Nitrogen- and Phosphorus-Doped Biocarbon with Enhanced Electrocatalytic Activity for Oxygen Reduction

The oxygen reduction reaction (ORR) at the cathode of fuel cells and metal–air batteries requires efficient electrocatalysts to accelerate its reaction rate due to its sluggish kinetics. Nitrogen- and phosphorus-doped biocarbon has been fabricated via a simple and low-cost biosynthesis method using yeast cells as a precursor. The as-prepared biocarbon exhibits excellent electrocatalytic activity for the ORR. An onset potential of −0.076 V (vs Ag/AgCl) and a negative shift of only about 29 mV in the half-wave potential of the biocarbon as compared to commercial Pt/C (20 wt % Pt on Vulcan XC-72, Johnson Matthey) is achieved. The biocarbon possesses enhanced electron poverty in carbon atoms and a decreasing amount of less electroactive nitrogen and phosphorus dopants due to the biomineralization during the synthesis. The surface gap layer along with the mesopores in the biocarbon increases accessible active sites and facilitates the mass transfer during the ORR. These factors correlate with the high ORR activity of the biocarbon. The results demonstrate that biomineralization plays a critical role in tailoring the structure and the electrocatalytic activity of the biocarbon for ORR.