Promotional effect of phosphorus doping on the activity of the Fe-N/C catalyst for the oxygen reduction reaction

Cost-effective, active and stable electrocatalysts for the oxygen reduction reaction (ORR) are highly desirable for the wide-spread adoption of technologies such as fuel cells and metal-air batteries. Among the already reported non-precious metal catalysts, carbon-supported transition metal-nitrogen complexes, i.e., M-N/C catalysts, are the most promising candidate. Herein, by comparing the ORR activities of standard Fe-N/C catalysts synthesized with or without the doped phosphorus species, the promotional effect of phosphorus doping is discerned. Such phosphorus doping is achieved by using an acidic phosphate ester as a dopant in the synthesis, which introduces no change in catalyst morphologies and structures. The linked structure of phosphate ester cations with the nitrogen precursor, i.e., polyaniline chain, is favored for the evenly P doping of the catalyst, showing to a superior ORR activity to that for the undoped Fe-N/C catalyst. The activity and durability of the catalysts are demonstrated in direct methanol fuel cells.