First principle calculations were used to screen the oxygen reduction activity of a series of Pd
3M@Pd
3Pt core-shell electrocatalysts for direct methanol fuel cells. Density functional theory (DFT) calculations indicate that the subsurface substitution of Pt by a 3d transition metal M improves the activity of the Pd
3Pt catalysts by reducing the oxygen binding energy [1]. Carbon-supported Pd
3M@Pd
3Pt (M=Ni, Co, Fe and Cr) core-shell electrocatalysts with similar particle size, a Pd
3Pt rich surface, and a Pd
3M alloy core were prepared by a galvanic replacement reaction [2] between PdM alloy nanoparticles with a 70:30 Pt:M atomic ratio and an aqueous solution of PtCl
42-. The predicted change in the surface Pt electronic structure was confirmed by comparing the calculated shift in the Pt 4f
7/2 core level binding energies with XPS data, and by comparing the change in the calculated CO binding energies with the shift in the position of the CO stripping peak. Optimal activity close to the maximum of a volcano curve [3] is predicted for Pd
3Fe@Pd
3Pt and Pd
3Mn@Pd
3Pt core-shell catalysts. In agreement with the DFT calculations, optimal activity and high methanol tolerance were observed for Pd
3Fe@Pd
3Pt. A lower activity is observed for the Pd
3Cr@Pd
3Pt catalyst with a lower CO binding energy and for the Pd
3Co@Pd
3Pt and Pd
3Ni@Pd
3Pt catalysts with higher CO binding energies. In the presence of 0.1 M methanol, the current density per Pt atom for the optimal Pd
3Fe@Pd
3Pt/C catalyst is 10 times higher than for commercial Pt/C catalysts. DFT calculations further indicate the CO and OH covered Pd
3Fe@Pd
3Pt electrocatalyst is stable towards Fe surface segregation.
References
1. J. Xu, J.H. Yang, J.Y. Lee, M. Saeys, Ind. Eng. Chem. Res., 49, 10251 (2010)
2. J.H. Yang, W.J. Zhou, C.H. Cheng, J.Y. Lee, Z.L. Liu, ACS Appl. Mater. Interfaces 2, 119 (2010)
3. J.K. Norskov, J. Rossmeisl, A. Logadottir, L. Lindqvist, J. Phys. Chem. B, 108, 17886 (2004)
