Electroenzymatic Nitrogen Fixation Using a MoFe Protein System Immobilized in an Organic Redox Polymer

We report an organic redox‐polymer‐based electroenzymatic nitrogen fixation system using a metal‐free redox polymer, namely neutral‐red‐modified poly(glycidyl methacrylate‐co‐methylmethacrylate‐co‐poly(ethyleneglycol)methacrylate) with a low redox potential of ?0.58 V vs. SCE. The stable and efficient electric wiring of nitrogenase within the redox polymer matrix enables mediated bioelectrocatalysis of N₃^?, NO₂^? and N₂ to NH₃ catalyzed by the MoFe protein via the polymer‐bound redox moieties distributed in the polymer matrix in the absence of the Fe protein. Bulk bioelectrosynthetic experiments produced 209±30 nmol NH₃ nmol MoFe^?1 h^?1 from N₂ reduction. ¹⁵N₂ labeling experiments and NMR analysis were performed to confirm biosynthetic N₂ reduction to NH₃.     

Polymer Meets Frustrated Lewis Pair: Second‐Generation CO2‐Responsive Nanosystem for Sustainable CO2 Conversion

Frustrated Lewis pairs (FLP), a couple comprising a sterically encumbered Lewis acid and Lewis base, can offer latent reactivity for activating inert gas molecules. However, their use as a platform for fabricating gas‐responsive materials has not yet developed. Merging the FLP concept with polymers, we report a new generation CO₂‐responsive system, differing from the first‐generation ones based on an acid–base equilibrium mechanism. Two complementary Lewis acidic and basic block copolymers, installing bulky borane‐ and phosphine‐containing blocks, were built as the macromolecular FLP. They can bind CO₂ to drive micellar formation, in which CO₂ as a cross‐linker bridges the block chains. This dative bonding endows the assembly with ultrafast response (<20 s), thermal reversibility, and excellent reproducibility. Moreover, such micelles bound highly active CO₂ can function as nanocatalysts for recyclable C₁ catalysis, opening a new direction of sustainable CO₂ conversion.     

Site Isolation Leads to Stable Photocatalytic Reduction of CO2 over a Rhenium‐Based Catalyst

A porous organic polymer incorporating [(α‐diimine)Re(CO)₃Cl] moieties was produced and tested in the photocatalytic reduction of CO₂, with NEt₃ as a sacrificial donor. The catalyst generated both H₂ and CO, although the Re moiety was not required for H₂ generation. After an induction period, the Re‐containing porous organic polymer produced CO at a stable rate, unless soluble [(bpy)Re(CO)₃Cl] (bpy=2,2′‐bipyridine) was added. This provides the strongest evidence to date that [(α‐diimine)Re(CO)₃Cl] catalysts for photocatalytic CO₂ reduction decompose through a bimetallic pathway.     

CO2‐Triggered Switchable Hydrophilicity of a Heterogeneous Conjugated Polymer Photocatalyst for Enhanced Catalytic Activity in Water

Water compatibility for heterogeneous photocatalysts has been pursued for energy and environmental applications. However, there exists a trade‐off between hydrophilicity and recyclability of the photocatalyst. Herein, we report a conjugated polymer photocatalyst with tertiary amine terminals that reversibly binds CO₂ in water, thereby generating switchable hydrophilicity. The CO₂‐assisted hydrophilicity boosted the photocatalytic efficiency in aqueous medium with minimum dosage. When CO₂ was desorbed, the photocatalyst could be simply regenerated from reaction media, facilitating the repeated use of photocatalyst. Hydrophilicity/hydrophobicity control of the polymer photocatalyst was successfully showcased through a variety of organic photoredox reactions under visible‐light irradiation in water.     

Metal‐Free Reduction of CO2 with Hydroboranes: Two Efficient Pathways at Play for the Reduction of CO2 to Methanol

Guanidines and amidines prove to be highly efficient metal‐free catalysts for the reduction of CO₂ to methanol with hydroboranes such as 9‐borabicyclo[3.3.1]nonane (9‐BBN) and catecholborane (catBH). Nitrogen bases, such as 1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene (TBD), 7‐methyl‐1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene (Me‐TBD), and 1,8‐diazabicycloundec‐7‐ene (DBU), are active catalysts for this transformation and Me‐TBD can catalyze the reduction of CO₂ to methoxyborane at room temperature with TONs and TOFs of up to 648 and 33 h^?1 (25 °C), respectively. Formate HCOOBR₂ and acetal H₂C(OBR₂)₂ derivatives have been identified as reaction intermediates in the reduction of CO₂ with R₂BH, and the first C?H‐bond formation is rate determining. Experimental and computational investigations show that TBD and Me‐TBD follow distinct mechanisms. The N?H bond of TBD is reactive toward dehydrocoupling with 9‐BBN and affords a novel frustrated Lewis pair (FLP) that can activate a CO₂ molecule and form the stable adduct 2 , which is the catalytically active species and can facilitate the hydride transfer from the boron to the carbon atoms. In contrast, Me‐TBD promotes the reduction of CO₂ through the activation of the hydroborane reagent. Detailed DFT calculations have shown that the computed energy barriers for the two mechanisms are consistent with the experimental findings and account for the reactivity of the different boron reductants.     

Electrochemical Reduction of CO2 at Coinage Metal Nanodendrites in Aqueous Ethanolamine

Electrocatalytic reduction of CO₂ into usable chemicals is a promising path to address climate change and energy challenges. Herein, we demonstrate the synthesis of unique coinage metal (Cu, Ag, and Au) nanodendrites (NDs) via a facile galvanic replacement reaction (GRR), which can be effective electrocatalysts for the reduction of CO₂ in an ethanolamine (EA) solution. Each metal ND surface was directly grown on glassy-carbon (GC) substrates from a mixture of Zn dust and the respective precursor solution. The electrocatalytic activities of the synthesized ND surfaces were optimized for CO₂ reduction in EA solution by varying their composition. It was determined that a 0.05 mol fraction of EA exhibited the highest catalytic activity for all metal NDs. Linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) techniques showed that metal-ND electrodes possessed higher current densities, lower onset potentials and lower charge-transfer resistances for CO₂ reduction than their smooth polycrystalline electrode counterparts, indicating improved CO₂ reduction catalytic activity. It was determined, using FTIR and NMR spectroscopy, that formate was produced as a result of the CO₂ reduction.     

Efficient Visible‐Light‐Driven CO2 Reduction Mediated by Defect‐Engineered BiOBr Atomic Layers

Solar CO₂ reduction efficiency is largely limited by poor photoabsorption, sluggish electron–hole separation, and a high CO₂ activation barrier. Defect engineering was employed to optimize these crucial processes. As a prototype, BiOBr atomic layers were fabricated and abundant oxygen vacancies were deliberately created on their surfaces. X‐ray absorption near‐edge structure and electron paramagnetic resonance spectra confirm the formation of oxygen vacancies. Theoretical calculations reveal the creation of new defect levels resulting from the oxygen vacancies, which extends the photoresponse into the visible‐light region. The charge delocalization around the oxygen vacancies contributes to CO₂ conversion into COOH* intermediate, which was confirmed by in situ Fourier‐transform infrared spectroscopy. Surface photovoltage spectra and time‐resolved fluorescence emission decay spectra indicate that the introduced oxygen vacancies promote the separation of carriers. As a result, the oxygen‐deficient BiOBr atomic layers achieve visible‐light‐driven CO₂ reduction with a CO formation rate of 87.4 μmol g^?1 h^?1, which was not only 20 and 24 times higher than that of BiOBr atomic layers and bulk BiOBr, respectively, but also outperformed most previously reported single photocatalysts under comparable conditions.     

High CO2‐Capture Ability of a Porous Organic Polymer Bifunctionalized with Carboxy and Triazole Groups

A new porous organic polymer, SNU‐C1 , incorporating two different CO₂‐attracting groups, namely, carboxy and triazole groups, has been synthesized. By activating SNU‐C1 with two different methods, vacuum drying and supercritical‐CO₂ treatment, the guest‐free phases, SNU‐C1‐va and SNU‐C1‐sca , respectively, were obtained. Brunauer–Emmett–Teller (BET) surface areas of SNU‐C1‐va and SNU‐C1‐sca are 595 and 830 m²g^?1, respectively, as estimated by the N₂‐adsorption isotherms at 77 K. At 298 K and 1 atm, SNU‐C1‐va and SNU‐C1‐sca show high CO₂ uptakes, 2.31 mmol g^?1 and 3.14 mmol g^?1, respectively, the high level being due to the presence of abundant polar groups (carboxy and triazole) exposed on the pore surfaces. Five separation parameters for flue gas and landfill gas in vacuum‐swing adsorption were calculated from single‐component gas‐sorption isotherms by using the ideal adsorbed solution theory (IAST). The data reveal excellent CO₂‐separation abilities of SNU‐C1‐va and SNU‐C1‐sca , namely high CO₂‐uptake capacity, high selectivity, and high regenerability. The gas‐cycling experiments for the materials and the water‐treated samples, experiments that involved treating the samples with a CO₂‐N₂ gas mixture (15:85, v/v) followed by a pure N₂ purge, further verified the high regenerability and water stability. The results suggest that these materials have great potential applications in CO₂ separation.     

Ionic Polymer Microspheres Bearing a CoIII–Salen Moiety as a Bifunctional Heterogeneous Catalyst for the Efficient Cycloaddition of CO2 and Epoxides

We report a unique strategy to obtain the bifunctional heterogeneous catalyst TBB‐Bpy@Salen‐Co (TBB=1,2,4,5‐tetrakis(bromomethyl)benzene, Bpy=4,4’‐bipyridine, Salen‐Co=N,N’‐bis({4‐dimethylamino}salicylidene)ethylenediamino cobalt(III) acetate) by combining a cross‐linked ionic polymer with a Co^III–salen Schiff base. The catalyst showed extra high activity for CO₂ fixation under mild, solvent‐free reaction conditions with no requirement for a co‐catalyst. The synthesized catalyst possessed distinctive spherical structural features, abundant halogen Br^? anions with good leaving group ability, and accessible Lewis acidic Co metal centers. These unique features, together with the synergistic role of the Co and Br^? functional sites, allowed TBB‐Bpy@Salen‐Co to exhibit enhanced catalytic conversion of CO₂ into cyclic carbonates relative to the corresponding monofunctional analogues. This catalyst can be easily recovered and recycled five times without significant leaching of Co or loss of activity. Moreover, based on our experimental results and previous work, a synergistic cycloaddition reaction mechanism was proposed.     

Boron‐Functionalized Graphene Oxide‐Organic Frameworks for Highly Efficient CO2 Capture

The capture and storage of CO₂ have been suggested as an effective strategy to reduce the global emissions of greenhouse gases. Hence, in recent years, many studies have been carried out to develop highly efficient materials for capturing CO₂. Until today, different types of porous materials, such as zeolites, porous carbons, N/B‐doped porous carbons or metal‐organic frameworks (MOFs), have been studied for CO₂ capture. Herein, the CO₂ capture performance of new hybrid materials, graphene‐organic frameworks (GOFs) is described. The GOFs were synthesized under mild conditions through a solvothermal process using graphene oxide (GO) as a starting material and benzene 1,4‐diboronic acid as an organic linker. Interestingly, the obtained GOF shows a high surface area (506 m² g⁻¹) which is around 11 times higher than that of GO (46 m² g⁻¹), indicating that the organic modification on the GO surface is an effective way of preparing a porous structure using GO. Our synthetic approach is quite simple, facile, and fast, compared with many other approaches reported previously. The synthesized GOF exhibits a very large CO₂ capacity of 4.95 mmol g⁻¹ at 298 K (1 bar), which is higher those of other porous materials or carbon‐based materials, along with an excellent CO₂/N₂ selectivity of 48.8.     

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 ).     

Synthesis of Two‐dimensional Microporous Carbonaceous Polymer Nanosheets and Their Application as High‐performance CO2 Capture Sorbent

The synthesis of two‐dimensional (2D) polymer nanosheets with a well‐defined microporous structure remains challenging in materials science. Here, a new kind of 2D microporous carbonaceous polymer nanosheets was synthesized through polymerization of a very low concentration of 1,4‐dicyanobenzene in molten zinc chloride at 400–500 °C. This type of nanosheets has a thickness in the range of 3–20 nm, well‐defined microporosity, a high surface area (～537 m² g^?1), and a large micropore volume (～0.45 cm³ g^?1). The microporous carbonaceous polymer nanosheets exhibit superior CO₂ sorption capability (8.14 wt % at 298 K and 1 bar) and a relatively high CO₂ selectivity toward N₂ (25.6). Starting from different aromatic nitrile monomers, a variety of 2D carbonaceous polymer nanosheets can be obtained showing a certain universality of the ionothermal method reported herein.     

N‐Heterocyclic Carbenes as Efficient Organocatalysts for CO2 Fixation Reactions

Getting a fix : N‐heterocyclic carbenes (NHCs) and NHC–CO₂ adducts serve as potent organocatalysts for carbonate synthesis by the addition of a CO₂ unit to propargylic alcohols or epoxides under mild and solvent‐free reaction conditions (see scheme). The enhanced Lewis basicity of imidazol‐2‐ylidenes bearing electron‐donating alkyl groups on the nitrogen atoms leads to utilizing CO₂ as a nucleophilic fragment in the chemical fixation processes.

     

Design of an Os Complex‐Modified Hydrogel with Optimized Redox Potential for Biosensors and Biofuel Cells

Multistep synthesis and electrochemical characterization of an Os complex‐modified redox hydrogel exhibiting a redox potential ≈+30 mV (vs. Ag/AgCl 3 m KCl) is demonstrated. The careful selection of bipyridine‐based ligands bearing N,N‐dimethylamino moieties and an amino‐linker for the covalent attachment to the polymer backbone ensures the formation of a stable redox polymer with an envisaged redox potential close to 0 V. Most importantly, the formation of an octahedral N6‐coordination sphere around the Os central atoms provides improved stability concomitantly with the low formal potential, a low reorganization energy during the Os^3+/2+ redox conversion and a negligible impact on oxygen reduction. By wiring a variety of enzymes such as pyrroloquinoline quinone (PQQ)‐dependent glucose dehydrogenase, flavin adenine dinucleotide (FAD)‐dependent glucose dehydrogenase and the FAD‐dependent dehydrogenase domain of cellobiose dehydrogenase, low‐potential glucose biosensors could be obtained with negligible co‐oxidation of common interfering compounds such as uric acid or ascorbic acid. In combination with a bilirubin oxidase‐based biocathode, enzymatic biofuel cells with open‐circuit voltages of up to 0.54 V were obtained.     

Mediated Inner-Sphere Electron Transfer Induces Homogeneous Reduction of CO2 via Through-Space Electronic Conjugation**

The electrocatalytic reduction of CO₂ is an appealing method for converting renewable energy sources into value-added chemical feedstocks. We report a co-electrocatalytic system for the reduction of CO₂ to CO comprised of a molecular Cr complex and dibenzothiophene-5,5-dioxide (DBTD) as a redox mediator, which achieves high activity (TOF=1.51–2.84×10⁵ s^?1) and quantitative selectivity. Under aprotic or protic conditions, DBTD produces a co-electrocatalytic response with 1 by coordinating trans to the site of CO₂ binding and mediating electron transfer from the electrode with quantitative efficiency for CO. This assembly is reliant on through-space electronic conjugation between the π frameworks of DBTD and the bpy fragment of the catalyst ligand, with contributions from dispersive interactions and weak sulfone coordination.     

Highly Efficient CO2 Electroreduction on ZnN4‐based Single‐Atom Catalyst

The electrochemical reduction reaction of carbon dioxide (CO2RR) to carbon monoxide (CO) is the basis for the further synthesis of more complex carbon‐based fuels or attractive feedstock. Single‐atom catalysts have unique electronic and geometric structures with respect to their bulk counterparts, thus exhibiting unexpected catalytic activities. A nitrogen‐anchored Zn single‐atom catalyst is presented for CO formation from CO2RR with high catalytic activity (onset overpotential down to 24 mV), high selectivity (Faradaic efficiency for CO (FE_CO) up to 95 % at ?0.43 V), remarkable durability (>75 h without decay of FE_CO), and large turnover frequency (TOF, up to 9969 h^?1). Further experimental and DFT results indicate that the four‐nitrogen‐anchored Zn single atom (Zn‐N₄) is the main active site for CO2RR with low free energy barrier for the formation of *COOH as the rate‐limiting step.     

Ce1-xZrxO2的氧化还原性能及其对CO2重整CH4反应的影响

 通过X射线衍射和程序升温还原技术对Ce1-xZrxO2(0≤x≤1)催化剂的结构和氧化还原性能进行了研究,同时考察了Ce1-xZrxO2催化剂在CO2重整CH4反应中的催化性能,并与其氧化还原性能进行了关联. 结果表明,当x≤0.25时, Ce1-x-ZrxO2以立方相Ce-Zr-O固溶体形式存在,氧化还原性随着Zr含量的增加而增加; 当x＞0.25时,以四方ZrO2相和立方相Ce-Zr-O固溶体的混合相存在,氧化还原性随着Zr含量的增加而减弱. Ce0.75Zr0.25O2具有最高的氧化还原性, Ce1-xZrxO2对CO2重整CH4反应的催化活性依赖于其氧化还原性,催化剂的氧化还原性越强,反应物(CO2和CH4)的转化率越高,催化剂的稳定性也越好. 氧化还原性能最强的Ce0.75Zr0.25O2催化剂表现出最高的催化活性、抗积炭能力和稳定性.     

Efficient CO2 Insertion and Reduction Catalyzed by a Terminal Zinc Hydride Complex

The terminal zinc hydride complex [Tntm]ZnH ( 2 ; Tntm=tris(6‐tert‐butyl‐3‐thiopyridazinyl)methanide) is an efficient hydrosilylation catalyst of CO₂ at room temperature without the need of Lewis acidic additives. The inherent electrophilicity of the system leads to selective formation of the monosilylated product (MeO)₃SiO₂CH (at room temperature with a TOF of 22.2 h^?1 and at 45 °C with a TOF of 66.7 h^?1). In absence of silanes, the intermediate formate complex [Tntm]Zn(O₂CH) ( 3 ) is quantitatively formed within 5 min. All complexes were fully characterized by ¹H and ¹³C NMR spectroscopy and single‐crystal X‐ray diffraction analyses. Density functional theory (DFT) calculations reveal a high positive charge on zinc and the increased preference of the ligand to adopt a κ³‐coordination mode.