Activity and stability of PtxCr/C catalyst for oxygen reduction reaction: Effect of the Pt:Cr ratio and heat treatment atmosphere

A series of PtxCr/C catalysts (where x is the Pt atomic number, equal to 1, 2, 3, 4 and 5) was prepared by impregnation-seeding technique for the oxygen reduction reaction (ORR). The effect of the Pt:Cr ratio (1:1 to 5:1) and the heat-treatment atmosphere (H2 or N2) on the ORR activity and stability were explored in an acid solution and in a PEM fuel cell under H2/O2 and H2/air environments. The preliminary results demonstrated that increasing the Pt:Cr ratio increased the electrochemical surface area (ESA) of the catalyst, but decreased the degree of alloying. The heat treatment of the PtxCr/C catalyst under H2 or N2 environments induced an increased degree of alloying, but decreased the ESA as well as the formation of different catalyst morphologies, which consequently affected the ORR activity and stability of the PtxCr/C catalyst. In the absence of heat treatment, the Pt3Cr/C catalyst provided higher ORR activity and stability than Pt/C and other PtxCr/C catalyst. In the presence of heat treatment, the Pt3Cr/C(N2) catalyst exhibited the highest ORR activity in both acid electrolyte and in PEM fuel cell at 60 °C and ambient pressure. It also provided the highest stability in the acid solution compared with the other PtxCr/C catalysts.