Phosphate adsorption and its effect on oxygen reduction reaction for PtxCoy alloy and Aucore–Ptshell electrocatalysts

The phosphate adsorption characteristics and its effect on oxygen reduction reaction (ORR) were examined for various carbon-supported catalysts (Pt/C, Pt3Co/C, PtCo/C, and Aucore–Ptshell/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 N2O reduction technique, the surface structures were analyzed using N2O 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 Aucore–Ptshell/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 Aucore–Ptshell (30.2%) compared with the Pt/C catalyst (27.8%), confirming the phosphate adsorption characteristics of each catalyst, as measured by CV and N2O reduction analysis.

► The phosphate adsorption characteristics and its effect on oxygen reduction reaction were investigated.
► The CV and N2O reduction technique were utilized to analyze surface structure and phosphate adsorption.
► Pt/C, Pt3Co/C, PtCo/C, and Aucore–Ptshell/C were tested.
► The phosphate adsorption was stronger for Pt alloys and weaker for the core–shell catalyst, which could be related to the degree of ORR activity decay with phosphoric acid addition.