Experimental section, discussion on high current density and heat rejection limit, and physical and electrochemical properties of different carbon supports (PDF)

We demonstrate the unprecedented proton exchange membrane fuel cell (PEMFC) performance durability of a family of dealloyed Pt-Ni nanoparticle catalysts for the oxygen reduction reaction (ORR), exceeding scientific and technological state-of-art activity and stability targets. We provide atomic-scale insight into key factors controlling the stability of the cathode catalyst by studying the influence of particle size, the dealloying protocol and post-acid-treatment annealing on nanoporosity and passivation of the alloy nanoparticles. Scanning transmission electron microscopy coupled to energy dispersive spectroscopy data revealed the compositional variations of Ni in the particle surface and core, which were combined with an analysis of the particle morphology evolution during PEMFC voltage cycling; together, this enabled the elucidation of alloy structure and compositions conducive to long-term PEMFC device stability. We found that smaller size, less-oxidative acid treatment and annealing significantly reduced Ni leaching and nanoporosity formation while encouraged surface passivation, all resulting in improved stability and higher catalytic ORR activity. This study demonstrates a successful example of how a translation of basic catalysis research into a real-life device technology may be done.DFG, SPP 1613, Regenerativ erzeugte Brennstoffe durch lichtgetriebene Wasserspaltung: Aufklärung der Elementarprozesse und Umsetzungsperspektiven auf technologische Konzep

Platinum alloy nanoparticles show great promise as electrocatalysts for the oxygen reduction reaction (ORR) in fuel cell cathodes. We report here on the use of N,N-dimethylformamide (DMF) as both solvent and reductant in the solvothermal synthesis of Pt alloy nanoparticles (NPs), with a particular focus on Pt-Ni alloys. Well-faceted alloy nanocrystals were generated with this method, including predominantly cubic and cuboctahedral nanocrystals of Pt(3)Ni, and octahedral and truncated octahedral nanocrystals of PtNi. X-ray diffraction (XRD) and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM), coupled with energy dispersive spectroscopy (EDS), were used to characterize crystallite morphology and composition. ORR activities of the alloy nanoparticles were measured with a rotating disk electrode (RDE) technique. While some Pt(3)Ni alloy nanoparticle catalysts showed specific activities greater than 1000 μA/cm(2)(Pt), alloy catalysts prepared with a nominal composition of PtNi displayed activities close to 3000 μA/cm(2)(Pt), or almost 15 times that of a state-of-the-art Pt/carbon catalyst. XRD and EDS confirmed the presence of two NP compositions in this catalyst. HAADF-STEM examination of the PtNi nanoparticle catalyst after RDE testing revealed the development of hollows in a number of the nanoparticles due to nickel dissolution. Continued voltage cycling caused further nickel dissolution and void formation, but significant activity remained even after 20,000 cycles.