Hf and Co Dual Single Atoms Co-Doped Carbon Catalyst Enhance the Oxygen Reduction Performance.

Single-atom metal-doped M-N-C (M═Fe, Co, Mn, or Ni) catalysts exhibit excellent catalytic activity toward oxygen reduction reactions (ORR). However, their performance still has a large gap considering the demand for their practical applications. This study reports a high-performance dual single-atom doped carbon catalyst (HfCo-N-C), which is prepared by pyrolyzing Co and Hf co-doped ZIF-8 . Co and Hf are atomically dispersed in the carbon framework and coordinated with N to form Co-N 4 and Hf-N 4 active moieties. The synergetic effect between Co-N 4 and Hf-N 4 significantly enhance the catalytic activity and durability of the catalyst. In an acidic medium, the ORR half-wave potential (E 1/2 ) of the catalyst is up to 0.82 V , which is much higher than that of the Co-N-C catalyst without Hf co-doping (0.80 V). The kinetic current density of the catalyst is up to 2.49 A cm -2 at 0.85 V , which is 1.74 times that of the Co-N-C catalyst without Hf co-doping. Moreover, the catalyst exhibits excellent cathodic performance in single proton exchange membrane fuel cells and Zn-air batteries. Furthermore, Hf co-doping can effectively suppress the formation of H 2 O 2 , resulting in significantly improved stability and durability.