Effect of thermal annealing on the properties of Corich core–Ptrich shell/C oxygen reduction electrocatalyst

The properties and the oxygen reduction reaction (ORR) characteristics of Pt/C and Corich core–Ptrich shell/C, which were prepared by the thermal decomposition and the chemical reduction methods, annealed in the various conditions were investigated. The alloying degree and grain size of Corich core–Ptrich shell/C analyzed by XRD was increased from 13.10% and 2.45 nm to 42.83% and 2.62 nm by increasing the time for annealing at 400 °C in N2 (annealing condition 1) from 0 to 15 h. When the Corich core–Ptrich shell/C was annealed in air at 250 °C and then reduced in 6% H2 at 400 °C (annealing condition 2), the alloying degree and grain size were obtained to be 47.26% and 3.79 nm, respectively. The decrease in the atomic ratio of Co/Pt from 4.77 to 1.34 by annealing Corich core–Ptrich shell/C in condition 1 from 0 to 15 h was deduced to be the increase in the Pt loading by the reduction of residual Pt precursor to Pt. The mass and specific activities (MA, SA) of the ORR at 0.9 V (versus RHE) on Pt/C annealed in condition 2 were obtained to be 4.11 A g−1 and 6.12 μA cm−2, respectively. The MA and SA of Corich core–Ptrich shell/C annealed by condition 2 were 10.07 A g−1 and 11.27 μA cm−2.