Sulfur-Doped Fe/N/C Nanosheets as Highly Efficient Electrocatalysts for Oxygen Reduction Reaction.

The high-temperature pyrolyzed Fe/N/C is one of the tremendous potential nonprecious metal electrocatalysts for oxygen reduction reaction (ORR). Metal-free carbon materials doped with heteroatoms have also demonstrated prominent electrocatalytic performance for ORR. The previous work of S-doping Fe/N/C was produced by pyrolyzing melamine and iron thiocyanate, in which S was from iron thiocyanate. Here, for the first time, we realized an in situ S-doping in Fe/N/C (denoted as S-Fe/N/C) electrocatalyst with S doping reaching 4.76 at % by pyrolyzing thiourea as the S source and iron acetate showing high-performance ORR activity in both alkaline and acid solution. The catalyst pyrolyzed at 700 °C and the mass ratio 1:0.2 shows the best activity for ORR. The optimal catalyst displays much greater durability and higher tolerance to methanol than Pt/C (20 wt %). Results of electrochemical measurements show that the S-Fe/N/C follows 4e pathway in alkaline and acid conditions.