Designing Co–N/C Cathode Catalysts with Dense Atomic Cobalt Sites for Enhanced PEMFC Performance

Metal‐nitrogen/carbon (M‐N/C) catalysts, particularly those incorporating Fe, Co, or Mn, are among the most promising non‐platinum group catalysts for the acidic oxygen reduction reaction (ORR) in fuel cells. This study reports a Co‐N/C catalyst featuring high (3 wt%) cobalt content exclusively present as atomic sites. Extended X‐ray absorption fine structure analysis confirms a tetrapyridinic Co‐N 4 coordination environment in the optimized (3.0)Co‐N/C Δ catalyst. The high cobalt loading leads to a significant density of electrochemically accessible active sites, 3.58 × 10 19 sites g −1 , quantified via the nitrite stripping method. The catalyst demonstrates excellent ORR activity in a rotating ring‐disk electrode setup, achieving a half‐wave potential (E 1/2 ) of 0.76 V at a low loading of 0.2 mg cm −2 and a mass activity of 3.5 A g −1 at 0.80 V RHE . Single‐cell hydrogen‐oxygen PEMFC tests achieve a peak power density exceeding 1.3 W cm −2 (iR‐corrected). Under hydrogen‐air condition, the catalyst delivers 0.54 A cm −2 at 0.60 V (0.39 W cm −2 ). Despite the intrinsically higher turnover frequency of Fe‐based sites, the optimized (3.0)Co‐N/C Δ catalyst achieves similar fuel cell performance to that of Fe‐N/C, highlighting the critical role of site density in overall activity.