Promotion mechanism of PtCo intermetallic ordered alloys in oxygen reduction reaction and its application in fuel cells

•A surface Pt-rich PtCo ordered alloy with 3 nm size was successfully synthesized.•The PtCo catalyst exhibited impressive performance of 1.4 W cm−2 @ 0.6 V in H2-air fuel cell.•The key intermediate of adsorbed O2* was detected by in-situ ATR-FTIR spectroscopy.•The adsorption intenty of O2* on the ordered PtCo intermetallic alloy is between Pt and disordered PtCo.