Industrial-Current-Density CO2-to-C2+ Electroreduction by Anti-swelling Anion-Exchange Ionomer-Modified Oxide-Derived Cu Nanosheets

Cu doping induced asymmetric Cu-Vs-In active sites in In2S3 for efficient photocatalytic C2H4 conversion from CO2

Selective reduction of CO2 to value-added C2-chemical fuels, (such as C2H4) holds great promise for directly converting solar energy into chemical energy. However, the weak adsorption of CO2 on photocatalysts directly affects its conversion efficiency. Here we use Cu doping to create asymmetric Cu-S-vacancies-In (Cu-VS-In) sites in the two-dimensional In2S3, which greatly improves CO2 adsorption, achieving efficient photocatalytic reduction of CO2 to C2H4. Experiments and DFT (Density functional theory) calculations show that Cu doping, due to the influence of charge balance, will induce S vacancies and change the coordination environment around In atoms. This changes the mode of CO2 adsorption and decreases the adsorption energy of CO2. The asymmetric Cu-VS-In sites promote charge transfer to the CO bond, increasing catalytic activity. The concept of using asymmetric sulfur vacancies to simultaneously regulate both adsorption and charge transfer between catalysts and reactants provides a design guide for the development of advanced catalytic materials aimed at photocatalytic CO2 reduction.

Dynamically Reconstructed Cu Nanowire Arrays Realizing Efficient Industrial-Current-Density CO2-to-C2+ Electroreduction

Selective C2+ production at industrial current densities is highly desirable but still colossally challenging, even for typical Cu-based catalysts. To address these issues, self-supporting Cu nanowire arrays assembled on a gas diffusion layer are first fabricated by in situ electroreduction of Cu(OH)2 nanowire arrays, while in situ X-ray diffraction patterns and in situ Raman measurements monitor their dynamic phase transformation process. The finite-element method calculations elucidate that the nanowire array structure enriches the local concentration of CO2/CO, further verified by operando Raman spectra. In situ attenuated total reflection-surface-enhanced infrared absorption spectroscopy reveals the Cu nanowire arrays promote *CO dimerization into *OCCO intermediates. Based on the above merits, the Cu nanowire arrays achieve a high Faradaic efficiency of 75.4% for C2+ products with a current density of 500 mA cm-2. Overall, this study provides new insights into designing array catalysts for creating confined spaces to enrich reactants and intermediates.

Constructing a Localized Buffer Interlayer to Elevate High-Rate CO2-to-C2+ Electrosynthesis

Catalytic surface and interface engineering for the electrosynthesis of multicarbon chemicals from CO2 are widely investigated, while the selective regulation of mass transport for reactant CO2 and intermediate CO remains rarely explored, which is a critical challenge limiting the C2+ production rate. Here, we strategically construct a buffer interlayer with soluble ionic liquid (IL) additives between the aqueous electrolyte and the catalytic surface, which not only regulates the microenvironment of CO and CO2 at different reaction stages but also stabilizes catalytic sites. The CO residence time is extended in the buffer interlayer ascribed to the attractive interactions via dipole-dipole interactions and hydrogen bonding. CO2 and its transport are enhanced by the buffer reactions in the aqueous interlayer within the flow-through compact cell. Meanwhile, the utilization of ILs stabilizes active sites (Cu2O-derived Cu) by facilitating the regeneration of Cu2O through the applied potentials. Consequently, C2+ products are synthesized at a high rate with a partial current density of 1.30 A/cm2 for over 200 h. This concept is further scaled to a 100 cm2 flow cell, exhibiting a carbon loss below 6%. Such a systematic investigation establishes a general construction strategy for the buffer interlayer and catalytic sites in electrolysis.

Highly selective CO2 electroreduction in an exsolution-induced flow cell using a hierarchical monolithic nano-Ag foam electrode

Electrochemical CO2 reduction driven by renewable energy offers a promising route to carbon neutrality. The flow-through induced dynamic triple-phase boundary cell (FTDT cell) addresses the key challenges of conventional gas diffusion electrodes (GDEs), including salt precipitation and electrode flooding, by enabling direct electrolysis of CO2-saturated solutions. However, the Ag catalyst with carbon cloth as a substrate in the FTDT cell exhibits the shortcomings of a few active sites and poor structural stability. Here, we reported a monolithic nano-Ag foam electrode featuring well-developed pores and a hierarchical nanostructure with a high electrochemically active surface area (ECSA), which is ten times that of the Ag NPs electrode, enhancing the CO2 electroreduction performance of the FTDT cell significantly. Classical nucleation theory (CNT) clarified that the nanostructures accelerate bubble nucleation, and visualization experiments confirmed that the periodically connected pore structure provides abundant dynamic gas-liquid-solid triple-phase boundaries (TPBs). At an industrial current density of 200 mA cm-2 and a cell voltage of 2.34 V, the nano-Ag foam electrode achieves a CO faradaic efficiency of 93% and an overall energy efficiency of 51.34%, presenting a promising approach for the commercialization of CO2 electrolysis.

Metal-organic double layer to stabilize selective multi-carbon electrosynthesis

Stable operation of the gas diffusion electrodes is key for industrial-scale electrochemical CO2 reduction (eCO2R). To enhance the electrolytic stability, we shield the Cu-coated gas diffusion electrode with a polycationic sheath via electrospinning and propose a Metal-Organic Double Layer (MODL) scheme to depict the triphasic interface. The as-fabricated electrode exhibits a high multi-carbon Faradaic efficiency of 91.2 ± 3.8%, along with operational stability for over 300 h at 300 mA cm-2 in an alkaline flow cell. In a membrane electrode assembly with pure water as the anolyte, it further achieves an ethylene Faradaic efficiency over 50% at 200 mA cm-2. Mechanistic investigations unveil that replacing hydrated cationic counter ions in the conventional double layer with hydrogen bond-woven polycationic groups in the MODL allows simultaneously tailoring the local electric field and interfacial water structure. This study introduces a molecular-level redesign of the electric double layer in eCO2R systems, achieving precisely tunable electrostatic characteristics and tailored chemical microenvironments while leveraging sustainable electrolysis systems to enable highly efficient and stable multi-carbon production.

Strategies for Enhancing Stability in Electrochemical CO2 Reduction

The electrochemical CO2 reduction reaction (CO2RR) holds significant promise as a sustainable approach to address global energy challenges and reduce carbon emissions. However, achieving long-term stability in terms of catalytic performance remains a critical hurdle for large-scale commercial deployment. This mini-review provides a comprehensive exploration of the key factors influencing CO2RR stability, encompassing catalyst design, electrode architecture, electrolyzer optimization, and operational conditions. We examine how catalyst degradation occurs through mechanisms such as valence changes, elemental dissolution, structural reconfiguration, and active site poisoning and propose targeted strategies for improvement, including doping, alloying, and substrate engineering. Additionally, advancements in electrode design, such as structural modifications and membrane enhancements, are highlighted for their role in improving stability. Operational parameters such as temperature, pressure, and electrolyte composition also play crucial roles in extending the lifespan of the reaction. By addressing these diverse factors, this review aims to offer a deeper understanding of the determinants of long-term stability in the CO2RR, laying the groundwork for the development of robust, scalable technologies for efficient carbon dioxide conversion.

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.

Heteroarchitectural Gas Diffusion Layer Promotes CO2 Reduction Coupled with Biomass Oxidation at Ampere-Level Current Density

Achieving high product selectivity at ampere-level current densities is essential for the industrial application of electrochemical CO2 reduction. However, the operational stability of CO2 electrolyzers at large current density has long been hindered by flooding of gas diffusion layer (GDL). Herein, a new heteroarchitectural GDL is designed to overcome flooding. Such GDL is constructed by sequentially sputtering the conductive silver and titanium boride (TiB2) onto a polytetrafluoroethylene substrate. Assembled with Cu catalyst in a flow cell, a maximum ethylene Faradaic efficiency of 64.7 % was achieved at a current density of 1.2 A cm-2 in 6 M KOH. Furthermore, the GDL is capable of stable operation for over 40 hours at 400 mA cm-2. Theoretical calculations and in situ experiments demonstrate enhanced intermediates adsorption on the TiB2-supported Cu surface, thereby reducing the energy barrier for C-C coupling. When coupling the CO2 reduction reaction with 5-hydroxymethylfurfural oxidation reaction, Faradaic efficiencies of 49.2 % for ethylene and 85.4 % for 2,5-furandicarboxylic acid were achieved at 1.2 A cm-2. This work provides a highly stable GDL for efficient CO2 conversion at ampere-level current density and paves the way for integrating biomolecules conversion in stack-level devices.

In Situ/Operando Insights into the Selectivity of CH4/C2H4 in CO2 Electroreduction by Fine-Tuning the Composition of Cu/SiO2 Catalysts

Copper-silica-based catalysts have drawn much attention for the remarkable product selectivity in the electrochemical CO2 reduction reaction, particularly toward CH4 and C2H4. However, systematic studies exploring the underlying reasons for the selectivity differences are lacking. Herein, Cu/SiO2 catalysts with different Cu/Si ratio are controllably synthesized by fine-tuning the precursor ratio, enabling selective CO2 electroreduction to CH4/C2H4. Specifically, at a current density of 200 mA cm-2, Cu/SiO2-10 including majority of CuSiO3 facilitates the electroreduction of CO2 to CH4 with a Faradaic selectivity ratio of CH4/C2H4 (9.3/1), whereas Cu/SiO2-50 primarily consisting of CuO exhibits a Faradaic selectivity ratio of C2H4/CH4 (16.7/1). X-ray photoelectron spectroscopy and in situ Raman spectroscopic characterization reveal that CuSiO3 in the catalysts remains stable and no valve state change occurs during the reaction, while CuO in the catalysts is reduced in situ to Cu0/Cu+ during the reaction. In situ infrared spectroscopic and temperature-programmed desorption of CO characterization further reveal that CuSiO3 has a stronger protonation capacity and promotes the direct protonation of adsorbed *CO species to CH4, while Cu0/Cu+ is more conducive to the CC coupling between the intermediate species *CHO with adsorbed *CO species to form C2H4 due to the stronger CO adsorption capacity and higher coverage.

Hydrophobic Ionic Liquid Engineering for Reversing CO Intermediate Configuration toward Ampere-Level CO2 Electroreduction to C2+ Products

Hydrophobic ionic liquid (HIL) engineering on the catalyst surface represents a simple yet potent direction for optimizing the CO2 electroreduction performance. However, the pivotal role of HIL engineering at an industrial current density is still ambiguous due to limited and conflicting research findings. Herein, HIL-engineered oxide-derived Cu porous nanoparticles with electron-delocalized groups and a specific ultramicropore structure are first constructed to facilitate CO2-to-C2+ electroreduction at ampere-level current densities. The uniformly decorated HIL is innovatively demonstrated by positron annihilation lifetime spectroscopy, which offers unparalleled advantages in ultramicropore characterization. Bader charge-dependent performance analyses and theoretical calculations disclose that the N atoms in the HIL lower the adsorption energy of CO on the atop site from -0.38 to -1.42 eV through electron donation, which inverts the most stable adsorption site and favors the energy-efficient dimerization of atop-bound CO. Operando Raman spectra and in situ attenuated total reflection-surface enhanced infrared absorption spectroscopy indicate that the adhered HIL increases *CO coverage and alters the *CO adsorption configuration to an atop-bound state with an abundant high-frequency band. Furthermore, staircase potential electrochemical impedance spectroscopy unravels the specific arrangement structure of HIL enlarges the electrochemical surface charge by about 1.5 times, thereby accelerating CO2 electroreduction. As a result, the HIL-engineered oxide-derived Cu porous nanoparticles achieve a prominent C2+ productivity with a Faradaic efficiency of 85.1% and a formation rate up to 2512 μmol h-1 cm-2, outperforming most reported Cu-based electrocatalysts.

Solvent Mediated Interfacial Microenvironment Design for High-Performance Electrochemical CO2 Reduction to C2+ Products

Electrochemical CO2 reduction (CO2RR) in membrane electrode assembly (MEA) represents a viable strategy for converting CO2 into value-added multi-carbon (C2+) compounds. Therefore, the microstructure of the catalyst layer (CL) affects local gas transport, charge conduction, and proton supply at three-phase interfaces, which is significantly determined by the solvent environment. However, the microenvironment of the CLs and the mechanism of the solvent effect on C2+ selectivity remains elusive. Herein, a tailored interfacial structure is designed by introducing a solvent-mediated catalyst-ionomer-solvent microenvironment. The acetone surface promotion strategy is beneficial for the unfolded ionomers to uniformly coat the catalysts, which contributes to enhancing interfacial hydrophobicity and inhibiting hydrogen evolution. Furthermore, molecular dynamics (MD) simulation and in situ ATR-SEIRAS are employed to elucidate the appropriate interfacial network with a balanced distribution of CO2 and H2O. The uniform and continuous network in acetone is advantageous for CO2-to-C2+. The optimized structure favors the production of C2+ products in Cu-based MEA, exhibiting a high C2+ faradaic efficiency (FE) of 80.27% at 400 mA cm-2.

Polymeric ionic liquid promotes acidic electrocatalytic CO2 conversion to multicarbon products with ampere level current on Cu

The acidic electroreduction of CO2 into multicarbon (C2+) products is much attractive for the improved carbon utilization than alkaline or neutral electroreduction. How to improve the efficiency of C2+ products generation by acidic electroreduction of CO2, is important, especially at high current density and in electrolyte with low K+ concentration. Herein, we propose a strategy of capping Cu surface with a polymeric ionic liquid (PIL) adlayer for boosting the acidic electrocatalytic CO2 conversion to C2+ products at high current densities (ampere-level) and low K+ concentration. In the electrolyte with a relatively low K+ concentration (1.0 M), the Faradaic efficiency (FE) for C2+ products reaches 82.2% under a current density 1.0 A·cm-2 in acidic environment (pH=1.8). Particularly, when the current density is as high as 1.5 A·cm-2, the C2+ FE still keeps 75.8%. Experimental and theoretical studies reveal that the presence of PIL adlayer on Cu catalyst can well inhibit H+ diffusion to catalyst surface, enrich more K+ and facilitate C-C coupling reaction.

A critical appraisal of advances in integrated CO2 capture and electrochemical conversion

This perspective work examines the current advancements in integrated CO2 capture and electrochemical conversion technologies, comparing the emerging methods of (1) electrochemical reactive capture (eRCC) though amine- and (bi)carbonate-mediated processes and (2) direct (flue gas) adsorptive capture and conversion (ACC) with the conventional approach of sequential carbon capture and conversion (SCCC). We initially identified and discussed a range of cell-level technological bottlenecks inherent to eRCC and ACC including, but not limited to, mass transport limitations of reactive species, limitation of dimerization, impurity effects, inadequate in situ generation of CO2 to sustain industrially relevant current densities, and catalyst instabilities with respect to some eRCC electrolytes, amongst others. We followed this with stepwise perspectives on whether these are considered intrinsic challenges of the technologies - otherwise recommendations were disclosed where appropriate. Furthermore, technoeconomic analysis (TEA) was conducted using a net present value (NPV) model to determine the minimum selling prices (MSPs) for CO, HCOOH, CH3OH, C2H5OH, and C2H4 as target products based on cell-performance metrics from contemporary literature for SCCC, eRCC, and ACC. Additionally, sensitivity analyses were performed, focusing on cell-level parameters (voltage requirements, Faradaic efficiencies, current density), production scale factors, and other relevant variables (levelized costs of electricity and stack). This analysis sheds light on the cost-driving factors influencing commercial viability, revealing key techno-economic challenges for eRCC, particularly with liquid products. However, it also identifies optimization opportunities in current designs. By pinpointing critical areas for improvement, this work helps advance electrochemical CO2 reduction technologies towards more sustainable and economically competitive applications at different scales.

Enigma of Sustainable CO2 Conversion to Renewable Fuels and Chemicals Through Photocatalysis, Electrocatalysis, and Photoelectrocatalysis: Design Strategies and Atomic Level Insights

Growing global population, escalating energy consumption, and climate change threaten future energy security. Fossil fuel combustion, primarily coal, oil, and natural gas, exacerbates the greenhouse effect driving global warming through CO2 emissions. To address such issues, research is focused on converting CO2 into valuable fuels and chemicals, which aims to reduce noxious CO2 and simultaneously bridge the gap between energy demands and sustainable supply. CO2 reduction has primarily been accomplished through three methodologies: photocatalysis, electrocatalysis, and photo-electrocatalysis. Review initially elucidates fundamental principles and kinetics that govern CO2 reduction across all three approaches. Subsequently, we have discussed emerging concepts such as role of hot carriers and plasmon-mediated processes in photocatalysis. In electrocatalysis process, we thoroughly discuss advanced design strategies including alloying, ligand-modified surfaces, and molecular tuning to regulate the specific nanostructures of metal-based compounds. Furthermore, it investigates impacts of distinct nanostructures to identify structure property-performance correlations and their mechanisms. Similarly, enhancement of photo-electrocatalytic efficiency is investigated using defect-engineered nanostructures, heterojunctions, and plasmonic metals. Finally, the review outlines potential and intricacies associated with design strategies to drive industrial-scale CO2 reduction. In summary, this comprehensive review offers a thorough analysis of current advances, challenges, and future perspectives for CO2 reduction to valuable products.

Engineering Atom-Scale Cascade Catalysis via Multi-Active Site Collaboration for Ampere-Level CO2 Electroreduction to C2+ Products

Electrochemical reduction of CO2 to value-added multicarbon (C2+) productions offers an attractive route for renewable energy storage and CO2 utilization, but it remains challenging to achieve high C2+ selectivity at industrial-level current density. Herein, a Mo1Cu single-atom alloy (SAA) catalyst is reported that displays a remarkable C2+ Faradaic efficiency of 86.4% under 0.80 A cm-2. Furthermore, the C2+ partial current density over Mo1Cu reaches 1.33 A cm-2 with a Faradaic efficiency surpasses 74.3%. The combination of operando spectroscopy and density functional theory (DFT) indicates the as-prepared Mo1Cu SAA catalyst enables atom-scale cascade catalysis via multi-active site collaboration. The introduced Mo sites promote the H2O dissociation to fabricate active *H, meanwhile, the Cu sites (Cu0) far from Mo atom are active sites for the CO2 activation toward CO. Further, CO and *H are captured by the adjacent Cu sites (Cu&+) near Mo atom, accelerating CO conversion and C─C coupling process. Our findings benefit the design of tandem electrocatalysts at atomic scale for transforming CO2 to multicarbon products under a high conversion rate.

Large Dipole Moment Enhanced CO2 Adsorption on Copper Surface: Achieving 68.9% Catalytic Ethylene Faradaic Efficiency at 1.0 A cm-2

The electrochemical conversion of carbon dioxide (CO2) into hydrocarbon products emerges as a pivotal sustainable strategy for carbon utilization. Cu-based catalysts are currently prioritized as the most effective means for this process, yet it remains a long-term goal to achieve high product selectivity at elevated current densities. This study delved into exploring the influence of a topological poly(2-aminoazulene) with a substantial dipole moment on modulating the Cu surface dipole field to augment the catalytic activity involved in CO2 reduction. The resulting Cu/poly(2-aminoazulene) heterojunction showcases a remarkable ethylene Faradaic efficiency of 68.9% even at a substantial current density of 1 A cm-2. Through in situ Raman and in situ Fourier-transform infrared spectroscopy, poly(2-aminoazulene)-modified Cu electrode exhibits a heightened concentration of intermediates as compared to the bare Cu, proving advantageous for C-C dimerization. Theoretical calculations demonstrate the reduced energy barrier for C-C dimerization, and meanwhile impeding hydrogen evolution reaction on Cu/poly(2-aminoazulene) heterojunction, which are beneficial to CO2 reduction. The catalyst design in this study, incorporating dipole moment considerations, not only investigates the influence of dipole moment on electrochemical carbon dioxide reduction but also pioneers an innovative strategy to augment catalytic activity by elevating the micro-concentration of reactants on catalyst surfaces.

Isolated Tin Enhanced CO Coverage-Regulation on Sn1Cu Alloy for Selective CO2 Electroreduction to C2+ Products

Electricity-powered C─C coupling of CO2 represents an attractive strategy for producing valuable commodity chemicals with renewable energy, but it is still challenging to gain high C2+ selectivity at high current density. Here, a Sn1Cu single-atom alloy (SAA) is reported with isolated Sn atom embedded into the Cu lattice, as efficient ectrocatalyst for CO2 reduction. The as prepared Sn1Cu-SAA catalyst shows a maximal C2+ Faradaic efficiency of 79.3% at 800 mA cm-2, which can be kept stable for at least 16 h. The combination of in situ spectroscopy and DFT calculation reveal that the introduced Sn atom promote the activation of CO2 to *CO, and enhance the CO coverage on Sn1Cu-SAA. As results, the reaction barrier of C─C coupling pathway is significantly reduced, boosting the generation of C2+ products. These findings offer a novel sight for fabricating multicarbon products from CO2 via regulation the concentration of intermediates on catalytic interface.

Constructing Ag/Cu2O Interface for Efficient Neutral CO2 Electroreduction to C2H4

Neutral CO2 electroreduction to multi-carbons (C2+) offers a promising pathway to reduce the CO2 and energy losses originating from the carbonate formation. However, the sluggish kinetics of C-C coupling brings a significant challenge of achieving high selectivity of a single product (such as ethylene), especially at industrial-relevant current densities (>300 mA cm-2). Here, we reported an optimized Ag-Cu2O interfacial catalyst that exhibited C2+ Faradaic efficiency (FE) of 73.6 % at 650 mA cm-2 in a flow cell. Remarkably, it obtained FEC2H4 of 66.0 % with a partial current density of 429.1 mA cm-2, making it stand out among the reported Cu-based electrocatalysts. In situ Raman spectra uncovered that the Ag/Cu2O interfaces enabled a high coverage of *CO around the partially reduced Cu+/Cu0 active sites. Furthermore, theoretical calculations demonstrated the enhanced CO formation and C-C coupling at the Ag/Cu2O interface. This work reported an unprecedented neutral CO2 electroreduction to C2H4 performance and provided an in-depth comprehension of the role of the bimetallic interface.

Mesostructure-Specific Configuration of *CO Adsorption for Selective CO2 Electroreduction to C2+ Products

The multi-carbon (C2+) alcohols produced by electrochemical CO2 reduction, such as ethanol and n-propanol, are considered as indispensable liquid energy carriers. In most C-C coupling cases, however, the concomitant gaseous C2H4 product results in the low selectivity of C2+ alcohols. Here, we report rational construction of mesostructured CuO electrocatalysts, specifically mesoporous CuO (m-CuO) and cylindrical CuO (c-CuO), enables selective distribution of C2+ products. The m-CuO and c-CuO show similar selectivity towards total C2+ products (≥76 %), but the corresponding predominant products are C2+ alcohols (55 %) and C2H4 (52 %), respectively. The ordered mesostructure not only induces the surface hydrophobicity, but selectively tailors the adsorption configuration of *CO intermediate: m-CuO prefers bridged adsorption, whereas c-CuO favors top adsorption as revealed by in situ spectroscopies. Computational calculations unravel that bridged *CO adsorbate is prone to deep protonation into *OCH3 intermediate, thus accelerating the coupling of *CO and *OCH3 intermediates to generate C2+ alcohols; by contrast, top *CO adsorbate is apt to undergo conventional C-C coupling process to produce C2H4. This work illustrates selective C2+ products distribution via mesostructure manipulation, and paves a new path into the design of efficient electrocatalysts with tunable adsorption configuration of key intermediates for targeted products.

Impact of Side Chains in 1-n-Alkylimidazolium Ionomers on Cu-Catalyzed Electrochemical CO2 Reduction

This study presents the impact of the side chains in 1-n-alkylimidazolium ionomers with varying side chain lengths (CnH2n+1 where n = 1, 4, 10, 16) on Cu-catalyzed electrochemical CO2 reduction reaction (CO2RR). Longer side chains suppress the H2 and CH4 formation, with the n-hexadecyl ionomer (n = 16) showing the greatest reduction in kinetics by up to 56.5% and 60.0%, respectively. On the other hand, C2H4 production demonstrates optimal Faradaic efficiency with the n-decyl ionomer (n = 10), a substantial increase of 59.9% compared to its methyl analog (n = 1). Through a combination of density functional theory calculations and material characterization, it is revealed that the engineering of the side chains effectively modulates the thermodynamic stability of key intermediates, thus influencing the selectivity of both CO2RR and hydrogen evolution reaction. Moreover, ionomer engineering enables industrially relevant partial current density of -209.5 mA cm-2 and a Faradaic efficiency of 52.4% for C2H4 production at 3.95 V, even with a moderately active Cu catalyst, outperforming previous benchmarks and allowing for further improvement through catalyst engineering. This study underscores the critical role of ionomers in CO2RR, providing insights into their optimal design for sustainable chemical synthesis.

Steering the Site Distance of Atomic Cu-Cu Pairs by First-Shell Halogen Coordination Boosts CO2-to-C2 Selectivity

Electrocatalytic reduction of CO2 into C2 products of high economic value provides a promising strategy to realize resourceful CO2 utilization. Rational design and construct dual sites to realize the CO protonation and C-C coupling to unravel their structure-performance correlation is of great significance in catalysing electrochemical CO2 reduction reactions. Herein, Cu-Cu dual sites with different site distance coordinated by halogen at the first-shell are constructed and shows a higher intramolecular electron redispersion and coordination symmetry configurations. The long-range Cu-Cu (Cu-I-Cu) dual sites show an enhanced Faraday efficiency of C2 products, up to 74.1 %, and excellent stability. In addition, the linear relationships that the long-range Cu-Cu dual sites are accelerated to C2H4 generation and short-range Cu-Cu (Cu-Cl-Cu) dual sites are beneficial for C2H5OH formation are disclosed. In situ electrochemical attenuated total reflection surface enhanced infrared absorption spectroscopy, in situ Raman and theoretical calculations manifest that long-range Cu-Cu dual sites can weaken reaction energy barriers of CO hydrogenation and C-C coupling, as well as accelerating deoxygenation of *CH2CHO. This study uncovers the exploitation of site-distance-dependent electrochemical properties to steer the CO2 reduction pathway, as well as a potential generic tactic to target C2 synthesis by constructing the desired Cu-Cu dual sites.

Selectively electrolyzing CO2 to ethylene by a Cu-Cu2O/rGO catalyst derived from copper hydroxide nanostrands/graphene oxide nanosheets

Electrolyzing CO2 into ethylene (C2H4) is a promising strategy for CO2 utilization and carbon neutrality since C2H4 is an important industrial feedstock. However, selectively converting CO2 into C2H4 via the CO2 electro-reduction reaction (CO2 ERR) is still a great challenge. Herein, Cu-Cu2O nanoparticles anchored on reduced graphene oxide nanosheets (Cu-Cu2O/rGO) were prepared from copper hydroxide nanostrands (CHNs) and graphene oxide (GO) nanosheets via in situ electrochemical reduction. Cu-Cu2O nanoparticles with diameter less than 10 nm were formed on the surface of rGO nanosheets. After assembling the Cu-Cu2O/rGO catalyst into a flow cell, it demonstrated high Faraday efficiencies (FEs) of 55.4%, 37.6%, and 6.7% for C2H4, C2H6, and H2, respectively, and a total 93% FE for C2 at -1.3 V vs. the standard hydrogen electrode (SHE). Moreover, its FE was 68.2% for C2H4, 10.2% for C2H6, and 20.5% for H2 at -1.4 (vs. SHE). Besides, no liquid carbon product was detected. This high selectivity is attributed to the synergistic effect arising from the small diameter of Cu-Cu2O NPs with the combination of Cu0-Cu+ and rGO nanosheets, which promotes the activation of CO2 molecules, facilitates C-C coupling, and enhances stability. This may provide a facile way for designing an efficient catalyst for selectively electrolyzing CO2 into valuable C2 chemicals.

Spectrometric monitoring of CO2 electrolysis on a molecularly modified copper surface

Since copper has been extensively studied due to its unique ability to reduce carbon dioxide to hydrocarbons and alcohols, it tends to yield a mixture of products. Among various efforts to improve the selectivity and efficiency of this catalysis, the introduction of organic molecules and polymers on the copper/electrolyte interface has proven to be an effective and promising way to improve surface activity, considering the variation and precise designability of organic structures. The role of surface molecular modifiers, however, is not as simple as that in homogeneous catalysts, and an understanding of a wide scale of interactions from the atomic scale to the whole electrode structure is required. This feature article classifies those different scale interactions caused by organic modifiers on copper catalysts, together with the experimental support by in situ vibrational spectroscopy which directly observes surface species and events. Based on these recent understandings, novel fabrication methods of organic structures on copper catalysts are also discussed.

Ionomer and Membrane Designs for Low-temperature CO2 and CO Electrolysis

Low-temperature electroreduction of CO2 and CO (CO(2)RR) into valuable chemicals and fuels offers a promising pathway to reduce greenhouse gas emissions and achieve carbon neutrality. Today's low-temperature CO(2)RR technology relies on the use of ionomers, polymers with ionized groups, primarily as catalyst layer (CL) additives. In the meantime, ionomers can assemble into ion-exchange membranes (IEMs), serving as important components of electrolyzers. According to the ion-exchange functions, ionomer additives are classified as cation-exchange ionomers (CEIs) and anion-exchange ionomers (AEIs); similarly, IEMs are divided into cation-exchange membranes (CEMs) and anion-exchange membranes (AEMs), as well as the multilayer polymer electrolytes (MPEs). Recent studies show that ionomer additives can regulate the catalytic microenvironment and thereby enhance performance towards desired products. This Review discusses the roles of ionomer additives and IEMs in CO2 and CO reduction reactions, highlighting the latest mechanistic insights and performance advances. It outlines challenges in designing ionomer additives and IEMs to improve product selectivity, energy efficiency (EE), and operational lifetime of CO(2)RR electrolyzers, while also providing perspectives on future research directions. The aim is to connect the current status of ionomer and membrane development with performance metrics analysis, offering insights for the advancement of commercially relevant low-temperature CO(2)RR electrolyzers.

Accelerating acidic CO2 electroreduction: strategies beyond catalysts

Carbon dioxide electrochemical reduction (CO2RR) into high-value-added chemicals offers an alternative pathway toward achieving carbon neutrality. However, in conventional neutral or alkaline electrolyte systems, a significant portion of CO2 is converted into (bi)carbonate due to the thermodynamically favorable acid-base neutralization reaction between CO2 and hydroxide ions. This results in the single-pass carbon efficiency (SPCE) being theoretically capped at 50%, presenting challenges for practical applications. Acidic CO2RR can completely circumvent the carbonate issue and theoretically achieve 100% SPCE, garnering substantial attention from researchers in recent years. Nevertheless, acidic CO2RR currently lags behind traditional neutral/alkaline systems in terms of product selectivity, stability, and energy efficiency, primarily because the abundance of H+ ions exacerbates the hydrogen evolution reaction (HER). Encouragingly, significant breakthroughs have been made to address these challenges, with numerous studies indicating that the regulation of the local catalytic environment may be more crucial than the catalyst itself. In this review, we will discuss the main challenges and latest strategies for acidic CO2RR, focusing on three key aspects beyond the catalyst: electrolyte regulation, local catalytic environment modification, and novel designs of gas diffusion electrodes (GDEs)/electrolyzers. We will also conclude the current advancement for acidic CO2RR and provide an outlook, with the hope that this technology will contribute to achieving carbon neutrality and advance towards practical application.

Confined CO in a sandwich structure promotes C-C coupling in electrocatalytic CO2 reduction

Microenvironment regulation near the catalyst surface plays a critical role in heterogeneous electrocatalytic reactions. The local concentration of reactants and intermediates significantly affects the reaction kinetics and product selectivity. Herein, we propose an innovative strategy of utilizing the spatial confinement effect in a sandwich-structured C/Cu/C assembly to regulate kinetic mass transport during the electrocatalytic CO2 reduction reaction. The sandwich C/Cu/C assembly catalyst was successfully prepared using a simple bidirectional freezing and freeze-drying method. The sandwich structure changes the free diffusion pathway of the CO intermediate within the sandwich interlayer and helps confine CO with locally increased CO concentration near the catalyst surface, which in turn promotes C-C coupling and thus improves the reaction activity and doubles the C2 product selectivity compared to its disordered mixture counterpart. This kinetics regulation in the sandwich structure may provide a new insight into the catalyst design and inspire the understanding of the structure-performance relationship in electrocatalysis.

Ampere-level CO2 electroreduction with single-pass conversion exceeding 85% in acid over silver penetration electrodes

Synthesis of valuable chemicals from CO2 electroreduction in acidic media is highly desirable to overcome carbonation. However, suppressing the hydrogen evolution reaction in such proton-rich environments remains a considerable challenge. The current study demonstrates the use of a hollow fiber silver penetration electrode with hierarchical micro/nanostructures to enable CO2 reduction to CO in strong acids via balanced coordination of CO2 and K+/H+ supplies. Correspondingly, a CO faradaic efficiency of 95% is achieved at a partial current density as high as 4.3 A/cm2 in a pH = 1 solution of H2SO4 and KCl, sustaining 200 h of continuous electrolysis at a current density of 2 A/cm2 with over 85% single-pass conversion of CO2. The experimental results and density functional theory calculations suggest that the controllable CO2 feeding induced by the hollow fiber penetration configuration primarily coordinate the CO2/H+ balance on Ag active sites in strong acids, favoring CO2 activation and key intermediate *COOH formation, resulting in enhanced CO formation.

Selective and stable CO2 electroreduction at high rates via control of local H2O/CO2 ratio

Controlling the concentrations of H2O and CO2 at the reaction interface is crucial for achieving efficient electrochemical CO2 reduction. However, precise control of these variables during catalysis remains challenging, and the underlying mechanisms are not fully understood. Herein, guided by a multi-physics model, we demonstrate that tuning the local H2O/CO2 concentrations is achievable by thin polymer coatings on the catalyst surface. Beyond the often-explored hydrophobicity, polymer properties of gas permeability and water-uptake ability are even more critical for this purpose. With these insights, we achieve CO2 reduction on copper with Faradaic efficiency exceeding 87% towards multi-carbon products at a high current density of -2 A cm-2. Encouraging cathodic energy efficiency (>50%) is also observed at this high current density due to the substantially reduced cathodic potential. Additionally, we demonstrate stable CO2 reduction for over 150 h at practically relevant current densities owning to the robust reaction interface. Moreover, this strategy has been extended to membrane electrode assemblies and other catalysts for CO2 reduction. Our findings underscore the significance of fine-tuning the local H2O/CO2 balance for future CO2 reduction applications.

Critical Role of Cu Nanoparticle-Loaded Cu(100) Surface Structures on Structured Copper-Based Catalysts in Boosting Ethanol Generation in CO2 Electroreduction

Presently, realizing high ethanol selectivity in CO2 electroreduction remains challenging due to difficult C-C coupling and fierce product competition. In this work, we report an innovative approach for improving the efficiency of Cu-based electrocatalysts in ethanol generation from electrocatalytic CO2 reduction using a crystal plane modification strategy. These novel Cu-based electrocatalysts were fabricated by electrochemically activating three-dimensional (3D) flower-like CuO micro/nanostructures grown in situ on copper foils and modifying with surfactants. It was demonstrated that the fabricated Cu-based electrocatalyst featured a predominantly exposed Cu(100) surface loaded with high-density Cu nanoparticles (NPs). The optimal Cu-based electrocatalyst displayed considerably improved CO2 electroreduction performance, with a Faraday efficiency of 37.9% for ethanol and a maximum Faraday efficiency of 68.0% for C2+ products at -1.4 V vs RHE in an H-cell, accompanied by a high current density of 69.9 mA·cm-2, much better than the particulate Cu-based electrocatalyst. It was unveiled that the Cu(100)-rich surface of nanoscale petals with abundant under-coordinated copper atoms from CuNPs was conducive to the formation and stabilization of key *CH3CHO and *OC2H5 intermediates, thereby promoting ethanol generation. This study highlighted the critical role of CuNP-loaded Cu(100) surface structures on structured Cu-based electrocatalysts in enhancing ethanol production for the CO2 electroreduction process.

Recent advances in dynamic reconstruction of electrocatalysts for carbon dioxide reduction

Electrocatalysts undergo structural evolution under operating electrochemical CO2 reduction reaction (CO2RR) conditions. This dynamic reconstruction correlates with variations in CO2RR activity, selectivity, and stability, posing challenges in catalyst design for electrochemical CO2RR. Despite increased research on the reconstruction behavior of CO2RR electrocatalysts, a comprehensive understanding of their dynamic structural evolution under reaction conditions is lacking. This review summarizes recent developments in the dynamic reconstruction of catalysts during the CO2RR process, covering fundamental principles, modulation strategies, and in situ/operando characterizations. It aims to enhance understanding of electrocatalyst dynamic reconstruction, offering guidelines for the rational design of CO2RR electrocatalysts.

Amine-Functionalized Metal-Free Nanocarbon to Boost Selective CO2 Electroreduction to CO in a Flow Cell

Highly efficient electrochemical CO2-to-CO conversion is a promising approach for achieving carbon neutrality. While nonmetallic carbon electrocatalysts have shown potential for CO2-to-CO utilization in H-type cells, achieving efficient conversion in flow cells at an industrial scale remains challenging. In this study, we present a cost-effective synthesis strategy for preparing ultrathin 2D carbon nanosheet catalysts through simple amine functionalization. The optimized catalyst, NCNs-2.5, demonstrates exceptional CO selectivity with a maximum Faradaic efficiency of 98% and achieves a high current density of 55 mA cm-2 in a flow cell. Furthermore, the catalyst exhibits excellent long-term stability, operating continuously for 50 h while maintaining a CO selectivity above 90%. The superior catalytic activity of NCNs-2.5 is attributed to the presence of amine-N active sites within the carbon lattice structure. This work establishes a foundation for the rational design of cost-effective nonmetallic carbon catalysts as sustainable alternatives to metals in energy conversion systems.

Rational Design of Local Reaction Environment for Electrocatalytic Conversion of CO2 into Multicarbon Products

The electrocatalytic conversion of CO2 into multi-carbon (C2+) products provides an attractive route for storing intermittent renewable electricity as fuels and feedstocks with high energy densities. Although substantial progress has been made in selective electrosynthesis of C2+ products via engineering the catalyst, rational design of the local reaction environment in the vicinity of catalyst surface also acts as an effective approach for further enhancing the performance. Here, we discuss recent advances and pertinent challenges in the modulation of local reaction environment, encompassing local pH, the choice of the species and concentrations of cations and anions as well as local reactant/intermediate concentrations, for achieving high C2+ selectivity. In addition, mechanistic understanding in the effects of the local reaction environment is also discussed. Particularly, the important progress extracted from in situ and operando spectroscopy techniques provides insights into how local reaction environment affects C-C coupling and key intermediates formation that lead to reaction pathways toward a desired C2+ product. The possible future direction in understanding and engineering the local reaction environment is also provided.

Noble-Metal-Free High-Entropy Alloy Nanoparticles for Efficient Solar-Driven Photocatalytic CO2 Reduction

Metal nanoparticle (NP) cocatalysts are widely investigated for their ability to enhance the performance of photocatalytic materials; however, their practical application is often limited by the inherent instability under light irradiation. This challenge has catalyzed interest in exploring high-entropy alloys (HEAs), which, with their increased entropy and lower Gibbs free energy, provide superior stability. In this study, 3.5 nm-sized noble-metal-free NPs composed of a FeCoNiCuMn HEA are successfully synthesized. With theoretic calculation and experiments, the electronic structure of HEA in augmenting the catalytic CO2 reduction has been uncovered, including the individual roles of each element and the collective synergistic effects. Then, their photocatalytic CO2 reduction capabilities are investigated when immobilized on TiO2. HEA NPs significantly enhance the CO2 photoreduction, achieving a 23-fold increase over pristine TiO2, with CO and CH4 production rates of 235.2 and 19.9 µmol g-1 h-1, respectively. Meanwhile, HEA NPs show excellent stability under simulated solar irradiation, as well high-energy X-ray irradiation. This research emphasizes the promising role of HEA NPs, composed of earth-abundant elements, in revolutionizing the field of photocatalysis.

Mo4+-Doped CuS Nanosheet-Assembled Hollow Spheres for CO2 Electroreduction to Ethanol in a Flow Cell

Electrocatalytic CO2 reduction reaction (CO2RR) to ethanol has been widely researched for potential commercial application. However, it still faces limited selectivity at a large current density. Herein, Mo4+-doped CuS nanosheet-assembled hollow spheres are constructed to address this issue. Mo4+ ion doping modifies the local electronic environments and diversifies the binding sites of CuS, which increases the coverage of linear *COL and produces bridge *COB for subsequent *COL-*COH coupling toward ethanol production. The optimal Mo9.0%-CuS can electrocatalyze CO2 to ethanol with a faradaic efficiency of 67.5% and a partial current density of 186.5 mA cm-2 at -0.6 V in a flow cell. This work clarifies that doping high valence transition metal ions into Cu-based sulfides can regulate the coverage and configuration of related intermediates for ethanol production during the CO2RR in a flow cell.

Switching CO2 Electroreduction toward Ethanol by Delocalization State-Tuned Bond Cleavage

The electrochemical CO2 reduction reaction by copper-based catalysts features a promising approach to generate value-added multicarbon (C2+) products. However, due to the unfavored formation of oxygenate intermediates on the catalyst surface, the selectivity of C2+ alcohols like ethanol remains unsatisfactory compared to that of ethylene. The bifurcation point (i.e., the CH2═CHO* intermediate adsorbed on Cu via a Cu-O-C linkage) is critical to the C2+ product selectivity, whereas the subsequent cleavage of the Cu-O or the O-C bond determines the ethanol or ethylene pathway. Inspired by the hard-soft acid-base theory, in this work, we demonstrate an electron delocalization tuning strategy of the Cu catalyst by a nitrene surface functionalization approach, which allows weakening and cleaving of the Cu-O bond of the adsorbed CH2═CHO*, as well as accelerating hydrogenation of the C═C bond along the ethanol pathway. As a result, the nitrene-functionalized Cu catalyst exhibited a much-enhanced ethanol Faradaic efficiency of 45% with a peak partial current density of 406 mA·cm-2, substantially exceeding that of unmodified Cu or amide-functionalized Cu. When assembled in a membrane electrode assembly electrolyzer, the catalyst presented a stable CO2-to-ethanol conversion for >300 h at an industrial current density of 400 mA·cm-2.

Pure-Water-Fed Forward-Bias Bipolar Membrane CO2 Electrolyzer

Coupling renewable electricity to reduce carbon dioxide (CO2) electrochemically into carbon feedstocks offers a promising pathway to produce chemical fuels sustainably. While there has been success in developing materials and theory for CO2 reduction, the widespread deployment of CO2 electrolyzers has been hindered by challenges in the reactor design and operational stability due to CO2 crossover and (bi)carbonate salt precipitation. Herein, we design asymmetrical bipolar membranes assembled into a zero-gap CO2 electrolyzer fed with pure water, solving both challenges. By investigating and optimizing the anion-exchange-layer thickness, cathode differential pressure, and cell temperature, the forward-bias bipolar membrane CO2 electrolyzer achieves a CO faradic efficiency over 80% with a partial current density over 200 mA cm-2 at less than 3.0 V with negligible CO2 crossover. In addition, this electrolyzer achieves 0.61 and 2.1 mV h-1 decay rates at 150 and 300 mA cm-2 for 200 and 100 h, respectively. Postmortem analysis indicates that the deterioration of catalyst/polymer-electrolyte interfaces resulted from catalyst structural change, and ionomer degradation at reductive potential shows the decay mechanism. All these results point to the future research direction and show a promising pathway to deploy CO2 electrolyzers at scale for industrial applications.

Revolutionizing CO2 Electrolysis: Fluent Gas Transportation within Hydrophobic Porous Cu2O

The success of electrochemical CO2 reduction at high current densities hinges on precise interfacial transportation and the local concentration of gaseous CO2. However, the creation of efficient CO2 transportation channels remains an unexplored frontier. In this study, we design and synthesize hydrophobic porous Cu2O spheres with varying pore sizes to unveil the nanoporous channel's impact on gas transfer and triple-phase interfaces. The hydrophobic channels not only facilitate rapid CO2 transportation but also trap compressed CO2 bubbles to form abundant and stable triple-phase interfaces, which are crucial for high-current-density electrocatalysis. In CO2 electrolysis, in situ spectroscopy and density functional theory results reveal that atomic edges of concave surfaces promote C-C coupling via an energetically favorable OC-COH pathway, leading to overwhelming CO2-to-C2+ conversion. Leveraging optimal gas transportation and active site exposure, the hydrophobic porous Cu2O with a 240 nm pore size (P-Cu2O-240) stands out among all the samples and exhibits the best CO2-to-C2+ productivity with remarkable Faradaic efficiency and formation rate up to 75.3 ± 3.1% and 2518.2 ± 8.1 μmol h-1 cm-2, respectively. This study introduces a novel paradigm for efficient electrocatalysts that concurrently addresses active site design and gas-transfer challenges.

CO2 Electrolyzers

CO2 electrolyzers have progressed rapidly in energy efficiency and catalyst selectivity toward valuable chemical feedstocks and fuels, such as syngas, ethylene, ethanol, and methane. However, each component within these complex systems influences the overall performance, and the further advances needed to realize commercialization will require an approach that considers the whole process, with the electrochemical cell at the center. Beyond the cell boundaries, the electrolyzer must integrate with upstream CO2 feeds and downstream separation processes in a way that minimizes overall product energy intensity and presents viable use cases. Here we begin by describing upstream CO2 sources, their energy intensities, and impurities. We then focus on the cell, the most common CO2 electrolyzer system architectures, and each component within these systems. We evaluate the energy savings and the feasibility of alternative approaches including integration with CO2 capture, direct conversion of flue gas and two-step conversion via carbon monoxide. We evaluate pathways that minimize downstream separations and produce concentrated streams compatible with existing sectors. Applying this comprehensive upstream-to-downstream approach, we highlight the most promising routes, and outlook, for electrochemical CO2 reduction.

Backbone Engineering of Polymeric Catalysts for High-Performance CO2 Reduction in Bipolar Membrane Zero-Gap Electrolyzer

Bipolar membranes (BPMs) have emerged as a promising solution for mitigating CO2 losses, salt precipitation and high maintenance costs associated with the commonly used anion-exchange membrane electrode assembly for CO2 reduction reaction (CO2RR). However, the industrial implementation of BPM-based zero-gap electrolyzer is hampered by the poor CO2RR performance, largely attributed to the local acidic environment. Here, we report a backbone engineering strategy to improve the CO2RR performance of molecular catalysts in BPM-based zero-gap electrolyzers by covalently grafting cobalt tetraaminophthalocyanine onto a positively charged polyfluorene backbone (PF-CoTAPc). PF-CoTAPc shows a high acid tolerance in BPM electrode assembly (BPMEA), achieving a high FE of 82.6 % for CO at 100 mA/cm2 and a high CO2 utilization efficiency of 87.8 %. Notably, the CO2RR selectivity, carbon utilization efficiency and long-term stability of PF-CoTAPc in BPMEA outperform reported BPM systems. We attribute the enhancement to the stable cationic shield in the double layer and suppression of proton migration, ultimately inhibiting the undesired hydrogen evolution and improving the CO2RR selectivity. Techno-economic analysis shows the least energy consumption (957 kJ/mol) for the PF-CoTAPc catalyst in BPMEA. Our findings provide a viable strategy for designing efficient CO2RR catalysts in acidic environments.

Ampere-Level Current Density CO2 Reduction with High C2+ Selectivity on La(OH)3-Modified Cu Catalysts

The carbon dioxide reduction reaction (CO2RR) driven by electricity can transform CO2 into high-value multi-carbon (C2+) products. Copper (Cu)-based catalysts are efficient but suffer from low C2+ selectivity at high current densities. Here La(OH)3 in Cu catalyst is introduced to modify its electronic structure towards efficient CO2RR to C2+ products at ampere-level current densities. The La(OH)3/Cu catalyst has a remarkable C2+ Faradaic efficiency (FEC2+) of 71.2% which is 2.2 times that of the pure Cu catalyst at a current density of 1,000 mA cm-2 and keeps stable for 8 h. In situ spectroscopy and density functional theory calculations both show that La(OH)3 modifies the electronic structure of Cu. This modification favors *CO adsorption, subsequent hydrogenation, *CO─*COH coupling, and consequently increases C2+ selectivity. This work provides a guidance on facilitating C2+ product formation, and suppressing hydrogen evolution by La(OH)3 modification, enabling efficient CO2RR at ampere-level current densities.

Enhancing Cu-ligand interaction for efficient CO2 reduction towards multi-carbon products

Electrochemical CO2 reduction (CO2R) to valuable products provides a promising strategy to enable CO2 utilization sustainably. Here, we report the strategy of using Cu-DAT (3,5-diamino-1,2,4-triazole) as a catalyst precursor for efficient CO2 reduction, demonstrating over 80% selectivity towards multicarbon products at 400 mA cm-2, with intrinsic activity over 19 times higher than that of Cu nanoparticles. The catalyst's active phase is determined to be metallic copper wrapped with the DAT ligand. We attribute this enhanced CO2R performance to the accelerated steps of *CO adsorption and C-C coupling induced by the closely cooperated DAT ligand.

Investigating Electrode-Ionomer Interface Phenomena for Electrochemical Energy Applications

The endeavor to develop high-performance electrochemical energy applications has underscored the growing importance of comprehending the intricate dynamics within an electrode's structure and their influence on overall performance. This review investigates the complexities of electrode-ionomer interactions, which play a critical role in optimizing electrochemical reactions. Our examination encompasses both microscopic and meso/macro scale functions of ionomers at the electrode-ionomer interface, providing a thorough analysis of how these interactions can either enhance or impede surface reactions. Furthermore, this review explores the broader-scale implications of ionomer distribution within porous electrodes, taking into account factors like ionomer types, electrode ink formulation, and carbon support interactions. We also present and evaluate state-of-the-art techniques for investigating ionomer distribution, including electrochemical methods, imaging, modeling, and analytical techniques. Finally, the performance implications of these phenomena are discussed in the context of energy conversion devices. Through this comprehensive exploration of intricate interactions, this review contributes to the ongoing advancements in the field of energy research, ultimately facilitating the design and development of more efficient and sustainable energy devices.

Dynamically Reconstructed Triple-Copper-Vacancy Associates Confined in Cu Nanowires Enabling High-Rate and Selective CO2 Electroreduction to C2+ Products

Electrochemically reconstructed Cu-based catalysts always exhibit enhanced CO2  electroreduction performance; however, it still remains ambiguous whether the reconstructed Cu vacancies have a substantial impact on CO2 -to-C2+ reactivity. Herein, Cu vacancies are first constructed through electrochemical reduction of Cu-based nanowires, in which high-angle annular dark-field scanning transmission electron microscopy image manifests the formation of triple-copper-vacancy associates with different concentrations, confirmed by positron annihilation lifetime spectroscopy. In situ attenuated total reflection-surface enhanced infrared absorption spectroscopy discloses the triple-copper-vacancy associates favor *CO adsorption and fast *CO dimerization. Moreover, density-functional-theory calculations unravel the triple-copper-vacancy associates endow the nearby Cu sites with enriched and disparate local charge density, which enhances the *CO adsorption and reduces the CO-CO coupling barrier, affirmed by the decreased *CO dimerization energy barrier by 0.4 eV. As a result, the triple-copper-vacancy associates confined in Cu nanowires achieve a high Faradaic efficiency of over 80% for C2+ products in a wide current density range of 400-800 mA cm-2 , outperforming most reported Cu-based electrocatalysts.

Vitamin C-induced CO2 capture enables high-rate ethylene production in CO2 electroreduction

High-rate production of multicarbon chemicals via the electrochemical CO2 reduction can be achieved by efficient CO2 mass transport. A key challenge for C-C coupling in high-current-density CO2 reduction is how to promote *CO formation and dimerization. Here, we report molecularly enhanced CO2-to-*CO conversion and *CO dimerization for high-rate ethylene production. Nanoconfinement of ascorbic acid by graphene quantum dots enables immobilization and redox reversibility of ascorbic acid in heterogeneous electrocatalysts. Cu nanowire with ascorbic acid nanoconfined by graphene quantum dots (cAA-CuNW) demonstrates high-rate ethylene production with a Faradaic efficiency of 60.7% and a partial current density of 539 mA/cm2, a 2.9-fold improvement over that of pristine CuNW. Furthermore, under low CO2 ratio of 33%, cAA-CuNW still exhibits efficient ethylene production with a Faradaic efficiency of 41.8%. We find that cAA-CuNW increases *CO coverage and optimizes the *CO binding mode ensemble between atop and bridge for efficient C-C coupling. A mechanistic study reveals that ascorbic acid can facilitate *CO formation and dimerization by favorable electron and proton transfer with strong hydrogen bonding.

New Insight into the Electronic Effect for Cu Porphyrin Catalysts in Electrocatalytic of CO2 into CH4

Perturbation of the copper (Cu) active site by electron manipulation is a crucial factor in determining the activity and selectivity of electrochemical carbon dioxide (CO2 ) reduction reaction (e-CO2 RR) in Cu-based molecular catalysts. However, much ambiguity is present concerning their electronic structure-function relationships. Here, three molecular Cu-based porphyrin catalysts with different electron densities at the Cu active site, Cu tetrakis(4-methoxyphenyl)porphyrin (Cu─T(OMe)PP), Cu tetraphenylporphyrin (Cu─THPP), and Cu tetrakis(4-bromophenyl)porphyrin (Cu─TBrPP), are prepared. Although all three catalysts exhibit e-CO2 RR activity and the same reaction pathway, their performance is significantly affected by the electronic structure of the Cu site. Theoretical and experimental investigations verify that the conjugated effect of ─OCH3 and ─Br groups lowers the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbitals (LUMO) gap of Cu─T(OMe)PP and Cu─TBrPP, promoting faster electron transfer between Cu and CO2 , thereby improving their e-CO2 RR activity. Moreover, the high inductive effect of ─Br group reduces the electron density of Cu active site of Cu─TBrPP, facilitating the hydrolysis of the bound H2 O and thus creating a preferable local microenvironment, further enhancing the catalytic performance. This work provides new insights into the relationships between the substituent group characteristics with e-CO2 RR performance and is highly instructive for the design of efficient Cu-based e-CO2 RR electrocatalysts.

Efficient and stable acidic CO2 electrolysis to formic acid by a reservoir structure design

Electrochemical synthesis of valuable chemicals and feedstocks through carbon dioxide (CO2) reduction in acidic electrolytes can surmount the considerable CO2 loss in alkaline and neutral conditions. However, achieving high productivity, while operating steadily in acidic electrolytes, remains a big challenge owing to the severe competing hydrogen evolution reaction. Here, we show that vertically grown bismuth nanosheets on a gas-diffusion layer can create numerous cavities as electrolyte reservoirs, which confine in situ-generated hydroxide and potassium ions and limit inward proton diffusion, producing locally alkaline environments. Based on this design, we achieve formic acid Faradaic efficiency of 96.3% and partial current density of 471 mA cm-2 at pH 2. When operated in a slim continuous-flow electrolyzer, the system exhibits a full-cell formic acid energy efficiency of 40% and a single pass carbon efficiency of 79% and performs steadily over 50 h. We further demonstrate the production of pure formic acid aqueous solution with a concentration of 4.2 weight %.

Dual-Role of Polyelectrolyte-Tethered Benzimidazolium Cation in Promoting CO2 /Pure Water Co-Electrolysis to Ethylene

Electrochemical CO2 reduction reaction (CO2 RR), as a promising route to realize negative carbon emissions, is known to be strongly affected by electrolyte cations (i.e., cation effect). In contrast to the widely-studied alkali cations in liquid electrolytes, the effect of organic cations grafted on alkaline polyelectrolytes (APE) remains unexplored, although APE has already become an essential component of CO2 electrolyzers. Herein, by studying the organic cation effect on CO2 RR, we find that benzimidazolium cation (Beim+ ) significantly outperforms other commonly-used nitrogenous cations (R4 N+ ) in promoting C2+ (mainly C2 H4 ) production over copper electrode. Cyclic voltammetry and in situ spectroscopy studies reveal that the Beim+ can synergistically boost the CO2 to *CO conversion and reduce the proton supply at the electrocatalytic interface, thus facilitating the *CO dimerization toward C2+ formation. By utilizing the homemade APE ionomer, we further realize efficient C2 H4 production at an industrial-scale current density of 331 mA cm-2 from CO2 /pure water co-electrolysis, thanks to the dual-role of Beim+ in synergistic catalysis and ionic conduction. This study provides a new avenue to boost CO2 RR through the structural design of polyelectrolytes.

Gaining Deep Understanding of Electrochemical CO2 RR with In Situ/Operando Techniques

Electrocatalysis for CO2 conversion has been extensively studied to mitigate the energy shortage and environmental issues, which are gaining ever-increasing attention. However, the complicated CO2 reduction process and the dynamic evolution occurring on electrocatalyst surface make it hard to understand the catalytic mechanism. The development of advanced in situ/operando techniques intelligently coupled with electrochemical cells sheds light on the related study via capturing surface atomic rearrangement, tracing chemical state change of catalysts, monitoring the behavior of intermediates and products, and depicting microenvironment near the electrode surface. In this review, fundamentals of the state-of-the-art in situ/operando techniques are clarified first. Case studies on the in situ/operando techniques performed to probe the CO2 reduction reaction processes are then discussed in detail. Finally, conclusions and outlook on this field are presented.

Electrochemical carbon-carbon coupling with enhanced activity and racemate stereoselectivity by microenvironment regulation

Enzymes are characteristic of catalytic efficiency and specificity by maneuvering multiple components in concert at a confined nanoscale space. However, achieving such a configuration in artificial catalysts remains challenging. Herein, we report a microenvironment regulation strategy by modifying carbon paper with hexadecyltrimethylammonium cations, delivering electrochemical carbon-carbon coupling of benzaldehyde with enhanced activity and racemate stereoselectivity. The modified electrode-electrolyte interface creates an optimal microenvironment for electrocatalysis-it engenders dipolar interaction with the reaction intermediate, giving a 2.2-fold higher reaction rate (from 0.13 to 0.28 mmol h-1 cm-2); Moreover, it repels interfacial water and modulates the conformational specificity of reaction intermediate by facilitating intermolecular hydrogen bonding, affording 2.5-fold higher diastereomeric ratio of racemate to mesomer (from 0.73 to 1.82). We expect that the microenvironment regulation strategy will lead to the advanced design of electrode-electrolyte interface for enhanced activity and (stereo)selectivity that mimics enzymes.

Alkaline Ionic Liquid Microphase Promotes Deep Reduction of CO2 on Copper

Electrochemical reduction of CO2 to multicarbon (C2+) products using renewable energy sources is an important route to storing sustainable energy and achieving carbon neutrality. It remains a challenge to achieve high C2+ product faraday efficiency (FE) at ampere-level current densities. Herein, we propose the immobilization of an alkaline ionic liquid on copper for promoting the deep reduction of CO2. By this strategy, a C2+ FE of 81.4% can be achieved under a current density of 0.9 A·cm-2 with a half-cell energy conversion efficiency of 47.4% at -0.76 V vs reversible hydrogen electrode (RHE). Particularly, when the current density is as high as 1.8 A·cm-2, the C2+ FE reaches 71.6% at an applied potential of -1.31 V vs RHE. Mechanistic studies demonstrate that the alkaline ionic liquid plays multiple roles of improving the accumulation of CO2 molecules on the copper surface, promoting the activation of the adsorbed CO2, reducing the energy barrier of CO dimerization, stabilizing intermediates, and facilitating the C2+ product formation.