Electrocatalytic study of mechanically alloyed Cu-Ni alloys

The electrocatalytic activity mechanically alloyed Cu- 30, 70 and 90 at. % Ni alloy powders was studied for the hydrogen-evolution reaction. Mechanically alloyed (MA) Cu-Ni alloys were prepared from pure metal powders in an austenitic stainless steel mill under an argon atmosphere. Milled powders were characterized by X-ray diffraction, scanning electron microscope and transmission electron microscope. The electrocatalytic efficiency of mechanically alloyed Cu-Ni alloys was evaluated on the basis of electrochemical data obtained from cathodic curves in an electrolyte of 1 M KOH at 25°C. The electrochemical results of these alloys were compared to those of pure Cu and Ni, as well as same composition Cu-Ni alloys prepared by melting. The X-ray diffraction and transmission electron microscopy results indicated that the mechanical alloying process enabled us to obtain a single-phase alloy with a grain size of 30-50 nm. The polarization curves of these alloys were compared to pure nickel, as well as same composition Cu-Ni alloys prepared by melting. The resulting Tafel lines displayed a change in the slope. The second Tafel slope varies from 110 to 150 mV decade^-1, indicating not a variation in the reaction mechanism, but a modification of the surface state of electrodes. The exchange current density, i_o, of mechanically alloyed Cu-Ni alloys was higher than that of conventionally prepared Cu-Ni alloys. This suggests that the electrocatalytic activity for hydrogen evolution reaction (HER) is higher for the former alloys. This electrocatalytic activity seems to be associated with the reduction in the size of crystallites in MA alloys.