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Electrochemically and Photochemically Induced Hydrogen Evolution Catalysis with Cobalt Tetraazamacrocycles Occurs Through Different Pathways


Grau, Sergi; Schilling, Mauro; Moonshiram, Dooshaye; Benet‐Buchholz, Jordi; Luber, Sandra; Llobet, Antoni; Gimbert‐Suriñach, Carolina (2020). Electrochemically and Photochemically Induced Hydrogen Evolution Catalysis with Cobalt Tetraazamacrocycles Occurs Through Different Pathways. ChemSusChem, 13(10):2745-2752.

Abstract

Cobalt complexes containing equatorial tetraazamacrocyclic ligands are active catalysts for the hydrogen evolution reaction in pure aqueous conditions. We investigated the effect of different groups directly linked to the macrocyclic ligand (−NH−, −NCH3−, or −N(CH2OH)−). In electrochemically induced hydrogen evolution catalysis at pH 4, the rate determining step is the protonation of the reduced CoI species that gives a cobalt hydride (CoIII−H), a key intermediate towards the H−H bond formation. In sharp contrast, under photochemical conditions using [Ru(bpy)3]2+ (bpy=2,2’‐bipyridine) as a photosensitizer and ascorbate as sacrificial electron donor, the formation of a Co0 species that quickly protonates to give a CoII−H is proposed. In this scenario, the rate determining step is the H−H bond formation that occurs in an intermolecular fashion from the CoII−H species and a water molecule. Both mechanisms are supported by DFT calculations, which allowed us to estimate the pKa values of the CoIII−H and CoII−H species and transition states based on intramolecular and intermolecular H−H bond formation from CoII−H.

Abstract

Cobalt complexes containing equatorial tetraazamacrocyclic ligands are active catalysts for the hydrogen evolution reaction in pure aqueous conditions. We investigated the effect of different groups directly linked to the macrocyclic ligand (−NH−, −NCH3−, or −N(CH2OH)−). In electrochemically induced hydrogen evolution catalysis at pH 4, the rate determining step is the protonation of the reduced CoI species that gives a cobalt hydride (CoIII−H), a key intermediate towards the H−H bond formation. In sharp contrast, under photochemical conditions using [Ru(bpy)3]2+ (bpy=2,2’‐bipyridine) as a photosensitizer and ascorbate as sacrificial electron donor, the formation of a Co0 species that quickly protonates to give a CoII−H is proposed. In this scenario, the rate determining step is the H−H bond formation that occurs in an intermolecular fashion from the CoII−H species and a water molecule. Both mechanisms are supported by DFT calculations, which allowed us to estimate the pKa values of the CoIII−H and CoII−H species and transition states based on intramolecular and intermolecular H−H bond formation from CoII−H.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Department of Chemistry
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:22 May 2020
Deposited On:01 Feb 2021 16:08
Last Modified:02 Feb 2021 21:00
Publisher:Wiley-VCH Verlag
ISSN:1864-5631
OA Status:Closed
Publisher DOI:https://doi.org/10.1002/cssc.202000283
Project Information:
  • : FunderSNSF
  • : Grant IDPP00P2_170667
  • : Project TitleIn Silico Investigation and Design of Bio-inspired Catalysts for Water Splitting

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