Selective CO2 Reduction Research Articles

Water-Induced Switching in Selectivity and Steric Control of Activity in Photochemical CO2 Reduction Catalyzed by RhCp*(bpy) Derivatives.

Photocatalytic reduction of CO2 to formic acid (HCOOH) was investigated in either organic or aqueous/organic media by employing three water-soluble [RhIIICp*(LH2)Cl]+ (LH2 = n,n'-dihydroxy-2,2'-bipyridine; n = 4, 5, or 6) in the presence of [Ru(bpy)3]2+, 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole (BIH) and triethanolamine (TEOA). Through studying the electron-donating effects of two hydroxyl groups introduced into the bipyridyl ligand, we found that the substituent positions greatly affect both the catalytic efficiency and selectivity in CO2 reduction. More importantly, the HCOOH selectivity shows a dramatic increase from 14 to 83% upon switching the solvent media from pure organic to an aqueous/organic mixture, where the H2 selectivity shows a reverse phenomenon. The enhanced HCOOH selectivity and the drastic decrease in the H2 yield are well rationalized by the fact that the catalytic CO2 hydrogenation is not only driven photochemically via the attack of RhIII(H)Cp*(LH2-·) on CO2 but also partly bypassed by a dark H2 addition reaction yielding [RhIII(H)Cp*(L)]- from [RhIIICp*(L)Cl]+, which was also separately investigated under dark conditions. A combination of experimental and theoretical approaches was made to clarify the pKa values of catalyst intermediates together with the abundant species responsible for the major catalytic processes. Our DFT studies unveil that the exceptionally large structural strain given by the steric contacts between the 6,6'-dihydroxyl groups and the Cp* moiety plays a significant role in bringing about an outstanding catalytic performance of the 6,6'-substituted derivative. The intrinsic reaction coordinate calculations were carried out to clarify the mechanism of hydride transfer steps leading to generating formate together with the heterolytic H2 cleavage steps leading to afford the key hydridorhodium intermediates. This study represents the first report on the water-induced high selectivity in CO2-to-HCOOH conversion, shedding new light on the strategy to control the efficiency and selectivity in the catalysis of CO2 reduction.

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

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

Unveiling the Structural Effects in Hybrid Copper Phosphonate Frameworks for Selective Electrocatalytic CO2 Reduction Reaction.

Electrochemical CO2 reduction holds tremendous promise for transforming carbon dioxide into several value-added energy feedstocks and utilizing renewable energy sources. Herein, we have developed two novel copper-based organophosphonates for selective electrocatalytic conversion of CO2 to CH3OH conversion. The two-dimensional layer structure of Cu3[(Hhedp)2(C4H4N2)].2H2O (I) and the three-dimensional Cu3[(H3hedp)2(C4H4N2)4(SO4)].2H2O (II) have been isolated as single crystals via a hydrothermal strategy. Compound I consists of Cu2+ oxidation states exclusively, while compound II has Cu1+ oxidation states in a network wherein a Cu2+-phosphonate template is embedded inside the framework. Depending on mixed valent oxidation states, compound II exhibits high selectivity compared to compound I for the electrocatalytic reduction of CO2 to CH3OH (C1) as the primary product and CH3COOH (C2) as the secondary product. Notably, product selectivity is enhanced as the Faradaic efficiency (FE) of the competing hydrogen evolution reaction (HER) is significantly reduced in compound II relative to that of I, particularly at higher applied reduction potentials. The optimal ratio of Cu1+ active sites in compound II plays a pivotal role in enhancing methanol selectivity, stabilizing critical intermediates, and maintaining ideal reduction potentials as a noble-metal free electrocatalyst. Moreover, the optical band gap and the Mott-Schottky measurements further suggest the title Cu-phosphonate materials could be promising and effective photocatalysts.

TM and P dual sites on polymeric carbon nitride enable highly selective CO reduction to C2 products with low potentials: A theoretical perspective.

The CO reduction reaction (CORR) for the production of high-value-added multi-carbon (C2+) products is currently being actively investigated, where searching for high-efficiency catalysts with moderate CO intermediate binding strength and low kinetic barrier for C-C coupling poses a significant challenge. In this study, we employed density functional theory computations to design four synergistic coupling dual sites catalysts for CORR to C2 products, namely, TM-P@melon, by co-doping transition metals (TM = Mn, Fe, Co, and Ni) and phosphorus (P) into the polymeric carbon nitride (i.e., melon-CN). Mn-P@melon and Ni-P@melon exhibit higher selectivity toward C2H5OH and C2H6, respectively, with limiting potentials (C-C coupling kinetic energy barriers) of -0.43V (0.52eV) and -0.17V (0.26eV), respectively. The introduction of TM and P atoms not only narrows the band gap of melon-CN but also favors the coupling of CO and *CHO, providing an active site for C-C coupling, thus facilitating the catalytic reaction. Our work provides rational insights for the design of stable, low-cost, and efficient CORR dual sites catalysts that facilitate the sustainable production of high-value C2 chemicals and fuels.

Amyloid-Like Protein-Modified Carbon Nitride as a Bioinspired Material for Enhanced Photocatalytic CO2 Reduction.

Modification of g-C3N4 with metal-free biomaterials through an environmentally friendly, low-energy, facile, and rapid single-step method is desired for the preparation of photocatalysts with efficient activity and high selectivity of CO2 reduction but remains a great challenge. Herein, we develop a phase-transitioned protein modification strategy for photocatalysts through superfast amyloid-like protein assembly on surfaces using a one-step sequential coating method. Metal-free carbon nitride/protein heterojunction composite photocatalysts (the phase-transitioned lysozyme (PTL), phase-transitioned bovine serum albumin (PTB), and phase-transitioned ovalbumin (PTO)-coated carbon nitride@SiO2 (CN@SiO2) and bioinspired carbon nitride hollow nanospheres (CN-HS) obtained by etching of CN@SiO2) are prepared using lysozyme, bovine serum albumin, and ovalbumin. The insulator-semiconductor heterojunctions formed at the protein-carbon nitride interface promote the migration and separation of photogenerated charges. The exposed hydrophobic alkyl and aryl groups of the surface-modified protein enable the formation of a CO2-aqueous solution-photocatalyst three-phase interface on the catalyst surface and the exposed -NH2 groups provide sites for CO2 adsorption, which effectively increases CO2 mass transfer and its adsorption as well as hydrophobicity, promoting CO2 reduction and inhibiting hydrogen production. Therefore, protein modification effectively improves the CO2 reduction activity and CO selectivity. For instance, compared to CN-HS, the CO yield of the PTL-modified CN-HS (1346.5 μmol g-1) increased by 24.5 times and the CO selectivity reached 90.5%. These findings represent a critical advancement in the surface modification of carbon nitride for CO2 reduction and the design of bioinspired materials for various applications.

Constructing an Active Sulfur-Vacancy-Rich Surface for Selective *CH3-CH3 Coupling in CO2-to-C2H6 Conversion With 92% Selectivity.

To achieve high selectivity in photocatalytic CO2 reduction to C2+ products, increasing the number of CO2 adsorption sites and lowering the energy barriers for key intermediates are critical. A ZnIn2S4 (ZIS)/MoO3-x (Z-M) photocatalyst is presented, in which plasmonic MoO3-x generates hot electrons, creating a multielectron environment in ZIS that facilitates efficient C─C coupling reactions. Density functional theory (DFT) calculations reveal that MoO3-x reduces the formation energy of sulfur vacancies (SV) in ZIS, thereby enhancing CO2 adsorption and activation. The SV-rich surface lowers the energy barrier for forming HCOO* to -0.33 eV whereas the energy barrier for forming *COOH is 0.77 eV. Successive hydrogenation of HCOO* leads to *CH2, which converts to *CH3 with an energy barrier of -0.63 eV. The energy barrier for *CH3-CH3 coupling is 0.54 eV, which is lower than the 0.73 eV for *CH2-CH2 coupling to form *C2H4. Thus, Z-M preferentially produces C2H6 over C2H4. Under visible light, Z-M achieves a CO2-to-C2H6 conversion rate of 467.3 µmol g-1 h-1 with 92.0% selectivity. This work highlights the dual role of plasmonic photocatalysts in enhancing CO2 adsorption and improving C2+ production in CO2 reduction.

Structurally Asymmetric Ni‐O‐Mn Node in Metal‐Organic Layers on Carbon Nitride Support for CO2 Photoreduction

The Jahn‐Teller (J‐T) effect‐induced lattice distortion presents an advantageous approach to tailor the electronic structure and CO2 adsorption properties of catalytic centers, consequently conferring desirable photocatalytic CO2 reduction activity and selectivity. Nevertheless, achieving precise J‐T distortion control over catalytic sites to enhance CO2 adsorption/activation and target‐product desorption remains a formidable challenge. In this work, we successfully induced J‐T lattice distortion in neighboring Ni sites by exchanging high‐spin Mn2+ into Ni‐O‐Ni nodes. EXAFS results and DFT simulations revealed that the highly asymmetric Ni‐O‐Mn nodes induced structural contraction (shortened Ni‐O bonds) in the adjacent Ni‐O lattice. The magnetic hysteresis loop (M‐H) confirmed that the introduction of Mn2+ increased the number of spin electrons, thereby increasing the magnetization intensity. The spin mismatch between photogenerated electrons and holes suppressed charge recombination. Significantly, the d orbitals of the Ni sites in the Ni‐O‐Mn nodes exhibited strong orbital hybridization with the p orbitals of CO2, as evidenced by the enhanced d‐p orbital overlap, facilitating rapid CO2 adsorption and activation. Consequently, the sample featuring lattice‐mismatched Ni‐O‐Mn nodes exhibited an 8.79‐fold enhancement in CO production rate compared to the Ni‐O‐Ni nodes, in the absence of cocatalysts and sacrificial reagents.

Structurally Asymmetric Ni-O-Mn Node in Metal-Organic Layers on Carbon Nitride Support for CO2 Photoreduction.

The Jahn-Teller (J-T) effect-induced lattice distortion presents an advantageous approach to tailor the electronic structure and CO2 adsorption properties of catalytic centers, consequently conferring desirable photocatalytic CO2 reduction activity and selectivity. Nevertheless, achieving precise J-T distortion control over catalytic sites to enhance CO2 adsorption/activation and target-product desorption remains a formidable challenge. In this work, we successfully induced J-T lattice distortion in neighboring Ni sites by exchanging high-spin Mn2+ into Ni-O-Ni nodes. EXAFS results and DFT simulations revealed that the highly asymmetric Ni-O-Mn nodes induced structural contraction (shortened Ni-O bonds) in the adjacent Ni-O lattice. The magnetic hysteresis loop (M-H) confirmed that the introduction of Mn2+ increased the number of spin electrons, thereby increasing the magnetization intensity. The spin mismatch between photogenerated electrons and holes suppressed charge recombination. Significantly, the d orbitals of the Ni sites in the Ni-O-Mn nodes exhibited strong orbital hybridization with the p orbitals of CO2, as evidenced by the enhanced d-p orbital overlap, facilitating rapid CO2 adsorption and activation. Consequently, the sample featuring lattice-mismatched Ni-O-Mn nodes exhibited an 8.79-fold enhancement in CO production rate compared to the Ni-O-Ni nodes, in the absence of cocatalysts and sacrificial reagents.

Synthesis of Benzoic Acids from Electrochemically Reduced CO2 Using Heterogeneous Catalysts.

A method for the synthesis of benzoic acids from aryl iodides using two of the most abundant and sustainable feedstocks, carbon dioxide (CO2) and water, is disclosed. Central to this method is an effective and selective electrochemical reduction of CO2 (eCO2RR) to CO, which mitigates unwanted dehalogenation reactions occurring when H2 is produced via the hydrogen evolution reaction (HER). In a 3-compartment set-up, CO2 was reduced to CO electrochemically by using a surface-modified silver electrode in aqueous electrolyte. The ex-situ generated CO further underwent hydroxycarbonylation of aryl iodides by MOF-supported palladium catalyst in excellent yields at room temperature. The method avoids the direct handling of hazardous CO gas and gives a wide range of benzoic acid derivatives. Both components of the tandem system can be recycled for several consecutive runs while keeping a high catalytic activity.

Altering preferential product selectivity in electrocatalytic CO2 reduction over fluorine-modified CuIn bimetallic materials

Integrating carbon dioxide (CO2)-derived renewable technologies into the petrochemical industry presents a promising avenue for carbon neutrality. The renewable-energy-powered electrochemical CO2 reduction (eCO2R) process, particularly over Cu-based electrocatalysts, is a valuable asset for our decarbonization efforts to avoid climate consequences. Intending to enhance process efficiency, this work is a distinctive case study emphasizing the need to develop electrocatalysts in conjunction with adjusting operating conditions. A representative case is presented using fluorine-modified CuIn bimetallic electrocatalysts with tunable In/Cu ratios, demonstrating how to alter selectivity preferences based on reactor configuration: Our optimized catalyst system led to the highest faradaic efficiency (FE) for C2+ products of 68 % and the highest C1 FE of 80 % using gas diffusion electrodes (GDE)- and H-cell-type based electrolyzer, respectively. Moreover, the controllable In/Cu ratio and the degree of fluoride doping played a pivotal role in governing the physicochemical properties of the bimetallic electrocatalysts and their eCO2R performance. Diverse characterization tools offered systematic insights into the relationships between catalyst structure and properties, reactor configuration, electrolyte, and performance, aiming to enhance the Technology Readiness Level of the eCO2R process.

TM@MoSSe (TM = Ni, Fe) as novel electrocatalysts for reduction of CO2 to CO: A DFT study

It is crucial to develop highly efficient, selective and low-overpotential electrocatalysts for CO2 reduction. This paper proposes an efficient iron and nickel single-atom catalyst using Janus MoSSe as the substrate to reduce CO2 to CO by using DFT calculations. The adsorption of a single TM atom like Fe, Co, Ni, Ru, Rh, Pd, Os, Ir and Pt on Janus MoSSe monolayer results in a decrease in band gap, which may accelerate the catalytic CO2 reduction. The excellent catalytic activity of Fe@MoSSe and Ni@MoSSe is owing to the high d-band center and hence the strong TM-CO2 bonding. The asymmetric structure of Janus MoSSe creates the local built-in electric field, which further increases by about 8% or 0.8% after the adsorption of single Ni or Fe atom so as to afford the better electrocatalytic performances for reduction of CO2 to CO in both TM modified systems. So, this work proposes the catalysts Fe@MoSSe and Ni@MoSSe with good selectivity and activity for CO2 reduction by revealing their underlying mechanisms, and Janus MoSSe may be used as a potential substrate material for CO2 reduction catalysts.

Selective Electrochemical CO2 Reduction to Ethylene and Multi-carbon Products on Oxide-derived Porous CuO Micro-cages

The electrochemical reduction of CO2 (CO2RR) presents a dual benefit: it helps mitigate environmental pollution while producing valuable multi-carbon (C2+) chemicals and storing renewable energy in chemical fuels. However, there is an urgent need for efficient electrocatalysts that can selectively increase the production of ethylene and C2+ products for the wide-scale implementation of CO2RR. Herein, we have facilely synthesized porous micro-caged oxide-derived copper oxide (OD-Cu MC) using a one-pot hydrothermal approach followed by air-annealing at 350 °C. The resulting electrocatalyst exhibited excellent performance for ethylene (C2H4) production, achieving a faradaic efficiency (FE) of 44.8 % for C2H4 and cumulative FE of 73.1 % for C2+ products at current density (ID) of 300 mA cm−2. At an ID of 400 mA cm−2, OD-Cu MC demonstrated a turnover frequency (TOF) of 0.012 s−1 for ethylene, which is 7.8 times higher than the TOF observed for commercially available copper oxide (CuO-CM). Moreover, at an ID of 300 mA cm−2, OD-Cu MC achieved a single-pass CO2 conversion (SPCC) of 35.2 % and a half-cell energy efficiency of 15.6 % for C2+ products. The catalyst also showed good stability, maintaining its performance for over 4 h at an ID of 200 mA cm−2. This straightforward synthesis approach opens new avenues for enhancing C2+ product selectivity in CO2RR.

Balanced Adsorption Toward Highly Selective Electrochemical Reduction of CO2 to Formate.

Tin-based materials have been designed as potential catalysts for the electrochemical conversion of CO2 into a single product. However, such tin-based materials still face the challenges of unsatisfactory selectivity, because the rate-determining step is situated within the slow desorption step. In this work, a variety of tin-based materials are synthesized using the electrospinning technique in an effort to control the adsorption strength during electrochemical reduction, therefore improving the selectivity of CO2 reduction toward formate. The optimized SnS material exhibits moderate adsorption strength to *OCHO and *HCOOH, and the appropriate atomic distance of Sn-Sn maintained the balanced adsorption posture of both intermediate. Therefore, the rate-determining step can be shifted from the slow desorption of the *HCOOH step (Sn) to the first hydrogenation of the *OCHO species step (SnS). Due to this shift, the SnS/C electrode demonstrated excellent selectivity, with a Faradaic efficiency of 96% for the production of formate. A maximum current density of -12.5mA cm-2 for formate is also achieved for a period of33h.

Effects of carbon support ozonation on the electrochemical reduction of CO2 to formate and syngas in a flow cell on Pd nanostructures

Pd convers electrochemically CO2 into formate at the most positive known potentials but with low activity. Additionally, Pd is CO selective at more negative potentials, but is poisoned by the strongly bound CO∗ intermediate. Improving the activity and stability of Pd-based electrocatalysts holds promise for improving the electrochemical production of formic acid. Herein, we studied the effects of carbon support and its ozonation on the selectivity of electrochemical CO2 reduction on Pd. The ozone treatment is found to improve the activity and formate selectivity at low overpotentials on single-walled carbon nanotube-supported catalysts with partial current densities up to −12 mA cm−2 in 0.5 M KHCO3 at potentials of −0.35 V and −0.45 V (vs. RHE). At more negative potentials, the catalysts become more selective towards CO and an opposite trend for CO-selectivity and ozonation duration is demonstrated. Unfortunately, the materials show deactivation in the form of decreased formate selectivity and increased hydrogen and CO evolution, especially when supports treated with ozone for a longer duration. The results and possible mechanisms are discussed based on previous findings and the physicochemical characterizations of the prepared catalysts. This work shows that a simple ozone treatment of carbons changes the efficiency of CO2 electroreduction.

CO2 Reduction by Transition‐Metal Complex Systems: Effect of Hydrogen Bonding on the Second Coordination Sphere

AbstractHomogeneous electrocatalysts typified by transition‐metal complex show transcendent potency in efficient energy catalysis through molecular design. For example, metal complexes with elaborate design performed wonderful activity and selectivity for electrocatalytic CO2 reduction. Primary coordination sphere of metal complexes plays a key role in regulating its intrinsic redox properties and catalytic activity. However, the overall reduction efficiency of CO2 is also bound up with the substrate activation process. Transition‐metal complexes are hoped to exhibit reasonable redox potential, reactive activity, and stability, while binding and activating CO2 molecules to achieve efficient CO2 reduction. Construction of second coordination sphere, especially hydrogen‐bonding network of transition‐metal complexes, is reported to be the “kill two birds with one stone” strategy to realize efficient CO2 reduction catalysis via systematic catalyst properties modulation and substrate activation. Herein, we present recent progress on the construction of hydrogen‐bonding network in the second coordination sphere of metal complexes by ligand modification or the introduction of exogenous organic ligand, and the resulted productive enhancement of the catalytic performance of metal complexes by the improvement of adsorption capacity and activation of CO2, proton transfer rate, and stability of reaction intermediates, and so forth.

Selective CO2 Reduction Electrocatalysis Using AgCu Nanoalloys Prepared by a "Host-Guest" Method.

Multimetallic nanoalloy catalysts have attracted considerable interest for enhancing the efficiency and selectivity of many electrochemically driven chemical processes. However, the preparation of homogeneous bimetallic alloy nanoparticles remains a challenge. Here, we present a room-temperature and scalable, host-guest approach for synthesis of dilute Cu in Ag alloy nanoparticles. In this approach, an ionic silver bromide precursor harboring exogenous Cu cations is reduced to yield ∼20 nm diameter AgCu alloy nanoparticles wherein the % Cu loading can be tuned precisely. AgCu nanoparticles with a 5% nominal loading of Cu exhibit peak activity (-0.23 mA/cm2 normalized partial current density) and selectivity (83.2% faradaic efficiency) for CO product formation from electrocatalytic reduction of CO2 at mild overpotentials. These AgCu nanoalloys exhibit a higher mass activity compared to Ag- and Cu-containing nanomaterials used for similar electrocatalytic transformations. Our host-guest synthesis platform holds promise for production of other nanoalloys with relevance in electrocatalysis and optics.

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

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

In-situ imaging and time-resolved investigation of local pH in electrocatalytic CO2 reduction

Local pH near the catalyst surface exerts a substantial influence on both catalytic selectivity and activity in electrocatalytic CO2 reduction (CO2RR). While the investigation of local pH remains challenging in the aspect of in-situ imaging and monitoring. In this study, a novel lateral-type surface-enhanced Raman spectroscopy (L-SERS) system with a wide pH testing range from acidic to alkaline, is developed for the in-situ observation of local pH distributions with high spatial and temporal resolution during CO2RR. Excellent in-situ imaging of local pH near the catalyst surface is obtained, showing good consistency with simulation results. Besides, the gradual pH elevation and stabilization can be monitored via this time-resolved local pH investigation. This study presents a direct visualization of local pH distribution and variation at the Nernst layer during CO2RR, providing direct evidence in local pH for the feasibility of acidic electrolyte and offering theoretical guidance for optimizing CO2RR conditions.

Descriptors for Electrochemical CO2 Reduction in Imidazolium-Based Electrolytes.

Electrochemical CO2 reduction (CO2R) allows us to close the carbon cycle and store intermittent renewable energy into chemical products. Among these, syngas, a mixture of hydrogen and carbon monoxide, is particularly valuable due to its high market share and the low energy required for its electrocatalytic production. In addition to catalyst optimization, lately, electrolyte modifications to achieve a suitable CO/H2 ratio have also been considered. Ionic liquid (IL)-based electrolytes have enabled high faradaic efficiency toward CO, depending on the chemical properties of the IL. In this work, we rationalized through density functional theory (DFT) descriptors the competition between hydrogen evolution (HER) and CO2R on silver in imidazolium-based electrolytes, developing a DFT-based analytical model. The electrolyte anion regulates the concentration ratio between cationic and carbene species of ILs cation, respectively, between the 1-ethyl-3-methylimidazolium cation (EMIM+) and carbene (EMIM:) species and between the 1-butyl-3-methylimidazolium cation (BMIM+) and carbene (BMIM:). The latter species, if formed, hinders the CO2R by blocking the active sites or trapping CO2 in solution. In the case of weak Lewis base anions as fluorinated ones, EMIM+ (BMIM+) cations, which serve as cocatalysts in CO2R, are more abundant, allowing high CO partial current densities and high electrochemically active surface area. Applying the here-defined descriptors to ILs not yet tested makes it possible to predict the HER and CO2R selectivity on silver, thus enabling guidelines for designing better ILs for CO2R.

Tailoring electrochemical CO2 reduction selectivity over CuSn by modulating surface oxidation state with infrared laser treatment

Infrared laser treatment was used to precisely modify the surface structure of CuSn electrodes, effectively fine-tuning the selectivity of reduction products. With increasing laser power, the metallic Cu and Sn surfaces became more oxidized, and the Sn/Cu composition ratio varied with depth and further changed post-EC reaction. The diversity of reduction products, including C1 (CO, CH4, and formate), C2 (C2H4, ethanol, acetate, acetaldehyde, and glycolaldehyde), and C3 (propanol and isopropanol) compounds, shifted towards a more selective production of C1 (CO and formate) products. These tailored behaviors are attributed to variations in interfacial electronic structures, oxidation states, composition ratios, and the interaction between CO2 and the density of states (Cu, O, and Sn) near the Fermi level. The laser treatment method enables precise tuning of electrode surfaces, modulation of reduction products, and enhancement of selectivity. Moreover, this technique presents a novel approach for electrode design in the field of CO2 reduction, offering new avenues for optimizing catalytic performance.