Molecular Catalysts Research Articles

The Feasibility of Using Electrostatic Interactions for Immobilizing Ru-bda Catalysts in Covalent Organic Framework: A Proof-of-Concept.

Heterogenization of molecular catalysts effectively resolves the separation issues of homogeneous catalysts and expands their application scenarios. In recent years, more and more studies have been using non-covalent interactions to achieve the heterogenization of molecular catalysts. Herein, electrostatic attraction was used to immobilize molecular catalysts, Ru-bda small molecular catalysts in COF materials, where the charged Ru-bda catalysts were immobilized in the oppositely charged COF with a high [Ru] loading content of ~0.2 mmol [Ru] g-1 COF. The leakage experiment verified that the immobilization of Ru-bda catalysts in COF by electrostatic interactions is stable in 0.1 M HClO4 and less than 5 % of molecular Ru-bda catalysts were leached into the solution in 2 hours. The chemical water oxidation experiment was conducted as a model catalysis reaction to verify the feasibility of using electrostatic interactions for immobilizing Ru-bda catalysts in COFs. The prepared Ru(bda)@COFs demonstrate a high catalytic activity of 268 μmol L-1 s-1 O2 for chemical water oxidation, illustrating the electrostatic attractions between COF and small molecules that can be used to immobilize homogeneous catalysts in heterogeneous materials. However, the robustness of COF material itself under catalytic conditions should be considered in practical applications.

Single Molecular Dispersion of Crown Ether‐Decorated Cobalt Phthalocyanine on Carbon Nanotubes for Robust CO2 Reduction through Host‐Guest Interactions

AbstractImmobilizing molecular catalysts on electro‐conductive supports (for example, multi‐walled carbon nanotubes, CNTs) represent a promising way to well‐defined catalyst/support interfaces, which has shown appreciable performance for catalytic transformation. However, their full potential is far from achieved due to insufficient utilization of the intrinsic activity for each immobilized molecular catalyst, especially at loadings that should allow decent current densities. In the present work, we discover host–guest interaction between tetra‐crown ether substituted cobalt phthalocyanine and metal ions, for example K+ ions, not only eliminate catalyst aggregation at immobilization procedures but also reinforce catalyst/support interactions by additional electrostatic attractions under operational conditions. Through simple dip‐coating procedures, a successful single molecular dispersion is achieved. Such a catalyst/electrode interface is stable and can selectively catalyze CO2‐to‐CO conversion with Faradaic efficiency over 96%. Importantly, this interface maintains an almost unchanged turnover frequency (TOF) across all loading conditions, implying a full utilization of the intrinsic activity of supported molecular catalysts. Therefore, a simultaneous achievement of high TOF and high current density (TOF of 111 s−1 at 38 mA cm−2) is achieved, in an aqueous H‐type electrolyzer at an overpotential of 570 mV.

Single Molecular Dispersion of Crown Ether-Decorated Cobalt Phthalocyanine on Carbon Nanotubes for Robust CO2 Reduction through Host-Guest Interactions.

Immobilizing molecular catalysts on electro-conductive supports (for example, multi-walled carbon nanotubes, CNTs) represent a promising way to well-defined catalyst/support interfaces, which has shown appreciable performance for catalytic transformation. However, their full potential is far from achieved due to insufficient utilization of the intrinsic activity for each immobilized molecular catalyst, especially at loadings that should allow decent current densities. In the present work, we discover host-guest interaction between tetra-crown ether substituted cobalt phthalocyanine and metal ions, for example K+ ions, not only eliminate catalyst aggregation at immobilization procedures but also reinforce catalyst/support interactions by additional electrostatic attractions under operational conditions. Through simple dip-coating procedures, a successful single molecular dispersion is achieved. Such a catalyst/electrode interface is stable and can selectively catalyze CO2-to-CO conversion with Faradaic efficiency over 96%. Importantly, this interface maintains an almost unchanged turnover frequency (TOF) across all loading conditions, implying a full utilization of the intrinsic activity of supported molecular catalysts. Therefore, a simultaneous achievement of high TOF and high current density (TOF of 111 s-1 at 38 mA cm-2) is achieved, in an aqueous H-type electrolyzer at an overpotential of 570 mV.

Molecular catalyst coordinatively bonded to organic semiconductors for selective light-driven CO2 reduction in water.

The selective photoreduction of CO2 in aqueous media based on earth-abundant elements only, is today a challenging topic. Here we present the anchoring of discrete molecular catalysts on organic polymeric semiconductors via covalent bonding, generating molecular hybrid materials with well-defined active sites for CO2 photoreduction, exclusively to CO in purely aqueous media. The molecular catalysts are based on aryl substituted Co phthalocyanines that can be coordinated by dangling pyridyl attached to a polymeric covalent triazine framework that acts as a light absorber. This generates a molecular hybrid material that efficiently and selectively achieves the photoreduction of CO2 to CO in KHCO3 aqueous buffer, giving high yields in the range of 22 mmol g-1 (458 μmol g-1 h-1) and turnover numbers above 550 in 48 h, with no deactivation and no detectable H2. The electron transfer mechanism for the activation of the catalyst is proposed based on the combined results from time-resolved fluorescence spectroscopy, in situ spectroscopies and quantum chemical calculations.

Deciphering Electrocatalytic Hydrogen Production in Water Through a Bioinspired Water-Stable Copper(II) Complex Adorned with (N2S2)-Donor Sites.

Electrocatalytic hydrogen production stands as a pivotal cornerstone in ushering the revolutionary era of the hydrogen economy. With a keen focus on emulating the significance of hydrogenase-like active sites in sustainable H2 generation, a meticulously designed and water-stable copper(II) complex, [Cl-Cu-LN2S2]ClO4, featuring the N,S-type ligand, LN2S2 (2,2'-((butane-2,3-diylbis(sulfanediyl))bis(methylene))dipyridine), has been crafted and assessed for its prowess in electrocatalytic H2 production in water, leveraging acetic acid as a proton source. The molecular catalyst, adopting a square pyramidal coordination geometry, undergoes -Cl substitution by H2O during electrochemical conditions yielding [H2O-Cu-LN2S2]2+ as the true catalyst, showcases outstanding activity in electrochemical proton reduction in acidic water, achieving an impressive rate of 241.75 s-1 for hydrogen generation. Controlled potential electrolysis at -1.2 V vs. Ag/AgCl for 1.6 h reveals a high turnover number of 73.06 with a commendable Faradic efficiency of 94.2 %. A comprehensive analysis encompassing electrochemical, spectroscopic, and analytical methods reveals an insignificant degradation of the molecular catalyst. However, the post-CPE electrocatalyst, present in the solution domain, signifies the coveted stability and effective activity under the specified electrochemical conditions. The synergy of electrochemical, spectroscopic, and computational studies endorses the proton-electron coupling mediated catalytic pathways, affirming the viability of sustainable hydrogen production.

Incorporation of a Binuclear Cobalt Complex into MOFs for Photocatalytic CO2 Reduction with H2O as an Electron Donor.

The development of molecular composite photocatalysts for cost-effective, sacrificial-reagent-free CO2 reduction is desirable but challenging. Herein, we employed an in situ encapsulation strategy to encapsulate the binuclear cobalt complex (Co2L) within NH2-MIL-125 and synthesized a range of MOF-based composites with varying cobalt content for photocatalytic CO2 reduction. The photocatalytic results showed that the catalytic performance increased with the increase in Co2L content, reaching a rapid CO generation rate of 27.95 μmol·g-1·h-1, over 5 times that of bare NH2-MIL-125, with water as the electron donor instead of any organic sacrificial agent. This composite catalyst effectively harnesses the advantages of both molecular catalysts and MOFs, leveraging the superior catalytic activity of molecular catalysts while also capitalizing on the light absorption and water oxidation capabilities of MOFs, resulting in a remarkable ability for photocatalytic CO2 reduction. The photocatalytic mechanism involving electron transfer and CO2 activation has been revealed by photoluminescence spectroscopy, in situ X-ray photoelectron spectroscopy, in situ diffuse reflectance infrared Fourier transform spectroscopy, and other control experiments.

Stabilization of High‐Valent Molecular Cobalt Sites through Oxidized Phosphorus in Reduced Graphene Oxide for Enhanced Oxygen Evolution Catalysis

AbstractHeterogeneous molecular cobalt (Co) sites represent one type of classical catalytic sites for electrochemical oxygen evolution reaction (OER) in alkaline solutions. There are dynamic equilibriums between Co2+, Co3+ and Co4+ states coupling with OH−/H+ interaction before and during the OER event. Since the emergence of Co2+ sites is detrimental to the OER cycle, the stabilization of high‐valent Co sites to shift away from the equilibrium becomes critical and is proposed as a new strategy to enhance OER. Herein, phosphorus (P) atoms were doped into reduced graphene oxide to link molecular Co2+ acetylacetonate toward synthesizing a novel heterogeneous molecular catalyst. By increasing the oxidation states of P heteroatoms, the linked Co sites were spontaneously oxidized from 2+ to 3+ states in a KOH solution through OH− ions coupling at an open circuit condition. With excluding the Co2+ sites, the as‐derived Co sites with 3+ initial states exhibited intrinsically high OER activity, validating the effectiveness of the strategy of stabilizing high valence Co sites.

Role of Active Centers in Predicting the Catalyst Turnover: A Theoretical Study.

Water oxidation catalysis has garnered significant attention due to its potential for sustainable energy conversion. Among molecular catalysts, [Fe(OTf)2 (Me2Pytacn)] complexes have exhibited notable turning-over rates. Although various [M(OTf)2 (Me2Pytacn)] complexes (M = Mn, Co, Ni) have been synthesized, however, the role of active centres has not been thoroughly investigated. In this study, we apply our newly developed catalytic models, efficiency conceptualization model (ECM) and the maximum kinetic efficiency MaxKinEff framework to assess the role of the active centres in its catalytic performance. Our computational analysis identifies cobalt-based [Co(OTf)2 (Me2Pytacn)] as a superior alternative for water oxidation reactions. Notably, cobalt catalysts exhibit a longer lifespan (~ 44 days) and higher turnover numbers (TON), with computed values of (ECM) = 3.30 h-1, (ECM) = 3456, (MaxKinEff) = 12.43 h-1, and (MaxKinEff) = 3616. These findings suggest that cobalt could play a pivotal role in improving the efficiency of molecular catalysts for water oxidation.

Recent Advances in Immobilizing and Benchmarking Molecular Catalysts for Artificial Photosynthesis.

Transition metal complexes have been widely used as catalysts or chromophores in artificial photosynthesis. Traditionally, they are employed in homogeneous settings. Despite their functional versatility and structural tunability, broad industrial applications of these catalysts are impeded by the limitations of homogeneous catalysis such as poor catalyst recyclability, solvent constraints (mostly organic solvents), and catalyst durability. Over the past few decades, researchers have developed various methods for molecular catalyst heterogenization to overcome these limitations. In this review, we summarize recent developments in heterogenization strategies, with a focus on describing methods employed in the heterogenization process and their effects on catalytic performances. Alongside the in-depth discussion of heterogenization strategies, this review aims to provide a concise overview of the key metrics associated with heterogenized systems. We hope this review will aid researchers who are new to this research field in gaining a better understanding.

Synthesis and carbon monoxide purification performance of ZSM-5 molecular sieve Co-doped Mn/V catalytic material

Trackless, rubber-tired, diesel-powered vehicles are widely used in the mining industry. In recent years, the use of high-performance catalysts to remove carbon monoxide (CO) from diesel vehicle exhaust has attracted much attention. In this paper, a series of manganese-vanadium doped ZSM-5 molecular sieve catalysts were prepared by an impregnation method. The structures of the catalysts were characterized and experiments were conducted to evaluate their performance. The CO catalytic oxidation performance experiments revealed that Mn0.6-V0.4-ZSM-5 had the best performance, with a conversion rate of 97.5 % at 300 °C. The catalyst was also tested for water resistance and stability. Kinetic measurements were performed and the fitted activation energy was 22.68 kJ/mol. Characterization studies revealed that the surface defects formed by Mn and V doping provided a large number of active sites and oxygen vacancies for CO oxidation, increased the number of adsorbed oxygen species on the surface, and enhanced the redox capacity through the interaction of Mn4+ and V5+ to improve the catalytic oxidation performance of the catalyst. The adsorption configurations, adsorption energy (Ebin), and formation energy of oxygen vacancies of CO at different adsorption sites and different active fractions were calculated with density functional theory. The Ebin of CO on Mn2V2O7, the active fraction of Mn0.6-V0.4-ZSM-5, was −1.29 eV, which was the most stable adsorption configuration. This configuration had good oxygen mobility, and was conducive to CO catalysis, confirming the characterization and performance experiments.

Effective synergistic interaction between InZnZrOx ternary metal oxides and SAPO-34 molecular sieve catalysts for CO2 hydrogenation to light olefins

The synergistic interaction of metal oxides with molecular sieves is essential for the catalytic hydrogenation of carbon dioxide (CO2) into light olefins (C2=–C4=) over bifunctional tandem catalysts. Herein, a series of In2O3-doped InZnZrOx (IZZ) ternary metal oxides was prepared and physically mixed with SAPO-34. The bifunctional catalyst was used in the direct conversion of CO2 to light olefins. The relationship between IZZ oxide structures prepared using different methods and the catalytic performance of bifunctional catalysts was investigated. Moreover, the migration of InOx in ternary metal oxides was revealed. Results revealed that for IZZ oxides prepared via precipitation coating and impregnation, InOx species migrated to the SAPO-34 surface during thermocatalytic reaction due to the dispersion of In2O3 on the ZnZrOx surface and its weak interaction with ZnZrOx. This led to the neutralization of acid centers on SAPO-34 by InOx, thereby destroying the synergistic interaction between the oxides and SAPO-34, resulting in a large amount of unneeded methane and poor light olefin selectivity. However, the co-precipitated IZZ-CP oxides exhibited a ternary solid solution structure and inhibited the migration of InOx. This enhanced CO2 and H2 activation, affording more formate (HCOO*) and methoxide (CH3O*) intermediates that strengthened the synergistic interaction between the oxides and molecular sieves. After optimizing the In2O3 doping amount in IZZ-CP oxide and the reaction conditions, the IZZ-CP/SAPO-34 bifunctional catalyst achieved 17.9 % CO2 conversion, 80.1 % C2=–C4= selectivity, only 7.6 % methane and 44.6 % CO selectivity. It also maintained excellent catalytic stability without significant deactivation after continuous reaction for 80 h.

Cobalt single-site molecular Catalyst-mediated electrochemical Hydrodechlorination for detoxification of halogenated Antibiotics: Performance, reaction pathway and mechanism

Electrocatalytic hydrodehalogenation (ECHD) offers a promising approach for detoxification of the halogenated antibiotics via hydrogenolysis of the C-X bonds (X = F, Cl or Br). Herein we demonstrated that the commercially-available cobalt phthalocyanine (CoPc) molecules with a high-loading of −[Co-N4]- moieties (Co wt%: 10.8 %) were exceptionally active for hydrogenolysis of the C-Cl bonds in florfenicol (FLO). It afforded an impressive mass activity of 6.2 gFLO h−1 g-1Co, a low Co leaching of 0.34 μg/L and a strong tolerance to interference from impurities in water, significantly surpassing reported Co/Fe/Ni-based particle and single-site counterparts. Mechanistic studies revealed that the ECHD on CoPc underwent a direct electron transfer manner rather than the atomic hydrogen (H*)-mediated indirect way, and the ECHD efficacy was affected by both the electron and proton transfer kinetics. The single-atom Co, with its d orbitals constituting the lowest unoccupied molecular orbitals of CoPc, served as the primary active site. It facilitated both electron and proton transfer, as well as the cleavage of the C-Cl bond but not the C-F bond. In a continuous-flow cell, the CoPc/C-driven ECHD reduced the antibacterial activity of a FLO-contaminated natural lake water sample by 90.8 % with an energy consumption of 0.19 kwh g-1FLO. This study highlighted great promise of the single-atom metal-bearing molecular catalyst toward the sustainable detoxification of halogenated antibiotics-contaminated water.

Confinement of Z-scheme organic-inorganic heterojunction into mesoporous zeolite for efficient photocatalytic solar fuel generation

Organic-inorganic heterojunction has drawn increasing interest in photocatalytic CO2 reduction (PCR) by immobilizing molecular catalysts on inorganic semiconductors. However, it is difficult to control the size and dispersion of inorganic semiconductors during the assembling process, which restricts the PCR performance due to limited active sites and charge separation efficiency. Herein, we utilized a commercial mesoporous zeolite (SBA-15) to confine TiO2 via an in situ approach followed by assembling with a Co(II) tetra(4-carboxylphenyl) porphyrin (Co-TCPP). As a result, a Z-scheme organic–inorganic heterojunction of TiO2/SBA-15@Co-TCPP was obtained, which demonstrated superior PCR performance among simulated solar light irradiation. The optimized TiO2/SBA-15@Co-TCPP demonstrated improved solar fuel evolution (241.63 μmolco g−1) via PCR process when compared to bulk TiO2 or pristine Co-TCPP. The experiment results and density functional theory (DFT) calculations reveal the superior PCR performance induced by the extended light-harvesting region from the Z-scheme heterojunction, elevated PCR selectivity induced by the hydrophilicity of SBA-15 and molecular Co(II) center, enhanced charge separation owing to the highly dispersed nanosized TiO2 and inner-building electronic field. This work highlights the importance of mesoporous zeolite substrate in control of the PCR activity and selectivity, which hold great potential to develop multiple zeolite-based heterojunctions for efficient solar-driven fuel generation.

Unlocking the Activity of Molecular Assemblies for CO2 Electroreduction in Zero-Gap Electrolysers via Catalyst Ink Engineering.

In recent years, CO2 electrolysis, particularly the electrochemical reduction of CO2 to CO in zero-gap systems, has gained significant attention. While Ag-coated gas diffusion electrodes are commonly used in state-of-the-art systems, heterogenized molecular catalysts like bis-coordinated homoleptic silver(I) N,N-bis(arylimino)-acenaphthene (Ag-BIAN) complexes are emerging as a promising alternative due to their tunability and high mass activity. In this study, the influence of ink composition on the performance of Ag-BIAN-based GDEs in zero-gap electrolyzers (ZGEs) are systematically explored at 60°C and 600mA cm⁻2. Sedimentation analyses across various solvents informed the selection of optimal solvent-catalyst and solvent-carbon additive combinations, streamlining the GDE optimization process and reducing associated costs and time. These results demonstrate that solvent choice and dilution state of the ink are critical factors impacting CO2 reduction, achieving faradaic efficiencies for CO production (FECO) up to 67% at 600mA cm⁻2 with catalyst loadings as low as 0.2mg cm⁻2. These findings lay the groundwork for advancing from homogeneous H-type cells to industrial ZGE systems through tailored ink engineering.

Corrolato(oxo)antimony(V) Dimer with Hydrogen-Bond Donor Groups in Secondary Coordination Sphere as a Catalyst for Hydrogen Evolution Reaction.

The focus is on developing alternative molecular catalysts using main-group elements and implementing strategic improvements for sustainable hydrogen production. For this purpose, a FB corrole with a (2-(2-((4-methylphenyl)sulfonamido)ethoxy)phenyl) group inserted into the meso position (C-10) of the corrole, along with its high-valent (corrolato)(oxo)antimony(V) dimer, was synthesized. In the crystal structure analysis of the FB corrole and the (corrolato)(oxo)antimony(V) dimer complex, it was noted that the sulfonamido group in the ligand periphery sits atop the corrole ring. The electrochemical hydrogen evolution reaction (HER) of the (corrolato)(oxo)antimony(V) dimer was studied and compared with a previously reported (corrolato)(oxo)antimony(V) complex, which lacks hydrogen-bond donor groups in the secondary coordination sphere. The newly designed molecules, featuring hydrogen-bond donor groups in the secondary coordination sphere, demonstrated clear superiority in the electrochemical HER. Controlled potential electrolysis was employed to evaluate the charge accumulation associated with hydrogen generation in a homogeneous three-electrode system in the presence of 50 mM TFA. The produced hydrogen exhibits a Faradaic efficiency of approximately 80.96%, a turnover frequency (TOF) of 0.44 h-1, and a production rate of 52.83 μL h-1, highlighting the effective catalytic activity of the (corrolato)(oxo)antimony(V) dimer in hydrogen evolution.

Engineering a Cu-Pd Paddle-Wheel Metal-Organic Framework for Selective CO2 Electroreduction.

Optimizing the binding energy between the intermediate and the active site is a key factor for tuning catalytic product selectivity and activity in the electrochemical carbon dioxide reduction reaction. Copper active sites are known to reduce CO2 to hydrocarbons and oxygenates, but suffer from poor product selectivity due to the moderate binding energies of several of the reaction intermediates. Here, we report an ion exchange strategy to construct Cu-Pd paddle wheel dimers within Cu-based metal-organic frameworks (MOFs), [Cu3-xPdx(BTC)2] (BTC=benzentricarboxylate), without altering the overall MOF structural properties. Compared to the pristine Cu MOF ([Cu3(BTC)2], HKUST-1), the Cu-Pd MOF shifts CO2 electroreduction products from diverse chemical species to selective CO generation. In situ X-ray absorption fine structure analysis of the catalyst oxidation state and local geometry, combined with theoretical calculations, reveal that the incorporation of Pd within the Cu-Pd paddle wheel node structure of the MOF promotes adsorption of the key intermediate COOH* at the Cu site. This permits CO-selective catalytic mechanisms and thus advances our understanding of the interplay between structure and activity toward electrochemical CO2 reduction using molecular catalysts.

Triphenylamine-Substituted Ni(II) Porphyrins for Urea Electro-oxidation.

Porphyrin-based molecular catalysts possess a typical aromatic macrocyclic structure regarding their metal centers and coordination frameworks, allowing for the development of promising electrocatalysts through precise selection of the metal and porphyrin ligand. However, reports on metalloporphyrins as catalysts for the electrocatalytic urea oxidation reaction (UOR) remain scarce. With these considerations in mind, the triphenylamine-Ni(II) porphyrin (NiPor-TPA) was synthesized through the solvothermal approach from 5,10,15,20-tetrakis [4-(diphenylamino)phenyl]porphyrin and nickel(II) acetate in this work. Experimental results reveal that the introduction of Ni species can serve as active sites and activate urea oxidation efficiently, and thus the prepared catalysts deliver better electrocatalytic activity than the metal-free TPA. The NiPor-TPA electrode delivers the lowest potential of 1.34 V versus reversible hydrogen electrode (RHE) at 10 mA cm-2 for UOR with a Tafel slope of 44.6 mV dec-1. This work proposes a new porphyrin-based molecular catalyst for effectively boosting electrocatalytic UOR activity. The π-conjugated macroring structure and the excellent electrocatalytic properties both make NiPor-TPA one of the burgeoning electrocatalytic UORs.

Physicochemical Analysis of Cu(II)-Driven Electrochemical CO2 Reduction and its Competition with Proton Reduction.

The reduction of CO2 has become a key role in reducing greenhouse gas emissions in efforts to search for long-term responses to climate change. We report a a couple of CO2-reducing molecular catalysts based on earth-abundant copper complexes. These are [Cu(DPA)(PyNAP)] (1) and [Cu(DPA)(PyQl)] (2) (where, DPA = pyridine-2,6-dicarboxylic acid, PyNAP = 2-(pyridin-2-yl)-1,8-naphthyridine, and PyQl = 2-(pyridin-2-yl)quinoline). The copper metal-catalysed 2-electron reduction of CO2 to CO in the presence of 2-protons is challenging. These catalysts exhibit the production of CO gas in DMF/water mixtures, achieving an impressive faradaic efficiency of 84% and 72% for complex 1 and 2 at -1.7 V vs. SCE, respectively, for selective CO2 reduction. The production of H2 due to 2H+ + 2e- was also observed as a byproduct through the competitive proton reduction reaction. This was cross-verified by online gas and mass analysis.Our investigations confirmed the stability of the electrocatalysts under the electrocatalytic conditions. The mechanistic pathways were proposed to work with the EECC and ECEC (E: electrochemical and C: chemical) mechanisms. A CO2 insertion into an in-situ generated hydride from the Cu-center generates CO through the favourable path.

A Survey of Reaction Energetics for Diverse Small Molecule Activation: Where Do Molecular Electrocatalysts Go From Here?

AbstractThe invention of technologies that can activate, transform, and upgrade small molecules is a significant challenge. The starting point for many such technologies is molecular catalysts. Their well‐defined active sites, multitude of tools to characterize their reactions, and their synthetic flexibility makes such molecules logical starting points. However, it is increasingly clear that challenges exist in the applications of molecular catalysts at the scales needed to address modern chemical and energy demands. In this review, we discuss selected classes of molecular electrocatalysts and highlight their development and key features. Of special interest are proton‐coupled transformations of H2, O2, N2, CO2, and related small molecules. We also frame important thermodynamic features for different catalysts using new approaches and ask forward looking questions about their applications in practical systems.

Operando Spectroelectrochemistry Unravels the Mechanism of CO2 Electrocatalytic Reduction by an Fe Porphyrin.

Iron porphyrins are molecular catalysts recognized for their ability to electrochemically and photochemically reduce carbon dioxide (CO2). The main reduction product is carbon monoxide (CO). CO holds significant industrial importance as it serves as a precursor for various valuable chemical products containing either a single carbon atom (C1), like methanol or methane, or multiple carbon atoms (Cn), such as ethanol or ethylene. Despite the long-established efficiency of these catalysts, optimizing their catalytic activity and stability and comprehending the intricate reaction mechanisms remain a significant challenge. This article presents a comprehensive investigation of the mechanistic aspects of the selective electroreduction of CO2 to CO using an iron porphyrin substituted with four trimethylammonium groups in the para position [(pTMA)FeIII-Cl]4+. By employing infrared and UV/Visible spectroelectrochemistry, changes in the electronic structure and coordination environment of the iron center can be observed in real-time as the electrochemical potential is adjusted, offering new insights into the reaction mechanisms. Catalytic species were identified, and evidence of a secondary reaction pathway was uncovered, potentially prompting a re-evaluation of the nature of the catalytically active species.