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Electrocatalytic Reduction of CO₂ to CO by Molecular Cobalt–Polypyridine Diamine Complexes

by Yong Yang, Fang Xie, Jiahui Chen, Si Qiu, Na Qiang, Ming Lu, Zhongli Peng, Jing Yang and Guocong Liu

Molecules 2024, 29(8), 1694; https://doi.org/10.3390/molecules29081694 - 9 Apr 2024

Cited by 2 | Viewed by 2271

Abstract

Cobalt complexes have previously been reported to exhibit high faradaic efficiency in reducing CO₂ to CO. Herein, we synthesized capsule-like cobalt–polypyridine diamine complexes [Co(L¹)](BF₄)₂ (1) and [Co(L²) (CH₃CN)](BF₄)₂ (2) as catalysts for the electrocatalytic reduction of CO₂. Under catalytic conditions, complexes 1 and 2 demonstrated the electrocatalytic reduction of CO₂ to CO in the presence or absence of CH₃OH as a proton source. Experimental and computational studies revealed that complexes 1 and 2 undergo two consecutive reversible one-electron reductions on the cobalt core, followed by the addition of CO₂ to form a metallocarboxylate intermediate [Co^II(L)–CO₂²⁻]⁰. This crucial reaction intermediate, which governs the catalytic cycle, was successfully detected using high resolution mass spectrometry (HRMS). In situ Fourier-transform infrared spectrometer (FTIR) analysis showed that methanol can enhance the rate of carbon–oxygen bond cleavage of the metallocarboxylate intermediate. DFT studies on [Co^II(L)–CO₂²⁻]⁰ have suggested that the doubly reduced species attacks CO₂ on the C atom through the d_z² orbital, while the interaction with CO₂ is further stabilized by the π interaction between the metal d_xz or d_xz orbital with p orbitals on the O atoms. Further reductions generate a metal carbonyl intermediate [Co^I(L)–CO]⁺, which ultimately releases CO. Full article

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13 pages, 1853 KB

Open AccessArticle

Rethinking Electronic Effects in Photochemical Hydrogen Evolution Using CuInS₂@ZnS Quantum Dots Sensitizers

by Antonio Orlando, Fiorella Lucarini, Elisabetta Benazzi, Federico Droghetti, Albert Ruggi and Mirco Natali

Molecules 2022, 27(23), 8277; https://doi.org/10.3390/molecules27238277 - 27 Nov 2022

Cited by 6 | Viewed by 2496

Abstract

Molecular catalysts based on coordination complexes for the generation of hydrogen via photochemical water splitting exhibit a large versatility and tunability of the catalytic properties through chemical functionalization. In the present work, we report on light-driven hydrogen production in an aqueous solution using a series of cobalt polypyridine complexes as hydrogen evolving catalysts (HECs) in combination with CuInS₂@ZnS quantum dots (QDs) as sensitizers, and ascorbate as the electron donor. A peculiar trend in activity has been observed depending on the substituents present on the polypyridine ligand. This trend markedly differs from that previously recorded using [Ru(bpy)₃]²⁺ (where bpy = 2,2’-bipyridine) as the sensitizer and can be ascribed to different kinetically limiting pathways in the photochemical reaction (viz. protonation kinetics with the ruthenium chromophore, catalyst activation via electron transfer from the QDs in the present system). Hence, this work shows how the electronic effects on light-triggered molecular catalysis are not exclusive features of the catalyst unit but depend on the whole photochemical system. Full article

(This article belongs to the Special Issue Emerging Catalytic, Energetic, and Inorganic Nonmetallic Materials)

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