Platinum-Nickel (Pt3Ni) Alloy Nanoparticles Decorated Graphene As a Catalyst of Oxygen Electrode in Li-O2 Cells
The catalytic activity of Pt3Ni-RGO is investigated by cyclic voltammetry and rotating disk electrode (RDE) studies in a non-aqueous electrolyte containing tetrabutyl ammonium perchlorate. Cyclic voltammograms recorded at several sweep rates consist of O2 reduction current peaks as well as oxygen evolution current peaks. Both peak currents increase with square root of sweep rate following the Randles Sevcik equation. The RDE studies provide diffusion limited current at several speeds of RDE. The data follow Levich and Koutecky-Levich equations. The values of number of electrons and diffusion coefficient of O2 calculated using these equations are 0.93 and 1.75 x 10-5 cm2 s-1, respectively.
Several Li-O2 cells employing Pt3Ni-RGO as the O2 electrode bi-functional catalyst are assembled and subjected to charge-discharge studies. The discharge capacity obtained at a current density of 0.3 mA cm-2 is 9016 mAh g-1 (8.36 mAh cm-2). It is seen that there is a decrease in discharge capacity initially on repeated charge-discharge cycling. Nevertheless, the discharge capacity stabilizes in a few cycles. The capacity obtained at the end of 10 cycles is 3641 mAh g-1 (3.27 mAh cm-2). Results of these studies will be presented.