(135b) Experimental and Theoretical Design of Novel Pt-Pd Nanocatalysts for the Oxygen Reduction Reaction
The oxygen reduction reaction currently limits the commercialization potential of fuel cells, due to the requirement of high Pt loadings at the fuel cell cathode1,2. We present the design of novel, shape-selected Pd@Pt core@shell nanoparticles with greatly reduced Pt loading and substantially enhanced activity using a combined experimental and theoretical approach. Through careful manipulation of synthesis conditions, we selectively deposit n (n = 1-8) uniform overlayers of Pt on Pd nanocrystal seeds with shapes including cubes3, octahedra4, and icosahedra. These nanocatalysts exhibit enhanced ORR activity and stability in comparison to the state-of-the-art commercial Pt catalyst; this activity depends on the number of Pt overlayers deposited. We additionally show that selective etching of Pd from these core@shell nanocrystals can leave behind Pt-Pd membranes of only a few atomic layers thick presenting further enhancements in ORR activity and stability. Detailed periodic, self-consistent density functional theory (DFT-GGA) calculations rationalize these trends by determining the ORR energetics on novel model surfaces. Our calculations show that OH removal is rate-determining, and that differences in OH binding energy explain the observed experimental trends. DFT calculations also offer insights into the mechanisms by which Pt is deposited onto the Pd seeds, as well as the process by which the Pd etching occurs.
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3. Xie, S.; Choi, S.-I.; Lu, N.; Roling, L. T.; Herron, J. A.; Zhang, L.; Park, J.; Wang, J.; Kim, M. J.; Xie, Z; Mavrikakis, M.; Xia, Y., Nano Letters 2014, 14, 3570.
4. Park, J.; Zhang, L.; Choi, S.-I.; Roling, L. T.; Lu, N.; Herron, J. A.; Xie, S.; Wang, J.; Kim, M. J.; Mavrikakis, M.; Xia, Y., ACS Nano 2015, 9, 2635.