The Role of Transition Metals in the Catalytic Activity of Pt Alloys
In this study, the number of Pt layers was controlled by using the Cu-UPD-Pt-displacement technique,5 which has been successfully used to deposit Pt monolayer on various substrates. 6 In this method, a Cu monolayer was underpotentially deposited (UPD) on a cleaned Pt3Ni/C (after 20 potential cycles between 0.05 and 1.2 V) deposited on a rotating disk electrode (RDE). It then was displaced by Pt in a K2PtCl4 solution via a simple reaction: Cu + PtCl42- → Cu2+ + 4Cl- + Pt.
Our experimental results clearly show that the ORR activity decreases with the thickness of the pure Pt shell and the activity enhancement disappears when the Pt shell is ~4 atomic layer thick on the 4.5 nm Pt3Ni nanoparticles. The shell thickness dependent behavior is associated with the oxygen binding energies on the Pt shell. Density functional theory (DFT) calculations performed on nanoparticles are able to estimate the strain and ligand effects from the Pt3Ni core with different Pt shell thickness and the results agree well with the experimental data.
1. J. R. Kitchin; J. K. Nørskov; M. A. Barteau; Chen, J. G., J. Chem. Phys. 2004, 120, 10240;
2. Stamenkovic, V. R.; Fowler, B.; Mun, B. S.; Wang, G. F.; Ross, P. N.; Lucas, C. A.; Markovic, N. M., Science 2007, 315 (5811), 493-497.
3. van der Vliet, D. F.; Wang, C.; Li, D.; Paulikas, A. P.; Greeley, J.; Rankin, R. B.; Strmcnik, D.; Tripkovic, D.; Markovic, N. M.; Stamenkovic, V. R., Angew. Chem. Int. Ed. 2012, 51 (13), 3139-3142.
4. Yu, Y.; Xin, H. L.; Hovden, R.; Wang, D.; Rus, E. D.; Mundy, J. A.; Muller, D. A.; Abrua, H. D., Nano Letters 2012, 12 (9), 4417-4423.
5. Shao, M.; Peles, A.; Shoemaker, K., Electrocatalysis on Platinum Nanoparticles: Particle Size Effect on Oxygen Reduction Reaction Activity. Nano Letters 2011, 11 (9), 3714-3719.
6. Adzic, R. R.; Zhang, J.; Sasaki, K.; Vukmirovic, M. B.; Shao, M.; Wang, J. X.; Nilekar, A. U.; Mavrikakis, M.; Valerio, J. A.; Uribe, F., Platinum monolayer fuel cell electrocatalysts. Top. Catal. 2007, 46 (3-4), 249-262.