Electrocatalytic CO2 Reduction to Ethylene: From Advanced Catalyst Design to Industrial Applications

Cu supraparticles with enhanced mass transfer and abundant C-C coupling sites achieving ampere-level CO2-to-C2+ electrosynthesis

The efficient electrochemical CO2 reduction to C2+ products at high current densities remains a significant challenge. Here we show inherently hydrophobic and hierarchically porous Cu supraparticles comprising sub-10 nm Cu constituent particles for ampere-level CO2-to-C2+ electrosynthesis. These supraparticles feature abundant grain boundaries for high C2+ selectivity, coupled with interconnected mesopores and interparticle macropore cavities to enhance the accessibility of the active sites and mass transfer, breaking the trade-off between activity and mass transfer in Cu-based catalysts. Moreover, the intrinsic hydrophobicity of the supraparticles mitigates the water-flooding issue of catalytic layer in flow cells, improving the stability at high current densities. Consequently, the Cu supraparticles achieve ampere-level CO2 electrolysis up to 3.2 A cm-2 with a C2+ Faradaic efficiency of 74.9% (compared to 1.21 A cm-2 and 55.4% for Cu nanoparticles) and maintain stability at 1 A cm-2 for over 100 h. This work provides profound insights into the effect of the coupling of mass transfer and catalytic reaction under a high current and presents a corresponding solution by superstructure design.

Cascade Catalytic Systems for Converting CO2 into C2+ Products

The excessive emission and continuous accumulation of CO2 have precipitated serious social and environmental issues. However, CO2 can also serve as an abundant, inexpensive, and non-toxic renewable C1 carbon source for synthetic reactions. To achieve carbon neutrality and recycling, it is crucial to convert CO2 into value-added products through chemical pathways. Multi-carbon (C2+) products, compared to C1 products, offer a broader range of applications and higher economic returns. Despite this, converting CO2 into C2+ products is difficult due to its stability and the high energy required for C-C coupling. Cascade catalytic reactions offer a solution by coordinating active components, promoting intermediate transfers, and facilitating further transformations. This method lowers energy consumption. Recent advancements in cascade catalytic systems have allowed for significant progress in synthesizing C2+ products from CO2. This review highlights the features and advantages of cascade catalysis strategies, explores the synergistic effects among active sites, and examines the mechanisms within these systems. It also outlines future prospects for CO2 cascade catalytic synthesis, offering a framework for efficient CO2 utilization and the development of next-generation catalytic systems.

Target High-Efficient Ethylene Production from Dilute CO2 Enabled by Sustainable Contact Electrons

The electrochemical CO2 reduction reaction (CO2RR) exhibits significant potential to efficiently convert CO2 into ethylene (C2H4). However, achieving high C2H4 selectivity remains a considerable challenge due to the difficulty in effective C─C coupling and stringent requirements on CO2 purity. Herein, a novel contact-electro-catalysis method for CO2RR is presented by constructing dual-active-site catalysts on the electronegative tribolayer of a triboelectric nanogenerator (TENG), including single copper atom anchored polymeric carbon nitride (Cu─PCN) and CuO nanoparticle, achieving an outstanding C2H4 Faradaic efficiency of 63.5% in dilute CO2. Experimental and theoretical studies indicate that Cu─PCN active sites exhibit the ability to heighten *H adsorption and facilitate its migration into CuO nanoparticles. This process effectively modulates the coverage of *H on CuO and promotes the transformation of *CO into *CHO. Subsequently, *CHO undergoes dimerization on the CuO surface, ultimately yielding C2H4. Furthermore, the electric field generated by the TENG enhances the coverage of *H and *CO on both the Cu─PCN and CuO surfaces, which subsequently reduces the energy barrier for C─C coupling. This work provides a new route to enhance the selective reduction of CO2 to C2H4 by integrating contact electrocatalysis with dual active site technologies.

Progress in Cu-Based Catalyst Design for Sustained Electrocatalytic CO2 to C2+ Conversion

The electrocatalytic conversion of CO2 into valuable multi-carbon (C2+) products using Cu-based catalysts has attracted significant attention. This review provides a comprehensive overview of recent advances in Cu-based catalyst design to improve C2+ selectivity and operational stability. It begins with an analysis of the fundamental reaction pathways for C2+ formation, encompassing both established and emerging mechanisms, which offer critical insights for catalyst design. In situ techniques, essential for validating these pathways by real-time observation of intermediates and material evolution, are also introduced. A key focus of this review is placed on how to enhance C2+ selectivity through intermediates manipulation, particularly emphasizing catalytic site construction to promote C─C coupling via increasing *CO coverage and optimizing protonation. Additionally, the challenge of maintaining catalytic activity under reaction conditions is discussed, highlighting the reduction of active charged Cu species and materials reconstruction as major obstacles. To address these, the review describes recent strategies to preserve active sites and control materials evolution, including novel catalyst design and the utilization and mitigation of reconstruction. By presenting these developments and the challenges ahead, this review aims to guide future materials design for CO2 conversion.

3D Cu Microbuds for Electrocatalytic CO Reduction Reaction

Cu-based materials can electrocatalytically reduce CO2 or CO into high-value-added multi-carbon (C2+) products. The features, including morphology, crystal plane, etc., have a great influence on their electrocatalytic performance. Herein, the 3D Cu microbuds (3D Cu MBs) are finely synthesized with enriched grain boundaries by controlling the reaction temperature, time, and pH. The obtained Cu MBs can work as an efficient catalyst for electrocatalytic CO reduction reaction (eCORR) in a flow cell. As compared to the commercial micron Cu, Cu MBs exhibit a significantly higher C2+ product selectivity (≈83% at -0.58 V vs reversible hydrogen electrode-RHE), higher partial current density (410 mA cm-2), and a lower overpotential. The typical 3D hierarchical structure and polycrystalline feature endow the Cu MBs with abundant active grain boundaries for eCORR to form C2+ products. This study offers a new insight into the crystalline-controlled synthesis of 3D Cu catalyst for CO electrolysis.

Promoting Hydrogen Transfer in Electrochemical CO2 Reduction via a Hydrogen on Demand Pathway

The proceeding of electrochemical CO2 reduction reaction (CO2RR) requires the formation of active hydrogen species for CO2 protonation, while traditional catalysts fail to balance the rate of hydrogen supply and CO2 protonation. Herein, we propose a "hydrogen on demand" mechanism, in which the polarity of the adsorbed CO2 is enhanced to allow the capture of hydrogen from water without forming free hydrogen species, realizing the matching rate of hydrogen supply and CO2 protonation. As a proof of concept, we construct Zn-N sites modified by Se atoms, allowing the proceeding of CO2RR under the "hydrogen on demand" mechanism with superior efficiency. The catalyst achieves an industrial CO current of -539.7 mA cm-2, faradaic efficiencies of CO >90 % over a broad window from -0.5 to -1.1 V vs. reversible hydrogen electrode and a high turnover frequency of 7.6×104 h-1 in flow cell. In situ characterization and theoretical calculations reveal that the introduced Se sites enhance the electron localization around the Zn sites, thus increasing the polarity of adsorbed CO2 - with improved ability to acquire hydrogen species from water to facilitate the protonation process.

Electrocatalytic reduction of CO2 to produce the C2+ products: from selectivity to rational catalyst design

Electrocatalytic reduction of CO2 (eCO2RR) into valuable multi-carbon (C2+) products is an effective strategy for combating climate change and mitigating energy crises. The high-energy density and diverse applications of C2+ products have attracted considerable interest. However, the complexity of the reaction pathways and the high energy barriers to C-C coupling lead to lower selectivity and faradaic efficiency for C2+ products than for C1 products. Therefore, a thorough understanding of the underlying mechanisms and identification of reaction conditions that influence selectivity, followed by the rational design of catalysts, are considered promising methods for the efficient and selective synthesis of multi-carbon products. This review first introduces the critical steps involved in forming multi-carbon products. Then, we discuss the reaction conditions that influence the selectivity of C2+ products and explore different catalyst design strategies to enhance the selective production of C2+ products. Finally, we summarize the significant challenges currently facing the eCO2RR field and suggest future research directions to address these challenges.

Crown ether functionalization boosts CO2 electroreduction to ethylene on copper-based MOFs

The electroconversion of CO2 into ethylene (C2H4) offers a promising solution to environmental and energy challenges. Crown ether (CE) modification significantly enhances the C2H4 selectivity of copper-based MOFs, improving C2H4 faradaic efficiency (FE) in CuBTC, CuBDC, and CuBDC-NH2 by 3.1, 1.7, and 2.4 times, respectively. Among these, CuBTC achieves the highest FE for C2H4, reaching ca. 52% at 120 mA cm-2. Control experiments and in situ Fourier transform infrared spectroscopy (FTIR) reveal that CE stabilizes Cu+ during the catalyst's in situ reconstruction, promoting the formation of Cu2O, which is more favorable for C2H4 production. Furthermore, CE increases the local concentration of K+ at the catalyst-electrolyte interface, enhancing *CO adsorption and facilitating C-C coupling reactions. This process promotes the formation of key intermediates, such as *CO*CO, *CO*COH and *COCHO, ultimately boosting C2H4 production.

Electrolyte Design Using "Porous Water" for High-purity Carbon Monoxide Electrosynthesis from Dilute Carbon Dioxide

Electrosynthesis of high-purity carbon monoxide (CO) from captured carbon dioxide (CO2) remains energy-intensive due to the unavoidable CO2 regeneration and post-purification stages. Here, we propose a direct high-purity CO electrosynthesis strategy employing an innovative electrolyte, termed porous electrolyte (PE), based on "porous water". Zeolite nanocrystals within PE provide permanent pores in the liquid phase, enabling physical CO2 adsorption through an intraparticle diffusion model, as demonstrated by molecular dynamics simulations and in situ spectral analysis. Captured CO2 spontaneously desorbs under applied reductive potential, driven by the interfacial CO2 concentration gradient, and is subsequently reduced electrochemically. The high CO2 concentration in PE enhances mass transfer, and surface ion exchange between Si-OH groups and K+ ions on the zeolite surface generates a stronger interfacial electric field, promoting electron transfer steps. This optimized kinetics for mass and electron transfer confers heightened intrinsic activity toward CO2 electroreduction. The PE-based electrolysis system demonstrated superior CO Faradaic efficiency and partial current density compared to the conventional CO2-fed system. A circular system using PE and a Ni-N/C cathode realized continuous production of high-purity CO (97.0 wt %) from dilute CO2 (15 %) and maintained >90.0 wt % under 150 mA cm-2, with significantly reduced energy consumption and costs.

Carbon Nanocage Supported Asymmetrically Coordinated Nickle Single-Atom for Enhanced CO2 Electroreduction in Membrane Electrode Assembly

Designing efficient catalysts for operating CO2 electroreduction in membrane electrode assembly (MEA) faces significant obstacles. Herein, we propose an asymmetrically coordinated Ni single-atom catalyst featuring axial Br coordination at NiN4Br sites anchoring onto hollow Br/N co-doped carbon nanocages, achieved through a NaBr-assisted confined-pyrolysis strategy. The Ni-NBr-C catalyst exhibits a high CO Faradaic efficiency (FECO>97 %) over the current density range of 50 to 350 mA cm-2 in the MEA device. Furthermore, Ni-NBr-C shows a stable cell voltage of 2.66±0.2 V while delivering a large current density of 350 mA cm-2 over an 85-hour long-term operation, demonstrating its potential for industrial-scale applications. Advanced characterization techniques and theoretical calculations reveal that the coordination and doping of Br not only enhance the intrinsic activity but also highlight that the unique pore structure improves mass transfer efficiency.

Switching CO-to-Acetate Electroreduction on Cu Atomic Ensembles

The electrocatalytic reaction pathway is highly dependent on the intrinsic structure of the catalyst. CO2/CO electroreduction has recently emerged as a potential approach for obtaining C2+ products, but it is challenging to achieve high selectivity for a single C2+ product. Herein, we develop a Cu atomic ensemble that satisfies the appropriate site distance and coordination environment required for electrocatalytic CO-to-acetate conversion, which shows outstanding overall performance with an acetate Faradaic efficiency of 70.2% with a partial current density of 225 mA cm-2 and a formation rate of 2.1 mmol h-1 cm-2. Moreover, a single-pass CO conversion rate of 91% and remarkable stability can be also obtained. Detailed experimental and theoretical investigations confirm the significant advantages of the Cu atomic ensembles in optimizing C-C coupling, stabilizing key ketene intermediate (*CCO), and inhibiting the *HOCCOH intermediate, which can switch the CO reduction pathway from the ethanol/ethylene on the conventional metallic Cu site to the acetate on the Cu atomic ensembles.

Electrochemical CO2 Reduction to Multicarbon Products on Non-Copper Based Catalysts

Electrochemical CO2 reduction reaction (eCO2RR) to value-added multicarbon (C2+) products offers a promising approach for achieving carbon neutrality and storing intermittent renewable energy. Copper (Cu)-based electrocatalysts generally play the predominant role in this process. Yet recently, more and more non-Cu materials have demonstrated the capability to convert CO2 into C2+, which provides impressive production efficiency even exceeding those on Cu, and a wider variety of C2+ compounds not achievable with Cu counterparts. This motivates us to organize the present review to make a timely and tutorial summary of recent progresses on developing non-Cu based catalysts for CO2-to-C2+. We begin by elucidating the reaction pathways for C2+ formation, with an emphasis on the unique C-C coupling mechanisms in non-Cu electrocatalysts. Subsequently, we summarize the typical C2+-involved non-Cu catalysts, including ds-, d- and p-block metals, as well as metal-free materials, presenting the state-of-the-art design strategies to enhance C2+ efficiency. The system upgrading to promote C2+ productivity on non-Cu electrodes covering microbial electrosynthesis, electrolyte engineering, regulation of operational conditions, and synergistic co-electrolysis, is highlighted as well. Our review concludes with an exploration of the challenges and future opportunities in this rapidly evolving field.

Cascade Conversion of CO2 to Ethylene Carbonate under Ambient Conditions

Ethylene carbonate (EC) is the simplest cyclic carbonate with great industrial significance, most importantly as the vital electrolyte component for lithium-ion batteries. Its conventional synthesis generally involves the use of toxic precursors and requires elevated temperatures and pressures. Herein, we propose a cascade catalytic route for converting CO2 to EC under ambient conditions. Such a hybrid reaction scheme consists of the electrochemical reduction of CO2 to ethylene catalyzed by copper in a membrane electrode assembly reactor, the bromine-mediated conversion of ethylene to bromoethanol catalyzed by WO3 nanoarrays grown on carbon cloth, and the reaction between bromoethanol and CO2 to form EC. By separately optimizing individual catalytic steps and then integrating them together in series, we achieved the conversion of CO2 to EC at a good yield under room temperature and atmospheric pressure. Our study also represents the first demonstration about the successful synthesis of organic carbonates from CO2 as the exclusive carbon source.

Anionic Metal-Organic Framework Derived Cu Catalyst for Selective CO2 Electroreduction to Hydrocarbons

Metal-organic frameworks (MOFs)-related Cu materials are promising candidates for promoting electrochemical CO2 reduction to produce valuable chemical feedstocks. However, many MOF materials inevitable undergo reconstruction under reduction conditions; therefore, exploiting the restructuring of MOF materials is of importance for the rational design of high-performance catalyst targeting multi-carbon products (C2). Herein, a facile solvent process is choosed to fabricate HKUST-1 with an anionic framework (a-HKUST-1) and utilize it as a pre-catalyst for alkaline CO2RR. The a-HKUST-1 catalyst can be electrochemically reduced into Cu with significant structural reconstruction under operating reaction conditions. The anionic HKUST-1 derived Cu catalyst (aHD-Cu) delivers a FEC2H4 of 56% and FEC2 of ≈80% at -150 mA cm-2 in alkaline electrolyte. The resulting aHD-Cu catalyst has a high electrochemically active surface area and low coordinated sites. In situ Raman spectroscopy indicates that the aHD-Cu surface displays higher coverage of *CO intermediates, which favors the production of hydrocarbons.

Identification of Degradation Reasons for a CO2 MEA Electrolyzer Using the Distribution of Relaxation Times Analysis

The application of membrane electrode assembly (MEA) in electrocatalytic CO2 reduction (ECO2R) technology is an essential step toward industrialization. Nevertheless, the issue of ECO2R failure in MEA during extended operation hinders its industrial application. In this work, we employed in situ, nondestructive electrochemical impedance spectroscopy (EIS) techniques combined with distribution of relaxation times (DRT) methodology to diagnose the causes of the failure. By systematically investigating the variations in polarization resistance throughout the degradation process and utilizing a controlled variable approach to identify the origin of polarization, we diagnosed the degeneration of ionomers as the primary cause of the performance degradation of ECO2R in this instance. We further confirmed the reliability of our findings through material characterization and respraying ionomers onto the catalyst surface. This research provides an effective diagnostic method for the failure analysis of ECO2R performance in MEA, which is crucial for advancing industrialization of ECO2R technology.

Atomically Dispersed Metal Catalysts for the Conversion of CO2 into High-Value C2+ Chemicals

The conversion of carbon dioxide (CO2) into value-added chemicals with two or more carbons (C2+) is a promising strategy that cannot only mitigate anthropogenic CO2 emissions but also reduce the excessive dependence on fossil feedstocks. In recent years, atomically dispersed metal catalysts (ADCs), including single-atom catalysts (SACs), dual-atom catalysts (DACs), and single-cluster catalysts (SCCs), emerged as attractive candidates for CO2 fixation reactions due to their unique properties, such as the maximum utilization of active sites, tunable electronic structure, the efficient elucidation of catalytic mechanism, etc. This review provides an overview of significant progress in the synthesis and characterization of ADCs utilized in photocatalytic, electrocatalytic, and thermocatalytic conversion of CO2 toward high-value C2+ compounds. To provide insights for designing efficient ADCs toward the C2+ chemical synthesis originating from CO2, the key factors that influence the catalytic activity and selectivity are highlighted. Finally, the relevant challenges and opportunities are discussed to inspire new ideas for the generation of CO2-based C2+ products over ADCs.

Strategies for overcoming challenges in selective electrochemical CO2 conversion to ethanol

The electrochemical conversion of carbon dioxide (CO2) to valuable chemicals is gaining significant attention as a pragmatic solution for achieving carbon neutrality and storing renewable energy in a usable form. Recent research increasingly focuses on designing electrocatalysts that specifically convert CO2 into ethanol, a desirable product due to its high-energy density, ease of storage, and portability. However, achieving high-efficiency ethanol production remains a challenge compared to ethylene (a competing product with a similar electron configuration). Existing electrocatalytic systems often suffer from limitations such as low energy efficiency, poor stability, and inadequate selectivity toward ethanol. Inspired by recent progress in the field, this review explores fundamental principles and material advancements in CO2 electroreduction, emphasizing strategies for ethanol production over ethylene. We discuss electrocatalyst design, reaction mechanisms, challenges, and future research directions. These advancements aim to bridge the gap between current research and industrialized applications of this technology.

The meso-substituent electronic effect of Fe porphyrins on the electrocatalytic CO2 reduction reaction

We report Fe porphyrins bearing different meso-substituents for the electrocatalytic CO2 reduction reaction (CO2RR). By replacing two and four meso-phenyl groups of Fe tetraphenylporphyrin (FeTPP) with strong electron-withdrawing pentafluorophenyl groups, we synthesized FeF10TPP and FeF20TPP, respectively. We showed that FeTPP and FeF10TPP are active and selective for CO2-to-CO conversion in dimethylformamide with the former being more active, but FeF20TPP catalyzes hydrogen evolution rather than the CO2RR under the same conditions. Experimental and theoretical studies revealed that with more electron-withdrawing meso-substituents, the Fe center becomes electron-deficient and it becomes difficult for it to bind a CO2 molecule in its formal Fe0 state. This work is significant to illustrate the electronic effects of catalysts on binding and activating CO2 molecules and provide fundamental knowledge for the design of new CO2RR catalysts.

Review on strategies for improving the added value and expanding the scope of CO2 electroreduction products

The electrochemical reduction of CO2 into value-added chemicals has been explored as a promising solution to realize carbon neutrality and inhibit global warming. This involves utilizing the electrochemical CO2 reduction reaction (CO2RR) to produce a variety of single-carbon (C1) and multi-carbon (C2+) products. Additionally, the electrolyte solution in the CO2RR system can be enriched with nitrogen sources (such as NO3-, NO2-, N2, or NO) to enable the synthesis of organonitrogen compounds via C-N coupling reactions. However, the electrochemical conversion of CO2 into valuable chemicals still faces challenges in terms of low product yield, poor faradaic efficiency (FE), and unclear understanding of the reaction mechanism. This review summarizes the promising strategies aimed at achieving selective production of diverse carbon-containing products, including CO, formate, hydrocarbons, alcohols, and organonitrogen compounds. These approaches involve the rational design of electrocatalysts and the construction of coupled electrocatalytic reaction systems. Moreover, this review presents the underlying reaction mechanisms, identifies the existing challenges, and highlights the prospects of the electrosynthesis processes. The aim is to offer valuable insights and guidance for future research on the electrocatalytic conversion of CO2 into carbon-containing products of enhanced value-added potential.

Structuring Cu Membrane Electrode for Maximizing Ethylene Yield from CO2 Electroreduction

Electrocatalytic ethylene (C2H4) evolution from CO2 reduction is an intriguing route to mitigate both the energy and environmental crises; however, to acquire industrially relevant high productivity and selectivity at low energy cost remains to be challenging. Membrane assembly electrode has shown great prospect and tailoring its architecture for maximizing C2H4 yield at minimum voltage with long-term stability becomes critical. Here a freestanding Cu membrane cathode is designed and constructed by electrochemically depositing mesoporous Cu film on Cu foam to simultaneously manage CO2, electron, water, and product transport, which shows an extraordinary C2H4 Faradaic efficiency of 85.6% with a full cell power conversion efficiency of 33% at a current density of 368 mA cm-2, heading the techno-economic viability for electrocatalytic C2H4 production.