In-situ ECSTM investigation of H2O2 production in cobalt–porphyrin-catalyzed oxygen reduction reaction

We report the in-situ investigation of the production of H2O2in 5,10,15,20-tetra(4-methoxyphenyl)-21H,23H-porphyrin cobalt(Ⅱ)(Co TMPP)-catalyzed oxygen reduction reaction(ORR) in neutral electrolytes by electrochemical scanning tunneling microscopy(ECSTM) at the molecular scale.The adsorption of OOH-on active sites can be observed in STM images and is found to be correlated with the pH value of the electrolyte.The thermodynamic parameters of the formation of Co TMPP–OOHcomplex are extracted by the quantitative analysis of the STM images.Two stages of the ORR including the formation of H2O2and further reduction of H2O2at different reduction potentials can be revealed by electrochemical measurements.In-situ ECSTM experiments unambiguously identify the formation of the Co TMPP–OOH-complex as the high contrast species and its reduction and oxidation process.This work provides the direct evidence for understanding the formation and transformation process of H2O2at the molecular scale,which benefits the rational design of the high-efficiency electrocatalysts for ORR and H2O2production.