Singly versus Doubly Reduced Nickel Porphyrins for Proton Reduction: Experimental and Theoretical Evidence for a Homolytic Hydrogen‐Evolution Reaction |
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| Authors: | Yongzhen Han Dr Huayi Fang Huize Jing Huiling Sun Haitao Lei Prof?Dr Wenzhen Lai Prof?Dr Rui Cao |
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| Institution: | 1. Department of Chemistry, Renmin University of China, Beijing, China;2. College of Chemistry and Molecular Engineering, Peking University, Beijing, China;3. School of Chemistry and Chemical Engineering, Shaanxi Normal University, Xi'an, China |
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| Abstract: | A nickel(II) porphyrin Ni‐P (P=porphyrin) bearing four meso‐C6F5 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. |
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| Keywords: | bimetallic reactions electrocatalysis homolysis hydrogen evolution nickel porphyrins |
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