| Summary: | It is of great importance to design highly active and stable electrocatalysts with low Pt loading to improve the sluggish kinetics of oxygen reduction reaction (ORR) for fuel cells. Herein, we report an epitaxial growth of a Pt–Pd bimetallic heterostructure with a Pt loading as low as 8.02 wt%. Both experimental studies and theoretical calculations confirm that the heterointerfaces play a major role in charge redistribution, which accelerates electron transfer from Pd to Pt, contributing to downshifting the d-band center of Pd and consequently greatly weakening the O adsorption energy for a critical optimal adsorption configuration of O∗ on the heterointerface. In particular, the adsorbed O∗, an intermediate in a bridge mode between adjacent Pt and Pd atoms, has a relative low adsorption energy, which easily forms H2O to escape for releasing the active sites toward ORR. The Pt–Pd heterostructured catalyst presents the highest mass activity of 6.06 A·mg−1Pt among all reported Pt–Pd alloyed or composited catalysts, which is 26.4 times of the sample Pt/C (0.23 A·mg−1Pt). Further, the fuel cell assembled by the electrocatalyst shows a current density of 1.23 A·cm−2 at 0.6 V and good stability for over 100 h.
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