Enhanced Carbon Dioxide Electroreduction to Carbon Monoxide over Defect‐Rich Plasma‐Activated Silver Catalysts

Efficient, stable catalysts with high selectivity for a single product are essential if electroreduction of CO₂ is to become a viable route to the synthesis of industrial feedstocks and fuels. A plasma oxidation pre‐treatment of silver foil enhances the number of low‐coordinated catalytically active sites, which dramatically lowers the overpotential and increases the activity of CO₂ electroreduction to CO. At −0.6 V versus RHE more than 90 % Faradaic efficiency towards CO was achieved on a pre‐oxidized silver foil. While transmission electron microscopy (TEM) and operando X‐ray absorption spectroscopy showed that oxygen species can survive in the bulk of the catalyst during the reaction, quasi in situ X‐ray photoelectron spectroscopy showed that the surface is metallic under reaction conditions. DFT calculations reveal that the defect‐rich surface of the plasma‐oxidized silver foils in the presence of local electric fields drastically decrease the overpotential of CO₂ electroreduction.     

Tuning of Silver Catalyst Mesostructure Promotes Selective Carbon Dioxide Conversion into Fuels

An electrode's performance for catalytic CO₂ conversion to fuels is a complex convolution of surface structure and transport effects. Using well‐defined mesostructured silver inverse opal (Ag‐IO) electrodes, it is demonstrated that mesostructure‐induced transport limitations alone serve to increase the turnover frequency for CO₂ activation per unit area, while simultaneously improving reaction selectivity. The specific activity for catalyzed CO evolution systematically rises by three‐fold and the specific activity for catalyzed H₂ evolution systematically declines by ten‐fold with increasing mesostructural roughness of Ag‐IOs. By exploiting the compounding influence of both of these effects, we demonstrate that mesostructure, rather than surface structure, can be used to tune CO evolution selectivity from less than 5 % to more than 80 %. These results establish electrode mesostructuring as a powerful complementary tool for tuning both catalyst selectivity and efficiency for CO₂ conversion into fuels.     

Elemental Boron for Efficient Carbon Dioxide Reduction under Light Irradiation

The photoreduction of CO₂ is attractive for the production of renewable fuels and the mitigation of global warming. Herein, we report an efficient method for CO₂ reduction over elemental boron catalysts in the presence of only water and light irradiation through a photothermocatalytic process. Owing to its high solar‐light absorption and effective photothermal conversion, the illuminated boron catalyst experiences remarkable self‐heating. This process favors CO₂ activation and also induces localized boron hydrolysis to in situ produce H₂ as an active proton source and electron donor for CO₂ reduction as well as boron oxides as promoters of CO₂ adsorption. These synergistic effects, in combination with the unique catalytic properties of boron, are proposed to account for the efficiency of the CO₂ reduction. This study highlights the promise of photothermocatalytic strategies for CO₂ conversion and also opens new avenues towards the development of related solar‐energy utilization schemes.     

Metal‐Free Fluorine‐Doped Carbon Electrocatalyst for CO2 Reduction Outcompeting Hydrogen Evolution

The electrochemical CO₂ reduction (ECDRR), as a key reaction in artificial photosynthesis to implement renewable energy conversion/storage, has been inhibited by the low efficiency and high costs of the electrocatalysts. Herein, we synthesize a fluorine‐doped carbon (FC) catalyst by pyrolyzing commercial BP 2000 with a fluorine source, enabling a highly selective CO₂‐to‐CO conversion with a maximum Faradaic efficiency of 90 % at a low overpotential of 510 mV and a small Tafel slope of 81 mV dec^?1, outcompeting current metal‐free catalysts. Moreover, the higher partial current density of CO and lower partial current density of H₂ on FC relative to pristine carbon suggest an enhanced inherent activity towards ECDRR as well as a suppressed hydrogen evolution by fluorine doping. Fluorine doping activates the neighbor carbon atoms and facilitates the stabilization of the key intermediate COOH* on the fluorine‐doped carbon material, which are also blocked for competing hydrogen evolution, resulting in superior CO₂‐to‐CO conversion.     

Metal–Organic‐Framework‐Derived Hollow N‐Doped Porous Carbon with Ultrahigh Concentrations of Single Zn Atoms for Efficient Carbon Dioxide Conversion

The development of efficient and low energy‐consumption catalysts for CO₂ conversion is desired, yet remains a great challenge. Herein, a class of novel hollow porous carbons (HPC), featuring well dispersed dopants of nitrogen and single Zn atoms, have been fabricated, based on the templated growth of a hollow metal–organic framework precursor, followed by pyrolysis. The optimized HPC‐800 achieves efficient catalytic CO₂ cycloaddition with epoxides, under light irradiation, at ambient temperature, by taking advantage of an ultrahigh loading of (11.3 wt %) single‐atom Zn and uniform N active sites, high‐efficiency photothermal conversion as well as the hierarchical pores in the carbon shell. As far as we know, this is the first report on the integration of the photothermal effect of carbon‐based materials with single metal atoms for catalytic CO₂ fixation.     

Electrochemically Driven Cation Exchange Enables the Rational Design of Active CO2 Reduction Electrocatalysts

Metal oxides or sulfides are considered to be one of the most promising CO₂ reduction reaction (CO₂RR) precatalysts, owing to their electrochemical conversion in situ into highly active electrocatalytic species. However, further improvement of the performance requires new tools to gain fine control over the composition of the active species and its structural features [e.g., grain boundaries (GBs) and undercoordinated sites (USs)], directly from a predesigned template material. Herein, we describe a novel electrochemically driven cation exchange (ED‐CE) method that enables the conversion of a predesigned CoS₂ template into a CO₂RR catalyst, Cu₂S. By means of ED‐CE, the final Cu₂S catalyst inherits the original 3 D morphology of CoS₂, and preserves its high density of GBs. Additionally, the catalyst's phase structure, composition, and density of USs were precisely tuned, thus enabling rational design of active CO₂RR sites. The obtained Cu₂S catalyst achieved a CO₂‐to‐formate Faradaic efficiency of over 87 % and a record high activity (among reported Cu‐based catalysts). Hence, this study opens the way for utilization of ED‐CE reactions to design advanced electrocatalysts.     

Acid–Base Interaction Enhancing Oxygen Tolerance in Electrocatalytic Carbon Dioxide Reduction

Hybrid electrodes with improved O₂ tolerance and capability of CO₂ conversion into liquid products in the presence of O₂ are presented. Aniline molecules are introduced into the pore structure of a polymer of intrinsic microporosity to expand its gas separation functionality beyond pure physical sieving. The chemical interaction between the acidic CO₂ molecule and the basic amino group of aniline renders enhanced CO₂ separation from O₂. Loaded with a cobalt phthalocyanine‐based cathode catalyst, the hybrid electrode achieves a CO Faradaic efficiency of 71 % with 10 % O₂ in the CO₂ feed gas. The electrode can still produce CO at an O₂/CO₂ ratio as high as 9:1. Switching to a Sn‐based catalyst, for the first time O₂‐tolerant CO₂ electroreduction to liquid products is realized, generating formate with nearly 100 % selectivity and a current density of 56.7 mA cm^?2 in the presence of 5 % O₂.     

Dispersed Nickel Cobalt Oxyphosphide Nanoparticles Confined in Multichannel Hollow Carbon Fibers for Photocatalytic CO2 Reduction

Materials for high‐efficiency photocatalytic CO₂ reduction are desirable for solar‐to‐carbon fuel conversion. Herein, highly dispersed nickel cobalt oxyphosphide nanoparticles (NiCoOP NPs) were confined in multichannel hollow carbon fibers (MHCFs) to construct the NiCoOP‐NPs@MHCFs catalysts for efficient CO₂ photoreduction. The synthesis involves electrospinning, phosphidation, and carbonization steps and permits facile tuning of chemical composition. In the catalyst, the mixed metal oxyphosphide NPs with ultrasmall size and high dispersion offer abundant catalytically active sites for redox reactions. At the same time, the multichannel hollow carbon matrix with high conductivity and open ends will effectively promote mass/charge transfer, improve CO₂ adsorption, and prevent the metal oxyphosphide NPs from aggregation. The optimized hetero‐metal oxyphosphide catalyst exhibits considerable activity for photosensitized CO₂ reduction, affording a high CO evolution rate of 16.6 μmol h^?1 (per 0.1 mg of catalyst).     

Efficient Photoelectrochemical Reduction of Carbon Dioxide to Formic Acid: A Functionalized Ionic Liquid as an Absorbent and Electrolyte

Photoelectrochemical (PEC) reduction of carbon dioxide (CO₂) is a potential method for production of fuels and chemicals from a C1 feedstock accumulated in the atmosphere. However, the low solubility of CO₂ in water, and complicated processes associated with capture and conversion, render CO₂ conversion inefficient. A new concept is proposed in which a PEC system is used to capture and convert CO₂ into formic acid. The process is assisted by an ionic liquid (1‐aminopropyl‐3‐methylimidazolium bromide) aqueous solution, which functions as an absorbent and electrolyte at ambient temperature and pressure. Within this PEC reduction strategy, the ionic liquid plays a critical role in promoting the conversion of CO₂ to formic acid and suppressing the reduction of H₂O to H₂. At an applied voltage of 1.7 V, the Faradaic efficiency for formic acid production is as high as 94.1 % and the electro‐to‐chemical efficiency is 86.2 %.     

Low‐Coordinated Edge Sites on Ultrathin Palladium Nanosheets Boost Carbon Dioxide Electroreduction Performance

Electrochemical conversion of carbon dioxide (CO₂) to value‐added products is a possible way to decrease the problems resulting from CO₂ emission. Thanks to the eminent conductivity and proper adsorption to intermediates, Pd has become a promising candidate for CO₂ electroreduction (CO₂ER). However, Pd‐based nanocatalysts generally need a large overpotential. Herein we describe that ultrathin Pd nanosheets effectively reduce the onset potential for CO by exposing abundant atoms with comparatively low generalized coordination number. Hexagonal Pd nanosheets with 5 atomic thickness and 5.1 nm edge length reached CO faradaic efficiency of 94 % at ?0.5 V, without any decay after a stability test of 8 h. It appears to be the most efficient among all of Pd‐based catalysts toward CO₂ER. Uniform hexagonal morphology made it reasonable to build models and take DFT calculations. The enhanced activity originates from mainly edge sites on palladium nanosheets.     

Understanding the Origin of Highly Selective CO2 Electroreduction to CO on Ni,N‐doped Carbon Catalysts

Ni,N‐doped carbon catalysts have shown promising catalytic performance for CO₂ electroreduction (CO₂R) to CO; this activity has often been attributed to the presence of nitrogen‐coordinated, single Ni atom active sites. However, experimentally confirming Ni?N bonding and correlating CO₂ reduction (CO₂R) activity to these species has remained a fundamental challenge. We synthesized polyacrylonitrile‐derived Ni,N‐doped carbon electrocatalysts (Ni‐PACN) with a range of pyrolysis temperatures and Ni loadings and correlated their electrochemical activity with extensive physiochemical characterization to rigorously address the origin of activity in these materials. We found that the CO₂R to CO partial current density increased with increased Ni content before plateauing at 2 wt % which suggests a dispersed Ni active site. These dispersed active sites were investigated by hard and soft X‐ray spectroscopy, which revealed that pyrrolic nitrogen ligands selectively bind Ni atoms in a distorted square‐planar geometry that strongly resembles the active sites of molecular metal–porphyrin catalysts.     

Carbamate Stabilities of Sterically Hindered Amines from Quantum Chemical Methods: Relevance for CO2 Capture

The influence of electronic and steric effects on the stabilities of carbamates formed from the reaction of CO₂ with a wide range of alkanolamines was investigated by quantum chemical methods. For the calculations, B3LYP, M11‐L, MP2, and spin‐component‐scaled MP2 (SCS‐MP2) methods were used, coupled with SMD and SM8 solvation models. A reduction in carbamate stability leads to an increased CO₂ absorption capacity of the amine and a reduction of the energy required for solvent regeneration. Important factors for the reduction of the carbamate stability were an increase in steric hindrance around the nitrogen atom, charge on the N atom and intramolecular hydrogen bond strength. The present study indicates that secondary ethanolamines with sterically hindering groups near the N atom show significant potential as candidates for industrial CO₂‐capture solvents.     

Simultaneous Capture of CO2 Boosting Its Electroreduction in the Micropores of a Metal–organic Framework

Integration of CO₂ capture capability from simulated flue gas and electrochemical CO₂ reduction reaction (eCO₂RR) active sites into a catalyst is a promising cost-effective strategy for carbon neutrality, but is of great difficulty. Herein, combining the mixed gas breakthrough experiments and eCO₂RR tests, we showed that an Ag₁₂ cluster-based metal–organic framework ( 1-NH₂ , aka Ag₁₂bpy-NH₂ ), simultaneously possessing CO₂ capture sites as “CO₂ relays” and eCO₂RR active sites, can not only utilize its micropores to efficiently capture CO₂ from simulated flue gas (CO₂ : N₂=15 : 85, at 298 K), but also catalyze eCO₂RR of the adsorbed CO₂ into CO with an ultra-high CO₂ conversion of 60 %. More importantly, its eCO₂RR performance (a Faradaic efficiency (CO) of 96 % with a commercial current density of 120 mA cm⁻² at a very low cell voltage of −2.3 V for 300 hours and the full-cell energy conversion efficiency of 56 %) under simulated flue gas atmosphere is close to that under 100 % CO₂ atmosphere, and higher than those of all reported catalysts at higher potentials under 100 % CO₂ atmosphere. This work bridges the gap between CO₂ enrichment/capture and eCO₂RR.     

Highly Efficient Porous Carbon Electrocatalyst with Controllable N‐Species Content for Selective CO2 Reduction

We report a straightforward strategy to design efficient N doped porous carbon (NPC) electrocatalyst that has a high concentration of easily accessible active sites for the CO₂ reduction reaction (CO₂RR). The NPC with large amounts of active N (pyridinic and graphitic N) and highly porous structure is prepared by using an oxygen‐rich metal–organic framework (Zn‐MOF‐74) precursor. The amount of active N species can be tuned by optimizing the calcination temperature and time. Owing to the large pore sizes, the active sites are well exposed to electrolyte for CO₂RR. The NPC exhibits superior CO₂RR activity with a small onset potential of ?0.35 V and a high faradaic efficiency (FE) of 98.4 % towards CO at ?0.55 V vs. RHE, one of the highest values among NPC‐based CO₂RR electrocatalysts. This work advances an effective and facile way towards highly active and cost‐effective alternatives to noble‐metal CO₂RR electrocatalysts for practical applications.     

Reversible Carbon Dioxide/Lithium Oxalate Regulation toward Advanced Aprotic Lithium Carbon Dioxide Battery

Li−CO₂ batteries have received significant attention owing to their advantages of combining greenhouse gas utilization and energy storage. However, the high kinetic barrier between gaseous CO₂ and the Li₂CO₃ product leads to a low operating voltage (<2.5 V) and poor energy efficiency. In addition, the reversibility of Li₂CO₃ has always been questioned owing to the introduction of more decomposition paths caused by its higher charging plateau. Here, a novel “trinity” Li−CO₂ battery system was developed by synergizing CO₂, soluble redox mediator (2,2,6,6-tetramethylpiperidoxyl, as TEM RM), and reduced graphene oxide electrode to enable selective conversion of CO₂ to Li₂C₂O₄. The designed Li−CO₂ battery exhibited an output plateau reaching up to 2.97 V, higher than the equilibrium potential of 2.80 V for Li₂CO₃, and an ultrahigh round-trip efficiency of 97.1 %. The superior performance of Li−CO₂ batteries is attributed to the TEM RM-mediated preferential growth mechanism of Li₂C₂O₄, which enhances the reaction kinetics and rechargeability. Such a unique design enables batteries to cope with sudden CO₂-deficient environments, which provides an avenue for the rationally design of CO₂ conversion reactions and a feasible guide for next-generation Li−CO₂ batteries.     

Lipase‐catalyzed Synthesis of Sugar Ester in Mixed Biphasic System of Ionic Liquids and Supercritical Carbon Dioxide

Lipase‐catalyzed synthesis of lauroyl glucose ester was continuously performed in a biphasic system consisting of supercritical CO₂ and an ionic liquid (IL). Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy are employed to identify the product lauroyl glucose ester. The effects of reaction pressure, temperature, substrate flow rate, the amount of enzyme, and the amount of IL on the glucose conversion rate are investigated. The highest glucose conversion of up to 95.5% could be achieved at the optimal condition, which is higher than that in the pure IL. The enzyme activity in the biphasic system was 18.19 μmol/g/min, which is much higher than that in the pure IL. The continuous reaction in the binary system could last for 10 h at high enzyme activity. The combination of supercritical CO₂ and ILs could not only improve the reaction rate and yield, which are attributed to the fast mass transfer rate and enhanced enzyme activity and lifespan, but also make the product separation and enzyme/ILs recycling easier.     

Synergistic Interplay of Dual-Active-Sites on Metallic Ni-MOFs Loaded with Pt for Thermal-Photocatalytic Conversion of Atmospheric CO2 under Infrared Light Irradiation

Infrared light driven photocatalytic reduction of atmospheric CO₂ is challenging due to the ultralow concentration of CO₂ (0.04 %) and the low energy of infrared light. Herein, we develop a metallic nickel-based metal–organic framework loaded with Pt (Pt/Ni-MOF), which shows excellent activity for thermal-photocatalytic conversion of atmospheric CO₂ with H₂ even under infrared light irradiation. The open Ni sites are beneficial to capture and activate atmospheric CO₂, while the photogenerated electrons dominate H₂ dissociation on the Pt sites. Simultaneously, thermal energy results in spilling of the dissociated H₂ to Ni sites, where the adsorbed CO₂ is thermally reduced to CO and CH₄. The synergistic interplay of dual-active-sites renders Pt/Ni-MOF a record efficiency of 9.57 % at 940 nm for converting atmospheric CO₂, enables the procurement of CO₂ to be independent of the emission sources, and improves the energy efficiency for trace CO₂ conversion by eliminating the capture media regeneration and molecular CO₂ release.     

Bipyridine‐Assisted Assembly of Au Nanoparticles on Cu Nanowires To Enhance the Electrochemical Reduction of CO2

We report a new strategy to prepare a composite catalyst for highly efficient electrochemical CO₂ reduction reaction (CO₂RR). The composite catalyst is made by anchoring Au nanoparticles on Cu nanowires via 4,4′‐bipyridine (bipy). The Au‐bipy‐Cu composite catalyzes the CO₂RR in 0.1 m KHCO₃ with a total Faradaic efficiency (FE) reaching 90.6 % at ?0.9 V to provide C‐products, among which CH₃CHO (25 % FE) dominates the liquid product (HCOO^?, CH₃CHO, and CH₃COO^?) distribution (75 %). The enhanced CO₂RR catalysis demonstrated by Au‐bipy‐Cu originates from its synergistic Au (CO₂ to CO) and Cu (CO to C‐products) catalysis which is further promoted by bipy. The Au‐bipy‐Cu composite represents a new catalyst system for effective CO₂RR conversion to C‐products.     

The Transition States for CO2 Capture by Substituted Ethanolamines

Quantum chemical studies are used to understand the electronic and steric effects on the mechanisms of the reaction of substituted ethanolamines with CO₂. SCS‐MP2/6‐311+G(2d,2p) calculations are used to obtain the activation energy barriers and reaction energies for both the carbamate and bicarbonate formation. Implicit solvent effects are included with the universal solvation model SMD. Carbamate formation is more favorable than bicarbonate formation for monoethanolamine (MEA) both kinetically and thermodynamically. Increase of the steric hindrance on the C atoms around the N atom in substituted ethanolamines favors bicarbonate formation over carbamate formation with lower activation barriers and thereby higher reaction rates. In contrast, substitution by an N‐methyl or N‐ethyl group on MEA leads to a lower activation barrier for both carbamate formation and bicarbonate formation. As a result, higher reaction rates are expected as compared to MEA, and therefore these compounds have significant potential as industrial CO₂ capturing solvents.     

Triazine‐based Organic Polymer‐catalysed Conversion of Epoxide to Cyclic Carbonate under Ambient CO2 Pressure

In this work we have achieved epoxide to cyclic carbonate conversion using a metal‐free polymeric catalyst under ambient CO₂ pressure (1.02 atm) using a balloon setup. The triazine containing polymer (CYA‐ANIS) was prepared from cyanuric chloride (CYA?Cl) and o‐dianisidine (ANIS) in anhydrous DMF as solvent by refluxing under the N₂ gas environment. The presence of triazine and amine functional groups in the polymer results in the adsorption of CO₂ up to 7 cc/g at 273 K. This inspired us to utilize the polymer for the conversion of a series of functionalised epoxides into their corresponding cyclic carbonates in the presence of tetrabutyl ammonium iodide (TBAI) as co‐catalyst. The product has wide range of applications like solvent in lithium ion battery, precursor for polycarbonate, etc. The catalyst was efficient for the conversion of different mono and di‐epoxides into their corresponding cyclic carbonates under atmospheric pressure in the presence of TBAI as co‐catalyst. The study indicates that epoxide attached with electron withdrawing groups (like, CH₂Cl, glycidyl ether, etc.) displayed better conversion compared to simple alkane chain attached epoxides. This is mainly due to the stabilization of electron rich intermediates produced during the reaction (e. g. epoxide ring opening or CO₂ incorporation into the halo‐alkoxide anion). This catalyst mixture was capable to maintain its reactivity up to five cycles without losing its activity. Post catalytic characterization clearly supports the heterogeneous and recyclable nature of the catalyst.