Electrocatalytic Properties of PtCo∕C and PtNi∕C alloys for the Oxygen Reduction Reaction in Alkaline Solution

The oxygen reduction reaction (ORR) was studied on carbon-dispersed , , and alloys in electrolyte. A detailed discussion of the enhancement of the reduction kinetics based on the physical and electronic properties of the catalysts is presented. The characterization techniques considered were high-resolution transmission electron microscopy, XRD (X-ray diffraction), in situ XANES (X-ray absorption near edge structure), and EXAFS (extended X-ray absorption fine structure) measurements. Cyclic voltammetry and steady-state polarization measurements for the ORR were conducted using a rotating ring-disk electrode. The XANES results at the edge at anodic potentials showed lower oxide coverage on the catalysts, while at the Co and edges the results evidenced compositions that include Co or Ni metals and oxides. The XRD and EXAFS analyses showed a slight reduction of the interatomic distance in the Pt alloys compared to . The polarization curves indicated that the 4-electron mechanism is mainly followed for the ORR on all materials. The highest electrocatalytic activity was obtained for the alloy (1:1 atomic ratio), and this was attributed to less formation or faster electroreduction due to a lower -band center.