Breaking ORR kinetic barriers in acid: Synergistic catalysis on PtPd dendrites featuring tailored asymmetry and high-index facets

Overcoming kinetic limitations in the acidic oxygen reduction reaction (ORR) demands Pt-based catalysts with optimized surface adsorption. Herein, we engineer hierarchical PtPd dendrite nanocrystals (PtPd NDs) featuring precisely tailored asymmetric sites and high-index facets (HIFs) to overcome the kinetic limitations in acidic media. Controlled Pd incorporation disrupts symmetry of the single-oriented crystal plane, generating inhomogeneous strain and promoting HIFs exposure. This synergistic structural engineering optimizes the adsorption/desorption of oxygen-containing intermediates, significantly accelerating ORR kinetics. Consequently, PtPd NDs deliver exceptional mass activity (MA = 1.37 A mgPt−1, 11.42 times higher than Pt/C) and remarkable stability (83.9 % MA retention after durability testing). In H2-Air fuel cells, PtPd NDs also achieve higher peak power density versus Pt/C cathodes. In situ synchrotron radiation infrared spectroscopy and theoretical studies reveal that the synergistic effect between asymmetric sites and HIFs stimulates the strain field and causes a downward shift in the d-band center, thereby lowering the *OOH formation barrier and weakening intermediate adsorption, directly boosting the ORR performance. This work underscores the critical role of facet and site engineering in designing high-performance fuel cell electrocatalysts.