摘要
In an effort to provide visualization and understanding to the electronic ‘‘push effect' of axial ligands on the catalytic activity of cobalt macrocyclic molecules, we design a simple model system involving an[5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin]cobalt(II)(TMMPCo) monolayer axially-coordinated on thiol ligand modified Au electrode and explore the activity of the axial-ligand coordinated TMPPCo toward oxygen reduction reaction(ORR) in acidic medium. Three different ligands, with a decreasing order of coordinating ability as: 4-mercaptopyridine(MPy) > 4-aminothiolphenol(APT) > 4-mercaptobenzonitrile(MBN) are used and a maximum difference in ORR onset potential of 80 mV is observed between the MPy(highest onset potential) and MBN systems(lowest onset potential). The ORR activity of TMPPCo increases with the increase in binding strength of the axial ligand. A detailed mechanism study reveals that ORR on the three ligand coordinated TMPPCo systems shares the same2-electron mechanism with H2 O2 as the terminal product. Theoretical calculation into the structure of the ligand coordinated cobalt porphyrins uncovers the variation in atomic charge of the Co(II) center and altered frontier molecular orbital distribution among the three ligand systems. Both properties have great influence on the back-bonding formation between the Co(II) center and O2 molecules, which has been suggested to be critical toward the O2 adsorption and subsequent activation process.
In an effort to provide visualization and understanding to the electronic ‘‘push effect" of axial ligands on the catalytic activity of cobalt macrocyclic molecules, we design a simple model system involving an[5,10,15,20-tetrakis（4-methoxyphenyl）porphyrin]cobalt（II）（TMMPCo） monolayer axially-coordinated on thiol ligand modified Au electrode and explore the activity of the axial-ligand coordinated TMPPCo toward oxygen reduction reaction（ORR） in acidic medium. Three different ligands, with a decreasing order of coordinating ability as: 4-mercaptopyridine（MPy） > 4-aminothiolphenol（APT） > 4-mercaptobenzonitrile（MBN） are used and a maximum difference in ORR onset potential of 80 mV is observed between the MPy（highest onset potential） and MBN systems（lowest onset potential）. The ORR activity of TMPPCo increases with the increase in binding strength of the axial ligand. A detailed mechanism study reveals that ORR on the three ligand coordinated TMPPCo systems shares the same2-electron mechanism with H2 O2 as the terminal product. Theoretical calculation into the structure of the ligand coordinated cobalt porphyrins uncovers the variation in atomic charge of the Co（II） center and altered frontier molecular orbital distribution among the three ligand systems. Both properties have great influence on the back-bonding formation between the Co（II） center and O2 molecules, which has been suggested to be critical toward the O2 adsorption and subsequent activation process.
基金
supported by the National Key Research and Development Program of China (2017YFA0206500)
the National Natural Science Foundation of China (21635004, 21675079)
作者简介
Corresponding author:Hai-Bo Ma,E-mail addresses:haibo@nju.edu.cn,is a Professor at School of Chemistry and Chemical Engineering,Nanjing University.His research interests include:(1)density matrix renormalization group and other advances on numerical renormalization group methods for large correlated systems;(2)molecule design through Materials Genome Initiative by via machine learning and high-throughput computational virtual screening;(3)optoelectronic processes in organic photovoltaics;(4)excited states in macromolecules and condensed phases;Corresponding author:Feng-Bin Wang,E-mail:fbwang@nju.edu.cn,received her B.S.degree from Shandong University in 1998,and Ph.D.degree from Changchun Institute of Applied Chemistry,Chinese Academy of Sciences in 2003.She now works as a teacher at School of Chemistry and Chemical Engineering,Nanjing University.Her research interests include:(1)fabrication of nanomaterials for the application in biosensing and fuel cells;(2)micro/nanofluidic bioanalytical systems;Corresponding author:Xing-Hua Xia,E-mail:xhxia@nju.edu.cn,is a Professor at the State Key Laboratory of Analytical Chemistry in Nanjing University.The ongoing researches in Xia’s group include:(1)the understanding of bio-and chemical processes occurring at interfaces/surfaces:kinetics and mechanism of bio/electro-chemical catalysis reactions at functional electrode surfaces using in situ spectroscopic techniques,relationship between conformation and orientation of biomolecules and their functions of direct electron transfer and biocatalytic activity;(2)mass transport in micro/nanofluidic systems;(3)synthesis of bio-inspired functional materials for electrochemical energy conversion and storage;Yue Zhou received his B.S.degree from Nanjing Normal University.He is now a Ph.D.candidate in Nanjing University under the guidance of Prof.Xing-Hua Xia.His research focuses on the electrocatalytic and photoelectrochemical properties of oriented molecular assembly on surfaces and interfaces.
