Metal-free nitrogen-doped carbon foam electrocatalysts for the oxygen reduction reaction in acid solution

Metal-free, nitrogen-doped carbon foam is utilized as a model non-precious electrocatalyst system to investigate the role of nitrogen in the oxygen reduction reaction (ORR) in the absence of iron contamination. This graphene-like foam displays relatively high activity for the ORR in acid, despite being proven free from transition-metal impurities. The onset potential is 0.85 V_RHE, the mass activity is 2.8 A/g at 0.6 V_RHE, and the current density is -4.0 mA/cm². The maximum electron transfer number is calculated to be 3.6, revealing that a 4-electron pathway is possible in nitrogen-doped carbon, even in the absence of transition-metal coordination sites. The excellent electrochemical activity is attributed to the large surface area (700 m²/g), improved conductivity after graphitization, and the relatively high proportion of tertiary (graphite-like) nitrogen.