Low-loading Pt nanoparticles combined with the atomically dispersed FeN4 sites supported by FeSA-N-C for improved activity and stability towards oxygen reduction reaction/hydrogen evolution reaction in acid and alkaline media

•The synergistic effect exists between Pt NPs and FeN4 sites in Pt@FeSA-N-C.•The FeN4 sites can anchor and isolate Pt NPs, which hinder its aggregation.•Pt NPs were reduced by urea hydrolysis, avoiding the large particles size with uneven distribution.•Pt@FeSA-N-C with a 5.5 wt.% low Pt loading.•High ORR and HER performances are obtained in both acid and alkaline media.