Selective CO2 Electroreduction to Ethylene and Multicarbon Alcohols via Electrolyte‐Driven Nanostructuring

Production of multicarbon products (C₂₊) from CO₂ electroreduction reaction (CO₂RR) is highly desirable for storing renewable energy and reducing carbon emission. The electrochemical synthesis of CO₂RR catalysts that are highly selective for C₂₊ products via electrolyte‐driven nanostructuring is presented. Nanostructured Cu catalysts synthesized in the presence of specific anions selectively convert CO₂ into ethylene and multicarbon alcohols in aqueous 0.1 m KHCO₃ solution, with the iodine‐modified catalyst displaying the highest Faradaic efficiency of 80 % and a partial geometric current density of ca. 31.2 mA cm^?2 for C₂₊ products at ?0.9 V vs. RHE. Operando X‐ray absorption spectroscopy and quasi in situ X‐ray photoelectron spectroscopy measurements revealed that the high C₂₊ selectivity of these nanostructured Cu catalysts can be attributed to the highly roughened surface morphology induced by the synthesis, presence of subsurface oxygen and Cu⁺ species, and the adsorbed halides.     

C-Metallierte chirale Aloxide als d2- und d3-Reagenzien für die Synthese enantiomerenreiner Produkte (EPC-Synthese)

C-Metallated Chiral Alkoxides as d²–-and d³ -Regents for the Synthesis of Enantiomerically Pure Compounds (EPC-Synthesis) The chloroalcohols (S)-1 -chloro-2-propanol ( 1 ), (S)-1 -chloro-2-methyl-2-pentanol ( 4 ), (R)-3-chloro-2-methyl-1 -propanol ( 7 ), (R)-4-chloro-2-butanol ( 10 ), and (2R, 3R)- 4-chloro-3-methyl-2-butanol (14), really available from the esters of lactic, 3-hydroxy-2-methylpropanoic, and 3-hydroxybutanoic acid are subjected to sequential metallation first with BuLi (or MeMgCl) and then with lithium naphthalenide (or Li metal powder) to give solutions of the highly reactive C -metallated alkoxides 15, 22, 26, 27 , and 28 , respectively. - These chiral d²- and d³ -reagents may be added to aldehydes (non-diastereoselectively), ketones, and CO₂ to give 1, 3- or 1 4-dioles ( 18-21, 24, 29-33 ) or δ-lactones ( 35, 36 ). Thiolations with dibenzyl disulfide (→ 16, 34 ) and a deuteration (→ 17 , (S)-(1-²H)propan-2-ol) were also carried out. Independent synthesis of (S)-1-benzylthio-2-propanol ( 16 ) and comparison of the specific rotations establish that no loss enantiomeric purity occurs on the metallation route. The results described represent and extension of the applicability of simple chiral building blocks to EPC-synthesis.     

Enzymatic Electrosynthesis of Glycine from CO2 and NH3

Enzymatic electrosynthesis has gained more and more interest as an emerging green synthesis platform, particularly for the fixation of CO₂. However, the simultaneous utilization of CO₂ and a nitrogenous molecule for the enzymatic electrosynthesis of value-added products has never been reported. In this study, we constructed an in vitro multienzymatic cascade based on the reductive glycine pathway and demonstrated an enzymatic electrocatalytic system that allowed the simultaneous conversion of CO₂ and NH₃ as the sole carbon and nitrogen sources to synthesize glycine. Through effective coupling and the optimization of electrochemical cofactor regeneration and the multienzymatic cascade reaction, 0.81 mM glycine was yielded with a highest reaction rate of 8.69 mg L⁻¹ h⁻¹ and faradaic efficiency of 96.8 %. These results imply a promising alternative for enzymatic CO₂ electroreduction and expand its products to nitrogenous chemicals.     

Dynamic Changes in the Structure,Chemical State and Catalytic Selectivity of Cu Nanocubes during CO2 Electroreduction: Size and Support Effects

In situ and operando spectroscopic and microscopic methods were used to gain insight into the correlation between the structure, chemical state, and reactivity of size‐ and shape‐controlled ligand‐free Cu nanocubes during CO₂ electroreduction (CO₂RR). Dynamic changes in the morphology and composition of Cu cubes supported on carbon were monitored under potential control through electrochemical atomic force microscopy, X‐ray absorption fine‐structure spectroscopy and X‐ray photoelectron spectroscopy. Under reaction conditions, the roughening of the nanocube surface, disappearance of the (100) facets, formation of pores, loss of Cu and reduction of CuO_x species observed were found to lead to a suppression of the selectivity for multi‐carbon products (i.e. C₂H₄ and ethanol) versus CH₄. A comparison with Cu cubes supported on Cu foils revealed an enhanced morphological stability and persistence of Cu^I species under CO₂RR in the former samples. Both factors are held responsible for the higher C₂/C₁ product ratio observed for the Cu cubes/Cu as compared to Cu cubes/C. Our findings highlight the importance of the structure of the active nanocatalyst but also its interaction with the underlying substrate in CO₂RR selectivity.     

Dynamic Changes in the Structure,Chemical State and Catalytic Selectivity of Cu Nanocubes during CO2 Electroreduction: Size and Support Effects

In situ and operando spectroscopic and microscopic methods were used to gain insight into the correlation between the structure, chemical state, and reactivity of size‐ and shape‐controlled ligand‐free Cu nanocubes during CO₂ electroreduction (CO₂RR). Dynamic changes in the morphology and composition of Cu cubes supported on carbon were monitored under potential control through electrochemical atomic force microscopy, X‐ray absorption fine‐structure spectroscopy and X‐ray photoelectron spectroscopy. Under reaction conditions, the roughening of the nanocube surface, disappearance of the (100) facets, formation of pores, loss of Cu and reduction of CuO_x species observed were found to lead to a suppression of the selectivity for multi‐carbon products (i.e. C₂H₄ and ethanol) versus CH₄. A comparison with Cu cubes supported on Cu foils revealed an enhanced morphological stability and persistence of Cu^I species under CO₂RR in the former samples. Both factors are held responsible for the higher C₂/C₁ product ratio observed for the Cu cubes/Cu as compared to Cu cubes/C. Our findings highlight the importance of the structure of the active nanocatalyst but also its interaction with the underlying substrate in CO₂RR selectivity.     

Selective and Efficient CO2 Electroreduction to Formate on Copper Electrodes Modified by Cationic Gemini Surfactants

Electroreduction of CO₂ into valuable chemicals and fuels is a promising strategy to mitigate energy and environmental problems. However, it usually suffers from unsatisfactory selectivity for a single product and inadequate electrochemical stability. Herein, we report the first work to use cationic Gemini surfactants as modifiers to boost CO₂ electroreduction to formate. The selectivity, activity and stability of the catalysts can be all significantly enhanced by Gemini surfactant modification. The Faradaic efficiency (FE) of formate could reach up to 96 %, and the energy efficiency (EE) could achieve 71 % over the Gemini surfactants modified Cu electrode. In addition, the Gemini surfactants modified commercial Bi₂O₃ nanosheets also showed an excellent catalytic performance, and the FE of formate reached 91 % with a current density of 510 mA cm⁻² using the flow cell. Detailed studies demonstrated that the double quaternary ammonium cations and alkyl chains of the Gemini surfactants played a crucial role in boosting electroreduction CO₂, which can not only stabilize the key intermediate HCOO* but also provide an easy access for CO₂. These observations could shine light on the rational design of organic modifiers for promoted CO₂ electroreduction.     

Nanostructured Materials for Heterogeneous Electrocatalytic CO2 Reduction and their Related Reaction Mechanisms

The gradually increased concentration of carbon dioxide (CO₂) in the atmosphere has been recognized as the primary culprit for the rise of the global mean temperature. In recent years, development of routes for highly efficient conversion of CO₂ has received much attention. This Review describes recent progress on the design and synthesis of solid‐state catalysts for the electrochemical reduction of CO₂. The significance of this catalytic conversion is presented, followed by the general parameters for CO₂ electroreduction and a summary of the reaction apparatus. We also discuss various types of solid catalysts based on their CO₂ conversion mechanisms. We summarize the crucial factors (particle size, surface structure, composition, etc.) determining the performance for electroreduction.     

Mechanistic Elucidations of Highly Dispersed Metalloporphyrin Metal-Organic Framework Catalysts for CO2 Electroreduction

Immobilization of porphyrin complexes into crystalline metal–organic frameworks (MOFs) enables high exposure of porphyrin active sites for CO₂ electroreduction. Herein, well-dispersed iron-porphyrin-based MOF (PCN-222(Fe)) on carbon-based electrodes revealed optimal turnover frequencies for CO₂ electroreduction to CO at 1 wt.% catalyst loading, beyond which the intrinsic catalyst activity declined due to CO₂ mass transport limitations. In situ Raman suggested that PCN-222(Fe) maintained its structure under electrochemical bias, permitting mechanistic investigations. These revealed a stepwise electron transfer-proton transfer mechanism for CO₂ electroreduction on PCN-222(Fe) electrodes, which followed a shift from a rate-limiting electron transfer to CO₂ mass transfer as the potential increased from −0.6 V to −1.0 V vs. RHE. Our results demonstrate how intrinsic catalytic investigations and in situ spectroscopy are needed to elucidate CO₂ electroreduction mechanisms on PCN-222(Fe) MOFs.     

FTIR spectroscopy study of the electrochemical reduction of CO2 on various metal electrodes in methanol

The electrochemical reduction of CO₂ on Sn, Cu, Au, In, Ni, Ru and Pt electrodes in methanol containing 0.1 M sodium perchlorate was studied by cyclic voltammetry and in-situ FTIR spectroscopy. Dissolved CO₂ increases the cathodic current at potentials below −1.3 V vs. Ag|0.01 M Ag⁺ with Sn, Au, Cu, In and Ni electrodes. It is concluded from the FTIR spectra obtained that there is no reduction of CO₂ on any of the metals studied, and that the only reaction product detected by Fourier transform (FT) IR spectroscopy, i.e. CO²⁻₃, is formed by reaction of CO₂ with hydroxyl anions produced in the electroreduction of residual water.In order to identify the electroreduction products of CO₂ it was necessary to obtain the FTIR spectra of sodium oxalate and sodium carbonate in methanol. They were obtained by the electroreduction of oxalic acid and the alkalinization of CO₂-saturated methanol respectively. It could be proved that the electroreduction of carboxylic acids to carboxylate anions in organic solvents does not require either a H-chemisorbing metal electrode, or the presence of water in the solvent.     

A Microporous Hydrogen Bonded Organic Framework for Highly Selective Separation of Carbon Dioxide over Acetylene

The separation of acetylene (C₂H₂) from carbon dioxide (CO₂) is a very important but challenging task due to their similar molecular dimensions and physical properties. In terms of porous adsorbents for this separation, the CO₂-selective porous materials are superior to the C₂H₂-selective ones because of the cost- and energy-efficiency but have been rarely achieved. Herein we report our unexpected discovery of the first hydrogen bonded organic framework (HOF) constructed from a simple organic linker 2,4,6-tri(1H-pyrazol-4-yl)pyridine (PYTPZ) (termed as HOF-FJU-88) as the highly CO₂-selective porous material. HOF-FJU-88 is a two-dimensional HOFs with a pore pocket of about 7.6 Å. The activated HOF-FJU-88 takes up a high amount of CO₂ (59.6 cm³ g⁻¹) at ambient conditions with the record IAST selectivity of 1894. Its high performance for the CO₂/C₂H₂ separation has been further confirmed through breakthrough experiments, in situ diffuse reflectance infrared spectroscopy and molecular simulations.     

Electrocatalytic CO2 Upgrading to Triethanolamine by Bromine-Assisted C2H4 Oxidation

The electrocatalytic carbon dioxide (CO₂) reduction is a promising approach for converting this greenhouse gas into value-added chemicals, while the capability of producing products with longer carbon chains (C_n>3) is limited. Herein, we demonstrate the Br-assisted electrocatalytic oxidation of ethylene (C₂H₄), a major CO₂ electroreduction product, into 2-bromoethanol by electro-generated bromine on metal phthalocyanine catalysts. Due to the preferential formation of Br₂ over *O or Cl₂ to activate the C=C bond, a high partial current density of producing 2-bromoethanol (46.6 mA⋅cm⁻²) was obtained with 87.2 % Faradaic efficiency. Further coupling with the electrocatalytic nitrite reduction to ammonia at the cathode allowed the production of triethanolamine with six carbon atoms. Moreover, by coupling a CO₂ electrolysis cell for in situ C₂H₄ generation and a C₂H₄ oxidation/nitrite reduction cell, the capability of upgrading of CO₂ and nitrite into triethanolamine was demonstrated.     

Electrochemical kinetics and cycling performance of nano Li[Li0.23Co0.3Mn0.47]O2 cathode material for lithium ion batteries

Li[Li_0.23Co_0.3Mn_0.47]O₂ cathode material was prepared by a sol–gel method. The material had a primary particle size of about 100 nm, covered by a 30 Å of Li₂CO₃ layer. The material showed promising electrochemical performance when cycled up to 3C rate. The electrochemical kinetics of the first charge was much slower than that of the second charge, due to the complex electrochemical process which involved not only Li⁺ diffusion but also release of oxygen. By taking account of this, the material was pre-charged very slowly (C/50) in the first cycle. This led to excellent electrochemical performance in the following cycles. For instance, the 1C-rate capacity increased to 168 mA h g⁻¹ after 50 cycles, comparing with the 145 mA h g⁻¹ obtained without pre-charging.     

On-line mass spectrometry investigation of the reduction of carbon dioxide in acidic media on polycrystalline Pt

Differential electrochemical mass spectrometry (DEMS) is used to investigate the reaction of electroreduction of CO₂ on platinum porous electrode in acidic media. This technique, which gives molecular specificity, permits the reaction products to be followed concurrently with potential and time. These results showed for the first time the on-line production of methanol in acidic media using a Pt electrodeposited electrode. Reduction of CO₂ in perchloric acid on Pt occurs in the H₂ evolution region leading to the formation of formic acid methanol and traces of methane. Experiments using CO show that this substance is the intermediate of the pathway leading to methanol.     

Silver and Copper Nitride Cooperate for CO Electroreduction to Propanol

The need of carbon sources for the chemical industry, alternative to fossil sources, has pointed to CO₂ as a possible feedstock. While CO₂ electroreduction (CO₂R) allows production of interesting organic compounds, it suffers from large carbon losses, mainly due to carbonate formation. This is why, quite recently, tandem CO₂R, a two-step process, with first CO₂R to CO using a solid oxide electrolysis cell followed by CO electroreduction (COR), has been considered, since no carbon is lost as carbonate in either step. Here we report a novel copper-based catalyst, silver-doped copper nitride, with record selectivity for formation of propanol (Faradaic efficiency: 45 %), an industrially relevant compound, from CO electroreduction in gas-fed flow cells. Selective propanol formation occurs at metallic copper atoms derived from copper nitride and is promoted by silver doping as shown experimentally and computationally. In addition, the selectivity for C₂₊ liquid products (Faradaic efficiency: 80 %) is among the highest reported so far. These findings open new perspectives regarding the design of catalysts for production of C₃ compounds from CO₂.     

Cu2O-Ag Tandem Catalysts for Selective Electrochemical Reduction of CO2 to C2 Products

The electrochemical carbon dioxide reduction reaction (CO₂RR) to C₂ chemicals has received great attention. Here, we report the cuprous oxide (Cu₂O) nanocubes cooperated with silver (Ag) nanoparticles via the replacement reaction for a synergetic CO₂RR. The Cu₂O-Ag tandem catalyst exhibits an impressive Faradaic efficiency (FE) of 72.85% for C₂ products with a partial current density of 243.32 mA·cm⁻². The electrochemical experiments and density functional theory (DFT) calculations reveal that the introduction of Ag improves the intermediate CO concentration on the catalyst surface and meanwhile reduces the C-C coupling reaction barrier energy, which is favorable for the synthesis of C₂ products.     

In Situ Reconstruction of a Hierarchical Sn-Cu/SnOx Core/Shell Catalyst for High-Performance CO2 Electroreduction

The electrochemical CO₂ reduction reaction (CO₂RR) to give C₁ (formate and CO) products is one of the most techno-economically achievable strategies for alleviating CO₂ emissions. Now, it is demonstrated that the SnO_x shell in Sn_2.7Cu catalyst with a hierarchical Sn-Cu core can be reconstructed in situ under cathodic potentials of CO₂RR. The resulting Sn_2.7Cu catalyst achieves a high current density of 406.7±14.4 mA cm⁻² with C₁ Faradaic efficiency of 98.0±0.9 % at −0.70 V vs. RHE, and remains stable at 243.1±19.2 mA cm⁻² with a C₁ Faradaic efficiency of 99.0±0.5 % for 40 h at −0.55 V vs. RHE. DFT calculations indicate that the reconstructed Sn/SnO_x interface facilitates formic acid production by optimizing binding of the reaction intermediate HCOO* while promotes Faradaic efficiency of C₁ products by suppressing the competitive hydrogen evolution reaction, resulting in high Faradaic efficiency, current density, and stability of CO₂RR at low overpotentials.     

In Situ Reconstruction of a Hierarchical Sn‐Cu/SnOx Core/Shell Catalyst for High‐Performance CO2 Electroreduction

The electrochemical CO₂ reduction reaction (CO₂RR) to give C₁ (formate and CO) products is one of the most techno‐economically achievable strategies for alleviating CO₂ emissions. Now, it is demonstrated that the SnO_x shell in Sn_2.7Cu catalyst with a hierarchical Sn‐Cu core can be reconstructed in situ under cathodic potentials of CO₂RR. The resulting Sn_2.7Cu catalyst achieves a high current density of 406.7±14.4 mA cm^?2 with C₁ Faradaic efficiency of 98.0±0.9 % at ?0.70 V vs. RHE, and remains stable at 243.1±19.2 mA cm^?2 with a C₁ Faradaic efficiency of 99.0±0.5 % for 40 h at ?0.55 V vs. RHE. DFT calculations indicate that the reconstructed Sn/SnO_x interface facilitates formic acid production by optimizing binding of the reaction intermediate HCOO* while promotes Faradaic efficiency of C₁ products by suppressing the competitive hydrogen evolution reaction, resulting in high Faradaic efficiency, current density, and stability of CO₂RR at low overpotentials.     

Perfluorinated Covalent Triazine Framework Derived Hybrids for the Highly Selective Electroconversion of Carbon Dioxide into Methane

Developing cost‐effective electrocatalysts for high‐selectivity CO₂ electroreduction remains challenging. We herein report a perfluorinated covalent triazine framework (CTF) electrocatalyst that displays very high selectivity in the electroreduction of CO₂ to CH₄ with a faradaic efficiency of 99.3 % in aqueous electrolyte. Systematic characterization and electrochemical studies, in combination with density functional theory calculations, demonstrate that the presence of both nitrogen and fluorine in the CTF provides a unique pathway that is inaccessible with the individual components for CO₂ electroreduction.     

Asymmetric electrocarboxylation of 1-phenylethyl chloride catalyzed by electrogenerated chiral [CoI(salen)]− complex

The feasibility of asymmetric electrocarboxylation of 1-phenylethyl chloride catalyzed by the electrogenerated chiral [Co^I(salen)]⁻ complex has been investigated for the first time. Using this system, optically active 2-phenylpropionic acid in 37% yield and 83% ee is synthesized from 1-phenylethyl chloride and CO₂. The electrochemical behavior of the catalyst and the optimization of synthesis conditions are discussed. This study provides a new procedure for the asymmetric synthesis of a chiral compound and expands the applications of chiral Co^II(salen) in the electrochemical asymmetric fixation of CO₂.     

Carbon-based catalysts: Synthesis and applications

This paper summarizes the main results obtained by the Fuel Combustion Group in three applications: (1) carbon-based catalysts for the selective catalytic reduction (SCR) process of NO_x, (2) Pt and Pt–Ru catalysts for direct alcohol fuel cells, (3) carbon-supported catalysts for the electroreduction of CO₂. Concerning the first aspect, low-cost catalysts able to work at lower temperatures have been prepared and compared with commercial catalysts; for the second one, new catalysts for methanol and ethanol electrochemical oxidation exhibiting current densities that are double those of the commercial ones have been developed; as regards the third one, carbon-supported catalysts for the electroreduction of CO₂ based on Fe and Pd were synthesized and tested. Formic acid was obtained as the main product on all Fe/C electrodes.