title: Singly versus Doubly Reduced Nickel Porphyrins for Proton Reduction: Experimental and Theoretical Evidence for a Homolytic Hydrogen-Evolution Reaction.
abstract: A nickel(II) porphyrin Ni-P (P=porphyrin) bearing four meso-C6 F5 groups to improve solubility and activity was used to explore different hydrogen-evolution-reaction (HER) mechanisms. Doubly reduced Ni-P ([Ni-P](2-) ) was involved in H2 production from acetic acid, whereas a singly reduced species ([Ni-P](-) ) initiated HER with stronger trifluoroacetic acid (TFA). High activity and stability of Ni-P were observed in catalysis, with a remarkable ic /ip value of 77 with TFA at a scan rate of 100 mV s(-1) and 20 °C. Electrochemical, stopped-flow, and theoretical studies indicated that a hydride species [H-Ni-P] is formed by oxidative protonation of [Ni-P](-) . Subsequent rapid bimetallic homolysis to give H2 and Ni-P is probably involved in the catalytic cycle. HER cycling through this one-electron-reduction and homolysis mechanism has been proposed previously but rarely validated. The present results could thus have broad implications for the design of new exquisite cycles for H2 generation.
authors.affiliation: Department of Chemistry, Renmin University of China, Beijing, 100872, China.
authors.forename: Yongzhen
authors.initials: Y
authors.lastname: Han
authors.affiliation: College of Chemistry and Molecular Engineering, Peking University, Beijing, 100871, China.
authors.forename: Huayi
authors.initials: H
authors.lastname: Fang
authors.affiliation: College of Chemistry and Molecular Engineering, Peking University, Beijing, 100871, China.
authors.forename: Huize
authors.initials: H
authors.lastname: Jing
authors.affiliation: Department of Chemistry, Renmin University of China, Beijing, 100872, China.
authors.forename: Huiling
authors.initials: H
authors.lastname: Sun
authors.affiliation: Department of Chemistry, Renmin University of China, Beijing, 100872, China.
authors.forename: Haitao
authors.initials: H
authors.lastname: Lei
authors.affiliation: Department of Chemistry, Renmin University of China, Beijing, 100872, China. wenzhenlai@ruc.edu.cn.
authors.forename: Wenzhen
authors.initials: W
authors.lastname: Lai
authors.affiliation: Department of Chemistry, Renmin University of China, Beijing, 100872, China. ruicao@ruc.edu.cn.|School of Chemistry and Chemical Engineering, Shaanxi Normal University, Xi'an, 710119, China. ruicao@ruc.edu.cn.
authors.forename: Rui
authors.initials: R
authors.lastname: Cao
keywords: bimetallic reactions; electrocatalysis; homolysis; hydrogen evolution; nickel porphyrins