Cu2O/CuO Electrocatalyst for Electrochemical Reduction of Carbon Dioxide to Methanol

Herein, we report the controlled and direct fabrication of Cu₂O/CuO thin film on the conductive nickel foam using electrodeposition route for the electrochemical reduction of carbon dioxide (CO₂) to methanol. The electrocatalytic reduction was performed in CO₂ saturated aqueous solution consisting of KHCO₃, pyridine and HCl at room temperature. CO₂ reduction was carried out at a constant potential of −1.3 V for 120 min to study the electrochemical performance of the prepared electrocatalysts. Cu₂O/CuO shows better electrocatalytic activity with highest current density of 46 mA/cm². The prepared catalyst can be an efficient and selective electrode for the production of methanol.     

Sulfur Changes the Electrochemical CO2 Reduction Pathway over Cu Electrocatalysts

Electrochemical CO₂ reduction to value-added chemicals or fuels offers a promising approach to reduce carbon emissions and alleviate energy shortage. Cu-based electrocatalysts have been widely reported as capable of reducing CO₂ to produce a variety of multicarbon products (e.g., ethylene and ethanol). In this work, we develop sulfur-doped Cu₂O electrocatalysts, which instead can electrochemically reduce CO₂ to almost exclusively formate. We show that a dynamic equilibrium of S exists at the Cu₂O-electrolyte interface, and S-doped Cu₂O undergoes in situ surface reconstruction to generate active S-adsorbed metallic Cu sites during the CO₂ reduction reaction (CO₂RR). Density functional theory (DFT) calculations together with in situ infrared absorption spectroscopy measurements show that the S-adsorbed metallic Cu surface can not only promote the formation of the *OCHO intermediate but also greatly suppress *H and *COOH adsorption, thus facilitating CO₂-to-formate conversion during the electrochemical CO₂RR.     

Catalyst Engineering for the Selective Reduction of CO2 to CH4: A First-Principles Study on X-MOF-74 (X=Mg,Mn, Fe,Co, Ni,Cu, Zn)

The conversion of carbon dioxide (CO₂) into more valuable chemical compounds represents a critical objective for addressing environmental challenges and advancing sustainable energy sources. The CO₂ reduction reaction (CO₂RR) holds promise for transforming CO₂ into versatile feedstock materials and fuels. Leveraging first-principles methodologies provides a robust approach to evaluate catalysts and steer experimental efforts. In this study, we examine the CO₂RR process using a diverse array of representative cluster models derived from X-MOF-74 (where X encompasses Mg, Mn, Fe, Co, Ni, Cu, or Zn) through first-principles methods. Notably, our investigation highlights the Fe-MOF-74 cluster's unique attributes, including favorable CO₂ binding and the lowest limiting potential of the studied clusters for converting CO₂ to methane (CH₄) at 0.32 eV. Our analysis identified critical factors driving the selective CO₂RR pathway, enabling the formation CH₄ on the Fe-MOF-74 cluster. These factors involve less favorable reduction of hydrogen to H₂ and strong binding affinities between the Fe open-metal site and reduction intermediates, effectively curtailing desorption processes of closed-shell intermediates such as formic acid (HCOOH), formaldehyde (CH₂O), and methanol (CH₃OH), to lead to selective CH₄ formation.     

The Functionality of Surface Hydroxy Groups on the Selectivity and Activity of Carbon Dioxide Reduction over Cuprous Oxide in Aqueous Solutions

Carbon dioxide (CO₂) reduction in aqueous solutions is an attractive strategy for carbon capture and utilization. Cuprous oxide (Cu₂O) is a promising catalyst for CO₂ reduction as it can convert CO₂ into valuable hydrocarbons and suppress the side hydrogen evolution reaction (HER). However, the nature of the active sites in Cu₂O remains under debate because of the complex surface structure of Cu₂O under reducing conditions, leading to limited guidance in designing improved Cu₂O catalysts. This paper describes the functionality of surface‐bonded hydroxy groups on partially reduced Cu₂O(111) for the CO₂ reduction reaction (CO₂RR) by combined density functional theory (DFT) calculations and experimental studies. We find that the surface hydroxy groups play a crucial role in the CO₂RR and HER, and a moderate coverage of hydroxy groups is optimal for promotion of the CO₂RR and suppression of the HER simultaneously. Electronic structure analysis indicates that the charge transfer from hydroxy groups to coordination‐unsaturated Cu (Cu_CUS) sites stabilizes surface‐adsorbed COOH*, which is a key intermediate during the CO₂RR. Moreover, the CO₂RR was evaluated over Cu₂O octahedral catalysts with {111} facets and different surface coverages of hydroxy groups, which demonstrates that Cu₂O octahedra with moderate coverage of hydroxy groups can indeed enhance the CO₂RR and suppress the HER.     

Wurtzite CuGaS2 with an In-Situ-Formed CuO Layer Photocatalyzes CO2 Conversion to Ethylene with High Selectivity

We present surface reconstruction-induced C−C coupling whereby CO₂ is converted into ethylene. The wurtzite phase of CuGaS_2. undergoes in situ surface reconstruction, leading to the formation of a thin CuO layer over the pristine catalyst, which facilitates selective conversion of CO₂ to ethylene (C₂H₄). Upon illumination, the catalyst efficiently converts CO₂ to C₂H₄ with 75.1 % selectivity (92.7 % selectivity in terms of R_electron) and a 20.6 μmol g⁻¹ h⁻¹ evolution rate. Subsequent spectroscopic and microscopic studies supported by theoretical analysis revealed operando-generated Cu²⁺, with the assistance of existing Cu⁺, functioning as an anchor for the generated *CO and thereby facilitating C−C coupling. This study demonstrates strain-induced in situ surface reconstruction leading to heterojunction formation, which finetunes the oxidation state of Cu and modulates the CO₂ reduction reaction pathway to selective formation of ethylene.     

Selective CO2 Reduction to Ethylene Mediated by Adaptive Small-molecule Engineering of Copper-based Electrocatalysts

Electrochemical CO₂ reduction reaction (CO₂RR) over Cu catalysts exhibits enormous potential for efficiently converting CO₂ to ethylene (C₂H₄). However, achieving high C₂H₄ selectivity remains a considerable challenge due to the propensity of Cu catalysts to undergo structural reconstruction during CO₂RR. Herein, we report an in situ molecule modification strategy that involves tannic acid (TA) molecules adaptive regulating the reconstruction of a Cu-based material to a pathway that facilitates CO₂ reduction to C₂H₄ products. An excellent Faraday efficiency (FE) of 63.6 % on C₂H₄ with a current density of 497.2 mA cm⁻² in flow cell was achieved, about 6.5 times higher than the pristine Cu catalyst which mainly produce CH₄. The in situ X-ray absorption spectroscopy and Raman studies reveal that the hydroxyl group in TA stabilizes Cu^δ+ during the CO₂RR. Furthermore, theoretical calculations demonstrate that the Cu^δ+/Cu⁰ interfaces lower the activation energy barrier for *CO dimerization, and hydroxyl species stabilize the *COH intermediate via hydrogen bonding, thereby promoting C₂H₄ production. Such molecule engineering modulated electronic structure provides a promising strategy to achieve highly selective CO₂ reduction to value-added chemicals.     

Regulating Efficient and Selective Single-atom Catalysts for Electrocatalytic CO2 Reduction

Anchoring transition metal (TM) atoms on suitable substrates to form single-atom catalysts (SACs) is a novel approach to constructing electrocatalysts. Graphdiyne with sp−sp² hybridized carbon atoms and uniformly distributed pores have been considered as a potential carbon material for supporting metal atoms in a variety of catalytic processes. Herein, density functional theory (DFT) calculations were performed to study the single TM atom anchoring on graphdiyne (TM₁−GDY, TM=Sc, Ti, V, Cr, Mn, Co and Cu) as the catalysts for CO₂ reduction. After anchoring metal atoms on GDY, the catalytic activity of TM₁−GDY (TM=Mn, Co and Cu) for CO₂ reduction reaction (CO₂RR) are significantly improved comparing with the pristine GDY. Among the studied TM₁−GDY, Cu₁−GDY shows excellent electrocatalytic activity for CO₂ reduction for which the product is HCOOH and the limiting potential (U_L) is −0.16 V. Mn₁−GDY and Co₁−GDY exhibit superior catalytic selectivity for CO₂ reduction to CH₄ with U_L of −0.62 and −0.34 V, respectively. The hydrogen evolution reaction (HER) by TM₁−GDY (TM=Mn, Co and Cu) occurs on carbon atoms, while the active sites of CO₂RR are the transition metal atoms . The present work is expected to provide a solid theoretical basis for CO₂ conversion into valuable hydrocarbons.     

单原子Ge助剂修饰Cu(111)晶面上CO2加氢制甲醇的机理研究

针对CO₂热催化转化制甲醇过程中CO₂吸附、活化较困难及副产物较多的问题,提出采用单原子Ge助剂修饰Cu(111)晶面的解决思路,通过密度泛函理论(DFT)计算研究了CO₂在Ge-Cu(111)晶面上加氢合成甲醇的反应机理。结果表明,单原子Ge助剂的电子调控增加了与其相邻的 Cu 原子的电子云密度,使 CO₂分子在含 Ge 活性界面上的吸附能力显著增强:CO₂在 Ge-Cu(111)晶面上的吸附能约为Cu(111)晶面的1.5倍,约为Pd改性Cu(111)晶面的2.4倍,进而使逆水煤气变换(RWGS)反应路径速控步骤的活化能降低了近 20 kJ·mol^-1,同时衍生出 3条生成甲醇的 RWGS新路径;此外,Ge-Cu(111)晶面上甲酸盐路径由于速控步骤活化能大幅上升而被禁阻,进而CO及烃类等副产物选择性大幅降低,Ge-Cu(111)晶面上CO₂加氢制甲醇选择性升高。     

单原子Ge助剂修饰Cu(111)晶面上CO2加氢制甲醇的机理研究

针对CO₂热催化转化制甲醇过程中CO₂吸附、活化较困难及副产物较多的问题,提出采用单原子Ge助剂修饰Cu (111)晶面的解决思路,通过密度泛函理论(DFT)计算研究了CO₂在Ge-Cu(111)晶面上加氢合成甲醇的反应机理。结果表明,单原子Ge助剂的电子调控增加了与其相邻的Cu原子的电子云密度,使CO₂分子在含Ge活性界面上的吸附能力显著增强：CO₂在Ge-Cu(111)晶面上的吸附能约为Cu (111)晶面的1.5倍,约为Pd改性Cu(111)晶面的2.4倍,进而使逆水煤气变换(RWGS)反应路径速控步骤的活化能降低了近20 kJ·mol^-1,同时衍生出3条生成甲醇的RWGS新路径;此外,Ge-Cu(111)晶面上甲酸盐路径由于速控步骤活化能大幅上升而被禁阻,进而CO及烃类等副产物选择性大幅降低,Ge-Cu(111)晶面上CO₂加氢制甲醇选择性升高。     

铬助剂对Cu/ZrO_2/CNTs-NH_2催化剂催化CO_2加氢合成甲醇性能的影响

采用并流共沉淀方法制备了一系列不同铬含量的Cu/ZrO2/CNTs-NH2催化剂,在固定床反应器上考察铬对催化剂催化CO2加氢合成甲醇反应性能的影响.当铬含量为1%(w),反应温度为260°C,压力为3.0MPa,原料气组成为V(H2):V(CO2):V(N2)=69:23:8,空速为3600 mL·h-1·g-1时,催化剂的促进效果最显著,甲醇收率达7.78%.氮吸附、粉末X射线衍射(XRD)、氢气程序升温脱附(H2-TPR)、X射线光电子能谱(XPS)、二氧化碳程序升温脱附(CO2-TPD)、差热分析(DTA)以及扫描电子显微镜(SEM)等表征结果表明,随着铬含量的增加,铜颗粒的粒径减小,催化剂的比表面积增大.铬的加入一方面提高了铜的分散性,抑制了ZrO2的相变和活性组分的烧结;另一方面提高了CO2的吸附量并促进CO2由弱吸附向强吸附转化,从而提高甲醇的收率;但是当铬含量大于1%时,催化剂表面Cu、Zr的总含量明显下降,降低了CO2的吸附量并且形成了超强CO2吸附物种,抑制了CO2及其中间产物的转化,从而降低了甲醇收率.     

柠檬酸辅助固相研磨法制备铜基催化剂及在CO_2加氢合成甲醇反应中的性能研究

通过柠檬酸辅助固相研磨法制备铜基催化剂,采用XRD、TPR、TG-DSC、SEM、BET、TEM、XPS、CO_2-TPD等手段对催化剂性能进行表征.结果表明室温固相研磨的前驱体在惰性气体N_2中焙烧使体系中的CuO绝大部分被原位还原成Cu~0,不需外加H_2还原,直接制得了C/I-Cu/ZnO催化剂,催化剂具有中孔.利用高压固定床连续反应装置对催化剂活性进行了评价,结果表明,柠檬酸用量、前驱体焙烧温度、焙烧升温速率等条件对催化剂活性产生影响,当C_6H_8O_7/(Cu+Zn)摩尔比为1.2/1并Cu/Zn摩尔比1/1,前驱体在N_2中以3 K·min~(-1)升温速率于623 K焙烧3 h,制得的C/I-Cu/ZnO催化剂比表面积最大,Cu~0粒径最小,在CO_2加氢合成甲醇反应中表现出最佳的活性,CO_2转化率、甲醇选择性和产率分别达到了28.28%、74.29%和21.01%.与外加H_2还原的C/H-Cu/ZnO催化剂相比,原位还原C/I-Cu/ZnO催化剂比表面积较大,Cu~0的粒径较小,活性较高.     

Cu/Cu2O Electrodes and CO2 Reduction to Formic Acid: Effects of Organic Additives on Surface Morphology and Activity

Copper/copper oxide (Cu/Cu₂O) electrodes are known to display interesting electrocatalytic performances for the reduction of CO₂, and thus, deserve further investigation for optimization. Here, we show that the addition of nitrogen‐based organic additives greatly improves the activity of these electrodes (higher current densities, greater selectivity, and higher faradaic yields). The best effector is found to be tetramethyl cyclam. For example, electrolysis at ?2.0 V versus Fc⁺/Fc in CO₂‐saturated DMF/H₂O (99:1, v/v) in the presence of this effector results in formic acid with almost 90 % faradaic yield. SEM and XPS analysis of the electrode surface reveals that the organic additive promotes the formation of active Cu⁰ nanoparticles from Cu₂O during electrolysis. This simple approach provides a straightforward strategy toward the optimization of Cu/Cu₂O electrodes.     

Tuning Interfacial Cu‐O Atomic Structures for Enhanced Catalytic Applications

Cu₂O/CuO_x (x=0, 1) nanocomposites with well‐defined morphologies have been widely applied in catalytic reactions. However, people still understand less about tuning interfacial Cu‐O atomic structures for enhanced catalytic applications, and a special review on this topic has not been reported so far. Herein, we summarize our understanding on tuning interfacial Cu‐O atomic structures based on the literature, including the formation as well as evolution mechanism of Cu‐O interfaces in Cu₂O/CuO and Cu₂O/Cu systems, and the improved performances in the fields of CO oxidation, NO_x oxidation, photoelectrocatalysis, water gas shift reaction, photodegradation of organic dyes, hydrogen evolution, and photoreduction of CO₂. Finally, we briefly propose several potential research directions.     

Tailoring Active Cu2O/Copper Interface Sites for N-Formylation of Aliphatic Primary Amines with CO2/H2

Heterogeneously catalyzed N-formylation of amines to formamide with CO₂/H₂ is highly attractive for the valorization of CO₂. However, the relationship of the catalytic performance with the catalyst structure is still elusive. Herein, mixed valence catalysts containing Cu₂O/Cu interface sites were constructed for this transformation. Both aliphatic primary and secondary amines with diverse structures were efficiently converted into the desired formamides with good to excellent yields. Combined ex and in situ catalyst characterization revealed that the presence of Cu₂O/Cu interface sites was vital for the excellent catalytic activity. Density functional theory (DFT) calculations demonstrated that better catalytic activity of Cu₂O/Cu(111) than Cu(111) is attributed to the assistance of oxygen at the Cu₂O/Cu interface (O_inter) in formation of O_inter-H moieties, which not only reduce the apparent barrier of HCOOH formation but also benefit the desorption of the desired N-formylated amine, leading to high activity and selectivity.     

Crystal‐Plane‐Controlled Selectivity of Cu2O Catalysts in Propylene Oxidation with Molecular Oxygen

The selective oxidation of propylene with O₂ to propylene oxide and acrolein is of great interest and importance. We report the crystal‐plane‐controlled selectivity of uniform capping‐ligand‐free Cu₂O octahedra, cubes, and rhombic dodecahedra in catalyzing propylene oxidation with O₂: Cu₂O octahedra exposing {111} crystal planes are most selective for acrolein; Cu₂O cubes exposing {100} crystal planes are most selective for CO₂; Cu₂O rhombic dodecahedra exposing {110} crystal planes are most selective for propylene oxide. One‐coordinated Cu on Cu₂O(111), three‐coordinated O on Cu₂O(110), and two‐coordinated O on Cu₂O(100) were identified as the catalytically active sites for the production of acrolein, propylene oxide, and CO₂, respectively. These results reveal that crystal‐plane engineering of oxide catalysts could be a useful strategy for developing selective catalysts and for gaining fundamental understanding of complex heterogeneous catalytic reactions at the molecular level.     

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.     

Stable Aqueous Photoelectrochemical CO2 Reduction by a Cu2O Dark Cathode with Improved Selectivity for Carbonaceous Products

Photocatalytic reduction of CO₂ to produce fuels is a promising way to reduce CO₂ emission and address the energy crisis. However, the H₂ evolution reaction competes with CO₂ photoreduction, which would lower the overall selectivity for carbonaceous products. Cu₂O has emerged as a promising material for suppressing the H₂ evolution. However, it suffers from poor stability, which is commonly regarded as the result of the electron‐induced reduction of Cu₂O. This paper describes a simple strategy using Cu₂O as a dark cathode and TiO₂ as a photoanode to achieve stable aqueous CO₂ reduction with a high Faradaic efficiency of 87.4 % and a selectivity of 92.6 % for carbonaceous products. We have shown that the photogenerated holes, instead of the electrons, primarily account for the instability of Cu₂O. Therefore, Cu₂O was used as a dark cathode to minimize the adverse effects of holes, by which an improved stability was achieved compared to the Cu₂O photocathode under illumination. Additionally, direct exposure of the Cu₂O surface to the electrolyte was identified as a critical factor for the high selectivity for carbonaceous products.     

Boosting CO2 Electroreduction to Multi-carbon Products via Oxygen-rich Vacancies and Ce4+−O2−−Cu+ Structure in Cu/CeO2 for Stabilizing Cu+

Cu is a promising electrocatalyst for the CO₂ reduction reaction (CO₂RR) to produce high-value C₂₊ products. Due to the fierce competition of the hydrogen evolution reaction, the slow diffusion of CO₂, and the high energy barrier of the C−C coupling reaction, it is still challenging to achieve high activity and high selectivity to produce multi-carbon products on copper-based electrocatalysts. In this work, we synthesized Cu/CeO₂ catalysts with varying amounts of Cu doping, aiming at effectively converting CO₂ into C₂₊ products through electroreduction. At a copper doping level of 9.77 wt%, the catalyst exhibited a current density of 16.8 mA cm⁻² using a standard H-type cell, achieving a C₂₊ faradaic efficiency (FE) of 78.3 %. Through additional experiments and material characterization, we confirmed that controlling the Cu loading on the surface of CeO₂ is an effective way to regulate the ratio of Cu⁺ to Cu⁰ active sites and the number of oxygen vacancies. Furthermore, the strong electron interaction between Ce⁴⁺−O²⁻−Cu⁺ structure can stabilize Cu⁺ species and enhance the overall stability of the catalyst. This strategy enhances the selectivity towards C₂₊ products and effectively suppresses the competing hydrogen evolution reaction.     

Electrocatalytic Production of C3‐C4 Compounds by Conversion of CO2 on a Chloride‐Induced Bi‐Phasic Cu2O‐Cu Catalyst

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 (Cu₂O_Cl) 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 Cu₂O_Cl 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.     

On the Oxidation State of Cu2O upon Electrochemical CO2 Reduction: An XPS Study

The encouraging selectivity of copper oxides for the electroreduction of CO₂ into ethylene and alcohols has led to a vivid debate on the possible relation between their operando (sub-)surface oxidation state (i. e. fully reduced or partially oxidized) and this distinct reactivity. The high roughness of the Cu oxides used in previous studies on this matter adds complexity to this controversy and motivated us to prepare quasi-planar Cu₂O thin films that displayed a CO₂ reduction selectivity similar to that of oxide-derived copper catalysts reported in previous studies. Most importantly, when the post-mortem thin films were transferred for characterization in an air-free environment, X-ray photoelectron spectroscopy measurements confirmed their complete reduction in the course of the CO₂ reduction reaction. Thus, our results indicate that the selectivity of the Cu oxides featured in previous studies stems from their enhanced roughness, highlighting the importance of controlled sample transfer upon post-mortem characterization with ex situ techniques.