Mechanistic Insights into Electrocatalytic Hydrogen Evolution by an Exceptionally Stable Cobalt Complex

Inorganic Chemistry, Journal Year: 2024, Volume and Issue: 63(18), P. 8484 - 8492

Published: April 19, 2024

Co(aPPy) is one of the most stable and active molecular first-row transition-metal catalysts for proton reduction reported to date. Understanding origin its high performance via mechanistic studies could aid in developing even better catalysts. In this work, catalytic mechanism was electrochemically probed, both organic solvents water. We found that different mechanisms can occur depending on solvent acidity medium. with a strong acid as source, catalysis initiates directly after single-electron CoII CoI, whereas presence weaker acid, cobalt center needs be reduced twice before occurs. aqueous phase, we drastically electrochemical behavior, where complex precatalyst electrocatalytic species. propose catalyst, pyridine ring has dissociated acts relay at pH ≤ 5, which opens up fast protonation pathway CoI intermediate results activity. Furthermore, determined constant potential bulk electrolysis catalyst 3. The thus functions optimally low an environment, shuttle also prevents deactivation.

Language: Английский

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Molecular Engineering of Electrocatalytic Nanomaterials for Hydrogen Evolution: The Impact of Structural and Electronic Modifications of Anchoring Linkers on Electrocatalysis

ACS Catalysis, Journal Year: 2024, Volume and Issue: 14(8), P. 5630 - 5638

Published: March 29, 2024

The anticipated shortage of an increasing number critical elements, especially metals, requires a shift toward molecularly defined materials with low metal loadings. More particularly, surface-anchored molecular catalysts are attractive to prospectively enable cost-effective electrochemical hydrogen evolution. However, the design ligands integrating specific anchoring unit(s) for immobilization can be challenging and has direct consequences intrinsic properties grafted complex. In this work, two cobalt tetraazamacrocyclic complexes bearing pyrene groups at different positions on macrocyclic were synthesized. unit allows simple characterization multi-walled carbon nanotube-based electrodes. Thorough electrocatalytic investigation demonstrates important differences between closely related in terms catalyst loading, catalytic response, stability over time, significantly higher observed pH 7 than 2.

Language: Английский

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Bioinspired Diiron Complex with Proton Shuttling and Redox-Active Ligand for Electrocatalytic Hydrogen Evolution

Inorganic Chemistry, Journal Year: 2024, Volume and Issue: 63(35), P. 16146 - 16160

Published: July 10, 2024

A μ-oxo diiron complex, featuring the pyridine-2,6-dicarboxamide-based thiazoline-derived redox-active ligand, H

Language: Английский

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Circumventing Kinetic Barriers to Metal Hydride Formation with Metal–Ligand Cooperativity

Journal of the American Chemical Society, Journal Year: 2024, Volume and Issue: 146(44), P. 30020 - 30032

Published: Oct. 23, 2024

We report the two-electron, one-proton mechanism of cobalt hydride formation for conversion [CoIIICp(PPh2NBn2)(CH3CN)]2+ to [HCoIIICp(PPh2NBn2)]+. This complex catalytically converts CO2 formate under reduction conditions, with as a key elementary step. Through combination electrochemical measurements, digital simulations, theoretical calculations, and additional mechanistic thermochemical studies, we outline explicit role PPh2NBn2 ligand in proton-coupled electron transfer (PCET) reactivity that leads formation. reveal three unique PCET mechanisms, show amine on serves kinetically accessible protonation site en route thermodynamically favored hydride. Cyclic voltammograms recorded proton sources span wide range pKa values four distinct regimes where changes function acid strength, concentration, timescale between steps. Peak shift analysis was used determine rate constants applicable. work highlights astute choices must be made when designing catalytic systems, including basicity kinetic accessibility sites, steps, maximize catalyst stability efficiency.

Language: Английский

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Exploring Acidity-Dependent PCET Pathways in Imino-Bipyridyl Cobalt Complexes

Dalton Transactions, Journal Year: 2025, Volume and Issue: unknown

Published: Jan. 1, 2025

This study explores the proton-coupled electron transfer (PCET) pathways of two high-spin Co complexes, highlighting how internal spin-state interactions and external p K a values proton sources influence catalytic mechanisms.

Language: Английский

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Harnessing the Cobalt-Catalyzed Hydrogen Evolution Reaction through a Data-Driven Approach

Inorganic Chemistry, Journal Year: 2025, Volume and Issue: unknown

Published: Feb. 4, 2025

The design of cobalt complexes for the hydrogen evolution reaction (HER) has garnered significant attention over past few decades. To address limitations traditional trial-and-error method, we introduced strategy a simplified mechanism-based approach with data-driven practice (SMADP) in this study. Our results indicate that polypyridyl DPA-Bpy family (DPA-Bpy = N,N-bis(2-pyridinylmethyl)-2,2′-bipyridine-6-methanamine) generally follow electron transfer (E)–chemical proton (C)–electron (C) pathway HER. However, involvement proton-coupled (PCET) formation [CoII(L)–H]+ intermediate been observed PY5Me2 (PY5Me2 2,6-bis(1,1-di(pyridin-2-yl)ethyl)pyridine). Furthermore, hydricity (ΔGH–) and CoIII–H/CoII–H reduction potential (ERed°) are found to be active descriptors cobalt-catalyzed Excellent two-parameter regression models (ΔGH– ERed°) H2 molecule have obtained (R2 0.9429 R2 0.9854 family). demonstrate SMADP is groundbreaking method delineating This could also accelerate novel enhanced

Language: Английский

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Effect of the proton sources on electrocatalytic hydrogen evolution by copper complex of bistriazolylpyridine

Dalton Transactions, Journal Year: 2025, Volume and Issue: unknown

Published: Jan. 1, 2025

The HER catalyzed by Cudbes followed the EECC or EEECC pathway with AcOH, whilst it CECE (or CEEC) TFA TsOH. reactions invoked PCET step and proton relay on triazolyl moiety of dbes.

Language: Английский

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Effect of Ligand Backbone on the Electrochemical Hydrogen Evolution Reaction and Hydrogen-Atom-Transfer Reactivity Using a Nickel Polypyridine Quinoline Complex

Inorganic Chemistry, Journal Year: 2025, Volume and Issue: unknown

Published: April 16, 2025

Redox-active quinoline-containing [NiII(2PyN2Q) (H2O)]2+ complex (1) has been developed for the electrocatalytic (e) hydrogen evolution reaction (HER) in presence of organic acids and water hydrogen-atom-transfer (HAT) with styrene acids. Complex 1 shows promising e-HER performance up to pH 9. It exhibits a stepwise (E)ECEC mechanism AcOH, while potential-dependent bimolecular homolytic pathway CEEC is operative p-toluene sulfonic acid during e-HER. The one- two-electron-reduced species are characterized by spectro-electrochemistry, optical, EPR studies. Moreover, inverse kinetic isotope effect (KIE = 0.83) between AcOH d4-AcOH e-HAT hydro-functionalization using catalyst possibly suggests involvement nickel hydride species. reactivity have compared redox-inactive [NiII(N4Py)(H2O)]2+ (2), demonstrating prominent quinoline pyridine e-HAT. proposed well supported DFT

Language: Английский

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Enhanced Catalytic Activity via Rapid Two-Electron Transfer in Low-Spin Fe(II) Complex and Spin-State Dependent Proton Reduction Pathways

Journal of the American Chemical Society, Journal Year: 2025, Volume and Issue: unknown

Published: April 23, 2025

The growing interest in green hydrogen gas production has brought significant attention to the development of efficient proton reduction catalysts. A comprehensive understanding and electron transfer processes within catalyst complexes is crucial for developing While process influenced by Brønsted acid used, an intrinsic property determined molecular orbitals spin states complexes. Complexes that rapidly electrons are associated with high catalytic performance. In this study, we present a first example low-spin FeII complex utilizes π* orbital ligand rapid two-electron transfer, resulting exceptional performance evolution. consecutive rate was measured at 33.24 s-1, combination achieved extraordinarily turnover frequency (TOF) 224,643 s-1 production. Conversely, high-spin Fe(II) produced relatively low TOF 8848 s-1. These comparative experiments confirmed observed efficiency unique complex, attributed its distinct mechanism.

Language: Английский

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Impact of Pendant Amine Basicity on Electrochemically-Promoted Cobalt Hydride Formation: Kinetic and Mechanistic Analysis

Inorganic Chemistry, Journal Year: 2025, Volume and Issue: unknown

Published: May 15, 2025

We report the role of pendant amine basicity on proton-coupled electron transfer (PCET) reactivity for conversion [CoIIICp(PPh2NR2)(CH3CN)]2+ complexes to [HCoIIICp(PPh2NR2)]+, which is a key transformation involved in catalytic CO2 formate and H2 evolution. Three were studied, where substituent (R) varies from benzyl, methoxyphenyl, or phenyl. In previous work benzyl system, we showed that PPh2NBn2 ligand serves as kinetically accessible protonation site enables three participating hydride formation mechanisms. this work, combination electrochemical measurements theoretical calculations used show electronic donation at influences PCET mechanism proton kinetics related cobalt under analogous reaction conditions. Notably, with most electron-donating correlates lowest barrier protonation, specific mechanisms can be shut off least substituent. The mechanistic kinetic changes upon modulation have great implications overall efficiency selectivity, especially generate intermediate selective reduction formate. This shows how exploit using ligand-cooperative design facilitate reactions energy transformations.

Language: Английский

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