Electrochemical CO₂ Reduction to Hydrocarbons on a Heterogeneous Molecular Cu Catalyst in Aqueous Solution

Gao S., Lin Y., Jiao X., Sun Y., Luo Q., Zhang W., Li D., Yang J., Xie Y.

Electroreduction of carbon dioxide into useful fuels helps to reduce fossil-fuel consumption and carbon dioxide emissions, but activating carbon dioxide requires impractically high overpotentials; here a metal atomic layer combined with its native oxide that requires low overpotentials to reduce carbon dioxide is developed, adapted from an existing cobalt-based catalyst. The production of useful fuels from carbon dioxide through electroreduction would be a clean way of replacing fossil fuels and reducing carbon dioxide emissions. Shan Gao et al. have turned cobalt, a metal generally considered not active for this reaction, into a very efficient electrocatalyst by synthesizing it in the form of four-atom-thick layers. This finding, and the observation that partial oxidation of the surface boosts activity further, points to a general strategy for turning otherwise unreactive metals into efficient electroreduction catalysts. Electroreduction of CO2 into useful fuels, especially if driven by renewable energy, represents a potentially ‘clean’ strategy for replacing fossil feedstocks and dealing with increasing CO2 emissions and their adverse effects on climate1,2,3,4. The critical bottleneck lies in activating CO2 into the CO2•− radical anion or other intermediates that can be converted further, as the activation usually requires impractically high overpotentials. Recently, electrocatalysts based on oxide-derived metal nanostructures have been shown5,6,7,8 to enable CO2 reduction at low overpotentials. However, it remains unclear how the electrocatalytic activity of these metals is influenced by their native oxides, mainly because microstructural features such as interfaces and defects9 influence CO2 reduction activity yet are difficult to control. To evaluate the role of the two different catalytic sites, here we fabricate two kinds of four-atom-thick layers: pure cobalt metal, and co-existing domains of cobalt metal and cobalt oxide. Cobalt mainly produces formate (HCOO−) during CO2 electroreduction; we find that surface cobalt atoms of the atomically thin layers have higher intrinsic activity and selectivity towards formate production, at lower overpotentials, than do surface cobalt atoms on bulk samples. Partial oxidation of the atomic layers further increases their intrinsic activity, allowing us to realize stable current densities of about 10 milliamperes per square centimetre over 40 hours, with approximately 90 per cent formate selectivity at an overpotential of only 0.24 volts, which outperforms previously reported metal or metal oxide electrodes evaluated under comparable conditions1,2,6,7,10. The correct morphology and oxidation state can thus transform a material from one considered nearly non-catalytic for the CO2 electroreduction reaction into an active catalyst. These findings point to new opportunities for manipulating and improving the CO2 electroreduction properties of metal systems, especially once the influence of both the atomic-scale structure and the presence of oxide are mechanistically better understood.

Costentin C., Robert M., Savéant J.

Recent attention aroused by the reduction of carbon dioxide has as main objective the production of useful products, the "solar fuels", in which solar energy would be stored. One route to this goal is the design of photochemical schemes that would operate this conversion using directly sun light energy. An indirect approach consists in first converting sunlight energy into electricity then using it to reduce CO2 electrochemically. Conversion of carbon dioxide into carbon monoxide is thus a key step through the classical dihydrogen-reductive Fischer-Tropsch chemistry. Direct and catalytic electrochemical CO2 reduction already aroused active interest during the 1980-1990 period. The new wave of interest for these matters that has been growing since 2012 is in direct conjunction with modern energy issues. Among molecular catalysts, electrogenerated Fe(0) porphyrins have proved to be particularly efficient and robust. Recent progress in this field has closely associated the search of more and more efficient catalysts in the iron porphyrin family with an unprecedentedly rigorous deciphering of mechanisms. Accordingly, the coupling of proton transfer with electron transfer and breaking of one of the two C-O bonds of CO2 have been the subjects of relentless scrutiny and mechanistic analysis with systematic investigation of the degree of concertedness of these three events. Catalysis of the electrochemical CO2-to-CO conversion has thus been a good testing ground for the mechanism diagnostic strategies and the all concerted reactivity model proposed then. The role of added Brönsted acids, both as H-bond providers and proton donors, has been elucidated. These efforts have been a preliminary to the inclusion of the acid functionalities within the catalyst molecule, giving rise to considerable increase of the catalytic efficiency. The design of more and more efficient catalysts made it necessary to propose "catalytic Tafel plots" relating the turnover frequency to the overpotential as a rational way of benchmarking the catalysts within iron porphyrins and among all available molecular catalysts, independently of the characteristics of the electrolytic cell in use. To be reliable, such assignments of the intrinsic characteristics of catalysts are grounded in the accurate elucidation of mechanisms. Without forgetting the importance of large scale electrolysis, not only mobilization of all resources of nondestructive techniques such as cyclic voltammetry was necessary to achieve this challenge, but also new approaches, such as foot-of-the-wave analysis combined with raising of scan rate, had to be applied. The latest improvement in catalyst design was to render it water-soluble while preserving, or even augmenting, its catalytic efficiency. The replacement of the nonaqueous solvents so far used by water makes the CO2-to-CO half-cell reaction much more attractive for applications, allowing its association with a water-oxidation anode through a proton-exchange membrane. Manipulation of pH and buffering then allow CO2-to-CO conversions from those involving complete CO-selectivity to ones with prescribed CO-H2 mixtures. Overall, it appears that not only are iron porphyrins the most efficient catalysts of the CO2-to-CO electrochemical conversion but also they can serve to illustrate general issues concerning the field of molecular catalysis as a whole, including other reductive or oxidative processes.

Kornienko N., Zhao Y., Kley C.S., Zhu C., Kim D., Lin S., Chang C.J., Yaghi O.M., Yang P.

A key challenge in the field of electrochemical carbon dioxide reduction is the design of catalytic materials featuring high product selectivity, stability, and a composition of earth-abundant elements. In this work, we introduce thin films of nanosized metal-organic frameworks (MOFs) as atomically defined and nanoscopic materials that function as catalysts for the efficient and selective reduction of carbon dioxide to carbon monoxide in aqueous electrolytes. Detailed examination of a cobalt-porphyrin MOF, Al2(OH)2TCPP-Co (TCPP-H2 = 4,4',4″,4‴-(porphyrin-5,10,15,20-tetrayl)tetrabenzoate) revealed a selectivity for CO production in excess of 76% and stability over 7 h with a per-site turnover number (TON) of 1400. In situ spectroelectrochemical measurements provided insights into the cobalt oxidation state during the course of reaction and showed that the majority of catalytic centers in this MOF are redox-accessible where Co(II) is reduced to Co(I) during catalysis.

Lee S., Kim D., Lee J.

Electrocatalytic conversion of carbon dioxide (CO2) has recently received considerable attention as one of the most feasible CO2 utilization techniques. In particular, copper and copper-derived catalysts have exhibited the ability to produce a number of organic molecules from CO2. Herein, we report a chloride (Cl)-induced bi-phasic cuprous oxide (Cu2O) and metallic copper (Cu) electrode (Cu2OCl) as an efficient catalyst for the formation of high-carbon organic molecules by CO2 conversion, and identify the origin of electroselectivity toward the formation of high-carbon organic compounds. The Cu2OCl electrocatalyst results in the preferential formation of multi-carbon fuels, including n-propanol and n-butane C3-C4 compounds. We propose that the remarkable electrocatalytic conversion behavior is due to the favorable affinity between the reaction intermediates and the catalytic surface.

Kortlever R., Shen J., Schouten K.J., Calle-Vallejo F., Koper M.T.

The electrochemical reduction of CO2 has gained significant interest recently as it has the potential to trigger a sustainable solar-fuel-based economy. In this Perspective, we highlight several heterogeneous and molecular electrocatalysts for the reduction of CO2 and discuss the reaction pathways through which they form various products. Among those, copper is a unique catalyst as it yields hydrocarbon products, mostly methane, ethylene, and ethanol, with acceptable efficiencies. As a result, substantial effort has been invested to determine the special catalytic properties of copper and to elucidate the mechanism through which hydrocarbons are formed. These mechanistic insights, together with mechanistic insights of CO2 reduction on other metals and molecular complexes, can provide crucial guidelines for the design of future catalyst materials able to efficiently and selectively reduce CO2 to useful products.

Lin S., Diercks C.S., Zhang Y., Kornienko N., Nichols E.M., Zhao Y., Paris A.R., Kim D., Yang P., Yaghi O.M., Chang C.J.

Improving cobalt catalysts Tethering molecular catalysts together is a tried and trusted method for making them easier to purify and reuse. Lin et al. now show that the assembly of a covalent organic framework (COF) structure can also improve fundamental catalytic performance. They used cobalt porphyrin complexes as building blocks for a COF. The resulting material showed greatly enhanced activity for the aqueous electrochemical reduction of CO 2 to CO. Science , this issue p. 1208

Shen J., Kortlever R., Kas R., Birdja Y.Y., Diaz-Morales O., Kwon Y., Ledezma-Yanez I., Schouten K.J., Mul G., Koper M.T.

The electrochemical conversion of carbon dioxide and water into useful products is a major challenge in facilitating a closed carbon cycle. Here we report a cobalt protoporphyrin immobilized on a pyrolytic graphite electrode that reduces carbon dioxide in an aqueous acidic solution at relatively low overpotential (0.5 V), with an efficiency and selectivity comparable to the best porphyrin-based electrocatalyst in the literature. While carbon monoxide is the main reduction product, we also observe methane as by-product. The results of our detailed pH-dependent studies are explained consistently by a mechanism in which carbon dioxide is activated by the cobalt protoporphyrin through the stabilization of a radical intermediate, which acts as Brønsted base. The basic character of this intermediate explains how the carbon dioxide reduction circumvents a concerted proton–electron transfer mechanism, in contrast to hydrogen evolution. Our results and their mechanistic interpretations suggest strategies for designing improved catalysts. The conversion of carbon dioxide to useful products is a major challenge in energy research. Here, the authors report a cobalt protoporphyrin immobilized on graphite that is capable of the selective and efficient electrochemical reduction of carbon dioxide, primarily to carbon monoxide, in acidic media.

Wu J., Yadav R.M., Liu M., Sharma P.P., Tiwary C.S., Ma L., Zou X., Zhou X., Yakobson B.I., Lou J., Ajayan P.M.

The challenge in the electrosynthesis of fuels from CO2 is to achieve durable and active performance with cost-effective catalysts. Here, we report that carbon nanotubes (CNTs), doped with nitrogen to form resident electron-rich defects, can act as highly efficient and, more importantly, stable catalysts for the conversion of CO2 to CO. The unprecedented overpotential (-0.18 V) and selectivity (80%) observed on nitrogen-doped CNTs (NCNTs) are attributed to their unique features to facilitate the reaction, including (i) high electrical conductivity, (ii) preferable catalytic sites (pyridinic N defects), and (iii) low free energy for CO2 activation and high barrier for hydrogen evolution. Indeed, DFT calculations show a low free energy barrier for the potential-limiting step to form key intermediate COOH as well as strong binding energy of adsorbed COOH and weak binding energy for the adsorbed CO. The highest selective site toward CO production is pyridinic N, and the NCNT-based electrodes exhibit no degradation over 10 h of continuous operation, suggesting the structural stability of the electrode.

Ren D., Deng Y., Handoko A.D., Chen C.S., Malkhandi S., Yeo B.S.

The selective electroreduction of carbon dioxide to C2 compounds (ethylene and ethanol) on copper(I) oxide films has been investigated at various electrochemical potentials. Aqueous 0.1 M KHCO3 was used as electrolyte. A remarkable finding is that the faradic yields of ethylene and ethanol can be systematically tuned by changing the thickness of the deposited overlayers. Films 1.7–3.6 μm thick exhibited the best selectivity for these C2 compounds at −0.99 V vs RHE, with faradic efficiencies (FE) of 34–39% for ethylene and 9–16% for ethanol. Less than 1% methane was formed. A high C2H4/CH4 products’ ratio of up to ∼100 could be achieved. Scanning electron microscopy, X-ray diffraction, and in situ Raman spectroscopy revealed that the Cu2O films reduced rapidly and remained as metallic Cu0 particles during the CO2 reduction. The selectivity trends exhibited by the catalysts during CO2 reduction in phosphate buffer, and KHCO3 electrolytes suggest that an increase in local pH at the surface of the electrode i...

Roberts F.S., Kuhl K.P., Nilsson A.

AbstractNanostructured surfaces have been shown to greatly enhance the activity and selectivity of many different catalysts. Here we report a nanostructured copper surface that gives high selectivity for ethylene formation from electrocatalytic CO2 reduction. The nanostructured copper is easily formed in situ during the CO2 reduction reaction, and scanning electron microscopy (SEM) shows the surface to be dominated by cubic structures. Using online electrochemical mass spectrometry (OLEMS), the onset potentials and relative selectivity toward the volatile products (ethylene and methane) were measured for several different copper surfaces and single crystals, relating the cubic shape of the copper surface to the greatly enhanced ethylene selectivity. The ability of the cubic nanostructure to so strongly favor multicarbon product formation from CO2 reduction, and in particular ethylene over methane, is unique to this surface and is an important step toward developing a catalyst that has exclusive selectivity for multicarbon products.

Lu Q., Rosen J., Jiao F.

Small is beautiful: Electrochemical CO2 reduction is an attractive approach to convert CO2 produced in power plants, refineries, and petrochemical plants to liquid fuels or useful chemicals. Recent progress in nanostructured metallic catalysts has exhibited tremendous promise for such realization. This review takes a closer look at those studies, and future research directions are proposed and discussed.

Manthiram K., Beberwyck B.J., Alivisatos A.P.

Although the vast majority of hydrocarbon fuels and products are presently derived from petroleum, there is much interest in the development of routes for synthesizing these same products by hydrogenating CO2. The simplest hydrocarbon target is methane, which can utilize existing infrastructure for natural gas storage, distribution, and consumption. Electrochemical methods for methanizing CO2 currently suffer from a combination of low activities and poor selectivities. We demonstrate that copper nanoparticles supported on glassy carbon (n-Cu/C) achieve up to 4 times greater methanation current densities compared to high-purity copper foil electrodes. The n-Cu/C electrocatalyst also exhibits an average Faradaic efficiency for methanation of 80% during extended electrolysis, the highest Faradaic efficiency for room-temperature methanation reported to date. We find that the level of copper catalyst loading on the glassy carbon support has an enormous impact on the morphology of the copper under catalytic conditions and the resulting Faradaic efficiency for methane. The improved activity and Faradaic efficiency for methanation involves a mechanism that is distinct from what is generally thought to occur on copper foils. Electrochemical data indicate that the early steps of methanation on n-Cu/C involve a pre-equilibrium one-electron transfer to CO2 to form an adsorbed radical, followed by a rate-limiting non-electrochemical step in which the adsorbed CO2 radical reacts with a second CO2 molecule from solution. These nanoscale copper electrocatalysts represent a first step toward the preparation of practical methanation catalysts that can be incorporated into membrane-electrode assemblies in electrolyzers.

Asadi M., Kumar B., Behranginia A., Rosen B.A., Baskin A., Repnin N., Pisasale D., Phillips P., Zhu W., Haasch R., Klie R.F., Král P., Abiade J., Salehi-Khojin A.

Electrochemical reduction of carbon dioxide has been recognized as an efficient way to convert carbon dioxide to energy-rich products. Noble metals (for example, gold and silver) have been demonstrated to reduce carbon dioxide at moderate rates and low overpotentials. Nevertheless, the development of inexpensive systems with an efficient carbon dioxide reduction capability remains a challenge. Here we identify molybdenum disulphide as a promising cost-effective substitute for noble metal catalysts. We uncover that molybdenum disulphide shows superior carbon dioxide reduction performance compared with the noble metals with a high current density and low overpotential (54 mV) in an ionic liquid. Scanning transmission electron microscopy analysis and first principle modelling reveal that the molybdenum-terminated edges of molybdenum disulphide are mainly responsible for its catalytic performance due to their metallic character and a high d-electron density. This is further experimentally supported by the carbon dioxide reduction performance of vertically aligned molybdenum disulphide. Electrochemical reduction is one process to produce higher value chemicals from carbon dioxide, and it is typically catalysed by noble metals. Here, the authors demonstrate that molybdenum disulphide is also capable of efficiently catalysing the reaction in the presence of an ionic liquid.

Zhang S., Kang P., Ubnoske S., Brennaman M.K., Song N., House R.L., Glass J.T., Meyer T.J.

Nitrogen-doped carbon nanotubes are selective and robust electrocatalysts for CO2 reduction to formate in aqueous media without the use of a metal catalyst. Polyethylenimine (PEI) functions as a co-catalyst by significantly reducing catalytic overpotential and increasing current density and efficiency. The co-catalysis appears to help in stabilizing the singly reduced intermediate CO2(•-) and concentrating CO2 in the PEI overlayer.

Reske R., Mistry H., Behafarid F., Roldan Cuenya B., Strasser P.

A study of particle size effects during the catalytic CO2 electroreduction on size-controlled Cu nanoparticles (NPs) is presented. Cu NP catalysts in the 2-15 nm mean size range were prepared, and their catalytic activity and selectivity during CO2 electroreduction were analyzed and compared to a bulk Cu electrode. A dramatic increase in the catalytic activity and selectivity for H2 and CO was observed with decreasing Cu particle size, in particular, for NPs below 5 nm. Hydrocarbon (methane and ethylene) selectivity was increasingly suppressed for nanoscale Cu surfaces. The size dependence of the surface atomic coordination of model spherical Cu particles was used to rationalize the experimental results. Changes in the population of low-coordinated surface sites and their stronger chemisorption were linked to surging H2 and CO selectivities, higher catalytic activity, and smaller hydrocarbon selectivity. The presented activity-selectivity-size relations provide novel insights in the CO2 electroreduction reaction on nanoscale surfaces. Our smallest nanoparticles (~2 nm) enter the ab initio computationally accessible size regime, and therefore, the results obtained lend themselves well to density functional theory (DFT) evaluation and reaction mechanism verification.

Abdullahi A.S., Mustapha U., Taialla O.A., Kotob E., Hussain I., Alhooshani K., Jillani S.M., Ganiyu S.A.

Rashid J., Arif A., Muhammad P., Xu M., Kumar R.

Ding D., Chen X., Wu H., Shen H., Zhang T., Wang K., Yang Y., She Y.

Yin S., Calvillo Solís J.J., Sandoval-Pauker C., Puerto-Diaz D., Villagrán D.

Ahmed S., Khan M.K., Kim J.

Shao Y., Zhou J.

Liu S., Guo Z., Li Z., Yang S., Wang D., Li H.

AbstractUpcycling CO2 into high‐value C1 products is impressive for achieving carbon neutrality and energy sustainability, while rational modulation of C1 product selectivity is one of the biggest challenges in electrocatalytic CO2 reduction reaction (eCO2RR) due to the competing reaction pathways and thermodynamic limitation. Here, we showcase a “proton fence” strategy enabled by in situ adsorbed *OH on sulfur vacancies (SV) to ultraselectively switch the C1 product between CH4 and CO during CO2RR, with Faraday efficiency of 93.6% and 95.3%, respectively. In situ measurements uncover that the photo‐generated holes counteract Cu2+ electroreduction to retain the intact structure of CuInS2/CuS, while *OH dissociated from water can spontaneously anchor toward SV to hinder the local proton migration, completely circumventing multiproton products. Meanwhile, the preferential desorption of *CO from Cu centers adjacent to the *OH‐anchored SV renders the exclusive formation of CO. In the absence of SV, *CO can be further hydrogenated in a lower free energy/even spontaneously to afford CH4. The proposed proton confinement effect furnishes a promising reference for the selectivity control of eCO2RR, and the photo‐assisted electroreductive protocol demonstrates a paradigm of in situ stabilization of electron‐intolerant catalytic structures.

Liu S., Guo Z., Li Z., Yang S., Wang D., Li H.

AbstractUpcycling CO2 into high‐value C1 products is impressive for achieving carbon neutrality and energy sustainability, while rational modulation of C1 product selectivity is one of the biggest challenges in electrocatalytic CO2 reduction reaction (eCO2RR) due to the competing reaction pathways and thermodynamic limitation. Here, we showcase a “proton fence” strategy enabled by in situ adsorbed *OH on sulfur vacancies (SV) to ultraselectively switch the C1 product between CH4 and CO during CO2RR, with Faraday efficiency of 93.6% and 95.3%, respectively. In situ measurements uncover that the photo‐generated holes counteract Cu2+ electroreduction to retain the intact structure of CuInS2/CuS, while *OH dissociated from water can spontaneously anchor toward SV to hinder the local proton migration, completely circumventing multiproton products. Meanwhile, the preferential desorption of *CO from Cu centers adjacent to the *OH‐anchored SV renders the exclusive formation of CO. In the absence of SV, *CO can be further hydrogenated in a lower free energy/even spontaneously to afford CH4. The proposed proton confinement effect furnishes a promising reference for the selectivity control of eCO2RR, and the photo‐assisted electroreductive protocol demonstrates a paradigm of in situ stabilization of electron‐intolerant catalytic structures.

Gallone M., Fortunati A., Hernández S.

The electrochemical CO2 reduction (eCO2RR) to valuable chemicals offers a promising method to combat global warming by recycling carbon. Among the possible products, syngas—a CO and H2 mixture—is especially valuable for industrial reactions. The use of Room Temperature Ionic Liquids (RTILs) electrolytes presents a promising pathway for eCO2RR because of the lower overpotential required and the increased CO2 solubility with respect to the aqueous ones. Ensuring a constant CO/H2 production is essential, and it relies on both the catalyst and reactor design. This study explores eCO2RR in RTIL mixtures of 1-butyl-3-methyl imidazolium trifluoromethanesulfonate (good for CO2 conversion) and 1-butyl-3-methyl imidazolium acetate (good for CO2 capture), with various amounts of water as a proton source. We evaluated syngas production stability across different electrochemical cells and ion exchange membranes after determining the appropriate electrolyte mixture for a suitable CO/H2 ratio near 1:1. The two-chamber cell configuration outperformed single-cell designs by reducing oxidative RTILs degradation and by-products formation. Using a bipolar membrane (BPM) in forward mode led to catholyte acidification, causing an increase of HER relative to eCO2RR over time, confirmed by Multiphysics modeling. Conversely, an anionic exchange membrane (AEM) maintained constant syngas production over extended periods. This work offers guidelines for syngas generation in RTIL-based systems from waste-CO2 reduction, which can be useful for other green chemical synthesis processes.

Wang H., Ma C., Lu Q., Gu M., Jiang L., Hao Y., Hu F., Li L., Wang G., Peng S., Zhang X.

AbstractMolecular catalysts play a critical role in regulating the selectivity of electrocatalytic CO2 reduction reaction (CO2RR), yet the understanding of ligand function is largely restricted to modulating the electronic structure of the metal and reaction kinetics. Herein, a hydroxyl (─OH) ligand is introduced into a sterically hindered amino‐porphyrin (o‐TAPP) to synthesize the atropisomers porphyrin‐salicylimine‐Cu (o‐Cu‐Por‐Sa) with hydrogen‐bonding interactions (O─H⋯O), enabling efficient selection of CO and CH4 under dual effects. Detailed analysis shows that the ─OH of o‐Cu‐Por‐Sa (αβαβ) forms a noncovalent hydrogen bond with carbonate, characterized by a bond length of 2.01 Å and an angle of 27.6°, and this interaction reduces the reaction energy barrier, achieving a faradaic efficiency (FE) of 84% for CH4. Moreover, the steric hindrance effect of the symmetric distribution of ─OH facilitates protonation reactions by preventing C–C coupling. In contrast, ─OH aggregated on o‐Cu‐Por‐Sa (αααα) forms a pocket‐like hydrogen bond grid, which restricts free CO2 adsorption, and the rapid dissociation of *CO also interrupts the reaction. This work highlights the pivotal role of dual effects induced by ligand atropisomerization in regulating selectivity, offering new insights for the design of efficient molecular catalysts.

Wang H., Ma C., Lu Q., Gu M., Jiang L., Hao Y., Hu F., Li L., Wang G., Peng S., Zhang X.

AbstractMolecular catalysts play a critical role in regulating the selectivity of electrocatalytic CO2 reduction reaction (CO2RR), yet the understanding of ligand function is largely restricted to modulating the electronic structure of the metal and reaction kinetics. Herein, a hydroxyl (─OH) ligand is introduced into a sterically hindered amino‐porphyrin (o‐TAPP) to synthesize the atropisomers porphyrin‐salicylimine‐Cu (o‐Cu‐Por‐Sa) with hydrogen‐bonding interactions (O─H⋯O), enabling efficient selection of CO and CH4 under dual effects. Detailed analysis shows that the ─OH of o‐Cu‐Por‐Sa (αβαβ) forms a noncovalent hydrogen bond with carbonate, characterized by a bond length of 2.01 Å and an angle of 27.6°, and this interaction reduces the reaction energy barrier, achieving a faradaic efficiency (FE) of 84% for CH4. Moreover, the steric hindrance effect of the symmetric distribution of ─OH facilitates protonation reactions by preventing C–C coupling. In contrast, ─OH aggregated on o‐Cu‐Por‐Sa (αααα) forms a pocket‐like hydrogen bond grid, which restricts free CO2 adsorption, and the rapid dissociation of *CO also interrupts the reaction. This work highlights the pivotal role of dual effects induced by ligand atropisomerization in regulating selectivity, offering new insights for the design of efficient molecular catalysts.

Ali I., Afshan G., Singh V.D., Dutta A., Pandey D.S.

Dutta N., Peter S.C.

Yin Z., Zhang M., Long Y., Lei H., Li X., Zhang X., Zhang W., Apfel U., Cao R.

AbstractDelivering CO2 molecules to catalyst sites is a vital step in the CO2 reduction reaction (CO2RR). Achievements have been made to develop efficient catalysts, but few efforts have been dedicated to improving CO2 delivering in solutions. Herein, we report on electrocatalytic CO2‐to‐CO conversion using Fe tetraphenylporphyrin (FeTPP) as a catalyst and triethanolamine as a CO2 shuttle. Compared to ethanol, the electrocatalytic CO2RR current with triethanolamine increases by more than three times. We show that triethanolamine can effectively capture a CO2 molecule to form a zwitterionic alkylcarbonate through the collaboration between its tripodal alcohol and amine units. This alkylcarbonate can release the bound CO2 molecule for activation at the Fe site upon its interaction with FeTPP. In addition to shuttling CO2, alkylcarbonates can also provide protons to assist the C−O bond cleavage. Therefore, this work is significant to demonstrate a new strategy to improve electrocatalytic CO2RR by shuttling CO2.

Yin Z., Zhang M., Long Y., Lei H., Li X., Zhang X., Zhang W., Apfel U., Cao R.

AbstractDelivering CO2 molecules to catalyst sites is a vital step in the CO2 reduction reaction (CO2RR). Achievements have been made to develop efficient catalysts, but few efforts have been dedicated to improving CO2 delivering in solutions. Herein, we report on electrocatalytic CO2‐to‐CO conversion using Fe tetraphenylporphyrin (FeTPP) as a catalyst and triethanolamine as a CO2 shuttle. Compared to ethanol, the electrocatalytic CO2RR current with triethanolamine increases by more than three times. We show that triethanolamine can effectively capture a CO2 molecule to form a zwitterionic alkylcarbonate through the collaboration between its tripodal alcohol and amine units. This alkylcarbonate can release the bound CO2 molecule for activation at the Fe site upon its interaction with FeTPP. In addition to shuttling CO2, alkylcarbonates can also provide protons to assist the C−O bond cleavage. Therefore, this work is significant to demonstrate a new strategy to improve electrocatalytic CO2RR by shuttling CO2.