Promoted activity of nitrogen-doped activated carbon as a highly efficient oxygen reduction catalyst in microbial fuel cells

Abstract

Despite the wide application of activated carbon (AC) as cathode electrocatalyst in microbial fuel cell (MFC), the enhancement of its catalytic activity is crucial to reduce its high loading on air-cathode. Herein, we synthesize nitrogen-doped activated carbon (NAC) by pyrolyzing phthalocyanine (Pc) adsorbed on AC to develop an efficient oxygen reduction reaction (ORR) electrocatalyst. The optimized mass ratio of AC to Pc improves the crystalline structure and porous structure of the NAC. Elemental analysis indicates that this material contains appropriate content of pyrrolic and pyridinic types of nitrogen and oxygen species. The NAC shows an ORR onset potential of 0.468 V (vs. Standard hydrogen electrode), an electron transfer number of 3.90, and high electrochemically accessible surface area, thereby illustrating enhanced electrocatalytic activity in the neutral medium relative to alkali-treated activated carbon (b-AC) and commercial platinum catalyst. Owing to the high activity, a small amount of NAC with a loading of 15 mg cm− 2 on the air-cathode of MFC is sufficient to achieve the maximum power density of 1026.07 ± 10.83 mW m− 2, which is higher than that of b-AC and comparable to platinum catalyst. The reduced loading of NAC indicates that the material can be used as cathode electrocatalyst for the ongoing effort to scale up MFC in the future.