Metal phthalocyanines (MPcs, M=Co, Fe) are promising for reduction of oxygen (O2) because of their high catalytic activity, chemical stability, and abundance. The first and key step of the oxygen reduction reaction is adsorption of O2 on MPc catalysts. Here we investigate molecular-scale adsorption of O2 on cobalt(II) phthalocyanines (CoPc) supported on Ag(111), Cu(111) and Au(111) surfaces using ultrahigh vacuum scanning tunneling microscopy (UHV-STM), tip-enhanced Raman spectroscopy (TERS) with isotopologue substitution, and density functional theory (DFT) calculations. Four different molecular and atomic oxygen adsorption configurations are observed for CoPc/Ag(111), unambiguously assigned as O2/CoPc/Ag(111), O/CoPc/Ag(111), (O)2/CoPc/Ag(111) and CoPc/(O)2/Ag(111). These adsorption configurations indicate that both 2e- (no O2 dissociation) and 4e- (with O2 dissociation) reduction pathways are possible, in contrast with bulk measurements where only 2e- reduction pathway is observed. No oxygen adsorption is observed for CoPc supported on Cu(111) and Au(111) surfaces. Our results suggest an active role of the supporting metal surface in dissociating molecular O2, thus facilitating oxygen adsorption on CoPc.

Probing molecular-scale catalytic interactions between oxygen and cobalt phthalocyanine supported on metal surfaces

2019 Spring National Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.