The exploration of new technologies for efficient energy management is attractive to reduce our dependence on environmentally unfriendly fossil fuels.
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This Pt–Pd–Au alloy possesses a suitable configuration for ORR, giving a relatively low free energy change for the final water formation from adsorbed OH intermediate during the reaction. Using aberration-corrected scanning transmission electron microscopy and atomically resolved elemental mapping, the origin of the activity change is revealed to be an atomic-scale evolution of the shell from an initial Pt–Pd alloy into a bilayer structure with a Pt-rich trimetallic surface, and finally into a uniform and stable Pt–Pd–Au alloy. The activity increases to 1.471 A mg Pt −1 after 30,000 potential cycles and is stable over a further 70,000 cycles. Here, we construct an unsupported nanoporous catalyst with a Pt–Pd shell of sub-nanometre thickness on Au, which demonstrates an initial ORR activity of 1.140 A mg Pt −1 at 0.9 V. Core–shell nanocatalysts have demonstrated potential as highly active low-Pt fuel cell cathodes for the oxygen reduction reaction (ORR) however, challenges remain in optimizing their surface and interfacial structures, which often exhibit undesirable structural degradation and poor durability.