Electro- and photocatalytic hydrogen generation in acetonitrile and aqueous solutions by a cobalt macrocyclic Schiff-base complex

Leung, Chi‐Fai; Chen, Yongzhen; Yu, Han‐Qing; Man, Wai‐Lun; Ko, Chi‐Chiu; Lau, Tai‐Chu

doi:10.1016/j.ijhydene.2011.06.062

Cited by 58 publications

(65 citation statements)

References 41 publications

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“…This structure was analogous to that of the Co II compound derived from 1 , with similar bond distances and angles . On the other hand, complex 3 is a Co III six‐coordinated compound with two chlorido ligands in the axial positions, which has very similar bond distances to those of 1 . The dangling alcohol on the amino group of the macrocyclic ligand in 3 is prone to coordination, generating compound 4 (Figure ).…”

Section: Resultsmentioning

confidence: 66%

“…A prominent example of a molecular hydrogen evolution catalyst precursor is the cobalt macrocyclic complex 1 (Figure ), which has shown remarkable stability under catalytic turnover in acidic water. This catalyst has been successfully used in electrocatalytic and photocatalytic systems in combination with metal‐based molecular photosensitizers, quantum dots, and organic dyes . The catalytic mechanism induced by 1 was recently studied through time‐resolved pump(laser)/X‐ray(probe) spectroscopy with pico‐microsecond time resolution under photocatalytic conditions, with a [Ru(bpy) 3 ] 2+ (bpy=2,2’‐bipyridine) photosensitizer.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2020

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Figure 8. Intermolecular vs. intramolecularH ÀHb ondformation. Transition states (TS) relevant to the hydrogen evolution reaction by catalysts 1-3.T he kinetic barriers (DG°)are indicated for each catalyst in kcal mol À1 and representative drawings of each TS is given for 1. DG°= G(TS)ÀG(Co II ÀH), see moredetails in the SupportingI nformation.Scheme1.Catalytic pathways towards hydrogen evolution by catalysts 1-3.RDS:rate determining step of the process.

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Section: Resultsmentioning

confidence: 66%

Section: Introductionmentioning

confidence: 99%

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

et al. 2020

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“…This result validates 1 as water-reduction catalyst with al ow onset overpotential similar to other water-reduction catalysts. [7][8][9] Bulk electrolysis was performed at À1.7 V Ag/AgCl during 3h to confirm the presence of H 2 .ATONo f9 50 was calculated after 3hwith %F of 95 %. Thea ctivity of the catalyst was assessed by performing an extended controlled potential experiment for 18 ha tÀ 1.7 V Ag/AgCl .A si ndicated in the inset in Figure 6 alinear charge build-up indicative of continued catalysis was observed over time associated with 5680 TONs and %F of 95 %.…”

Section: Methodsmentioning

confidence: 99%

“…Themost studied systems for H 2 generation from water [7] include cobalt complexes of tetra-and pentapyridines [8] as well as iminopyridines. [9] We have shown that [N 2 O 3 ]l igands support cobalt complexes in catalytic proton reduction. [10] Adapting this design to pyridine-rich environments yielded water reduction catalysts capable of 7000 turnovers.…”

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confidence: 99%

Distinct Proton and Water Reduction Behavior with a Cobalt(III) Electrocatalyst Based on Pentadentate Oximes

et al. 2015

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A new pentadentate oxime has been designed to drive the preferential coordination favored by Co(I) in catalysts used for proton/water reduction. The ligand incorporates water upon metal coordination and is water soluble. This Co(III) species is doubly reduced to Co(I) and exhibits H(+) reduction activity in the presence of weak acids in MeCN and evolves H2 upon protonation suggesting that the ligand design increases catalyst effectiveness. Superior catalysis is observed in water with a turnover number (TON) of 5700 over 18 h. However, the catalyst yields Co-based nanoparticles, indicating that the solvent media may dictate the nature of the catalyst.

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“…[4][5][6][7][8][9] The catalyst precursor [LCo III Cl 2 ] + (L = macrocyclic ligand) in Scheme 1 belongs to this family of HEC and has been used in electrochemical as well as photochemical catalysis showing excellent results. [10][11][12][13][14] In contrast to many other molecular HEC that are active only in organic solvents, complex [LCo III Cl 2 ] + works in pure aqueous conditions showing remarkable stability over a period of several hours. Although mechanistic studies based on electrochemical and spectroscopic methods such as electron paramagnetic resonance or UV-Vis spectroscopy have been reported, 12 a full understanding of the reaction pathway for the hydrogen evolution reaction catalyzed by [LCo III Cl 2 ] + has not been described.…”

Section: -Introductionmentioning

confidence: 99%

Tracking the Structural and Electronic Configurations of a Cobalt Proton Reduction Catalyst in Water

Moonshiram¹,

Gimbert‐Suriñach

Guda

et al. 2016

J. Am. Chem. Soc.

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Time resolved X-ray absorption spectroscopy (X-TAS) has been used to study the light induced hydrogen evolution reaction catalyzed by a highly stable tetradentate macrocyclic cobalt complex with the formula [LCo III Cl 2 ] + (L = macrocyclic ligand), [Ru(bpy) 3 ] 2+ photosensitizer and an equimolar mixture of sodium ascorbate/ascorbic acid electron donor in pure water. XANES and EXAFS analysis of a binary mixture of the octahedral Co(III) pre-catalyst and [Ru(bpy) 3 ] 2+ after illumination, revealed in-situ formation of a Co(II) intermediate with significantly distorted geometry and electron transfer kinetics of 51 ns. On the other hand, X-TAS experiments of the complete photocatalytic system in the presence of the electron donor showed the formation of a square planar Co(I) intermediate species within a few nanoseconds followed by its decay in the microsecond timescales. The Co(I) structural assignment is supported by calculations based on density functional theory (DFT). At longer reaction times, we observe the formation of the initial Co(III) species concomitant to the decay of Co(I), thus closing the catalytic cycle. The experimental Xray absorption spectra of the molecular species formed along the catalytic cycle are modeled using a combination of molecular orbital DFT calculations (DFT-MO) and Finite Difference Method (FDM). These findings allowed us to unequivocally assign the full mechanistic pathway followed by the catalyst as well as to determine the rate limiting step of the process, which consists in the protonation of the Co(I). This study provides a complete kinetics scheme for the hydrogen evolution reaction by a cobalt catalyst, revealing unique information for the development of better catalysts for the reductive side of hydrogen fuel cells.

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Electro- and photocatalytic hydrogen generation in acetonitrile and aqueous solutions by a cobalt macrocyclic Schiff-base complex

Cited by 58 publications

References 41 publications

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

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

Distinct Proton and Water Reduction Behavior with a Cobalt(III) Electrocatalyst Based on Pentadentate Oximes

Tracking the Structural and Electronic Configurations of a Cobalt Proton Reduction Catalyst in Water

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