Cobalt/nitrogen co-doped porous carbon nanosheets as highly efficient catalysts for the oxygen reduction reaction in both basic and acidic media

Abstract

Porous carbon materials have been widely developed as catalysts for the oxygen reduction reaction (ORR) under basic conditions but very few under acidic conditions. In this work, two-dimensional (2D) cobalt/nitrogen co-doped porous carbon nanosheets were prepared as catalysts for the ORR under both basic and acidic conditions by using a cobalt porphyrin based 2D conjugated microporous polymer as a precursor. Remarkably, the as-prepared porous carbon nanosheets exhibited excellent electrochemical catalytic performance for the ORR, with a low half-wave potential (E_1/2) at −0.146 V in 0.1 M KOH and 0.54 V in 0.5 M H₂SO₄ (versus Ag/AgCl) as well as a dominant four-electron transfer mechanism (n = 3.8 at −0.28 V in 0.1 M KOH; n = 3.8 at 0.55 V in 0.5 M H₂SO₄). The high catalytic ORR performance can be attributed to the high activity of CoN_x active sites as well as the high specific surface area that derived from the cobalt porphyrin blocks among the conjugated microporous polymer nanosheets. It's believed that this method opens up new avenues for metal/heteroatom co-doped porous carbon materials with promising performance for energy storage and conversion.