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Hydrogen evolution by cobalt hangman porphyrins under operating conditions studied by vibrational spectro-electrochemistry

Kielb, Patrycja and Horch, Marius and Wrzolek, Pierre and Goetz, Robert and Ly, Khoa H. and Kozuch, Jacek and Schwalbe, Matthias and Weidinger, Inez M. (2018) Hydrogen evolution by cobalt hangman porphyrins under operating conditions studied by vibrational spectro-electrochemistry. Catalysis Science and Technology, 8 (7). pp. 1849-1857. ISSN 2044-4753.

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Cobalt hangman complexes are promising catalysts for dihydrogen production, yet their electrocatalytic performance in aqueous environment is still a topic of dispute. Surface-enhanced resonance Raman (SERR) spectro-electrochemistry has a great potential to give insight into the reaction mechanism of such molecular catalysts attached to electrodes under turnover conditions. However, the intrinsic catalytic activity of plasmonic supports and photoinduced side-reactions make the in situ analysis of their structures very challenging. In this work, the structure of hangman complexes attached to electrodes via dip-coating was investigated during catalytic turnover by electrochemistry and SERR spectroscopy. In order to explore the relevance of the hanging group for proton supply, complexes bearing a carboxylic acid and an ester hanging group were compared. For the former, SERR spectra recorded under turnover conditions indicate the reductive formation of a Co^(III)–H species, followed by laser-induced translocation of a proton to the carboxylic hanging group and the associated formation of the Co^I state. Due to the lack of a proton accepting group, hangman complexes with an ester group could not be trapped in the Co^I intermediate state and as a consequence SERR spectra solely reflected the (photo-enriched) Co^(II) resting state under turnover conditions. These results represent the first Raman spectroscopic insights into intermediates of dihydrogen evolution catalysed by cobalt hangman complexes on electrodes and support the direct involvement of the hanging group as a proton shuttle.

Item Type:Article
Related URLs:
URLURL TypeDescription Information
Kielb, Patrycja0000-0003-2809-0813
Kozuch, Jacek0000-0002-2115-4899
Schwalbe, Matthias0000-0003-4209-1601
Weidinger, Inez M.0000-0001-9316-6349
Additional Information:© 2018 The Royal Society of Chemistry. Received 3rd November 2017, Accepted 20th February 2018, First published on 21st February 2018. We thank Prof. Peter Hildebrandt for helpful discussions. Financial support from the DFG (EXC 314 UniCat, KO 5464/1-1) and the European Union via the Horizon 2020 program (Marie Curie Grant GAN 701192 – ‘VSHER’ for K. H. Ly) is gratefully acknowledged.
Funding AgencyGrant Number
Deutsche Forschungsgemeinschaft (DFG)KO 5464/1-1
Marie Curie Fellowship701192
Issue or Number:7
Record Number:CaltechAUTHORS:20180308-104748160
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:85201
Deposited By: Tony Diaz
Deposited On:08 Mar 2018 21:55
Last Modified:09 Mar 2020 13:18

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