Sub-Nanometer-Resolution Elemental Mapping of “Pt3Co” Nanoparticle Catalyst Degradation in Proton-Exchange Membrane Fuel Cells

• Published in: The journal of physical chemistry letters Vol. 3; no. 2; pp. 161 - 166
• Main Authors: Carlton, Christopher E, Chen, Shuo, Ferreira, Paulo J, Allard, Lawrence F, Shao-Horn, Yang
• Format: Journal Article
• Language: English
• Published: American Chemical Society 19.01.2012
• Subjects: Surfaces, Interfaces, Catalysis
• ISSN: 1948-7185; 1948-7185
• DOI: 10.1021/jz2016022

The efficiency of proton exchange membrane fuel cells (PEMFCs) is limited largely by sluggish oxygen reduction reaction (ORR) kinetics, even when promoted by Pt-based alloy nanoparticles (NPs). Acid-leached Pt alloys such as “Pt3Co” have shown considerably higher specific (2–5 times) and mass (2 to 3 times) ORR activity than Pt NPs. However, the specific activity enhancement of “Pt3Co” NPs decreases during PEMFC operation, which has been attributed to the formation of a Pt-enriched shell near the NP surfaces. In this study, we report direct evidence of surface Pt and Co compositional changes in acid-treated “Pt3Co” NPs after PEMFC voltage cycling using energy-dispersive spectroscopy mapping in an aberration-corrected scanning transmission electron microscope with subnanometer resolution. Acid-treated “Pt3Co” NPs were found to have Pt-enriched shells of ∼0.5 nm, whereas the Pt-enriched-shell became thicker (∼1–6 nm) after PEMFC voltage cycling, where greater shell thicknesses were associated with larger “Pt3Co” NPs.