Hierarchical Copper with Inherent Hydrophobicity Mitigates Electrode Flooding for High-Rate CO2 Electroreduction to Multicarbon Products

Boosting selective CO2 reduction via strong spin-spin coupling on dual-atom spin-catalysts

Achieving high selectivity in electrochemical conversion of carbon dioxide (CO2) into valuable products remains a significant challenge. This study investigates the influence of spin states on dual-atom catalysts within two-dimensional metal-organic frameworks (2D-MOFs) and zero-dimensional molecular metal complexes (0D-MMCs), emphasizing their role in the selective electrocatalytic reduction of CO2. Utilizing first-principles calculations, we systematically evaluate dual-atom spin-catalysts (DASCs) TM2S4(NH)2(C6H4)2 0D-MMC and TM2S4(NH)2C4 2D-MOF for CO2 reduction reactions (CO2RR) across various spin states: antiferromagnetic (AFM), ferromagnetic (FM), and non-magnetic (NM). Our analysis confirms that, beyond successfully designing and screening highly active catalysts, the selectivity for various C1 products in CO2 reduction can be readily adjusted by DASCs via spin-spin coupling. Specifically, Mn2 and Fe2 2D-MOF DASCs with an AFM ground state are more inclined to produce formic acid, while their FM counterparts favor the formation of methane, surpassing formic acid among others. Additionally, we demonstrate that 0D-MMCs, as molecular units of 2D-MOFs, achieve comparable catalytic performance. Combining theoretical insights with machine learning highlights the crucial role of electronic and geometric descriptors in the catalytic performance. Our work establishes the correlation between spin-spin coupling and highly selective CO2 reduction in DASCs, offering an effective strategy for designing tunable and efficient electrocatalysts.

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.

In Situ Observation of Post-CO Intermediates to Decode C─C Coupling Pathways in CO2 Electroreduction

Electrocatalytic carbon dioxide (CO2) reduction reaction (CO2RR) has emerged as a promising strategy for sustainable energy conversion and carbon utilization. Despite intensive research efforts, the understanding of intermediates and pathways leading from CO2RR to multicarbon (C2+) chemicals remains incomplete. The challenge is to gain insight into the activation of adsorbed CO and the subsequent pathways. Here, we design a specially tailored Cu nanowire array facing a hydrophobic interface as an electrode to highly enhance Raman signals in the in situ environment, allowing sensitive observation of the sequential change of various elusive intermediates during CO2RR, such as CO, CH2, CO coexisting with CH2, CH2CO, and CH3. Density functional theory calculations reveal that the C─C coupling during CO2RR originates from an asymmetric coupling between CH2 and CO to form CH2CO, identified as the rate-determining step in the formation of C2+ products. These findings deepen the understanding of the C─C coupling processes, which are crucial for advancing catalyst development in electrochemical CO2 upgrading.

Small Interparticle Spacing in Catalyst Layers Forms an Expansive Triple-Phase Interface for Boosting the Current Density of CO2-to-C2+ Conversion

Achieving both high current density and high selectivity for high-value products is crucial for the widespread implementation of CO2 electrolysis. Toward high-current-density electrolysis, it is crucial to design a triple-phase interface, where the catalyst, electrolyte, and gaseous substrate intersect, serving as the active reaction site for CO2 electrolysis. In this study, aims to establish design principles for the triple-phase interface composed of copper nanoparticles (CuNPs) to achieve ultra-high-current-density electrolysis of gaseous CO2 into multicarbon (C2+) products. The C2+ formation activity of electrodes carrying various CuNPs is systematically evaluated under high-current-density (>1 A cm-2) electrolysis conditions. By analyzing the correlations between the electrochemical performances and the physicochemical properties of the catalysts and electrodes, it is identified that the average size of interparticle spacing in the catalyst layer is correlated with the maximum partial current density for C2+ production (jC2+). Smaller interparticle spacings are found to enhance jC2+ by suppressing the excessive electrolyte penetration into the catalyst layer and forming an expansive triple-phase interface. Based on these insights, the optimized electrode, with an average interparticle spacing of 59.4 nm, exhibited a record jC2+ of 2.00 A cm-2 with a faradaic efficiency of 80.1%.

Microenvironment Tailoring for Electrocatalytic CO2 Reduction: Effects of Interfacial Structure on Controlling Activity and Selectivity

The performance of the electrocatalytic CO2 reduction reaction (CO2RR) is highly dependent on the microenvironment around the cathode. Despite efforts to optimize the microenvironment by modifying nanostructured catalysts or microporous gas diffusion electrodes, their inherent disorder presents a significant challenge to understanding how interfacial structure arrangement within the electrode governs the microenvironment for CO2RR. This knowledge gap limits fundamental understanding of CO2RR while also hindering efforts to enhance CO2RR selectivity and activity. In this work, we investigate this knowledge gap using a tunable system featuring superhydrophobic hierarchical Cu nanowire arrays with microgrooves (NAMs). Adjusting the NAM structure tunes multiple synergistic effects in the microenvironment, which include stabilization of the microwetting state, confinement of CO*, improvement to local CO2 concentration, and modulation of the local pH. Notably, using mass transport modeling, we quantify the role of the gas-liquid-solid interface in boosting local CO2 concentrations within several microns of the interface itself. Leveraging these effects, we elucidate how CO* and H* competitively occupy active sites, influencing reaction pathways toward multicarbon products based on tuning the microenvironment. Consequently, we provide new insights into why the optimized configuration significantly increased CO2RR activity by 690% (as normalized by electrochemical active surface area), C2+ product selectivity by 72%, and Faradaic efficiency by 36%, compared to CO2RR with hydrophobic Cu foil. Based on these insights, our findings unlock new opportunities to engineer the CO2RR microenvironment through the rational organization of hierarchical interface materials in gas diffusion electrodes toward improved CO2RR selectivity and activity.

Acidic CO2 Electrolysis With Near-Ideal Selectivity and Carbon Efficiency Enabled by Overcoming Its Inherent Trade-Off

Carbon dioxide electroreduction (CO2R) in acid tends to be a promising route to avoid CO2 loss in alkaline and neutral electrolytes; however, high alkali cation concentrations (typically ≥3 M) are required to activate CO2 and suppress water electroreduction, causing carbonate formation and thus unsatisfied single-pass carbon efficiency (SPCE). Based on theoretical and experimental analyses, we show that an inherent trade-off exists: increasing cation concentrations improves Faradaic efficiency (FE) toward CO2R products but comes at the expense of reduced SPCE. We demonstrate a polyimide-modification strategy to overcome this trade-off by taking advantage of the amino groups that can effectively capture protons, creating a local alkaline microenvironment surrounding the electrode surface. In a proof-of-concept experiment, SnO2 nanoparticles were modified with polyimide and acted as a CO2R catalyst, which achieved, simultaneously, near-ideal SPCE of 95.7% and FE of 96% (toward HCOOH) at pH 1.36 with dilute potassium ions down to even 0.1 M. We expect that these findings will accelerate the development of carbon- and electron-efficient acidic CO2 electrolysis.

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.

Polymer-Halogen Pockets Steering *CO Adsorption Configurations for Highly Selective CO2 Electroreduction

The selective CO2 electroreduction (CO2R) toward specific C2 products represents a critical challenge for practical applicability, requiring precise control over *CO intermediates. Herein, a "polymer-halogen" pocketed Cu catalyst is proposed, wherein the adjustable concentration of Iodide ion (I-) within the pocket enables continuous modulation of *CO adsorption configurations on the Cu, thereby enabling tailored CO2R toward ethylene or ethanol production. A perfluorosulfonic acid (PFSA)-modified CuI catalyst is constructed, where I- is in situ leaching from CuI and subsequently confined by PFSA as an anion shielding layer to form polymer-halogen pockets. By tuning the thickness of PFSA shell, the amount of I- in the pocket can be controlled. The surface-enhanced in situ Raman spectroscopy demonstrates that the coverage of *CO intermediates on Cu surface increases and tends to adsorb at low coordination Cu sites in catalyst granule for dimerization reaction as the I- concentration in the pocket increases. Furthermore, the coordination environment exhibits distinct product selectivity. *CO at medium-coordinated sites favor ethanol production, while those at low-coordinated sites are conducive to ethylene formation. This strategy enables wide modulation of ethylene-to-ethanol ratios from 0.65 to 3.96, achieving peak Faradaic efficiencies (FE) of 60.3 ± 2.1% for ethylene and 48.3 ± 1.3% for ethanol.

Tuning catalyst-support interactions enable steering of electrochemical CO2 reduction pathways

Tuning of catalyst-support interactions potentially offers a powerful means to control activity. However, rational design of the catalyst support is challenged by a lack of clear property-activity relationships. Here, we uncover how the electronegativity of a support influences reaction pathways in electrochemical CO2 reduction. This was achieved by creating a model system consisting of Cu nanoparticles hosted on a series of carbon supports, each with a different heteroatom dopant of varying electronegativity. Notably, we discovered that dopants with high electronegativity reduce the electron density on Cu and induce a selectivity shift toward multicarbon (C2+) products. With this design principle, we built a composite Cu and F-doped carbon catalyst that achieves a C2+ Faradaic efficiency of 82.5% at 400 mA cm-2, with stable performance for 44 hours. Using simulated flue gas, the catalyst attains a C2+ FE of 27.3%, which is a factor of 5.3 times higher than a reference Cu catalyst.

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.

In situ Raman spectroscopic studies of CO2 reduction reactions: from catalyst surface structures to reaction mechanisms

The electrochemical CO2 reduction reaction (eCO2RR) has gained widespread attention as an important technology for carbon cycling and sustainable chemistry. In situ Raman spectroscopy, due to its molecular structure, sensitive advantage and real-time monitoring capability, has become an effective tool for studying the reaction mechanisms and structure-performance relationships in eCO2RR. This article reviews recent advancements in the application of in situ Raman spectroscopy in eCO2RR research, focusing on its critical role in monitoring reaction intermediates, analyzing catalyst surface states, and optimizing catalyst design. Through systematic studies of different catalysts and reaction conditions, in situ Raman spectroscopy has revealed the formation and transformation pathways of various intermediates, deeply exploring their relationship with the active sites of the catalysts. Furthermore, the review discusses the integration of in situ Raman spectroscopy with other characterization techniques to achieve a more comprehensive understanding of the reaction mechanisms. Finally, we summarize the current challenges and opportunities in this research area and look ahead to the future applications of in situ Raman spectroscopy in the field of eCO2RR.

Electrocatalytic biomass upgrading coupled with hydrogen evolution and CO2 reduction

Clean energy production and CO2 utilization have attracted increasing interest. Electrocatalysis represents an effective way to produce green hydrogen from water and reduce CO2 to valuable compounds. However, for either the hydrogen evolution reaction (HER) or the CO2 reduction reaction (CO2RR), the reaction efficiency is significantly limited by the slow kinetics of the oxygen evolution reaction (OER) at the anode, which consumes most of the input energy. Therefore, great efforts have been made to replace the OER with organic oxidation reactions at the anode to decrease the reaction energy barrier. Biomass has an advantage of broad source, and when it is employed as an OER alternative in the anode oxidation reactions, not only can the reduction reaction efficiency at the cathode including the HER and CO2RR be enhanced but high-value chemicals can also be obtained, representing an attractive OER alternative. This review comprehensively summarizes the recent achievements in electrocatalytic biomass upgrading coupled with the HER and CO2RR, cataloged based on the type of biomass. The design of electrocatalysts for such coupled reaction systems is discussed. Finally, the challenges and perspectives in the field of this energy-saving and value-added coupling system are provided to inspire more efforts in pushing forward the development of this field.

Electrochemical epoxidation enhanced by C2H4 activation and hydroxyl generation at the Ag/SnO2 interface

Direct electrochemical ethylene (C2H4) epoxidation with water (H2O) represents a promising approach for the production of value-added ethylene oxide (EO) in a sustainable way. However, the activity remains limited due to the sluggish activation of C2H4 and the stiff formation of *OH intermediate. This paper describes the design of a Ag/SnO2 electrocatalyst to achieve efficient electrochemical C2H4 epoxidation with a high faradaic efficiency of 39.4% for EO and a high selectivity of 91.5% at 25 mA/cm2 in a membrane electrode assembly. Results of in situ attenuated total reflection infrared spectra characterizations and computational calculations reveal that the Ag/SnO2 interface promotes C2H4 adsorption and activation to obtain *C2H4. Moreover, electrophilic *OH is generated on the catalyst surface through H2O dissociation, which further reacts with *C2H4 to facilitate the formation of *C2H4OH, contributing to the enhanced electrochemical epoxidation activity. This work would provide general guidance for designing catalysts for electrochemical olefin epoxidation through interface engineering.

Additives-Modified Electrodeposition for Synthesis of Hydrophobic Cu/Cu2O with Ag Single Atoms to Drive CO2 Electroreduction

Copper-based electrocatalysts are recognized as crucial catalysts for CO2 electroreduction into multi-carbon products. However, achieving copper-based electrocatalysts with adjustable valences via one-step facile synthesis remains a challenge. In this study, Cu/Cu2O heterostructure is constructed by adjusting the anion species of the Cu ions-containing electrolyte during electrodeposition synthesis. Then, Cu/Cu2O with tuned nanoarchitectures ranging from dendrites to polyhedrons is achieved by introducing transition metal ions as additives, leading to an adjustable interfacial microenvironment for CO2/H2O adsorption on the Cu/Cu2O electrodes. Additionally, the polyhedral Cu/Cu2O catalysts are used as templates for depositing Ag single atoms (AgSA), which are known as synergistic active sites for promoting *CO to *COH toward C2+ products. The prepared AgSA-Cu/Cu2O catalyst is evaluated in a flow cell and exhibited a FEC2+ of 90.2% and a partial current density (jc2+) of 426.6 mA cm-2 for CO2 electroreduction. As revealed by in situ Raman spectra and density functional theory calculations, the introduction of Ag single atoms slows down the reduction of Cu+ during CO2 electroreduction, especially at a high current density. This work provides a promising paradigm for diverse control of the compositions and hydrophobicity of Cu-based catalysts for selective CO2 electroreduction to C2+ products.

Macro- and Nano-Porous Ag Electrodes Enable Selective and Stable Aqueous CO2 Reduction

Electrochemical carbon dioxide (CO2) reduction from aqueous solutions offers a promising strategy to overcome flooding and salt precipitation in gas diffusion electrodes used in gas-phase CO2 electrolysis. However, liquid-phase CO2 electrolysis often exhibits low CO2 reduction rates because of limited CO2 availability. Here, a macroporous Ag mesh is employed and activated to achieve selective CO2 conversion to CO with high rates from an aqueous bicarbonate solution. It is found that activation of Ag surface using oxidation/reduction cycles produces nanoporous surfaces that favor CO2-to-CO conversion. Notably, it is found that a combination of dissolved CO2 in bicarbonate solution with CO2 generated in situ from bicarbonate ions enables increased CO2 availability and a CO2-to-CO conversion rate over 100 mA cm-2. By optimizing the oxidation/reduction cycles to fine-tune the structure of Ag surface, CO2-to-CO conversion is reported from a bicarbonate solution with CO Faradaic efficiency of over 85% at current density of 100 mA cm-2, high concentration of 24.7% at outlet gas stream and stability of over 100 h with maintaining CO FE over 85% during whole reaction time.

Overcoming Gas Mass Transfer Limitations Using Gas-Conducting Electrodes for Efficient Nitrogen Reduction

Electrocatalytic nitrogen reduction reaction (NRR) is a very attractive strategy for ammonia synthesis due to its energy savings and sustainability. However, the ammonia yield and Faraday efficiency of electrocatalytic nitrogen reduction have been challenges due to low nitrogen solubility and competitive hydrogen evolution reaction (HER) in electrolyte solution. Herein, inspired by the asymmetric wetting behavior, i.e., superhydrophobicity/hydrophilicity, of floating lotus leaves, we demonstrated a gas-conduction electrode with asymmetric gas wetting behavior on the opposite surface, i.e., Janus-Ni/MoO2@NF, for efficient nitrogen reduction. It can provide an abundant three-phase interface (TPI) at interfaces of Janus-Ni/MoO2@NF in electrolyte solution to enhance the contact among N2, electrolyte, and electrode. Ascribed to this advantage, the hydrophobic side of the Janus electrode not only can repel water molecules to suppress the HER process but also can increase the concentration of N2 on the interface microenvironment. Consequently, the well-designed gas-conducting electrode breaks gas mass transfer limitation. Furthermore, Janus-Ni/MoO2@NF delivers a record-high NH3 yield rate of 5.865 μg·h-1·cm-2 and a Faradaic efficiency of 36.14% at an extremely low potential of 0 V vs RHE in 0.1 M Na2SO4 under ambient conditions, which are 22 and 18 times higher than those of the conventional electrode, respectively. Therefore, the gas-conducting electrodes can dramatically improve the activity and selectivity in electrocatalytic NRR. Additionally, the unique interface design provides inspiration for other sustainable electrochemical reactions involving gas electrocatalytic correlation.

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.

Highly Selective CO2 Electroreduction to Multi-Carbon Alcohols via Amine Modified Copper Nanoparticles at Acidic Conditions

Electroreduction of CO2 into multi-carbon (C2+) products (e.g. C2+ alcohols) offers a promising way for CO2 utilization. Use of strong alkaline electrolytes is favorable to producing C2+ products. However, CO2 can react with hydroxide to form carbonate/bicarbonate, which results in low carbon utilization efficiency and poor stability. Using acidic electrolyte is an efficient way to solve the problems, but it is a challenge to achieve high selectivity of C2+ products. Here we report that the amine modified copper nanoparticles exhibit high selectivity of C2+ products and carbon utilization at acidic condition. The Faradaic efficiency (FE) of C2+ products reach up to 81.8 % at acidic media (pH=2) with a total current density of 410 mA cm-2 over n-butylamine modified Cu. Especially the FE of C2+ alcohols is 52.6 %, which is higher than those reported for CO2 electroreduction at acidic condition. In addition, the single-pass carbon efficiency towards C2+ production reach up to 60 %. Detailed studies demonstrate that the amine molecule on the surface of Cu cannot only enhance the formation, adsorption and coverage of *CO, but also provide a hydrophobic environment, which result in the high selectivity of C2+ alcohols at acidic condition.

Recent advances in microenvironment regulation for electrocatalysis

High-efficiency electrocatalysis could serve as the bridge that connects renewable energy technologies, hydrogen economy and carbon capture/utilization, promising a sustainable future for humankind. It is therefore of paramount significance to explore feasible strategies to modulate the relevant electrocatalytic reactions and optimize device performances so as to promote their large-scale practical applications. Microenvironment regulation at the catalytic interface has been demonstrated to be capable of effectively enhancing the reaction rates and improving the selectivities for specific products. In this review we summarize the latest advances in microenvironment regulation in typical electrocatalytic processes (including water electrolysis, hydrogen-oxygen fuel cells, and carbon dioxide reduction) and the related in situ/operando characterization techniques and theoretical simulation methods. At the end of this article, we present an outlook on development trends and possible future directions.

Electrochemical CO2 Reduction Reaction: Comprehensive Strategic Approaches to Catalyst Design for Selective Liquid Products Formation

The escalating concern regarding the release of CO2 into the atmosphere poses a significant threat to the contemporary efforts in mitigating climate change. Amidst a multitude of strategies for curtailing CO2 emissions, the electrochemical CO2 reduction presents a promising avenue for transforming CO2 molecules into a diverse array of valuable gaseous and liquid products, such as CO, CH3OH, CH4, HCO2H, C2H4, C2H5OH, CH3CO2H, 1-C3H7OH and others. The mechanistic investigations of gaseous products (e. g. CO, CH4, C2H4, C2H6 and others) broadly covered in the literature. There is a noticeable gap in the literature when it comes to a comprehensive summary exclusively dedicated to coherent roadmap for the designing principles for a selective catalyst all possible liquid products (such as CH3OH, C2H5OH, 1-C3H7OH, 2-C3H7OH, 1-C4H9OH, as well as other C3-C4 products like methylglyoxal and 2,3-furandiol, in addition to HCO2H, AcOH, oxalic acid and others), selectively converted by CO2 reduction. This entails a meticulous analysis to justify these approaches and a thorough exploration of the correlation between materials and their electrocatalytic properties. Furthermore, these insightful discussions illuminate the future prospects for practical applications, a facet not exhaustively examined in prior reviews.

Exploration of Gas-Dependent Self-Adaptive Reconstruction Behavior of Cu2O for Electrochemical CO2 Conversion to Multi-Carbon Products

Structural reconstruction of electrocatalysts plays a pivotal role in catalytic performances for CO2 reduction reaction (CO2RR), whereas the behavior is by far superficially understood. Here, we report that CO2 accessibility results in a universal self-adaptive structural reconstruction from Cu2O to Cu@CuxO composites, ending with feeding gas-dependent microstructures and catalytic performances. The CO2-rich atmosphere favors reconstruction for CO2RR, whereas the CO2-deficient one prefers that for hydrogen evolution reaction. With the assistance of spectroscopic analysis and theoretical calculations, we uncover a CO2-induced passivation behavior by identifying a reduction-resistant but catalytic active Cu(I)-rich amorphous layer stabilized by *CO intermediates. Additionally, we find extra CO production is indispensable for the robust production of C2H4. An inverse correlation between durability and FECO/FEC2H4 is disclosed, suggesting that the self-stabilization process involving the absorption of *CO intermediates on Cu(I) sites is essential for durable electrolysis. Guided by this insight, we design hollow Cu2O nanospheres for durable and selective CO2RR electrolysis in producing C2H4. Our work recognizes the previously overlooked passivation reconstruction and self-stabilizing behavior and highlights the critical role of the local atmosphere in modulating reconstruction and catalytic processes.

Hierarchically conductive electrodes unlock stable and scalable CO2 electrolysis

Electrochemical CO2 reduction has emerged as a promising CO2 utilization technology, with Gas Diffusion Electrodes becoming the predominant architecture to maximize performance. Such electrodes must maintain robust hydrophobicity to prevent flooding, while also ensuring high conductivity to minimize ohmic losses. Intrinsic material tradeoffs have led to two main architectures: carbon paper is highly conductive but floods easily; while expanded Polytetrafluoroethylene is flooding resistant but non-conductive, limiting electrode sizes to just 5 cm2. Here we demonstrate a hierarchically conductive electrode architecture which overcomes these scaling limitations by employing inter-woven microscale conductors within a hydrophobic expanded Polytetrafluoroethylene membrane. We develop a model which captures the spatial variability in voltage and product distribution on electrodes due to ohmic losses and use it to rationally design the hierarchical architecture which can be applied independent of catalyst chemistry or morphology. We demonstrate C2+ Faradaic efficiencies of ~75% and reduce cell voltage by as much as 0.9 V for electrodes as large as 50 cm2 by employing our hierarchically conductive electrode architecture.

Microenvironment Engineering of Heterogeneous Catalysts for Liquid-Phase Environmental Catalysis

Environmental catalysis has emerged as a scientific frontier in mitigating water pollution and advancing circular chemistry and reaction microenvironment significantly influences the catalytic performance and efficiency. This review delves into microenvironment engineering within liquid-phase environmental catalysis, categorizing microenvironments into four scales: atom/molecule-level modulation, nano/microscale-confined structures, interface and surface regulation, and external field effects. Each category is analyzed for its unique characteristics and merits, emphasizing its potential to significantly enhance catalytic efficiency and selectivity. Following this overview, we introduced recent advancements in advanced material and system design to promote liquid-phase environmental catalysis (e.g., water purification, transformation to value-added products, and green synthesis), leveraging state-of-the-art microenvironment engineering technologies. These discussions showcase microenvironment engineering was applied in different reactions to fine-tune catalytic regimes and improve the efficiency from both thermodynamics and kinetics perspectives. Lastly, we discussed the challenges and future directions in microenvironment engineering. This review underscores the potential of microenvironment engineering in intelligent materials and system design to drive the development of more effective and sustainable catalytic solutions to environmental decontamination.

In situ Reconstructured Alloy Nanosheets Heterojunction for Highly Selective Electrochemical CO2 Reduction to Formate

Tin (Sn)-based materials are expected to realize efficient CO2 electroreduction into formate. Herein, we constructed a heterojunction by depositing Cu on Cu-doped SnS2 nanosheets. During the electrochemical reaction, this heterojunction evolves to a highly active phase of Cu2O@Cu6Sn5 while maintaining its two-dimensional morphology. Specifically, a partial current density of 35 mA cm-2 with an impressive faradaic efficiency of 93 % for formate production was achieved over the evolved heterojunction. In situ and ex situ experiments elucidated the formation mechanism of the Cu₂O@Cu₆Sn₅ heterojunction. Cu₆Sn₅ nanosheets were formed via a stepwise desulfurization process, while Cu₂O was generated through its reaction with hydroxyl radicals. This evolved heterojunction with a high electrochemically active surface area synergistically stabilized the *OCHO intermediate, thereby significantly enhancing the selectivity and activity. Our findings provide insight into the structural evolution process and guide the development of selective electrocatalysts for CO2 reduction.

State of Play of Critical Mineral-Based Catalysts for Electrochemical E-Refinery to Synthetic Fuels

The pursuit of decarbonization involves leveraging waste CO2 for the production of valuable fuels and chemicals (e.g., ethanol, ethylene, and urea) through the electrochemical CO2 reduction reactions (CO2RR). The efficacy of this process heavily depends on electrocatalyst performance, which is generally reliant on high loading of critical minerals. However, the supply of these minerals is susceptible to shortage and disruption, prompting concerns regarding their usage, particularly in electrocatalysis, requiring swift innovations to mitigate the supply risks. The reliance on critical minerals in catalyst fabrication can be reduced by implementing design strategies that improve the available active sites, thereby increasing the mass activity. This review seeks to discuss and analyze potential strategies, challenges, and opportunities for improving catalyst activity in CO2RR with a special attention to addressing the risks associated with critical mineral scarcity. By shedding light onto these aspects of critical mineral-based catalyst systems, this review aims to inspire the development of high-performance catalysts and facilitates the practical application of CO2RR technology, whilst mitigating adverse economic, environmental, and community impacts.

Stabilizing High-Valence Copper(I) Sites with Cu-Ni Interfaces Enhances Electroreduction of CO2 to C2+ Products

In this study, the copper-nickel (Cu-Ni) bimetallic electrocatalysts for electrochemical CO2 reduction reaction(CO2RR) are fabricated by taking the finely designed poly(ionic liquids) (PIL) containing abundant Salen and imidazolium chelating sites as the surficial layer, wherein Cu-Ni, PIL-Cu and PIL-Ni interaction can be readily regulated by different synthetic scheme. As a proof of concept, Cu@Salen-PIL@Ni(NO3)2 and Cu@Salen-PIL(Ni) hybrids differ significantly in the types and distribution of Ni species and Cu species at the surface, thereby delivering distinct Cu-Ni cooperation fashion for the CO2RR. Remarkably, Cu@Salen-PIL@Ni(NO3)2 provides a C2+ faradaic efficiency (FEC2+) of 80.9% with partial current density (jC 2+) of 262.9 mA cm-2 at -0.80 V (versus reversible hydrogen electrode, RHE) in 1 m KOH in a flow cell, while Cu@Salen-PIL(Ni) delivers the optimal FEC2+ of 63.8% at jC2+ of 146.7 mA cm-2 at -0.78 V. Mechanistic studies indicates that the presence of Cu-Ni interfaces in Cu@Salen-PIL@Ni(NO3)2 accounts for the preserve of high-valence Cu(I) species under CO2RR conditions. It results in a high activity of both CO2-to-CO conversion and C-C coupling while inhibition of the competitive HER.

Electroreduction of CO to 2.8 A cm⁻2 C2+ Products: Maximizing Efficiency with Minimalist Electrode Design Featuring a Mesopore-Rich Hydrophobic Copper Catalyst Layer

This work shows how hydrophobicity and porosity can be incorporated into copper catalyst layers (CLs) for the efficient electroreduction of CO (CORR) in a flow cell. Oxide-derived (OD) Cu catalysts are synthesized using K+ and Cs+ as templates, termed respectively as OD-Cu-K and OD-Cu-Cs. CLs, assembled from OD-Cu-K and OD-Cu-Cs, exhibit enhanced CORR performance compared to "unmodified" OD-Cu CL. OD-Cu-Cs can notably reduce CO to C2+ products with Faradaic efficiencies (FE) as high as 96% (or 4% FE H2). During CO electrolysis at -3000 mA cm-2 (-0.73 V vs reversible hydrogen electrode), C2+ products and the alcohols are formed with respective current densities of -2804 and -1205 mA cm- 2. The mesopores in the OD-Cu-Cs CL act as barriers against electrolyte flooding. Contact angle measurements confirm the CL's hydrophobicity ranking: OD-Cu-Cs > OD-Cu-K > OD-Cu. The enhanced hydrophobicity of a catalyst is proposed to allow more triple-phase (CO-electrolyte-catalyst) interfaces to be available for CORR. This study shows how the pore size-hydrophobicity relationship can be harvested to guide the design of a less-is-more Cu electrode, which can attain high CORR current density and selectivity, without the additional use of hydrophobic polytetrafluoroethylene particles or dopants, such as Ag.

Direct Microenvironment Modulation of CO2 Electroreduction: Negatively Charged Ag Sites Going beyond Catalytic Surface Reactions

Electrochemical reduction of CO2 is an important way to achieve carbon neutrality, and much effort has been devoted to the design of active sites. Apart from elevating the intrinsic activity, expanding the functionality of active sites may also boost catalytic performance. Here we designed "negatively charged Ag (nc-Ag)" active sites featuring both the intrinsic activity and the capability of regulating microenvironment, through modifying Ag nanoparticles with atomically dispersed Sn species. Different from conventional active sites (which only mediate the surface processes by bonding with the intermediates), the nc-Ag sites could also manipulate environmental species. Therefore, the sites could not only activate CO2, but also regulate interfacial H2O and CO2, as confirmed by operando spectroscopies. The catalyst delivers a high current density with a CO faradaic efficiency of 97 %. Our work here opens up new opportunities for the design of multifunctional electrocatalytic active sites.

High-efficiency C3 electrosynthesis on a lattice-strain-stabilized nitrogen-doped Cu surface

The synthesis of multi-carbon (C2+) fuels via electrocatalytic reduction of CO, H2O using renewable electricity, represents a significant stride in sustainable energy storage and carbon recycling. The foremost challenge in this field is the production of extended-chain carbon compounds (Cn, n ≥ 3), wherein elevated *CO coverage (θco) and its subsequent multiple-step coupling are both critical. Notwithstanding, there exists a "seesaw" dynamic between intensifying *CO adsorption to augment θco and surmounting the C-C coupling barrier, which have not been simultaneously realized within a singular catalyst yet. Here, we introduce a facilely synthesized lattice-strain-stabilized nitrogen-doped Cu (LSN-Cu) with abundant defect sites and robust nitrogen integration. The low-coordination sites enhance θco and concurrently, the compressive strain substantially fortifies nitrogen dopants on the catalyst surface, promoting C-C coupling activity. The n-propanol formation on the LSN-Cu electrode exhibits a 54% faradaic efficiency and a 29% half-cell energy efficiency. Moreover, within a membrane electrode assembly setup, a stable n-propanol electrosynthesis over 180 h at a total current density of 300 mA cm-2 is obtained.

Dynamic Bubbling Balanced Proactive CO2 Capture and Reduction on a Triple-Phase Interface Nanoporous Electrocatalyst

The formation and preservation of the active phase of the catalysts at the triple-phase interface during CO2 capture and reduction is essential for improving the conversion efficiency of CO2 electroreduction toward value-added chemicals and fuels under operational conditions. Designing such ideal catalysts that can mitigate parasitic hydrogen generation and prevent active phase degradation during the CO2 reduction reaction (CO2RR), however, remains a significant challenge. Herein, we developed an interfacial engineering strategy to build a new SnOx catalyst by invoking multiscale approaches. This catalyst features a hierarchically nanoporous structure coated with an organic F-monolayer that modifies the triple-phase interface in aqueous electrolytes, substantially reducing competing hydrogen generation (less than 5%) and enhancing CO2RR selectivity (∼90%). This rationally designed triple-phase interface overcomes the issue of limited CO2 solubility in aqueous electrolytes via proactive CO2 capture and reduction. Concurrently, we utilized pulsed square-wave potentials to dynamically recover the active phase for the CO2RR to regulate the production of C1 products such as formate and carbon monoxide (CO). This protocol ensures profoundly enhanced CO2RR selectivity (∼90%) compared with constant potential (∼70%) applied at -0.8 V (V vs RHE). We further achieved a mechanistic understanding of the CO2 capture and reduction processes under pulsed square-wave potentials via in situ Raman spectroscopy, thereby observing the potential-dependent intensity of Raman vibrational modes of the active phase and CO2RR intermediates. This work will inspire material design strategies by leveraging triple-phase interface engineering for emerging electrochemical processes, as technology moves toward electrification and decarbonization.

Enhancing local K+ adsorption by high-density cube corners for efficient electroreduction of CO2 to C2+ products

Reducing carbon dioxide (CO2) to high value-added chemicals using renewable electricity is a promising approach to reducing CO2 levels in the air and mitigating the greenhouse effect, which depends on high-efficiency electrocatalysts. Copper-based catalysts can be used for electroreduction of CO2 to produce C2+ products with high added value, but suffer from poor stability and low selectivity. Herein, we propose a strategy to enhance the field effect by varying the cubic corner density on the surface of Cu2O microspheres for improving the electrocatalytic performance of CO2 reduction to C2+ products. Finite element method (FEM) simulation results show that the high density of cubic corners helps to enhance the local electric field, which increases the K+ concentration on the catalyst surface. The results of CO2 electroreduction tests show that the FEC2+ of the Cu2O catalyst with high-density cubic corners is 71% at a partial current density of 497 mA cm-2. Density functional theory (DFT) calculations reveal that Cu2O (111) and Cu2O (110) can effectively reduce the energy barrier of C-C coupling and improve the FEC2+ at high K+ concentrations relative to Cu2O (100). This study provides a new perspective for the design and development of efficient CO2RR catalysts.

[2+1] Cycloadditions Modulate the Hydrophobicity of Ni-N4 Single-Atom Catalysts for Efficient CO2 Electroreduction

Microenvironment regulation of M-N4 single-atom catalysts (SACs) is a promising way to tune their catalytic properties toward the electrochemical CO2 reduction reaction. However, strategies that can effectively introduce functional groups around the M-N4 sites through strong covalent bonding and under mild reaction conditions are highly desired. Taking the hydrophilic Ni-N4 SAC as a representative, we report herein a [2+1] cycloaddition reaction between Ni-N4 and in situ generated difluorocarbene (F2C:), and enable the surface fluorocarbonation of Ni-N4, resulting in the formation of a super-hydrophobic Ni-N4-CF2 catalyst. Meanwhile, the mild reaction conditions allow Ni-N4-CF2 to inherit both the electronic and structural configuration of the Ni-N4 sites from Ni-N4. Enhanced electrochemical CO2-to-CO Faradaic efficiency above 98 % is achieved in a wide operating potential window from -0.7 V to -1.3 V over Ni-N4-CF2. In situ spectroelectrochemical studies reveal that a highly hydrophobic microenvironment formed by the -CF2- group repels asymmetric H-bonded water at the electrified interface, inhibiting the hydrogen evolution reaction and promoting CO production. This work highlights the advantages of [2+1] cycloaddition reactions on the covalent modification of N-doped carbon-supported catalysts.

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.

Efficient CO2 electroreduction to ethanol enabled by tip-curvature-induced local electric fields

Electrocatalytic reduction of CO2 into multicarbon (C2+) products offers a promising pathway for CO2 utilization. However, achieving high selectivity towards multicarbon alcohols, such as ethanol, remains a challenge. In this work, we present a novel CuO nanoflower catalyst with engineered tip curvature, achieving remarkable selectivity and efficiency in the electroreduction of CO2 to ethanol. This catalyst exhibits an ethanol faradaic efficiency (FEethanol) of 47% and a formation rate of 320 μmol h-1 cm-2, with an overall C2+ product faradaic efficiency (FEC2+) reaching ∼77.8%. We attribute this performance to the catalyst's sharp tip, which generates a strong local electric field, thereby accelerating CO2 activation and facilitating C-C coupling for deep CO2 reduction. In situ Raman spectroscopy reveals an increased *OH coverage under operating conditions, where the enhanced *OH adsorption facilitates the stabilization of *CHCOH intermediates through hydrogen bonding interaction, thus improving ethanol selectivity. Our findings demonstrate the pivotal role of local electric fields in altering reaction kinetics for CO2 electroreduction, presenting a new avenue for catalyst design aiming at converting CO2 to ethanol.

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.

Enhancing electrochemical carbon dioxide reduction efficiency through heat-induced metamorphosis of copper nanowires into copper oxide/copper nanotubes with tunable surface

Electrochemical CO2 reduction reaction (CO2RR) presents a unique opportunity to convert carbon dioxide (CO2) to value-added products while simultaneously storing renewable energy in the form of chemical energy. However, particle applications of this technology are limited due to the poor efficiency and product selectivity of the existing catalyst. In this study, we demonstrate a facile method for the heat-induced transformation of copper nanowires into CuOx/Cu nanotubes with defect-enriched surfaces. During this transformation, the outward migration of copper results in the formation of tubular structures encased within nanosized oxide grains. Notably, the hydrogen faradaic efficiency (FE) decreases with extended heat treatment, while carbon monoxide (CO) FE increases. As compared to Cu NWs, Cu NTs exhibit lower selectivity towards H2 and single-carbon (C1) products and favor the formation of multi-carbon (C2+) products. Consequently, a 2-fold increase in the single pass CO2 conversion (SPCC) and C2+ half-cell energy efficiency (EEhalf cell) was noted after heat treatment. The Cu NT-4 variant, synthesized under optimized conditions, exhibits the highest FE of 72.1 % for C2+ products at an operating current density (ID) of 500 mA cm-2.

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.

High yield electrosynthesis of oxygenates from CO using a relay Cu-Ag co-catalyst system

As a sustainable alternative to fossil fuel-based manufacture of bulk oxygenates, electrochemical synthesis using CO and H2O as raw materials at ambient conditions offers immense appeal. However, the upscaling of the electrosynthesis of oxygenates encounters kinetic bottlenecks arising from the competing hydrogen evolution reaction with the selective production of ethylene. Herein, a catalytic relay system that can perform in tandem CO capture, activation, intermediate transfer and enrichment on a Cu-Ag composite catalyst is used for attaining high yield CO-to-oxygenates electrosynthesis at high current densities. The composite catalyst Cu/30Ag (molar ratio of Cu to Ag is 7:3) enables high efficiency CO-to-oxygenates conversion, attaining a maximum partial current density for oxygenates of 800 mA cm-2 at an applied current density of 1200 mA cm-2, and with 67 % selectivity. The ability to finely control the production of ethylene and oxygenates highlights the principle of efficient catalyst design based on the relay mechanism.

Overcoming Low C2+ Yield in Acidic CO2 Electroreduction: Modulating Local Hydrophobicity for Enhanced Performance

Operating electrochemical CO2 reduction reaction (CO2RR) in acidic media has garnered considerable attention due to its sustainable electrolyte cycling and stable performance. Nevertheless, the severe parasitic hydrogen evolution reaction (HER) and decayed multi-carbon species (C2+) yield still hampers efficient CO2RR in acid. Here, this work investigates the influence of local hydrophobicity on the acidic CO2RR. By employing direct electrodeposition, the hydrophobicity of the catalyst layer can be finely tuned over a wide range without additive. It is revealed that the hydrophobic microenvironment significantly suppressed HER, improved CO2RR performance and boosted C2+ yield. A Faradaic efficiency (FE) of ≈74% for C2+ is achieved in pH = 2 on electrodeposited copper with a highly hydrophobic environment. Moreover, this phenomenon can be extended to industrial application. An ≈81% total FE for the CO2RR, along with a ≈62% FE for C2+ species, is achieved even with commercial copper. Remarkably, the system exhibited stable operation for a continuous period exceeding 50 h at an industrially applied current density of 300 mA cm-2. This work highlights the crucial role of interface hydrophobicity in acidic CO2RR and proposes a facile and universally applicable method for achieving efficient and stable CO2RR to high-value products in acidic media.

Bioinspired Gas Manipulation for Regulating Multiphase Interactions in Electrochemistry

The manipulation of gas in multiphase interactions plays a crucial role in various electrochemical processes. Inspired by nature, researchers have explored bioinspired strategies for regulating these interactions, leading to remarkable advancements in design, mechanism, and applications. This paper provides a comprehensive overview of bioinspired gas manipulation in electrochemistry. It traces the evolution of gas manipulation in gas-involving electrochemical reactions, highlighting the key milestones and breakthroughs achieved thus far. The paper then delves into the design principles and underlying mechanisms of superaerophobic and (super)aerophilic electrodes, as well as asymmetric electrodes. Furthermore, the applications of bioinspired gas manipulation in hydrogen evolution reaction (HER), carbon dioxide reduction reaction (CO2RR), and other gas-involving electrochemical reactions are summarized. The promising prospects and future directions in advancing multiphase interactions through gas manipulation are also discussed.

Local CO Generator Enabled by a CO-Producing Core for Kinetically Enhancing Electrochemical CO2 Reduction to Multicarbon Products

CO plays a crucial role as an intermediate in electrochemical CO2 conversion to generate multicarbon (C2+) products. However, optimizing the coverage of the CO intermediate (*CO) to improve the selectivity of C2+ products remains a great challenge. Here, we designed a hierarchically structured double hollow spherical nanoreactor featuring atomically dispersed nickel (Ni) atoms as the core and copper (Cu) nanoparticles as the shell, which can greatly improve the catalytic activity and selectivity for C2+ compounds. Within this configuration, CO generated at the active Ni sites on the inner layer accumulates in the cavity before spilling over neighboring Cu sites on the outer layer, thus enhancing CO dimerization within the cavity. Notably, this setup achieves a sustained faradaic efficiency of 74.4% for C2+ production, with partial current densities reaching 337.4 mA cm-2. In situ Raman spectroscopy and finite-element method (FEM) simulations demonstrate that the designed local CO generator can effectively increase the local CO concentration and restrict CO evolution, ultimately boosting C-C coupling. The hierarchically ordered architectural design represents a promising solution for achieving highly selective C2+ compound production in the electroreduction of CO2.

Introduction of a Conductive Layer into Flood-Resistant Gas Diffusion Electrodes with Polymer Substrate for an Efficient Electrochemical CO2 Reduction with Copper Oxide

Conversion of atmospheric carbon dioxide (CO2) into valuable feedstocks is a crucial technology, and electrochemical reduction of CO2 is a promising approach that can provide a useful source of ethylene (C2H4). Gas diffusion electrodes (GDEs) placed at the interface of the CO2 gas and electrolyte can achieve high current density through a sufficient supply of dissolved CO2 to the reaction site, making them indispensable in industrial applications. However, conventional GDEs with carbon substrate have suffered from electrolyte flooding and consequent loss of efficiency, posing an obstacle for practical application. While flood-resistant GDEs with hydrophobic polymer substrate have been proposed recently, only conductive materials can be employed as electrocatalysts because of their insulative properties, despite the high activities of oxide materials such as copper oxide. Here, we introduce an aluminum conductive layer in GDE with polymer substrate to enable the use of electrically resistive catalysts. Cuprous oxide (Cu2O) with silver particles was tested as a model material and has shown prolonged stability (>17 h) with high C2H4 Faraday efficiency (>50%) while suppressing flooding. A thorough characterization revealed that the conductive layer makes Cu2O an efficient electrocatalyst, even on the polymer substrate, by providing sufficient electrons through its conduction path. This research significantly expands the scope of electrode design by enabling the incorporation of a wide range of nonelectrically conductive materials on GDEs with polymer substrate.

Coupling Curvature and Hydrophobicity: A Counterintuitive Strategy for Efficient Electroreduction of Nitrate into Ammonia

The electrochemical upcycling of nitrate (NO3-) to ammonia (NH3) holds promise for synergizing both wastewater treatment and NH3 synthesis. Efficient stripping of gaseous products (NH3, H2, and N2) from electrocatalysts is crucial for continuous and stable electrochemical reactions. This study evaluated a layered electrocatalyst structure using copper (Cu) dendrites to enable a high curvature and hydrophobicity and achieve a stratified liquid contact at the gas-liquid interface of the electrocatalyst layer. As such, gaseous product desorption or displacement from electrocatalysts was enhanced due to the separation of a wetted reaction zone and a nonwetted zone for gas transfer. Consequently, this electrocatalyst structure yielded a 2.9-fold boost in per-active-site activity compared with that with a low curvature and high hydrophilic counterpart. Moreover, a NH3 Faradaic efficiency of 90.9 ± 2.3% was achieved with nearly 100% NO3- conversion. This high-curvature hydrophobic Cu dendrite was further integrated with a gas-extraction membrane, which demonstrated a comparable NH3 yield from the real reverse osmosis retentate brine.

Surface coating combined with in situ cyclic voltammetry to enhance the stability of gas diffusion electrodes for electrochemical CO2 reduction

Electrochemical CO2 reduction (CO2RR), fueled by clean and renewable energy, presents a promising method for utilizing CO2 effectively. The electrocatalytic reduction of CO2 to CO using a gas diffusion electrode (GDE) has shown great potential for industrial applications due to its high reaction rate and selectivity. However, guaranteeing its long-term stability still poses a significant challenge. In this study, we conducted a comprehensive investigation into various strategies to enhance the stability of the GDE. These strategies involved modifying the structure of the substrate, such as the gas diffusion layer (GDL) and the back side of the GDL (macroporous layer side). Additionally, we explored modifications to the catalyst layer (CL) and the front of the CL. To address these stability concerns, we proposed a practical approach that involved surface coating using carbon black in combination with in situ cyclic voltammetry (CV) cycles on Ag/Ag300/polytetrafluoroethylene (PTFE). The partial Faradaic efficiency exceeded 80 % within a span of 70 h. Electron microscopy and electrochemical characterization revealed that the implementation of in situ CV led to a reduction in catalyst particle size and the formation of a porous surface structure. By enhancing the stability of the GDE, this research opens up possibilities for the advancement of hybrid systems that focus on the production and utilization of syngas.

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.

Triple-Phase Photocatalytic H2O2 Production on a Janus Fiber Membrane with Asymmetric Hydrophobicity

Photocatalytic O2 reduction is an intriguing approach to producing H2O2, but its efficiency is often hindered by the limited solubility and mass transfer of O2 in the aqueous phase. Here, we design and fabricate a two-layered (2L) Janus fiber membrane photocatalyst with asymmetric hydrophobicity for efficient photocatalytic H2O2 production. The top layer of the membrane consists of superhydrophobic polytetrafluoroethylene (PTFE) fibers with a dispersed modified carbon nitride (mCN) photocatalyst. Amphiphilic Nafion (Naf) ionomer is sprayed onto this layer to modulate the microenvironment and achieve moderate hydrophobicity. In contrast, the bottom layer consists of bare PTFE fibers with high hydrophobicity. The elaborate structural configuration and asymmetric hydrophobicity feature of the optimized membrane photocatalyst (designated as 2L-mCN/F-Naf; F, PTFE) allow most mCN to be exposed with gas-liquid-solid triple-phase interfaces and enable rapid mass transfer of gaseous O2 within the hierarchical membrane, thus increasing the local O2 concentration near the mCN photocatalyst. As a result, the optimized 2L-mCN/F-Naf membrane photocatalyst shows remarkable photocatalytic H2O2 production activity, achieving a rate of 5.38 mmol g-1 h-1 under visible light irradiation.

A Cu hollow fiber with coaxially grown Bi nanosheet arrays as an integrated gas-penetrable electrode enables high current density and durable formate electrosynthesis

While high current density formate (HCOO-) electrosynthesis from CO2 reduction has been achieved in a flow cell assembly, the inevitable flooding and salt precipitation of traditional gas-diffusion electrodes (GDEs) severely limit the overall energy efficiency and stability. In this work, an integrated gas-penetrable electrode (GPE) for HCOO- electrosynthesis was developed by coaxially growing vertically aligned high density Bi nanosheet arrays on a porous Cu hollow fiber (Bi NSAs@Cu HF) via controllable galvanic replacement. The interior porous Cu HF serves as a robust gas-penetrable and conductive host for continuously delivering CO2 gas to surface-anchored Bi NSAs, resulting in numerous well-balanced triphase active interfaces for the electrocatalytic CO2 reduction reaction (CO2RR). The most active Bi NSAs@Cu HF GPE exhibits a high HCOO- faradaic efficiency (FEHCOO-) of over 80% in a wide potential window (330 mV) with a linearly increased partial current density (jHCOO-) up to -261.6 mA cm-2 at -1.11 V vs. the reversible hydrogen electrode (RHE). The Bi NSAs@Cu HF GPE also sustains a FEHCOO- of >80% at a high total current density of -300 mA cm-2, corresponding to a jHCOO- of >-240 mA cm-2, for more than 60 h. This work provides new perspectives on designing efficient and durable integrated GPEs for a sustainable CO2RR on a large scale.

Gas diffusion enhanced electrode with ultrathin superhydrophobic macropore structure for acidic CO2 electroreduction

Carbon dioxide (CO2) electroreduction reaction (CO2RR) offers a promising strategy for the conversion of CO2 into valuable chemicals and fuels. CO2RR in acidic electrolytes would have various advantages due to the suppression of carbonate formation. However, its reaction rate is severely limited by the slow CO2 diffusion due to the absence of hydroxide that facilitates the CO2 diffusion in an acidic environment. Here, we design an optimal architecture of a gas diffusion electrode (GDE) employing a copper-based ultrathin superhydrophobic macroporous layer, in which the CO2 diffusion is highly enhanced. This GDE retains its applicability even under mechanical deformation conditions. The CO2RR in acidic electrolytes exhibits a Faradaic efficiency of 87% with a partial current density [Formula: see text] of -1.6 A cm-2 for multicarbon products (C2+), and [Formula: see text] of -0.34 A cm-2 when applying dilute 25% CO2. In a highly acidic environment, C2+ formation occurs via a second order reaction which is controlled by both the catalyst and its hydroxide.

Exploring how cation entropy influences electric double layer formation and electrochemical reactivity

Electric double layers are crucial to energy storage and electrocatalytic device performance. While double layer formation originates in electrostatic interactions, electric double layer properties are governed by a balance of both electrostatic and entropic driving forces. Favorable ion-surface electrostatic interactions attract counterions to charged surfaces to compensate, or "screen," potentials, but the confinement of these same ions from a bulk reservoir to the interface incurs an entropic penalty. Here, we use a dicationic imidazolium ionic liquid and its monovalent analogue to explore how cation valence and entropy influence double layer formation and electrochemical reactivity using CO2 electroreduction as a model reaction. We find that divalent and monovalent cations display similar CO2 reduction kinetics but differ vastly in steady-state reactivity due to rapid electrochemically induced precipitation of insulating dicationic (bi)carbonate films. Using in situ surface-enhanced Raman scattering spectroscopy, we find that potential-dependent cation reorientation occurs at similar potentials between the two ionic liquids, but the introduction of a covalent link in the divalent cation imparts a more ordered double layer structure that favors (bi)carbonate precipitation. In mixed monovalent-divalent electrolytes, we find that the divalent cations dominate interfacial properties by preferentially accumulating at surfaces even at very low relative concentrations. Our findings confirm that ion entropy plays a key role in modulating local electrochemical environments. Furthermore, we highlight how double layer properties are sensitive to the properties of counterions that pay the lowest entropic penalty to accumulate at interfaces. Overall, we illustrate that ion entropy provides a new knob to tune reaction microenvironments and unveil how entropy plays a major role in modulating electrochemical reactivity in mixed ion electrolytes.