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Two Novel Dinuclear Cobalt Polypyridyl Complexes in Electro- and Photocatalysis for Hydrogen Production: Cooperativity Increases Performance


Weder, Nicola; Grundmann, Nora S; Probst, Benjamin; Blacque, Olivier; Ketkaew, Rangsiman; Creazzo, Fabrizio; Luber, Sandra; Alberto, Roger (2022). Two Novel Dinuclear Cobalt Polypyridyl Complexes in Electro- and Photocatalysis for Hydrogen Production: Cooperativity Increases Performance. ChemSusChem, 15(17):e202201049.

Abstract

Syntheses and mechanisms of two dinuclear Co-polypyridyl catalysts for the H2 evolution reaction (HER) were reported and compared to their mononuclear analogue (R1). In both catalysts, two di-(2,2’-bipyridin-6-yl)-methanone units were linked by either 2,2’-bipyridin-6,6’-yl or pyrazin-2,5-yl. Complexation with CoII gave dinuclear compounds bridged by pyrazine (C2) or bipyridine (C1). Photocatalytic HER gave turnover numbers (TONs) of up to 20000 (C2) and 7000 (C1) in water. Electrochemically, C1 was similar to the R1, whereas C2 showed electronic coupling between the two Co centers. The E(CoII/I) split by 360 mV into two separate waves. Proton reduction in DMF was investigated for R1 with [HNEt3](BF4) by simulation, foot of the wave analysis, and linear sweep voltammetry (LSV) with in-line detection of H2. All methods agreed well with an (E)ECEC mechanism and the first protonation being rate limiting (≈104 m−1 s−1). The second reduction was more anodic than the first one. pKa values of around 10 and 7.5 were found for the two protonations. LSV analysis with H2 detection for all catalysts and acids with different pKa values [HBF4, pKa(DMF)≈3.4], intermediate {[HNEt3](BF4), pKa(DMF)≈9.2} to weak [AcOH, pKa(DMF)≈13.5] confirmed electrochemical H2 production, distinctly dependent on the pKa values. Only HBF4 protonated CoI intermediates. The two metals in the dualcore C2 cooperated with an increase in rate to a competitive 105 m−1 s−1 with [HNEt3](BF4). The overpotential decreased compared to R1 by 100 mV. Chronoamperometry established high stabilities for all catalysts with TONlim of 100 for R1 and 320 for C1 and C2.

Abstract

Syntheses and mechanisms of two dinuclear Co-polypyridyl catalysts for the H2 evolution reaction (HER) were reported and compared to their mononuclear analogue (R1). In both catalysts, two di-(2,2’-bipyridin-6-yl)-methanone units were linked by either 2,2’-bipyridin-6,6’-yl or pyrazin-2,5-yl. Complexation with CoII gave dinuclear compounds bridged by pyrazine (C2) or bipyridine (C1). Photocatalytic HER gave turnover numbers (TONs) of up to 20000 (C2) and 7000 (C1) in water. Electrochemically, C1 was similar to the R1, whereas C2 showed electronic coupling between the two Co centers. The E(CoII/I) split by 360 mV into two separate waves. Proton reduction in DMF was investigated for R1 with [HNEt3](BF4) by simulation, foot of the wave analysis, and linear sweep voltammetry (LSV) with in-line detection of H2. All methods agreed well with an (E)ECEC mechanism and the first protonation being rate limiting (≈104 m−1 s−1). The second reduction was more anodic than the first one. pKa values of around 10 and 7.5 were found for the two protonations. LSV analysis with H2 detection for all catalysts and acids with different pKa values [HBF4, pKa(DMF)≈3.4], intermediate {[HNEt3](BF4), pKa(DMF)≈9.2} to weak [AcOH, pKa(DMF)≈13.5] confirmed electrochemical H2 production, distinctly dependent on the pKa values. Only HBF4 protonated CoI intermediates. The two metals in the dualcore C2 cooperated with an increase in rate to a competitive 105 m−1 s−1 with [HNEt3](BF4). The overpotential decreased compared to R1 by 100 mV. Chronoamperometry established high stabilities for all catalysts with TONlim of 100 for R1 and 320 for C1 and C2.

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Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Department of Chemistry
08 Research Priority Programs > Solar Light to Chemical Energy Conversion
Dewey Decimal Classification:540 Chemistry
Scopus Subject Areas:Physical Sciences > Environmental Chemistry
Physical Sciences > General Chemical Engineering
Physical Sciences > General Materials Science
Physical Sciences > General Energy
Uncontrolled Keywords:General Energy, General Materials Science, General Chemical Engineering, Environmental Chemistry
Language:English
Date:7 September 2022
Deposited On:05 Jan 2023 13:13
Last Modified:22 Jun 2024 03:42
Publisher:Wiley-VCH Verlag
ISSN:1864-5631
OA Status:Hybrid
Free access at:Publisher DOI. An embargo period may apply.
Publisher DOI:https://doi.org/10.1002/cssc.202201049
Project Information:
  • : FunderUniversity Research Priority Program LightChEC
  • : Grant ID
  • : Project Title
  • : FunderSwiss National Science Foundation
  • : Grant IDIZLSZ2_170856
  • : Project Title
  • Content: Published Version
  • Licence: Creative Commons: Attribution 4.0 International (CC BY 4.0)