Structure–activity relationship in Co–N–C catalysts for multiple H2O2-related electrochemical reactions

Abstract

H₂O₂-related electrochemical reactions, including the two-electron oxygen reduction reaction (2e-ORR), H₂O₂ oxidation reaction (HPOR), and H₂O₂ reduction reaction (HPRR), have received significant attention for the electrosynthesis of H₂O₂ and energy storage. Understanding the complex structure–activity relationships among 2e-ORR/HPOR/HPRR and their connections is crucial for further developing highly efficient catalysts and working systems. Herein, we unveil these intricacies by employing model Co–N–C catalysts with a well-defined active site configuration (Co–N_4-pyrrolic and Co–N_4-pyridinic) in a combined experimental and computational approach. We report the higher 2e-ORR/HPOR but lower HPRR activity of the CoN_4-pyrrolic site than the CoN_4-pyridinic site based on their reaction free energy landscapes remodeled considering the chemisorption steps of O₂ and H₂O₂. The results reveal that the binding free energy of *OOH (ΔG_*OOH) can only be utilized as a reliable descriptor for 2e-ORR/HPOR activity, but not indicative of HPRR activity, regardless of the scaling relationship of the common reaction intermediates (*OOH or *OH). The HPRR activity of CoN₄ sites strongly depends on the H₂O₂ adsorption strength and configuration. These findings provide valuable insights into the design of catalysts for H₂O₂-related electrochemical energy conversion and storage systems.