Highlights A unique catalyst surface where ultrathin Pt edges are modified by the isolated Pd atoms and BiOx adatoms is rational designed and achieved. The Pd1/Pt-BiOx electrocatalyst exhibits an ultrahigh mass activity of 16.01 A mg−1 Pt+Pd toward ethanol oxidation and enables a direct ethanol fuel cell of peak power density of 56.7 mW cm−2. The surrounding BiOx adatoms are critical for mitigating CO-poisoning on Pt surface, and the Pd1/Pt single-atom alloy further facilitates the electrooxidation of CH3CH2OH.