Oxygen reduction reaction on cobalt-nickel alloys prepared by mechanical alloying

Mechanical alloying technique was used to prepare several Co-Ni alloys in a high-energy SPEX 8000 mill. The initial ratios of elemental Co-Ni powders were 30:70, 40:60, 50:50, 60:40 and 70:30 wt.%. Elemental cobalt and nickel powders were milled separately during 20 h as a reference. XRD results indicated that crystalline solid solutions were achieved after 5 h of milling. TEM observations revealed that mechanical alloys consist of agglomerated fine particles of about 10 nm in size. Electrochemical measurements showed that the Co-Ni 30:70 wt.%, in particular, exhibited the highest current density for the oxygen reduction reaction (ORR) via four electrons.