Preventing Alloy Electrocatalyst Segregation in Air Using Sacrificial Passivating Overlayers.

Area of Science:

• Materials Science
• Electrochemistry
• Surface Science

Background:

• Alloy electrocatalysts, particularly intermetallics, are prone to surface segregation when exposed to air.
• This segregation, driven by electronic dissimilarities, buries less reactive metals, altering catalytic properties.
• A significant gap exists between ultrahigh vacuum (UHV) characterization and ambient condition electrocatalytic testing.

Purpose of the Study:

• To develop and validate a novel experimental approach to bridge the pressure gap in alloy characterization.
• To protect alloy surfaces from air-induced segregation during transfer and handling.
• To enable reliable correlations between near-surface electronic structure and electrocatalytic activity.

Main Methods:

• Encapsulation of alloy surfaces with a sacrificial aluminum oxide (Al2O3) passivating overlayer.
• Removal of the Al2O3 overlayer in an alkaline electrochemical environment under potential control.
• Characterization of near-surface composition and validation of electrocatalytic activity of protected alloys.

Main Results:

• The aluminum oxide overlayer effectively prevented air-induced segregation of alloy constituents.
• Protected alloy surfaces exhibited near-surface compositions consistent with bulk material after air exposure.
• The protection scheme did not alter the electrocatalytic activity of benchmark electrocatalysts.

Conclusions:

• The developed encapsulation method successfully bridges the pressure gap between UHV and ambient conditions.
• This approach enables accurate assessment of alloy electrocatalyst properties by preserving their pristine surface composition.
• Implementation facilitates reliable correlations between electronic structure and electrocatalytic performance.