therefore difficult to observe in situ.…”

“…One spectacular example of the possible interaction between a semiconductive matrix, the NPs, and the surrounding environment is the photochromic behavior of Ag NPs dispersed in mesoporous TiO 2 . − In this case, visible light induces a photo-oxidation reaction of silver because of a plasmon-induced electron transfer between the metallic NP and the semiconductive host, and acts as a reversible, photosensitive support for information storage. In the domain of catalysis and electrocatalysts, the evolution of NPs is still a major industrial issue as it has been proven that properties are usually strongly affected by the fact that particles evolve during the catalytic process, inducing migration and size and shape evolution, , also known as catalysis leaching. , This usually leads to a significant reduction in material properties and is therefore a major drawback for most industrial applications. Catalysts are extremely small particles embedded in a solid matrix and are therefore difficult to observe in situ.…”