(135e) Iridium-Platinum Core-Shell Nanoparticles As Catalysts for the Oxygen Reduction Reaction

Authors: 
Strickler, A., Stanford University
Jackson, A., Stanford University
Jaramillo, T. F., Stanford University

Fuel cells are widely considered as a promising source of clean energy. Inadequate device efficiencies and expensive Pt electrocatalysts, however, present technological and economic hurdles that currently restrict the widespread commercialization of fuel cell technology. To overcome these barriers, considerable research has focused on developing more active, lower Pt content electrocatalysts for the kinetically slow oxygen reduction reaction (ORR) at the fuel cell cathode. Recently, many have looked to reduce Pt loading via core-shell nanostructures where a Pt shell surrounds the core of a different metal or alloy. In addition to increasing Pt specific activity, the core material allows for the tuning of electronic properties of the catalyst by altering the binding energies of reaction intermediates. To select a core material, we utilized a systematic approach for catalyst design developed in a previous study in which it was shown that catalytic activity could be enhanced by selecting a core material that is theoretically predicted to over-weaken the oxygen binding energy on a Pt monolayer on a flat metal surface.1 The binding energy can then be strengthened towards its optimum value through nanoscale effects and by adjusting shell thickness. Through this approach, iridium was identified as a promising core material. Therefore, this work focuses on examining the performance and properties of Ir-Pt core-shell nanoparticles. Ir-Pt nanoparticles with several shell thicknesses and core sizes were synthesized using a highly scalable, inexpensive polyol method. Particle size and composition were characterized using TEM and STEM-EDS.  Electrochemical activities of the Ir-Pt catalysts were compared to synthesized Ir-only and Pt-only nanoparticles as well as to the state-of-the-art commercial standard Pt catalyst, TKK. Electrochemical evaluation reveals that our Ir@Pt catalyst is highly active with a mass activity similar to TKK and a specific activity 1.4 times higher than TKK. This catalyst was also found to be highly stable, and after 10,000 stability cycles, showed improvements in both Pt mass and specific activity with the specific activity increasing to 2.1 times that of TKK.

1. A. Jackson et al., ChemElectroChem 1, 67-71 (2014).