Pt, PtCo and PtNi electrocatalysts prepared by mechanical alloying for the oxygen reduction reaction in 0.5 M H₂SO₄

Electrocatalysts of Pt, PtCo and PtNi powders for the oxygen reduction reaction (ORR) were processed by Mechanical Alloying. Physical characterization was made by X-ray diffraction, scanning electron microscopy and scanning transmission electron microscopy. It was found that milled powders formed agglomerates in the range of 0.2-20 μm formed by nanometric size crystallites. The synthesized powders were alloys of PtFe, PtCoFe and PtNiFe due to iron incorporation during the milling process. The binding energies of Pt in the alloys were determined by XPS. Polarization curves were obtained by Rotating Disk Electrode technique in 0.5 M H₂SO₄ to determine the electrocatalytic activity of the mechanically alloyed powders. Tafel curves were plotted and kinetic parameters for the ORR were calculated. The PtFe alloy showed the highest electrocatalytic activity for the ORR. However, the lowest overpotential was found for the PtCoFe alloy and it also showed a higher current exchange density. A linear relationship was found between the Pt-binding energy in the alloys and the overpotential at the same current density independent of the Pt alloy composition.