(583ez) Development of Novel Pt Monolayer Electrocatalysts for Oxygen Reduction in PEM Fuel Cells

It is well known that platinum exhibits superior oxygen reduction (OR) activity compared with other elements, making it an attractive cathode material for fuel cell applications.  However, pure platinum is far from an ideal material because of its large activation losses, limited stability, and high material cost; these deficiencies have greatly inhibited the development of efficient, reliable, and inexpensive proton exchange membrane fuel cells (PEM FCs) [1].  Previous experimental and computational studies have shown that it is possible to improve the performance of platinum cathodes by selectively tuning the chemical reactivity of catalytic sites through geometric and electronic effects induced by alloying [2-4].  Our group has previously developed a screening model that can predict OH binding energy, an important chemical descriptor that is correlated with OR activity [5].

Utilizing this model, our work aims to design novel electrocatalysts with superior performance compared with pure platinum.  Furthermore, by synthesizing a series of alloys of differing composition, we can experimentally validate the structure-activity relationship predicted by the model. In particular, we prepare several Pt monolayer catalysts through the galvanic replacement of underpotentially deposited Cu monolayers on Au alloy cores [6].  Extensive in situ and ex situ characterization verify the atomic and electronic structure of these core-shell Pt electrocatalysts. The oxygen reduction activity is determined through electrochemical testing of supported catalysts on a rotating disc electrode in a three-electrode cell.  All electrochemical measurements were performed at room temperature in a 0.1M HClO₄ electrolyte. Our results demonstrate that the compression of an Au lattice core improves OR activity until the lattice spacing approaches that of Pt.  At this point, OH will bind too weakly to facilitate the initial O₂ dissociation. 

References

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2. Kitchin, J.R.; Norskov, J.K.; Barteau, M.A.; Chen, J.G.; J. Chem. Phys. 2004, 120, 10240-10246.

3. Kitchin, J. R.; Norskov, J.K.; Barteau, M. A.; Chen, J. G.; Phys. Rev. Letters, 2004, 93, 15, 156801-4.

4.  Wang,C.; Chi, M.; Li, D.; Strmcnik, D.; van der Vliet, D.; Wang, F.; Komnicky, V.; Chang, K-C.; Paulikas, A.P.; Tripkovic, D. Pearson, J.; More, K.L.; Markovic, N.M.; Stemenkovic, V.R.; J. Am. Chem. Soc. 2011, 133, 14396-14403.

5. Xin, H.; Holewinski, A.; Linic, S.; ACS Catalysis, 2012, 2 (1), 12-16.

6. Sasaki, K.; Naohara, H.; Cai, Y.; Choi, Y. M.; Liu, P. Vukmirovic, M. B.; Wang, J. X.; Adzic, R. R.; Angew. Chem. Int. Ed.  2010, 49, 8206-8207.