Non‐natural Cofactor and Formate‐Driven Reductive Carboxylation of Pyruvate

A non‐natural cofactor and formate driven system for reductive carboxylation of pyruvate is presented. A formate dehydrogenase (FDH) mutant, FDH*, that favors a non‐natural redox cofactor, nicotinamide cytosine dinucleotide (NCD), for generation of a dedicated reducing equivalent at the expense of formate were acquired. By coupling FDH* and NCD‐dependent malic enzyme (ME*), the successful utilization of formate is demonstrated as both CO₂ source and electron donor for reductive carboxylation of pyruvate with a perfect stoichiometry between formate and malate. When ¹³C‐isotope‐labeled formate was used in in vitro trials, up to 53 % of malate had labeled carbon atom. Upon expression of FDH* and ME* in the model host E. coli, the engineered strain produced more malate in the presence of formate and NCD. This work provides an alternative and atom‐economic strategy for CO₂ fixation where formate is used in lieu of CO₂ and offers dedicated reducing power.     

Infrared Spectroscopy Elucidates the Inhibitor Binding Sites in a Metal-Dependent Formate Dehydrogenase

Biological carbon dioxide (CO₂) reduction is an important step by which organisms form valuable energy-richer molecules required for further metabolic processes. The Mo-dependent formate dehydrogenase (FDH) from Rhodobacter capsulatus catalyzes reversible formate oxidation to CO₂ at a bis-molybdopterin guanine dinucleotide (bis-MGD) cofactor. To elucidate potential substrate binding sites relevant for the mechanism, we studied herein the interaction with the inhibitory molecules azide and cyanate, which are isoelectronic to CO₂ and charged as formate. We employed infrared (IR) spectroscopy in combination with density functional theory (DFT) and inhibition kinetics. One distinct inhibitory molecule was found to bind to either a non-competitive or a competitive binding site in the secondary coordination sphere of the active site. Site-directed mutagenesis of key amino acid residues in the vicinity of the bis-MGD cofactor revealed changes in both non-competitive and competitive binding, whereby the inhibitor is in case of the latter interaction presumably bound between the cofactor and the adjacent Arg587.     

Interfacing Formate Dehydrogenase with Metal Oxides for the Reversible Electrocatalysis and Solar‐Driven Reduction of Carbon Dioxide

The integration of enzymes with synthetic materials allows efficient electrocatalysis and production of solar fuels. Here, we couple formate dehydrogenase ( FDH ) from Desulfovibrio vulgaris Hildenborough (DvH) to metal oxides for catalytic CO₂ reduction and report an in‐depth study of the resulting enzyme–material interface. Protein film voltammetry (PFV) demonstrates the stable binding of FDH on metal‐oxide electrodes and reveals the reversible and selective reduction of CO₂ to formate. Quartz crystal microbalance (QCM) and attenuated total reflection infrared (ATR‐IR) spectroscopy confirm a high binding affinity for FDH to the TiO₂ surface. Adsorption of FDH on dye‐sensitized TiO₂ allows for visible‐light‐driven CO₂ reduction to formate in the absence of a soluble redox mediator with a turnover frequency (TOF) of 11±1 s^?1. The strong coupling of the enzyme to the semiconductor gives rise to a new benchmark in the selective photoreduction of aqueous CO₂ to formate.     

In Situ Bismuth Nanosheet Assembly for Highly Selective Electrocatalytic CO2 Reduction to Formate

The reduction of carbon dioxide (CO₂) into value-added fuels using an electrochemical method has been regarded as a compelling sustainable energy conversion technology. However, high-performance electrocatalysts for CO₂ reduction reaction (CO₂RR) with high formate selectivity and good stability need to be improved. Earth-abundant Bi has been demonstrated to be active for CO₂RR to formate. Herein, we fabricated an extremely active and selective bismuth nanosheet (Bi-NSs) assembly via an in situ electrochemical transformation of (BiO)₂CO₃ nanostructures. The as-prepared material exhibits high activity and selectivity for CO₂RR to formate, with nearly 94% faradaic efficiency at −1.03 V (versus reversible hydrogen electrode (vs. RHE)) and stable selectivity (>90%) in a large potential window ranging from −0.83 to −1.18 V (vs. RHE) and excellent durability during 12 h continuous electrolysis. In addition, the Bi-NSs based CO₂RR/methanol oxidation reaction (CO₂RR/MOR) electrolytic system for overall CO₂ splitting was constructed, evidencing the feasibility of its practical implementation.     

Non-natural Cofactor and Formate-Driven Reductive Carboxylation of Pyruvate

A non-natural cofactor and formate driven system for reductive carboxylation of pyruvate is presented. A formate dehydrogenase (FDH) mutant, FDH*, that favors a non-natural redox cofactor, nicotinamide cytosine dinucleotide (NCD), for generation of a dedicated reducing equivalent at the expense of formate were acquired. By coupling FDH* and NCD-dependent malic enzyme (ME*), the successful utilization of formate is demonstrated as both CO₂ source and electron donor for reductive carboxylation of pyruvate with a perfect stoichiometry between formate and malate. When ¹³C-isotope-labeled formate was used in in vitro trials, up to 53 % of malate had labeled carbon atom. Upon expression of FDH* and ME* in the model host E. coli, the engineered strain produced more malate in the presence of formate and NCD. This work provides an alternative and atom-economic strategy for CO₂ fixation where formate is used in lieu of CO₂ and offers dedicated reducing power.     

Metal–Organic Framework‐Derived Carbon Nanorods Encapsulating Bismuth Oxides for Rapid and Selective CO2 Electroreduction to Formate

Carbon dioxide (CO₂) conversion is promising in alleviating the excessive CO₂ level and simultaneously producing valuables. This work reports the preparation of carbon nanorods encapsulated bismuth oxides for the efficient CO₂ electroconversion toward formate production. This resultant catalyst exhibits a small onset potential of ?0.28 V vs. RHE and partial current density of over 200 mA cm^?2 with a stable and high Faradaic efficiency of 93 % for formate generation in a flow cell configuration. Electrochemical results demonstrate the synergistic effect in the Bi₂O₃@C promotes the rapid and selective CO₂ reduction in which the Bi₂O₃ is beneficial for improving the reaction kinetics and formate selectivity, while the carbon matrix would be helpful for enhancing the activity and current density of formate production. This work provides effective bismuth‐based MOF derivatives for efficient formate production and offers insights in promoting practical CO₂ conversion technology.     

A Biomimetic Nickel Complex with a Reduced CO2 Ligand Generated by Formate Deprotonation and Its Behaviour towards CO2

Reduced CO₂ species are key intermediates in a variety of natural and synthetic processes. In the majority of systems, however, they elude isolation or characterisation owing to high reactivity or limited accessibility (heterogeneous systems), and their formulations thus often remain uncertain or are based on calculations only. We herein report on a Ni?CO₂^2? complex that is unique in many ways. While its structural and electronic features help understand the CO₂‐bound state in Ni,Fe carbon monoxide dehydrogenases, its reactivity sheds light on how CO₂ can be converted into CO/CO₃^2? by nickel complexes. In addition, the complex was generated by a rare example of formate β‐deprotonation, a mechanistic step relevant to the nickel‐catalysed conversion of H_xCO_y^z? at electrodes and formate oxidation in formate dehydrogenases.     

Reduction of Carbon Dioxide to Formate at Low Overpotential Using a Superbase Ionic Liquid

A new low‐energy pathway is reported for the electrochemical reduction of CO₂ to formate and syngas at low overpotentials, utilizing a reactive ionic liquid as the solvent. The superbasic tetraalkyl phosphonium ionic liquid [P₆₆₆₁₄][124Triz] is able to chemisorb CO₂ through equimolar binding of CO₂ with the 1,2,4‐triazole anion. This chemisorbed CO₂ can be reduced at silver electrodes at overpotentials as low as 0.17 V, forming formate. In contrast, physically absorbed CO₂ within the same ionic liquid or in ionic liquids where chemisorption is impossible (such as [P₆₆₆₁₄][NTf₂]) undergoes reduction at significantly increased overpotentials, producing only CO as the product.     

Metal–Organic Framework-Derived Carbon Nanorods Encapsulating Bismuth Oxides for Rapid and Selective CO2 Electroreduction to Formate

Carbon dioxide (CO₂) conversion is promising in alleviating the excessive CO₂ level and simultaneously producing valuables. This work reports the preparation of carbon nanorods encapsulated bismuth oxides for the efficient CO₂ electroconversion toward formate production. This resultant catalyst exhibits a small onset potential of −0.28 V vs. RHE and partial current density of over 200 mA cm⁻² with a stable and high Faradaic efficiency of 93 % for formate generation in a flow cell configuration. Electrochemical results demonstrate the synergistic effect in the Bi₂O₃@C promotes the rapid and selective CO₂ reduction in which the Bi₂O₃ is beneficial for improving the reaction kinetics and formate selectivity, while the carbon matrix would be helpful for enhancing the activity and current density of formate production. This work provides effective bismuth-based MOF derivatives for efficient formate production and offers insights in promoting practical CO₂ conversion technology.     

Bismuth-Oxide-Decorated Graphene Oxide Hybrids for Catalytic and Electrocatalytic Reduction of CO2

Global warming challenges are fueling the demand to develop an efficient catalytic system for the reduction of CO₂, which would contribute significantly to the control of climate change. Herein, as-synthesized bismuthoxide-decorated graphene oxide (Bi₂O₃@GO) was used as an electro/thermal catalyst for CO₂ reduction. Bi₂O₃@GO is found to be distributed uniformly, as confirmed by scanning electron and transmission electron microscopic analysis. The X-ray diffraction (XRD) pattern shows that the Bi₂O₃ has a β-phase with 23.4 m² g⁻¹ BET surface area. Significantly, the D and G bands from Raman spectroscopic analysis and their intensity ratio (I_D/I_G) reveal the increment in defective sites on GO after surface decoration. X-ray photoelectron spectroscopic (XPS) analysis shows clear signals for Bi, C, and O, along with their oxidation states. An ultra-low onset potential (−0.534 V vs. RHE) for the reduction of CO₂ on Bi₂O₃@GO is achieved. Furthermore, potential-dependent (−0.534, −0.734, and −0.934 vs. RHE) bulk electrolysis of CO₂ to formate provides Faradaic efficiencies (FE) of approximately 39.72, 61.48, and 83.00 %, respectively. Additionally, in time-dependent electrolysis at a potential of −0.934 versus RHE for 3 and 5 h, the observed FEs are around 84.20 % and 87.17 % respectively. This catalyst is also used for the thermal reduction of CO₂ to formate. It is shown that the thermal reduction provides a path for industrial applications, as this catalyst converts a large amount of CO₂ to formate (10 mm ).     

Rapid Selective Electrocatalytic Reduction of Carbon Dioxide to Formate by an Iridium Pincer Catalyst Immobilized on Carbon Nanotube Electrodes

An iridium pincer dihydride catalyst was immobilized on carbon nanotube‐coated gas diffusion electrodes (GDEs) by using a non‐covalent binding strategy. The as‐prepared GDEs are efficient, selective, durable, gas permeable electrodes for electrocatalytic reduction of CO₂ to formate. High turnover numbers (ca. 54 000) and turnover frequencies (ca. 15 s^?1) were enabled by the novel electrode architecture in aqueous solutions saturated in CO₂ with added HCO₃^?.     

Bioinspired Photocatalytic NADH Regeneration by Covalently Metalated Carbon Nitride for Enhanced CO2 Reduction

Natural photosynthesis is a highly unified biocatalytic system, which coupled cofactor (NAD(P)H) regeneration and enzymatic CO₂ reduction efficiently for solar energy conversion. Mimicking nature, a novel system with Rh complex covalently grafted onto NH₂-functionalized polymeric carbon nitride (NH₂-PCN) was constructed. The integrated connection of the light-harvesting and electron mediation modules as Rh_m3-N-PCN could promote the efficient NAD⁺ reduction to NADH. As a result, the integrated system exhibited a conversion of ∼66 % within 20 minutes. By further coupling in situ generated NADH with formate dehydrogenase (FDH), a photoenzymatic production of formic acid (HCOOH) from CO₂ was accomplished. Moreover, by immobilizing FDH onto a hydrophobic membrane, an enhanced HCOOH production of ∼5.0 mM can be obtained due to the concentrated CO₂ on the gas-liquid-solid three-phase interface. Our work herein provides an integrated strategy for coupling the anchored electron mediator with immobilized enzyme for enhanced artificial photosynthesis.     

Copper‐Bismuth Bimetallic Microspheres for Selective Electrocatalytic Reduction of CO2 to Formate

Electrocatalytic carbon dioxide reduction holds great promise for reducing the atmospheric CO₂ level and alleviating the energy crisis. High‐performance electrocatalysts are often required in order to lower the high overpotential and expedite the sluggish reaction kinetics of CO₂ electroreduction. Copper is a promising candidate metal. However, it usually suffers from the issues of poor stability and low product selectivity. In this work, bimetallic Cu‐Bi is obtained by reducing the microspherical copper bismuthate (CuBi₂O₄) for selectively catalyzing the CO₂ reduction to formate (HCOO^–). The bimetallic Cu‐Bi electrocatalyst exhibits high activity and selectivity with the Faradic efficiency over 90% in a wide potential window. A maximum Faradaic efficiency of ~95% is obtained at –0.93 V versus reversible hydrogen electrode. Furthermore, the catalyst shows high stability over 6 h with Faradaic efficiency of ~95%. This study provides an important clue in designing new functional materials for CO₂ electroreduction with high activity and selectivity.     

Design of a Single-Atom Indiumδ+–N4 Interface for Efficient Electroreduction of CO2 to Formate

Main-group element indium (In) is a promising electrocatalyst which triggers CO₂ reduction to formate, while the high overpotential and low Faradaic efficiency (FE) hinder its practical application. Herein, we rationally design a new In single-atom catalyst containing exclusive isolated In^δ+–N₄ atomic interface sites for CO₂ electroreduction to formate with high efficiency. This catalyst exhibits an extremely large turnover frequency (TOF) up to 12500 h⁻¹ at −0.95 V versus the reversible hydrogen electrode (RHE), with a FE for formate of 96 % and current density of 8.87 mA cm⁻² at low potential of −0.65 V versus RHE. Our findings present a feasible strategy for the accurate regulation of main-group indium catalysts for CO₂ reduction at atomic scale.     

Metalloproteins/metalloenzymes for the synthesis of acetyl-CoA in the Wood-Ljungdahl pathway

This paper focuses on the group of metalloproteins/metalloenzymes in the acetyl-coenzyme A synthesis pathway of anaerobic microbes called Wood-Ljungdahl pathway, including formate dehydrogenase (FDH), corrinoid iron sulfur protein (CoFeSP), acetyl-CoA synthase (ACS) and CO dehydrogenase (CODH). FDH, a key metalloenzyme involved in the conversion of carbon dioxide to methyltetrahydrofolate, catalyzes the reversible oxidation of formate to carbon dioxide. CoFeSP, as a methyl group transformer, accepts the methyl group from CH₃-H₄ folate and then transfers it to ACS. CODH reversibly catalyzes the reduction of CO₂ to CO and ACS functions for acetyl-coenzyme A synthesis through condensation of the methyl group, CO and coenzyme A, to finish the whole pathway. This paper introduces the structure, function and reaction mechanisms of these enzymes.     

Electroreduction of CO2 to Formate with Low Overpotential using Cobalt Pyridine Thiolate Complexes

Electrocatalytic CO₂ reduction to value‐added products provides a viable alternative to the use of carbon sources derived from fossil fuels. Carrying out these transformations at reasonable energetic costs, for example, with low overpotential, remains a challenge. Molecular catalysts allow fine control of activity and selectivity via tuning of their coordination sphere and ligand set. Herein we investigate a series of cobalt(III) pyridine‐thiolate complexes as electrocatalysts for CO₂ reduction. The effect of the ligands and proton sources on activity was examined. We identified bipyridine bis(2‐pyridinethiolato) cobalt(III) hexaflurophosphate as a highly selective catalyst for formate production operating at a low overpotential of 110 mV with a turnover frequency (TOF) of 10 s^?1. Electrokinetic analysis coupled with density functional theory (DFT) computations established the mechanistic pathway, highlighting the role of metal hydride intermediates. The catalysts deactivate via the formation of stable cobalt carbonyl complexes, but the active species could be regenerated upon oxidation and release of coordinated CO ligands.     

A Three‐Dimensional MnII‐[MoIII(CN)7]4– Ferrimagnet Containing Formate as a Second Bridging Ligand

Self‐assembly of the [Mo(CN)₇]^4– anion and the Mn²⁺ ion in the aqueous solution containing ammonium formate results in a new coordination polymer, {(NH₄)₃[(H₂O)Mn₃(HCOO)][Mo(CN)₇]₂·4H₂O}_n. Single crystal X‐ray analysis revealed a very complicated three‐dimensional (3D) framework, where both the [Mo(CN)₇]^4– and the formate anions act as bridges between the Mn^II centers. Magnetic measurements revealed that this compound displays ferrimagnetic ordering below 70 K. Competing antiferromagnetic interactions between the spin carriers might lead to spin frustration and non‐linear alignment of the magnetic moments. Specifically, this compound is the first mixed [Mo(CN)₇]^4–/HCOO^– bridged molecule magnet.     

Facile Insertion of Carbon Dioxide into Cu2(μ‐H) Dinuclear Units Supported by Tetraphosphine Ligands

Reactions of meso‐bis[(diphenylphosphinomethyl)phenylphosphino]methane (dpmppm) with Cu^I species in the presence of NaBH₄ afforded di‐ and tetranuclear copper hydride complexes, [Cu₂(μ‐H)(μ‐dpmppm)₂]X ( 1 ) and [Cu₄(μ‐H)₂(μ₄‐H)(μ‐dpmppm)₂]X ( 2 ) (X=BF₄, PF₆). Complex 1 undergoes facile insertion of CO₂ (1 atm) at room temperature, leading to a formate‐bridged dicopper complex [Cu₂(μ‐HCOO)(dpmppm)₂]X ( 3 ). The experimental and DFT theoretical studies clearly demonstrate that CO₂ insertion into the Cu₂(μ‐H) unit occurred with the flexible dicopper platform. Complex 2 also undergoes CO₂ insertion to give a formate‐bridged complex, [Cu₄(μ‐HCOO)₃(dpmppm)₂]X, during which the square Cu₄ framework opened up to a linear tetranuclear chain.     

Molten-Salt-Assisted Synthesis of Bismuth Nanosheets for Long-term Continuous Electrocatalytic Conversion of CO2 to Formate

Two-dimensional (2D) monometallic pnictogens (antimony or Sb, and bismuth or Bi) nanosheets demonstrate potential in a variety of fields, including quantum devices, catalysis, biomedicine and energy, because of their unique physical, chemical, electronic and optical properties. However, the development of general and high-efficiency preparative routes toward high-quality pnictogen nanosheets is challenging. A general method involving a molten-salt-assisted aluminothermic reduction process is reported for the synthesis of Sb and Bi nanosheets in high yields (>90 %). Electrocatalytic CO₂ reduction was investigated on the Bi nanosheets, and high catalytic selectively to formate was demonstrated with a considerable current density at a low overpotential and an impressive stability. Bi nanosheets continuously convert CO₂ into formate in a flow cell operating for one month, with a yield rate of 787.5 mmol cm⁻² h⁻¹. Theoretical results suggest that the edge sites of Bi are far more active than the terrace sites.     

Catholyte‐Free Electrocatalytic CO2 Reduction to Formate

Electrochemical reduction of carbon dioxide (CO₂) into value‐added chemicals is a promising strategy to reduce CO₂ emission and mitigate climate change. One of the most serious problems in electrocatalytic CO₂ reduction (CO₂R) is the low solubility of CO₂ in an aqueous electrolyte, which significantly limits the cathodic reaction rate. This paper proposes a facile method of catholyte‐free electrocatalytic CO₂ reduction to avoid the solubility limitation using commercial tin nanoparticles as a cathode catalyst. Interestingly, as the reaction temperature rises from 303 K to 363 K, the partial current density (PCD) of formate improves more than two times with 52.9 mA cm^?2, despite the decrease in CO₂ solubility. Furthermore, a significantly high formate concentration of 41.5 g L^?1 is obtained as a one‐path product at 343 K with high PCD (51.7 mA cm^?2) and high Faradaic efficiency (93.3 %) via continuous operation in a full flow cell at a low cell voltage of 2.2 V.