Abstract
The phosphate adsorption characteristics and its effect on oxygen reduction reaction (ORR) were examined for various carbon-supported catalysts (Pt/C, Pt 3Co/C, PtCo/C, and Au core–Pt shell/C). Using cyclic voltammetry (CV) and the addition of phosphoric acid, the degree of phosphate adsorption for each catalyst was evaluated based on the intensity of the phosphate adsorption peaks (0.25–0.3 V and 0.5–0.65 V) and on the decrease in the platinum oxidation current (0.9 V). In the N 2O reduction technique, the surface structures were analyzed using N 2O as an electrochemical probe, which showed that as the Co content increased, (i) steps or defects were introduced by surface reconstruction, (ii) the phosphate adsorbed more strongly compared to Pt/C with a preference for the terrace sites, and (iii) the potential of zero total charge (PZTC) shifted to negative potentials. In the case of the Au core–Pt shell/C, the phosphate adsorption was found to be weaker than other catalysts, including Pt/C catalyst. The relative ORR activity with PA addition, normalized by that with no phosphate adsorption, was significantly smaller for Co containing alloy catalysts (PtCo/C: 18.2%) and larger for Au core–Pt shell (30.2%) compared with the Pt/C catalyst (27.8%), confirming the phosphate adsorption characteristics of each catalyst, as measured by CV and N 2O reduction analysis.
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