DFT Study of Oxygen Reduction Reaction on Os/Pt Core−Shell Catalysts Validated by Electrochemical Experiment

Abstract

Proton exchange membrane fuel cells (PEMFCs) have attracted much attention as an alternative source of energy with a number of advantages, including high efficiency, sustainability, and environmentally friendly operation. However, the low kinetics of the oxygen reduction reaction (ORR) restricts the performance of PEMFCs. Various types of catalysts have been developed to improve the ORR efficiency, but this problem still needs further investigations and improvements. In this paper, we propose advanced Os/Pt core–shell catalysts based on our previous study on segregation of both bare surfaces and surfaces exposed to ORR adsorbates, and we evaluate the catalytic activity of the proposed materials by density functional theory (DFT). Quantum mechanics was applied to calculate binding energies of ORR species and reaction energy barriers on Os/Pt core–shell catalysts. Our calculations predict a much better catalytic activity of the Os/Pt system than that of pure Pt. We find that the ligand effect of the Os substrate is more important than the lattice compression strain effect. To validate our DFT prediction, we demonstrate the fabrication of Os/Pt core–shell nanoparticles using the underpotential deposition (UPD) technique and succeeding galvanic displacement reaction between the Pt ions and Cu-coated Os nanoparticles. The Os/Pt/C samples were evaluated for electrocatalytic activities toward the ORR in acidic electrolytes. The samples with two consecutive UPD-displacement reaction cycles show 3.5 to 5 times better ORR activities as compared to those of commercially available Pt/C. Our results show good agreement between the computational predictions and electrochemical experimental data for the Os/Pt core–shell ORR catalysts.

Group Members

William A. Goddard III

Charles and Mary Ferkel Professor