We report our recent advances in highly active, stable electrocatalysts comprising Pt monolayers (MLs) on Pd and PdAu alloy nanoparticles for the oxygen reduction reaction (ORR).1,2Their high advantageous characteristics resulted from the interactions induced by supporting nanoparticle cores on Pt shells. The PtML/Pd/C electrocatalystexhibited only a small loss of activity after 100,000 potential cycles from 0.7 to 0.9V. With the more stable Pd9Au1 alloy core, the PtML/Pd9Au1/C catalyst showed minimal degradation in activity over 100,000 cycles between potentials 0.6 and 1.0 V. Under more severe conditions with a potential range of 0.6–1.4 V, again we registered no marked losses in Pt and Au despite the dissolution of Pd.
The present workalso explores the changes in structural and electronic properties of Pt and Pt ML electrocatalysts using electrochemical cells by combining in situX-ray absorption spectroscopy (XAS) measurements.3 The XAS measurement demonstrated that Pt nanoparticle surfaces were oxidized from metallic Pt to α-PtO2-type oxide during the potential sweep from 0.41 V to 1.5 V, and the transition state of O or OH adsorption on Pt and the onset of the place exchange process were revealed by the delta mu (Δμ) method. Only the top layers of Pt nanoparticles were oxidized. At higher potential over 1.9 V, α-PtO2-type surface oxides dissolve due to local acidification caused by the oxygen evolution reaction and carbon corrosion. On the other hand, Pt oxidation of PtML on Pd nanoparticle electrocatalyst is considerably hampered compared with the Pt/C catalyst, because of preferential Pd oxidation/dissolution.
The remaining obstacles that are hindering commercialization of fuel cells include needs for increased Pt catalyst activity, improved durability, and reduced costs. To overcome these obstacles, we have investigated (i) nitride-stabilized core components,4 (ii) ordered intermetallics as cores or non-platinum electrocatalysts,5 and (iii) Au interlayer to improve Pt ML performance on refractory metal cores. In the meeting we will discuss potentials of these approaches. The results from thePt MLelectrocatalysts significantly impact the science of electrocatalysis and fuel-cell technology, as they demonstrated an exceptionally effective way of using Pt that can resolve problems encountered in other approaches.
Acknowledgement
This research was performed at Brookhaven National laboratory under contract DE-SC00112704 with the US Department of Energy, Office of Basic Energy Science, Material Science and Engineering Division, Division of Chemical Sciences, Geosciences and Biosciences Division.
References
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