Effects of the Pt Shell Thickness on the Oxygen Reduction Reaction on a Well-Defined Pd@Pt Core-Shell Model Surface.

Area of Science:

• Catalysis
• Materials Science
• Electrochemistry

Background:

• The oxygen reduction reaction (ORR) is crucial for fuel cell efficiency.
• Developing advanced catalysts like core-shell structures is key to improving ORR performance.
• Understanding the influence of shell thickness on catalytic activity is essential.

Purpose of the Study:

• To investigate the effect of platinum (Pt) shell thickness on the ORR activity of Pd@Pt core-shell catalysts.
• To elucidate the relationship between electronic properties (charge transfer, binding energy) and ORR activity.
• To explore the potential of precisely controlled core-shell structures for enhanced catalysis.

Main Methods:

• Surface science techniques were employed to analyze catalyst properties.
• Computational approaches, including density functional theory (DFT) calculations, were utilized.
• Model surfaces with varying Pt shell thicknesses (0.5 and 1 monolayer) on Pd substrates were studied.

Main Results:

• Platinum shells (0.5-1 ML) on palladium (Pd) substrates exhibited negative charge due to charge transfer.
• ORR activity of these thin Pt shells was more than double that of commercial Pt/C or bulk Pt.
• A strong inverse correlation was observed between ORR activity and Pt binding energy with increasing shell thickness.
• Negatively charged Pt demonstrated higher ORR activity, confirmed by DFT calculations.

Conclusions:

• Thin, negatively charged Pt shells on Pd substrates significantly enhance ORR activity.
• The electronic properties, specifically charge transfer and resulting Pt shell negativity, are critical determinants of ORR performance.
• Pd@Pt core-shell catalysts with controlled ultrathin Pt layers offer a promising pathway for advanced fuel cell applications.