High Selectivity for Ethylene from Carbon Dioxide Reduction over Copper Nanocube Electrocatalysts

Nanostructured 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.     

氧化还原刻蚀铜表面对二氧化碳电催化还原性能的研究

大规模化石燃料的使用排放了大量的二氧化碳（CO₂）,导致环境中二氧化碳的含量急剧增加. 为了降低大气中二氧化碳的含量,以电催化的方法将二氧化碳转化为有用的化工原料和燃料是解决能源和环境问题的重要途径. 本文主要利用氧化还原刻蚀法,在铜表面形成复合纳米结构,用于二氧化碳的电催化还原反应研究. 首先,作者通过一定浓度的三氯化铁（FeCl₃）溶液与铜片的氧化还原反应,在刻蚀铜表面时形成具有立方体结构的氯化亚铜纳米材料,用于二氧化碳的电催化还原反应. 为了研究反应时间对催化性能的影响,作者通过改变反应时间（1、2、3和4 h）合成了不同结构的铜基催化剂. 研究发现,在反应3 h后,Cu-3h催化剂对二氧化碳的电催化还原具有较小的起始电压（-0.3 V vs. RHE）和较大的电流密度值,表现出了较强的还原能力. 经检测,所得到主要还原产物为一氧化碳（CO）和甲烷（CH₄）. 在-0.6 V时,二氧化碳催化还原的法拉第效率可达到60%,表明以氧化还原法刻蚀铜表面具有较好的改善二氧化碳电催化还原的能力.     

A Molecular Copper Catalyst for Electrochemical Water Reduction with a Large Hydrogen‐Generation Rate Constant in Aqueous Solution

The copper complex [(bztpen)Cu](BF₄)₂ (bztpen=N‐benzyl‐N,N′,N′‐tris(pyridin‐2‐ylmethyl)ethylenediamine) displays high catalytic activity for electrochemical proton reduction in acidic aqueous solutions, with a calculated hydrogen‐generation rate constant (k_obs) of over 10000 s^?1. A turnover frequency (TOF) of 7000 h^?1 cm^?2 and a Faradaic efficiency of 96 % were obtained from a controlled potential electrolysis (CPE) experiment with [(bztpen)Cu]²⁺ in pH 2.5 buffer solution at ?0.90 V versus the standard hydrogen electrode (SHE) over two hours using a glassy carbon electrode. A mechanism involving two proton‐coupled reduction steps was proposed for the dihydrogen generation reaction catalyzed by [(bztpen)Cu]²⁺.     

Electrochemical Reduction of Carbon Dioxide to 1-Butanol on Oxide-Derived Copper

The electroreduction of carbon dioxide using renewable electricity is an appealing strategy for the sustainable synthesis of chemicals and fuels. Extensive research has focused on the production of ethylene, ethanol and n-propanol, but more complex C₄ molecules have been scarcely reported. Herein, we report the first direct electroreduction of CO₂ to 1-butanol in alkaline electrolyte on Cu gas diffusion electrodes (Faradaic efficiency=0.056 %, j_1-Butanol=−0.080 mA cm⁻² at −0.48 V vs. RHE) and elucidate its formation mechanism. Electrolysis of possible molecular intermediates, coupled with density functional theory, led us to propose that CO₂ first electroreduces to acetaldehyde-a key C₂ intermediate to 1-butanol. Acetaldehyde then undergoes a base-catalyzed aldol condensation to give crotonaldehyde via electrochemical promotion by the catalyst surface. Crotonaldehyde is subsequently electroreduced to butanal, and then to 1-butanol. In a broad context, our results point to the relevance of coupling chemical and electrochemical processes for the synthesis of higher molecular weight products from CO₂.     

Oxygenates from the Electrochemical Reduction of Carbon Dioxide

Electrochemical reduction of carbon dioxide (CO₂) driven by renewable electricity to give chemicals and fuels is considered an ideal approach that can alleviate both carbon emission and energy tension stress. High‐value chemicals such as oxygenates can be effectively produced from the electroreduction of CO₂, and this is highly attractive to promote the economy and applicability of CO₂ utilization. This review focuses on recent advancements in the electrochemical reduction of CO₂ to formic acid, methanol, ethanol, acetic acid, and other oxygenates. The principles of the process, influencing factors, and typical catalysts are summarized. On the basis of the aforementioned discussions, we present future prospects for further development of the electroreduction of CO₂ to oxygenates.     

基于流动池的电化学二氧化碳还原研究进展

采用电化学方法将二氧化碳（CO₂）还原转化为基础化学品或碳基燃料是目前极具前景的碳资源利用新方式. 考虑到该技术未来的发展方向和大规模应用需求,人们亟需开发具有高转化效率和高稳定性的电解设备. 在本文中,作者详细介绍了现阶段发展的两种流动池的结构特点及性能优势,阐述了每种反应体系的内在局限性, 深入分析了整个反应体系所用组件（电解池、气体扩散电极、离子交换膜）对于性能的影响. 最后,针对目前该领域存在的挑战及未来发展趋势进行了总结与展望.     

三相界面电催化二氧化碳还原研究进展

电催化二氧化碳还原是能源化学及催化科学的研究重点与难点.气-固-液三相界面模型作为物理化学中的基本概念,近年来被越来越多地应用于电催化二氧化碳还原反应的研究,其相比于传统固-液两相体系表现出了诸多优点.本综述阐述了三相界面电催化二氧化碳还原研究进展,对三相界面电催化体系进行分类及原理探究.再具体到二氧化碳还原反应,讨论...     

Atomically Dispersed Nickel(I) on an Alloy-Encapsulated Nitrogen-Doped Carbon Nanotube Array for High-Performance Electrochemical CO2 Reduction Reaction

Single-atom catalysts (SACs) show great promise for electrochemical CO₂ reduction reaction (CRR), but the low density of active sites and the poor electrical conduction and mass transport of the single-atom electrode greatly limit their performance. Herein, we prepared a nickel single-atom electrode consisting of isolated, high-density and low-valent nickel(I) sites anchored on a self-standing N-doped carbon nanotube array with nickel–copper alloy encapsulation on a carbon-fiber paper. The combination of single-atom nickel(I) sites and self-standing array structure gives rise to an excellent electrocatalytic CO₂ reduction performance. The introduction of copper tunes the d-band electron configuration and enhances the adsorption of hydrogen, which impedes the hydrogen evolution reaction. The single-nickel-atom electrode exhibits a specific current density of −32.87 mA cm⁻² and turnover frequency of 1962 h⁻¹ at a mild overpotential of 620 mV for CO formation with 97 % Faradic efficiency.     

Facile Synthesis of Sub-Nanometric Copper Clusters by Double Confinement Enables Selective Reduction of Carbon Dioxide to Methane

Previous density-functional theory (DFT) calculations show that sub-nanometric Cu clusters (i.e., 13 atoms) favorably generate CH₄ from the CO₂ reduction reaction (CO₂RR), but experimental evidence is lacking. Herein, a facile impregnation-calcination route towards Cu clusters, having a diameter of about 1.0 nm with about 10 atoms, was developed by double confinement of carbon defects and micropores. These Cu clusters enable high selectivity for the CO₂RR with a maximum Faraday efficiency of 81.7 % for CH₄. Calculations and experimental results show that the Cu clusters enhance the adsorption of *H and *CO intermediates, thus promoting generation of CH₄ rather than H₂ and CO. The strong interactions between the Cu clusters and defective carbon optimize the electronic structure of the Cu clusters for selectivity and stability towards generation of CH₄. Provided here is the first experimental evidence that sub-nanometric Cu clusters facilitate the production of CH₄ from the CO₂RR.     

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.     

Alkylative Carboxylation of Ynamides and Allenamides with Functionalized Alkylzinc Halides and Carbon Dioxide by a Copper Catalyst

The alkylative carboxylation of ynamides and allenamides with CO₂ and alkylzinc halides catalyzed by a copper catalyst was developed. A variety of alkylzinc halides bearing functional groups were used for this transformation to afford α,β-unsaturated carboxylic acids, which contain the α,β-dehydroamino acid skeleton, introducing the corresponding alkyl group and CO₂ across the carbon–carbon triple or double bond. This alkylative carboxylation formally consists of Cu-catalyzed carbozincation of ynamides or allenamides with alkylzinc halides and the subsequent nucleophilic carboxylation of the resulting alkenylzinc species with CO₂. This protocol would be a useful method for the synthesis of α,β-dehydroamino acid derivatives possessing a functionalized alkyl group due to the high regio- and stereoselectivity, simple one-pot procedure as well as the use of CO₂ as a starting material.     

A Resin-Supported Formate Catalyst for the Transformative Reduction of Carbon Dioxide with Hydrosilanes

A heterogeneous formate anion catalyst for the transformative reduction of carbon dioxide (CO₂) based on a polystyrene and divinylbenzene copolymer modified with alkylammonium formate was prepared from a widely available anion exchange resin. The catalyst preparation was easy and the characterization was carried out by using elemental analysis, Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and solid-state ¹³C cross-polarization/magic-angle spinning nuclear magnetic resonance (¹³C CP/MAS NMR) spectroscopy. The catalyst displayed good catalytic activity for the direct reduction of CO₂ with hydrosilanes, tunably yielding silylformate or methoxysilane products depending on the hydrosilanes used. The catalyst was also active for the reductive insertion of CO₂ into both primary and secondary amines. The catalytic activity of the resin-supported formate can be predicted from the FTIR spectra of the catalyst, probably because of the difference in the ionic interaction strength between the supported alkylammonium cations and formate anions. The ion pair density is thought to influence the catalytic activity, as shown by the elemental and solid-state ¹³C NMR analyses.     

Formate Dehydrogenase Mimics as Catalysts for Carbon Dioxide Reduction

Formate dehydrogenases (FDH) reversibly catalyze the interconversion of CO₂ to formate. They belong to the family of molybdenum and tungsten-dependent oxidoreductases. For several decades, scientists have been synthesizing structural and functional model complexes inspired by these enzymes. These studies not only allow for finding certain efficient catalysts but also in some cases to better understand the functioning of the enzymes. However, FDH models for catalytic CO₂ reduction are less studied compared to the oxygen atom transfer (OAT) reaction. Herein, we present recent results of structural and functional models of FDH.     

CO2电化学还原研究进展

综述了利用电化学方法研究CO2在水溶剂，非水溶剂中的转化情况和机理，以及将CO2固定在有机络合物中或用光电化学，光催化还原CO2及仿光合作用转移CO2的最新研究情况，旨在寻求一种合理，高效的CO2转化方法以缓解温室效应。     

Probing the Local Reaction Environment During High Turnover Carbon Dioxide Reduction with Ag-Based Gas Diffusion Electrodes

Discerning the influence of electrochemical reactions on the electrode microenvironment is an unavoidable topic for electrochemical reactions that involve the production of OH⁻ and the consumption of water. That is particularly true for the carbon dioxide reduction reaction (CO₂RR), which together with the competing hydrogen evolution reaction (HER) exert changes in the local OH⁻ and H₂O activity that in turn can possibly affect activity, stability, and selectivity of the CO₂RR. We determine the local OH⁻ and H₂O activity in close proximity to a CO₂-converting Ag-based gas diffusion electrode (GDE) with product analysis using gas chromatography. A Pt nanosensor is positioned in the vicinity of the working GDE using shear-force-based scanning electrochemical microscopy (SECM) approach curves, which allows monitoring changes invoked by reactions proceeding within an otherwise inaccessible porous GDE by potentiodynamic measurements at the Pt-tip nanosensor. We show that high turnover HER/CO₂RR at a GDE lead to modulations of the alkalinity of the local electrolyte, that resemble a 16 m KOH solution, variations that are in turn linked to the reaction selectivity.     

Metal-Organic Frameworks for Efficient Electrochemical Reduction of Carbon Dioxide

The large concentration of carbon dioxide (CO₂) in the atmosphere can be utilized in industrial production using effective electrocatalysts such as metal-organic frameworks (MOFs). Due to good properties such as high surface area, designable functionality, and uniform constitution, MOFs are regarded as promising electrocatalysts for the carbon dioxide electrochemical reduction reaction (eCO₂RR). This review covers the importance, challenges, and mechanism of eCO₂RR, and simply discusses the progress in the synthesis methods and characterization of MOFs. The review also thoroughly discusses the advances of single metal-based MOFs, mixed metal-based MOFs, and MOF derivatives as electrocatalysts for efficient eCO₂RR.     

Regioselective Alkylative Carboxylation of Allenamides with Carbon Dioxide and Dialkylzinc Reagents Catalyzed by an N‐Heterocyclic Carbene–Copper Complex

The alkylative carboxylation of allenamide catalyzed by an N‐heterocyclic carbene (NHC)–copper(I) complex [(IPr)CuCl] with CO₂ and dialkylzinc reagents was investigated. The reaction of allenamides with dialkylzinc reagents (1.5 equiv) and CO₂ (1 atm.) proceeded smoothly in the presence of a catalytic quantity of [(IPr)CuCl] to afford (Z)‐α,β‐dehydro‐β‐amino acid esters in good yields. The reaction is regioselective, with the alkyl group introduced onto the less hindered γ‐carbon, and the carboxyl group introduced onto the β‐carbon atom of the allenamides. The first step of the reaction was alkylative zincation of the allenamides to give an alkenylzinc intermediate followed by nucleophilic addition to CO₂. A variety of cyclic and acyclic allenamides were found to be applicable to this transformation. Dialkylzinc reagents bearing β‐hydrogen atoms, such as Et₂Zn or Bu₂Zn, also gave the corresponding alkylative carboxylation products without β‐hydride elimination. The present methodology provides an easy route to alkyl‐substituted α,β‐dehydro‐β‐amino acid ester derivatives under mild reaction conditions with high regio‐ and stereoselectivtiy.     

Atomically Dispersed Nickel(I) on an Alloy‐Encapsulated Nitrogen‐Doped Carbon Nanotube Array for High‐Performance Electrochemical CO2 Reduction Reaction

Single‐atom catalysts (SACs) show great promise for electrochemical CO₂ reduction reaction (CRR), but the low density of active sites and the poor electrical conduction and mass transport of the single‐atom electrode greatly limit their performance. Herein, we prepared a nickel single‐atom electrode consisting of isolated, high‐density and low‐valent nickel(I) sites anchored on a self‐standing N‐doped carbon nanotube array with nickel–copper alloy encapsulation on a carbon‐fiber paper. The combination of single‐atom nickel(I) sites and self‐standing array structure gives rise to an excellent electrocatalytic CO₂ reduction performance. The introduction of copper tunes the d‐band electron configuration and enhances the adsorption of hydrogen, which impedes the hydrogen evolution reaction. The single‐nickel‐atom electrode exhibits a specific current density of ?32.87 mA cm^?2 and turnover frequency of 1962 h^?1 at a mild overpotential of 620 mV for CO formation with 97 % Faradic efficiency.     

二氧化碳电化学还原的研究进展

利用低品阶的可再生电能,将二氧化碳(CO_2)电化学还原生成高附加值的化学品或燃料,既可以变废为宝、减少CO_2排放,又能将可再生能源转变为高能量密度的燃料储存,具有重要的现实意义。电化学还原CO_2的研究,是目前世界范围内的研究热点,许多标志性的重要研究成果不断涌现。本文首先简要介绍了CO_2电化学还原的基本原理,然后概述了近5年来在其电催化剂材料和反应机理相关的实验与理论研究方面的昀新研究进展,昀后对其发展趋势进行了展望。     

超薄氮掺杂碳纳米片负载单原子镍用于高效电催化还原二氧化碳

将二氧化碳转化为高附加值的燃料和化学品是缓解当前能源危机和控制温室气体排放的有效策略之一,但此法受限于缺乏高活性与高选择性的电催化剂。因此,我们通过热解含镍金属有机框架结构(MOF)和二氰二胺制得负载高含量镍单原子(7.77% (w))的超薄氮掺杂二维碳纳米片用于电催化还原CO₂生成CO。研究发现高温热解能将MOF中Ni²⁺转化为Ni⁺-N-C和Ni²⁺-N-C结构,且Ni⁺-N-C含量依赖于热解温度——其含量随热解温度增加呈现火山型变化。800 ℃下,Ni²⁺到Ni⁺-N-C的转化和石墨化的C生成达到最优水平。Ni⁺-N-C结构有适宜的*CO中间体结合能,能有效地抑制析氢反应的同时还能促进CO生成。因此,800 ℃热处理制得的材料(Ni-N-C-800)催化CO₂生成CO效率最高。调节电解液浓度,能进一步优化电催化性能。当电解液(碳酸氢钾)浓度为0.5 mol·L^-1时,Ni-N-C-800的CO生成选择性在较宽电压窗口内(-0.77到-1.07 V vs. RHE)都高于90%,且具有优良的稳定性。这些结果表明,选择合适的前躯体通过调控热解温度以及氮掺杂可以有效提高镍基MOF衍生催化剂的二氧化碳电催化性能。