Controlling Near-Surface Ni Composition in Octahedral PtNi(Mo) Nanoparticles by Mo Doping for a Highly Active Oxygen...

Area of Science:

• Electrocatalysis
• Materials Science
• Nanotechnology

Background:

• Advanced platinum-based alloy nanoparticles are crucial for efficient oxygen electroreduction reaction (ORR) in fuel cells.
• Understanding the role of dopants and particle morphology is essential for optimizing catalyst performance and stability.

Purpose of the Study:

• To translate high ORR activity of molybdenum-doped PtNi octahedral nanoparticles from electrode to fuel cell tests.
• To investigate the atomic-level impact of molybdenum on PtNi catalyst surface composition and stability.
• To identify strategies for preserving the active surface structure for enhanced durability.

Main Methods:

• Rotating disk electrode (RDE) screening and membrane electrode assembly (MEA) single fuel cell testing.
• Scanning transmission electron microscopy with energy-dispersive X-ray analysis (STEM-EDX).
• In situ wide-angle X-ray spectroscopy, X-ray fluorescence, and electrochemical measurements.

Main Results:

• Achieved sustained Pt mass activity of 0.45 A mg_Pt^-1 at 0.9 V_cell in MEA tests, demonstrating excellent ORR performance.
• Molybdenum preferentially segregates to Pt-rich edges and vertices of octahedral PtNi particles.
• High Ni retention was achieved in PtNiMo nanoparticles after stability tests, with stability losses linked to shape degradation and Pt oxidation potentials.

Conclusions:

• Molybdenum adatoms significantly influence Ni surface composition, leading to exceptional ORR reactivity.
• Preserving the specific Mo-influenced surface composition is critical for catalyst durability.
• Strategies are needed to maintain the octahedral shape and surface structure against degradation for long-term fuel cell applications.