Effect of thermal annealing on the properties of Co_(rich core)-Pt_(rich shell)/C oxygen reduction electrocatalyst

摘要

The properties and the oxygen reduction reaction (ORR) characteristics of Pt/C and Co_(rich core)-Pt_(rich 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 Co_(rich core)-Pt_(rich 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℃ in N_2 (annealing condition 1) from 0 to 15h. When the Co_(rich core)-Pt_(rich shell)/C was annealed in air at 250℃ and then reduced in 6% H_2 at 400℃ (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 Co_(rich core)-Pt_(rich 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, S A) of the ORR at 0.9 V (versus RHE) on Pt/C annealed in condition 2 were obtained to be 4.11 Ag~(-1) and 6.12μA cm~(-2), respectively. The MA and SA of Co_(rich core)-Pt_(rich shell)/C annealed by condition 2 were 10.07 Ag~(-1) and 11.27μA cm~(-2).