A comparative study of PtCo, PtCr, and PtCoCr catalysts for oxygen electro-reduction reaction

A comparative study of carbon supported Pt30Co70, Pt30Cr70, and Pt30Co30Cr40 catalysts for oxygen electro-reduction reaction (ORR) activity was performed. In alloy catalysts synthesized via NaBH4 reduction, more than a 3-fold improvement was observed in ORR specific activity compared with that of Pt/C catalyst, while mass activities did not show significant improvement. After annealing at 900 °C under reducing conditions, the ORR specific activities of the alloy catalysts increased to give a relative ORR catalytic activity ordering of PtCo/C-900 (2800 μA cmPt−2) > PtCoCr/C-900 (1770 μA cmPt−2) > PtCr/C-900 (871 μA cmPt−2) > Pt/C-900 (393 μA cmPt−2) > Pt/C (334 μA cmPt−2). On the other hand, the ORR mass activity followed an order of PtCr/C-900 (140 mA mgPt−1) > PtCoCr/C-900 (111 mA mgPt−1) > PtCo/C-900 (84.1 mA mgPt−1). Cyclic voltammetry results suggest that incorporation of Cr resulted in a large electrochemically active surface area producing higher mass activity in the PtCr/C-900 catalyst although it showed the lowest specific activity among the alloy catalysts. The intermediate EAS and ORR activity values of the PtCoCr/C-900 catalyst suggest that the characteristics of the PtCo/C-900 (low mass and high specific activities) and PtCr/C-900 (high mass and low specific activities) are combined by alloying of Pt with both Co and Cr.