Kinetics of oxygen reduction reaction on Corich core-Ptrich shell/C electrocatalysts

The nanostructured Co-rich (core)-Pt-rich (shell)/C electrocatalysts were prepared by combining the thermal decomposition and the chemical reduction methods. The particle size of homemade Co-rich (core)-Pt-rich (shell)/C analyzed by TEM was significantly greater than that of Pt grain size calculated from the XRD data due to the existence of Co in core. The mass activity and specific activity of oxygen reduction reaction (ORR) at the overpotential (eta) of 0.1 V were 6.69 Ag (1) and 1.51 x 10 (5) Acm(2) For Pt/C, and 10.22 Ag-1 and 2.73 x 10 (5) Acm (2) for Co-rich core-Pt-rich shell in 0.5M HClO4 aqueous solution at 25 C. The Tafel slopes of ORR on Pt/C and Co-rich core-Pt-rich shell electrocatalysts were obtained as 64 and 67 mV dec (1) at a lower eta (50-100 mV), and 116 and 110 mV dec (1) at a higher eta(120-200 mV). The exchange current densities of ORR on Pt/C and Co-rich core-Pt-rich shell/C evaluated based oil the higher Tafel slope regions were 6.76 x 10 (5) and 9.21 x 10 (5) A cm (2), respectively. The experimental results indicated that the ORR on Co-rich core-Pt-rich shell/C electrocatalyst in 0.5 M HClO4 aqueous Solution was a four electron transfer mechanism and first order with respect to the dissolved oxygen. (C) 2008 Elsevier B.V. All rights reserved.