Simulations of the Oxidation and Degradation of Platinum Electrocatalysts

• Published in: Small
• Main Authors: Kirchhoff, Björn, Braunwarth, Laura, Jung, Christoph, Jónsson, Hannes, Fantauzzi, Donato, Jacob, Timo
• Other Authors: Raunvísindastofnun (HÍ), Science Institute (UI), School of Engineering and Natural Sciences (UI), Verkfræði- og náttúruvísindasvið (HÍ), Háskóli Íslands, University of Iceland
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2019
• Subjects: Electrocatalysis; Fuel cells; Oxidation; Platinum catalysts; ReaxFF; Oxun; Efnarafalar; Ryð; Hermun; Marcos; Iceland
• Online Access: https://hdl.handle.net/20.500.11815/1549; https://doi.org/10.1002/smll.201905159

Publisher's version (útgefin grein) Improved understanding of the fundamental processes leading to degradation of platinum nanoparticle electrocatalysts is essential to the continued advancement of their catalytic activity and stability. To this end, the oxidation of platinum nanoparticles is simulated using a ReaxFF reactive force field within a grand-canonical Monte Carlo scheme. 2–4 nm cuboctahedral particles serve as model systems, for which electrochemical potential-dependent phase diagrams are constructed from the thermodynamically most stable oxide structures, including solvation and thermochemical contributions. Calculations in this study suggest that surface oxide structures should become thermodynamically stable at voltages around 0.80–0.85 V versus standard hydrogen electrode, which corresponds to typical fuel cell operating conditions. The potential presence of a surface oxide during catalysis is usually not accounted for in theoretical studies of Pt electrocatalysts. Beyond 1.1 V, fragmentation of the catalyst particles into [Pt6O8]4− clusters is observed. Density functional theory calculations confirm that [Pt6O8]4− is indeed stable and hydrophilic. These results suggest that the formation of [Pt6O8]4− may play an important role in platinum catalyst degradation as well as the electromotoric transport of Pt2+/4+ ions in fuel cells. B.K. thanks the University of Iceland Research Fund for support through a PhD fellowship, Dr. Anna Garden for access to nanoparticle DFT structures, and Marcos Tacca for translation help of Spanish primary literature. Andrey Sinyavskiy is acknowledged for implementing the 2PT method. This work was supported by the German Federal Ministry of Education and Research through the BMBF-project ?GEP ? Grundlagen elektrochemischer Phasengrenzen? (Grant No. 13XP5023D), the Deutsche Forschungsgemeinschaft (DFG) through Grant No. SFB-1316 (collaborative research center), as well as through the Icelandic Research Fund under Grant No. 174582-052. Computational resources were ...