Mechanically activated Pt–Ni and Pt–Co alloys as electrocatalysts in the oxygen reduction reaction

• Ni0.75Pt0.25 and Co0.75Pt0.25 alloys were obtained by means of mechanical alloying, and they showed activity towards ORR.
• After 9 h of milling ZrO/CoO or ZrO/NiO were obtained.
• After 9 h of milling Co0.75Pt0.25 increased Pt d-band vacancy compared with Pt nanoparticles and Pt foil.
• The electrocatalytic activity of Co0.75Pt0.25/C-9 h in the ORR is higher than Pt ETEK.

Mixtures of powders of platinum with nickel or cobalt to obtain Ni0.75Pt0.25 or Co0.75Pt0.25 were mechanical alloyed by high energy ball milling. The results of crystal structure, morphology and electrocatalytic performance are presented for mechanically activated powders after 3 and 9 h of ball milling. Total solid solutions of Ni and Co with platinum were analyzed by X-ray diffraction after 3 h of ball milling. After 9 h of ball milling, in both cases, the total solid solution was accompanied by the appearance of NiO or CoO and ZrO associated with a redox reaction with the milling media. The presence of zirconium monoxide was confirmed by energy dispersive spectroscopy analysis. In both cases, an amorphization was detected. X ray absorption spectroscopy measurements showed changes in atomic and electronic environment of platinum, a reduction of the distance to the first coordination sphere and increased d-band vacancy vs pure Pt and Pt nanoparticles were observed for both studied systems. The electrocatalytic activity was determined using cyclic and linear voltammetry. The Co0.75Pt0.25 alloy milled for 9 h showed a higher electrochemical activity for the oxygen reduction reaction (ORR) compared with the other samples, including Pt-Etek. The degree of the ORR electrochemical activity was correlated with the presence of ZrO, which could affect the oxygen adsorption and improve the catalytic activity for the oxygen reduction reaction.

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