Electrochemical oxygen reduction activity of carbon nitride supported on carbon black

Electrochemical oxygen reduction via nonprecious, Fe/N/C catalysts has potential to reduce the cost and increase acceptance of hydrogen-powered polymer electrolyte membrane fuel cells. However, because these materials are a complex mixture of carbon, nitrogen, and iron, the nature of the active site is still much debated. By using carbon nitride as an ideal, nitrogen-rich, iron-free catalyst we shed light on the role of carbon-nitrogen bonding in electrochemical oxygen reduction. Carbon nitride was synthesized on a carbon black support via a simple solvothermal process. The resulting material was pyrolyzed and characterized via a variety of techniques. Electrochemical testing revealed that carbon nitride pyrolyzed at 1000°C displayed the best oxygen reduction activity, with an onset potential of 0.90 V and a low selectivity to H ₂ O₂ formation, indicating a 4-electron oxygen reduction pathway. Due to small amounts of Fe contamination in this series of samples, an Fe-free sample was prepared without the carbon black support, resulting in similar electrochemical properties. The enhanced activity is tentatively attributed to enriched quaternary nitrogen in the material at this temperature, as suggested by X-ray photoelectron spectroscopy.