The structure modification and activity improvement of Pd-Co/C electrocatalysts by the addition of Au for the oxygen reduction reaction

In this study, Pd75Co25-xAux/C ternary catalysts with varying x content are synthesized by the deposition-precipitation approach with hydrogen reduction at 390 K for the oxygen reduction reaction (ORR). The roles of Au in the modification of structures, surface species and electrochemical properties of PdCo/C catalysts are investigated. X-ray diffraction results reveal that although the low reduction temperature does not benefit the Co alloying with Pd, Pd-Au alloys are preferentially formed. Moreover, it confirms that the incorporation of Au into a Pd-Co system contributes to the generation of inhomogeneous alloy structure. Fine structural details determined by X-ray absorption spectroscopy indicate that Au addition improves the heteroatomic intermixing extent of alloy nanocatalysts, especially for Pd75Co10Au15/C (Au-15) catalysts. Surface characterization by temperature programmed reduction suggests that a Pd-rich surface gradually changes to Pd, Au and alloy mixed surfaces when the Au content is larger than 15 at%. Regarding the electrochemical results, Au-15 displays the superior ORR performance among all samples due to the improved heteroatomic intermixing extent, large electrochemical surface area and multiple coexisting surface species. Furthermore, it also displays a better stability than Pd/C and Pd75Co25/C catalysts after accelerated durability tests.