Anodic and Cathodic Platinum Dissolution Processes Involve Different Oxide Species.

Area of Science:

• Electrochemistry
• Materials Science
• Surface Science

Background:

• Degradation of platinum (Pt)-based catalysts is a major challenge for fuel cell performance and longevity.
• Electrochemical surface oxidation and reduction of Pt are key mechanisms contributing to catalyst degradation.

Purpose of the Study:

• To investigate the atomic-scale mechanisms of Pt surface restructuring and dissolution during electrochemical oxidation-reduction cycles.
• To elucidate the role of different platinum oxide phases in Pt dissolution.

Main Methods:

• Operando high-energy surface X-ray diffraction (HSXRD) for atomic-scale structural analysis.
• Online mass spectrometry (MS) to detect dissolved species.
• Density functional theory (DFT) calculations to model surface processes.

Main Results:

• Two distinct platinum oxide phases were identified, correlating with different dissolution mechanisms.
• Anodic dissolution is associated with the formation of a stripe-like oxide.
• Cathodic dissolution is linked to a second, amorphous Pt oxide phase (resembling PtO2) that forms upon saturation of the first oxide.

Conclusions:

• Platinum dissolution during electrochemical cycling is a complex process mediated by specific oxide phases.
• Understanding these oxide phases and their formation is crucial for designing more stable Pt catalysts for fuel cells.
• Surface restructuring becomes potential-independent after the initial stripe-like oxide reaches saturation coverage.