Complexes of earth-abundant metals for catalytic electrochemical hydrogen generation under aqueous conditions

Thoi, V. Sara; Sun, Yujie; Long, Jeffrey R.; Chang, Christopher J.

doi:10.1039/c2cs35272a

Cited by 619 publications

(525 citation statements)

References 105 publications

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“…Therefore, the development of homogeneous and heterogeneous earth-abundant alternatives to Pt is of considerable interest. [8,9,[69][70][71] Important metrics for evaluating the activity of HER catalysts are the overpotential to achieve acurrent density of 10 mA cm À2 ,t he FE for H 2 production, and the Ta fel slope. Overpotentials near thet hermodynamic potentialf or the HER and efficienciesn ear unity are necessary if replacement of Pt is to be realized.…”

Section: Hermentioning

confidence: 99%

Electrocatalytic Metal–Organic Frameworks for Energy Applications

2017

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With the global energy demand expected to increase drastically over the next several decades, the development of a sustainable energy system to meet this increase is paramount. Renewable energy sources can be coupled with electrochemical conversion processes to store energy in chemical bonds. To promote these difficult transformations, electrocatalysts that operate at high conversion rates and efficiency are required. Metal–organic frameworks (MOFs) have emerged as a promising class of materials; however, the insulating nature of MOFs has limited their application as electrocatalysts. The recent development of conductive MOFs has led to several electrocatalytic MOFs that display activity comparable to that of the best‐performing heterogeneous catalysts. Although many electrocatalytic MOFs exhibit low activity and stability, the few successful examples highlight the possibility of MOF electrocatalysts as replacements for noble‐metal‐based catalysts in commercial energy‐converting devices. We review herein the use of pristine MOFs as electrocatalysts to facilitate important energy‐related reactions.

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Section: Hermentioning

confidence: 99%

Electrocatalytic Metal–Organic Frameworks for Energy Applications

2017

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“…In this context, the use of molecular cobalt-based catalysts, stabilized by nitrogen donor ligands, has proven to be a good alternative given the high turnover numbers and stability achieved under catalytic conditions. [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.…”

Section: -Introductionmentioning

confidence: 99%

“…Non centrosymmetric geometries have been shown to have an increased intensity in their pre-edge features due to an increase in the metal 4 p mixing into the 3 d orbitals contributing towards the electric dipole 1s to 4 p character of this transition as shown in Solomon et al [46][47][48] . Octahedral Co(III) complexes have a d 6 configuration showing a predominant pre-edge peak 46 . However, local distortions of the octahedron around Co result in additional splitting of the d levels ( Figure S4, Supporting Information).…”

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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“…Hydrogen is an ideal energy carrier to meet future energy demands 1, 2, 3, 4, 5. Its generation by proton reduction is a key step in solar‐to‐chemical energy conversion 6, 7, 8.…”

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confidence: 99%

Singly versus Doubly Reduced Nickel Porphyrins for Proton Reduction: Experimental and Theoretical Evidence for a Homolytic Hydrogen‐Evolution Reaction

et al. 2016

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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 i c/i p 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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Complexes of earth-abundant metals for catalytic electrochemical hydrogen generation under aqueous conditions

Cited by 619 publications

References 105 publications

Electrocatalytic Metal–Organic Frameworks for Energy Applications

Electrocatalytic Metal–Organic Frameworks for Energy Applications

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

Singly versus Doubly Reduced Nickel Porphyrins for Proton Reduction: Experimental and Theoretical Evidence for a Homolytic Hydrogen‐Evolution Reaction

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