What Is the Rate-Limiting Step of Oxygen Reduction Reaction on Fe–N–C Catalysts?

Oxygen reduction reaction (ORR) is essential to various renewable energy technologies. An important catalyst for ORR is single iron atoms embedded in nitrogen-doped graphene (Fe–N–C). However, the rate-limiting step of the ORR on Fe–N–C is unknown, significantly impeding understanding and improvement. Here, we report the activation energies of all of the steps, calculated by ab initio molecular dynamics simulations under constant electrode potential. In contrast to the common belief that a hydrogenation step limits the reaction rate, we find that the rate-limiting step is oxygen molecule replacing adsorbed water on Fe. This occurs through concerted motion of H2O desorption and O2 adsorption, without leaving…

• NS
  National Science Foundation

  Awards: 1900039, 2029442
• WF
  Welch Foundation

  Award: F-1959-20180324