Synthesis and Characterization of Bimetallic Core-Shell-Supported Platinum Monolayer Electrocatalysts for the Oxygen Reduction Reaction

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Kuttiyiel, Kurian Abraham
The Graduate School, Stony Brook University: Stony Brook, NY.
<p>Fuel cells are expected to be one of the major clean energy sources in the near future. However, the slow kinetics of electrocatalytic oxygen reduction reaction (ORR) and the high loading of Platinum (Pt) for the cathode material are the urgent issues to be addressed since they determine the efficiency and the cost of this energy source. In this study, a new approach was developed for designing electrocatalysts for the ORR in fuel cells. These electrocatalysts consist of only one Pt monolayer on suitable carbon-supported Iridium-Nickel (IrNi) core-shell nanoparticles. The synthesis involved depositing a monolayer of Copper (Cu) on IrNi metal alloy surface at under-potentials, followed by galvanic displacement of the Cu monolayer with Pt.</p><p> It was found that the electronic properties of Pt monolayer could be fine-tuned by the electronic and geometric effects introduced by the substrate metal. The Pt mass activity of the new Pt monolayer IrNi electrocatalysts was up to six times higher than the state-of-the-art commercial Pt/C catalysts. The structure and composition of the core-shell nanoparticles were verified using transmission electron microscopy and in situ X-ray absorption spectroscopy, while potential cycling test was employed to confirm the stability of the electrocatalyst. The formation of Ir shell on IrNi alloy during annealing due to thermal segregation was monitored by time-resolved synchrotron XRD measurements. Our experimental results, supported by computations, demonstrated an effective way of using Pt that can resolve key ORR problems which include inadequate activity and durability while minimizing the Pt loading.</p>