Concentration Gradient Pd-Ir-Ni/C Electrocatalyst with Enhanced Activity and Methanol Tolerance for Oxygen Reduction Reaction in Acidic Medium

This study demonstrates a concept of concentration gradient (CG) Pd-Ir-Ni/C electrocatalyst consisting of IrNi alloy core, concentration gradient IrPd layer and Pd surface for the oxygen reduction reaction (ORR), which is synthesized by a facile sequential polyol method without any additional surfactant. The CG Pd-Ir-Ni/C electrocatalyst is characterized by X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. It is found that the Pd-Ir-Ni nanoparticles with a mean diameter of 5.8 ± 1.5 nm are uniformly distributed on the carbon support. These Pd-Ir-Ni nanoparticles possess a certain degree of Pd alloying through the spontaneous replacement reaction, and concentration gradient IrPd shell with Pd-rich surface. The ORR polarization measurement of the CG Pd-Ir-Ni/C catalyst illustrates a mass activity of 5.6 and 9.9 times that of Pd/C catalyst at 0.80 V and 0.7 V, respectively. Moreover, this catalyst exhibits a better ORR selectivity than commercial Pt/C catalyst in the presence of methanol. The enhanced electrocatalytic activity is mainly attributed to the optimal compressive lattice strain of surface Pd induced by the underlying concentration gradient layer. Our work provides a highly potential strategy to develop high performance and low cost electrocatalytic materials for fuel cells.