Tuning strain effect and surface composition in PdAu hollow nanospheres as highly efficient ORR electrocatalysts and SERS substrates

•PdAu hollow nanospheres with ultrathin shells composed of Au-rich interlayers and tunable skins were synthesized by a simple one-pot strategy.•Pd-to-Au ratio can tune surface composition and strain, which makes it a paradigm for exploring optimal bimetallic PdAu catalyst structure.•Such nanocrystals are multifunctional nanocomposites with the integration of ORR and SERS performances, arising from Pd and Au respectively.•The mechanism of the enhanced ORR and SERS performances of PdAu hollow nanospheres was proposed.