Local Activity and Selectivity Hotspots in Cu-Pt Model Thin-Film Electrocatalysts for Oxygen Reduction

Area of Science:

• Materials Science
• Electrochemistry
• Surface Science

Background:

• Platinum-rich alloys are state-of-the-art electrocatalysts for oxygen reduction reaction (ORR).
• Copper-platinum (Cu-Pt) alloys show high activity and selectivity for the four-electron pathway of ORR.
• Understanding active sites in Cu-Pt alloys is key for developing efficient sustainable energy technologies.

Purpose of the Study:

• To investigate the behavior of Cu-Pt model thin film alloy catalysts.
• To identify active sites and catalytic surface areas under reaction conditions for ORR.
• To determine how active site location influences the reaction pathway (water vs. hydrogen peroxide production).

Main Methods:

• Electrochemical scanning tunneling microscopy (EC-STM) was employed to visualize catalyst surfaces.
• In-situ analysis under reaction conditions allowed for real-time observation of catalytic processes.
• Cu-Pt thin film model alloy catalysts were utilized for controlled experimentation.

Main Results:

• Active centers for the four-electron ORR pathway were located on the (111) terraces of Cu-Pt alloys.
• A shift in active centers to step defects was observed when hydrogen peroxide (H2O2) generation occurred.
• Grain boundaries of the Cu-Pt alloys did not appear to contribute significantly to the catalytic activity.

Conclusions:

• The location and nature of active sites in Cu-Pt alloy catalysts are dependent on the ORR product (H2O or H2O2).
• Surface morphology, specifically terraces and step defects, plays a critical role in catalytic activity and selectivity.
• These findings provide insights for designing improved nanostructured materials for energy applications by controlling nanoparticle shape and defect sites.