Isolated metal-nitrogen sites are highly active to catalyze the oxygen and carbon dioxide electroreduction, however, the limited content of isolated metal-nitrogen sites within carbon matrix urgently requires full exposure of the active sites on the surface for efficient catalysis. Herein, post-synthetic modification strategy is explored to selectively confine ammonium ferric citrate on the surface of zeolitic imidazolate framework-8 (ZIF-8) nanoparticles. After pyrolysis, isolated iron-nitrogen sites are generated and located on the carbon matrix surface. The highly exposed iron-nitrogen sites demonstrate excellent mass activity toward oxygen reduction reaction in acidic medium, outperforming most reported non-noble metal catalysts, and also show superior selectivity and mass activity toward carbon dioxide electroreduction compared to most reported noble metal catalysts.