Synthesis and hydrogenation properties of Ni-Co bimetallic nanoparticles

The kinetics of the formation of bimetallic Ni-Co nanoparticles (Ni-Co-NPs) via the reduction of Ni and Co hydroxides by hydrazine in alkaline water/ethylene glycol solution has been studied. It was found that the rate of the Ni-Co-NPs nucleation linearly depends on the initial concentration of Ni(OH)(2). However, the rate of nanoparticles growth is sharply increased in the case of bimetallic Ni-Co-NPs compared to Ni-NPs and almost does not change over the entire range of Ni/Co ratio. Using the scanning electron microscopy (SEM) and the X-ray diffraction analysis, it was found that the mean size and the polydispersity of Ni-Co-NPs are decreased with the decrease of the fraction of Ni up to 50% but are increased in the case of Ni25Co75. The electrochemical charge/discharge multicycling of NPs electrodes was carried out in view of material potential usefulness as conductive metallic binder with own capacity for Ni/MH batteries. Replacing the Ni by Co in Ni-Co-NPs increases the discharge capacity of the electrode to 63 mAh/g for the Ni50Co50 composition. Cyclic stability of Co-free NPs is visibly better in comparison with binary Ni-Co-NPs. Additional electrochemical measurements for the Ni-NPs and Ni50Co50-NPs showed that the high rate dischargeability, HRD1000, is increased from 54 to 74%, but the discharge time according to the chronoamperometric data drastically is decreased at constant potential of - 0.6 V vs Ag/AgCl electrode.