Rationally designed synthesis strategy for well-defined morphology which can endow the catalysts with unexpectedly enhanced catalytic properties remains a significant challenge in heterogeneous catalytic reactions. Hence, here we report a facile and controllable synthesis of polystyrene microsphere-supported Ag–Ni-alloyed catalysts (PS@Ag–Ni) with uniform core–shell structures through sulfonated treatment coupled with the subsequent liquid-phase reduction strategy. In this typical synthesis, sulfuric acid acts as the bifunctional roles in directing the core–shell morphology and the linker between the polystyrene microspheres and Ag–Ni alloy. The as-obtained PS@Ag–Ni optimized by tuning in a mass ratio of 1:1 shows superior oxygen reduction reaction activity and electrocatalytic performance toward the degradation of p-nitrophenol in comparison with other range of polystyrene microspheres and Ag–Ni alloy feeding ratios. The superior electrocatalytic and oxygen reduction reaction activity are attributed to its highly uniform core–shell morphology and exposure of much more active sites. Moreover, our as-prepared core–shell electrocatalysts will enable further investigation in other catalytic reactions. GRAPHICAL ABSTRACT