Single-Molecule Study on the Catalytic Role of Co–O<sub>2</sub> Binding in ORR by In Situ ECSTM
Yuqi Wang, Xiaohan Dan, Zhen-Yu Yi, Xiang Wang, Ya‐Chen Feng, Yue Feng, Dong Wang, Li‐Jun Wan
Abstract
We report here the in situ electrochemical scanning tunneling microscopy (ECSTM) study of O 2 adsorption and reduction on cobalt porphyrin (CoOEP) and phthalocyanine (CoPc). Electrochemical measurements reveal higher ORR activity of CoOEP than CoPc. Self-assembled CoOEP and CoPc monolayers are fabricated on Au(111) substrates and molecularly resolved by ECSTM. The direct molecular imaging demonstrates that O 2 adsorbs on Co II sites and barely on Co III sites. The CoOEP–O 2 and CoPc–O 2 complexes exhibit high contrast in ECSTM images due to O 2 binding. The surface coverage of CoOEP–O 2 is ca. 1.4 times higher than that of CoPc–O 2 . The dynamics of O 2 adsorption is measured quantitatively by fitting data from potential step experiments to obtain rate constants for O 2 adsorption ( k ad ) and dissociation ( k di ) on Co centers. k ad and k di are higher on CoOEP than on CoPc, indicating higher dynamics of O 2 binding and lower barriers to Co–O dissociation on CoOEP.