Ternary Pt-Fe-Co Alloy Electrocatalysts Prepared by Electrodeposition: Elucidating the Roles of Fe and Co in the Oxygen Reduction Reaction

An electrodeposition-based protocol for the synthesis of ternary Pt-Fe-Co electrocatalysts for the oxygen reduction reaction (ORR) has been developed. The eletrodeposition method suits the purpose of fast catalyst screening and mechanism studies. Here, we survey the composition effect of Fe and Co atoms in ternary Pt-Fe-Co alloy electrocatalysts on the electrocatalytic activity toward the ORR in terms of geometric (Pt-Pt distance) and electronic (core-level binding energy, d-band center) aspects. A wide range of Pt-Fe-Co catalysts can easily be obtained using electrodeposition under simple and mild conditions. Among the various compositions, Pt85Fe10Co5 catalyst shows excellent mass activity that is 3.5 times higher than that of pure Pt. Interestingly, the ORR kinetic current density reveals a double-volcano plot as a function of alloy composition. Extended X-ray absorption fine structure (EXAFS) spectroscopy and high-resolution X-ray photoelectron spectroscopy (HRXPS) experiments were conducted to explain the abnormal double-volcano behavior. The results also reveal that the d-band center of Pt85Fe10Co5 is downshifted by about 0.1 eV compared to that of Pt, which explains its superior activity toward the ORR.