Hydroxide promotes carbon dioxide electroreduction to ethanol on copper via tuning of adsorbed hydrogen

Transient pulsed discharge preparation of graphene aerogel supports asymmetric Cu cluster catalysts promote CO2 electroreduction

Designing asymmetrical structures is an effective strategy to optimize metallic catalysts for electrochemical carbon dioxide reduction reactions. Herein, we demonstrate a transient pulsed discharge method for instantaneously constructing graphene-aerogel supports asymmetric copper nanocluster catalysts. This process induces the convergence of copper atoms decomposed by copper chloride onto graphene originating from the intense current pulse and high temperature. The catalysts exhibit asymmetrical atomic and electronic structures due to lattice distortion and oxygen doping of copper clusters. In carbon dioxide reduction reaction, the selectivity and activity for ethanol production are enhanced by the asymmetric structure and abundance of active sites on catalysts, achieving a Faradaic efficiency of 75.3% for ethanol and 90.5% for multicarbon products at -1.1 V vs. reversible hydrogen electrode. Moreover, the strong interactions between copper nanoclusters and graphene-aerogel support confer notable long-term stability. We elucidate the key reaction intermediates and mechanisms on Cu4O-Cu/C2O1 moieties through in situ testing and density functional theory calculations. This study provides an innovative approach to balancing activity and stability in asymmetric-structure catalysts for energy conversion.

Integrated "Two-in-One" Strategy for High-Rate Electrocatalytic CO2 Reduction to Formate

The electrochemical CO2 reduction reaction (ECR) is a promising pathway to producing valuable chemicals and fuels. Despite extensive studies reported, improving CO2 adsorption for local CO2 enrichment or water dissociation to generate sufficient H* is still not enough to achieve industrial-relevant current densities. Herein, we report a "two-in-one" catalyst, defective Bi nanosheets modified by CrOx (Bi-CrOx), to simultaneously promote CO2 adsorption and water dissociation, thereby enhancing the activity and selectivity of ECR to formate. The Bi-CrOx exhibits an excellent Faradaic efficiency (≈100 %) in a wide potential range from -0.4 to -0.9 V. In addition, it achieves a remarkable formate partial current density of 687 mA cm-2 at a moderate potential of -0.9 V without iR compensation, the highest value at -0.9 V reported so far. Control experiments and theoretical simulations revealed that the defective Bi facilitates CO2 adsorption/activation while the CrOx accounts for enhancing the protonation process via accelerating H2O dissociation. This work presents a pathway to boosting formate production through tuning CO2 and H2O species at the same time.

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.

Establishing Non-Stoichiometric Ti4O7 Assisted Asymmetrical C-C Coupling for Highly Energy-Efficient Electroreduction of Carbon Monoxide

Exploring an appropriate support material for Cu-based electrocatalyst is conducive for stably producing multi-carbon chemicals from electroreduction of carbon monoxide. However, the insufficient metal-support adaptability and low conductivity of the support would hinder the C-C coupling capacity and energy efficiency. Herein, non-stoichiometric Ti4O7 was incorporated into Cu electrocatalysts (Cu-Ti4O7), and served as a highly conductive and stable support for highly energy-efficient electrochemical conversion of CO. The abundant oxygen vacancies originated from ordered lattice defects in Ti4O7 facilitate the water dissociation and the CO adsorption to accelerate the hydrogenation to *COH. The highly adaptable metal-support interface of Cu-Ti4O7 enables a direct asymmetrical C-C coupling between *CO on Cu and *COH on Ti4O7, which significantly lowers the reaction energy barrier for C2+ products formation. Additionally, the excellent electroconductivity of Ti4O7 benefits the reaction charge transfer through robust Cu/Ti4O7 interface for minimizing the energy loss. Thus, the optimized 20Cu-Ti4O7 catalyst exhibits an impressive selectivity of 96.4 % and ultrahigh energy efficiency of 45.1 % for multi-carbon products, along with a remarkable partial current density of 432.6 mA cm-2. Our study underscores a novel C-C coupling strategy between Cu and the support material, advancing the development of Cu-supported catalysts for highly efficient electroreduction of carbon monoxide.

Interfacial Oxygen Vacancy-Copper Pair Sites on Inverse CeO2/Cu Catalyst Enable Efficient CO2 Electroreduction to Ethanol in Acid

Renewable electricity-driven electrochemical reduction of CO2 offers a promising route for the production of high-value ethanol. However, the current state of this technology is hindered by low selectivity and productivity, primarily due to a limited understanding of the atomic-level active sites involved in ethanol formation. Herein, we identify that the interfacial oxygen vacancy-neighboring Cu (Ov-Cu) pair sites are the active sites for CO2 electroreduction to ethanol. A linear correlation between the density of Ov-Cu pair sites and ethanol productivity is experimentally evidenced. Moreover, a high Faradaic efficiency of 48.5 % and a partial current density of 344.0 mA cm-2 for ethanol production are achieved over the inverse CeO2/Cu catalyst with a high density of Ov-Cu pair sites in acid. Mechanistic studies that combine density functional theory calculations and spectroscopic techniques propose an Ov-involved mechanism where interfacial Ov sites directly activate and dissociate CO2 into *CO in a thermodynamically spontaneous manner, thus favoring the subsequent *CHO formation and asymmetric CHO-CO coupling. Besides, the asymmetric Ov-Cu pair sites could preferentially stabilize the *CH2CHOH intermediate, resulting in the favorable formation of ethanol over ethylene. Our findings provide new atomic-level insights into CO2 electroreduction to ethanol, paving the way for the rational design of future catalysts.

Nickel-Doped Facet-Selective Copper Nanowires for Activating CO-to-Ethanol Electrosynthesis

Ethanol isa promising energy vector for closing the anthropogenic carbon cycle through reversible electrochemical redox. Currently, ethanol electrosynthesissuffers from low product selectivity due to the competitive advantage of ethylene in CO2/CO electroreduction. Here, a facet-selective metal-doping strategy is reported, tuning the reaction kinetics of CO reduction paths and thus enhancing the ethanol selectivity. The theoretical calculations reveal that nickel (Ni)doped Cu(100) surface facilitates water dissociation to form adsorbed hydrogen, which promotesselective electrochemical hydrogenation of a key C2 intermediate (*CHCOH) toward ethanol path over ethylene path. Experimentally, a solution-phase synthesis of a Ni-doped {100}-dominated Copper nanowires (Cu NWs) catalyst is reported, enabling an ethanol Faradaic efficiency of 56% and a selectivity ratio of ethanol to ethylene of 2.7, which are ≈4 and 15 times larger than those of undoped Cu NWs, respectively. The operando spectroscopic characterizations confirm that Ni-doping in Cu NWs can alter the interfacial water activity and thus regulate the C2 product selectivity. With further electrode engineering, a membrane electrode assembly electrolyzer using Ni-doped Cu NWs catalysts demonstrates an ethanol Faradaic efficiency over 50% at 300 mA cm-2 with a full cell voltage of ≈2.7 V and operates stably for over 300 h.

Promoting CO Electroreduction to C2+ Oxygenates by Distribution of Water Dissociation Sites

The electrocatalytic CO2 or CO reduction reaction is a complex proton-coupled electron transfer reaction, in which protons in the electrolyte have a critical effect on the surface adsorbed *H species and the multi-carbon oxygenate products such as ethanol. However, the coupling of *H and carbon-containing intermediates into C2+ oxygenates can be severely hampered by the inappropriate distributions of those species in the catalytic interfaces. In this work, the controlled distribution of highly dispersed CeOx nanoclusters is demonstrated on Cu nanosheets as an efficient CO electroreduction catalyst, with Faradaic efficiencies of ethanol and total oxygenates of 35% and 58%, respectively. The CeOx nanoclusters (2-5 nm) enabled efficient water dissociation and appropriate distribution of adsorbed *H species on the Cu surface with carbon-containing species, thus facilitating the generation of C2+ oxygenate products. In contrast, pristine Cu without CeOx tended to form ethylene, while the aggregated CeOx nanoparticles promoted the surface density of *H and subsequent H2 evolution.

Addressing the Carbonate Issue: Electrocatalysts for Acidic CO2 Reduction Reaction

Electrochemical CO2 reduction reaction (CO2RR) powered by renewable energy provides a promising route to CO2 conversion and utilization. However, the widely used neutral/alkaline electrolyte consumes a large amount of CO2 to produce (bi)carbonate byproducts, leading to significant challenges at the device level, thereby impeding the further deployment of this reaction. Conducting CO2RR in acidic electrolytes offers a promising solution to address the "carbonate issue"; however, it presents inherent difficulties due to the competitive hydrogen evolution reaction, necessitating concerted efforts toward advanced catalyst and electrode designs to achieve high selectivity and activity. This review encompasses recent developments of acidic CO2RR, from mechanism elucidation to catalyst design and device engineering. This review begins by discussing the mechanistic understanding of the reaction pathway, laying the foundation for catalyst design in acidic CO2RR. Subsequently, an in-depth analysis of recent advancements in acidic CO2RR catalysts is provided, highlighting heterogeneous catalysts, surface immobilized molecular catalysts, and catalyst surface enhancement. Furthermore, the progress made in device-level applications is summarized, aiming to develop high-performance acidic CO2RR systems. Finally, the existing challenges and future directions in the design of acidic CO2RR catalysts are outlined, emphasizing the need for improved selectivity, activity, stability, and scalability.

Simultaneous High Current Density and Selective Electrocatalytic CO2-to-CH4 through Intermediate Balancing

The electrochemical reduction of CO2 to CH4 is promising for carbon neutrality and renewable energy storage but confronts low CH4 selectivity, especially at high current densities. The key challenge lies in promoting *CO intermediate and *H coupling while minimizing side reactions including C-C coupling and H-H coupling, which is particularly difficult at high current density due to abundant intermediates. Here we report a cooperative strategy to address this challenge using Cu-based catalysts comprising Cu-N coordination polymer and CuO component that can simultaneously manage the key intermediates *CO and *H. A fast CO2-to-CH4 conversion rate of 3.14 mmol cm-2 h-1 is achieved at 1,300 mA cm-2 with a Faradaic efficiency of 51.7 %. In situ spectroscopy and theoretical calculations show that the increased Cu-Cu distance in the Cu-N coordination polymer component favors multistep *CO hydrogenation over the dimerization, and the CuO component ensures an adequate supply of *H, together contributing to the selective CO2-to-CH4 conversion at high current densities. This work develops a cooperative strategy for the electrosynthesis of CH4 with simultaneous high current density and high selectivity by rational catalyst design, paving the way for its applications.

Regulating Interfacial Hydrogen-Bonding Networks by Implanting Cu Sites with Perfluorooctane to Accelerate CO2 Electroreduction to Ethanol

Efficient CO2 electroreduction (CO2RR) to ethanol holds promise to generate value-added chemicals and harness renewable energy simultaneously. Yet, it remains an ongoing challenge due to the competition with thermodynamically more preferred ethylene production. Herein, we presented a CO2 reduction predilection switch from ethylene to ethanol (ethanol-to-ethylene ratio of ~5.4) by inherently implanting Cu sites with perfluorooctane to create interfacial noncovalent interactions. The 1.83 %F-Cu2O organic-inorganic hybrids (OIHs) exhibited an extraordinary ethanol faradaic efficiency (FEethanol) of ∼55.2 %, with an impressive ethanol partial current density of 166 mA cm-2 and excellent robustness over 60 hours of continuous operation. This exceptional performance ranks our 1.83 %F-Cu2O OIHs among the best-performing ethanol-oriented CO2RR electrocatalysts. Our findings identified that C8F18 could strengthen the interfacial hydrogen bonding connectivity, which consequently promotes the generation of active hydrogen species and preferentially favors the hydrogenation of *CHCOH to *CHCHOH, thus switching the reaction from ethylene-preferred to ethanol-oriented. The presented investigations highlight opportunities for using noncovalent interactions to tune the selectivity of CO2 electroreduction to ethanol, bringing it closer to practical implementation requirements.

Proton Ionic Liquid Modulates Hydrogen Coverage and Subsurface Absorbed Hydrogen to Enhance Pd Metallene Electrocatalytic Semi-hydrogenation of Alkynols

Electrochemical semi-hydrogenation of alkynols to produce high-value alkenols is a green and sustainable approach. Although Pd can exhibit excellent semi-hydrogenation properties, its intrinsic mechanism still lacks in-depth study. Herein, a proton ionic liquid (PIL)-modified Pd metallene (Pdene@PIL) is synthesized for the electrocatalytic semi-hydrogenation of 2-methyl-3-butyn-2-ol (MBY) to 2-methyl-3-buten-2-ol (MBE). The PIL modification of Pdene@PIL resulted in an MBY conversion of 96.1% and MBE selectivity of 97.2%, respectively. Theoretical calculations indicate the electron transfer between Pdene and PIL, leading to easier adsorption of MBY on the Pd surface. The d-band center of Pdene@PIL shifts away from the Fermi level, which weakens the adsorption of over-hydrogenated intermediates. At the same time, the PIL modification facilitates the adsorption of surface-adsorbed hydrogen (H*ads) and inhibits the formation of subsurface-absorbed hydrogen (H*abs). In particular, the PIL modification optimizes Hads* coverage, reduces the reaction energy of the rate-determining step (C5H8O*-C5H9O*), and inhibits HER. The reduction of H*abs formation inhibits the transfer of Pd to PdHx and suppresses the over-hydrogenation. This work provides new insights into the modulation of H* to enhance the alkynol electrocatalytic semi-hydrogenation reaction (ESHR) process from the perspective of surface modification.

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.

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.

Atomically Isolated Pd Sites Promote Electrochemical CO Reduction to Acetate through a Protonation-Regulated Mechanism

Electrochemical CO reduction reaction (CORR) offers a promising approach for sustainable acetate production, the promotion of which requires the control of multiple protonation steps. This paper describes the synthesis of atomically isolated Pd sites onto Cu nanoflakes to regulate the protonation of key intermediates. The Pd sites with moderate water activation capability are found to enhance the protonation of *CO at the neighboring Cu site to *COH, which is confirmed to be the rate-determining step through kinetic isotope effect studies. The formation of *COH-*CO is therefore promoted. Additionally, the Pd sites would preferentially protonate the C-OH group in *COH-*CO due to the spatial approximability and electronic modulation effects, generating *CCO for the selective formation of acetate. An acetate Faradaic efficiency of 59.5% is achieved at -0.78 V vs reversible hydrogen electrode (RHE), with a maximum partial current density of 286 mA cm-2 at -0.86 V vs RHE. The optimized catalyst also exhibits long-term stability for 500 h at 100 mA cm-2 in a membrane electrode assembly. This work reveals a new promoting mechanism for selective CORR with simultaneous tuning of the structural and electronic properties of the proton-supplying sites.

Preserving Molecular Tuning for Enhanced Electrocatalytic CO2-to-Ethanol Conversion

Modifying catalyst surface with small molecular-additives presents a promising avenue for enhancing electrocatalytic performance. However, challenges arise in preserving the molecular-additives and maximizing their tuning effect, particularly at high current densities. Herein, we develop an effective strategy to preserve the molecular-additives on electrode surface by applying a thin protective layer. Taking 4-dimethylaminopyridine (DMAP) as an example of a molecular-additive, the hydrophobic protection layer on top of the DMAP-functionalized Cu-catalyst effectively prevents its leaching during CO2 electroreduction (CO2R). Consequently, the confined DMAP molecules substantially promote the CO2-to-multicarbon conversion at low overpotentials. For instance, at a potential as low as -0.47 V vs. reversible hydrogen electrode, the DMAP-functionalized Cu exhibits over 80 % selectivity towards multi-carbon products, while the pristine Cu shows only ~35 % selectivity for multi-carbon products. Notably, ethanol appears as the primary product on DMAP-functionalized Cu, with selectivity approaching 50 % at a high current density of 400 mA cm-2. Detailed kinetic analysis, in situ spectroscopies, and theoretical calculations indicate that DMAP-induced electron accumulations on surface Cu-sites decrease the reaction energy for C-C coupling. Additionally, the interactions between DMAP and oxygenated intermediates facilitate the ethanol formation pathway in CO2R. Overall, this study showcases an effective strategy to guide future endeavors involving molecular tuning effects.

Hydrogen radical-boosted electrocatalytic CO2 reduction using Ni-partnered heteroatomic pairs

The electrocatalytic reduction of CO2 to CO is slowed by the energy cost of the hydrogenation step that yields adsorbed *COOH intermediate. Here, we report a hydrogen radical (H•)-transfer mechanism that aids this hydrogenation step, enabled by constructing Ni-partnered hetero-diatomic pairs, and thereby greatly enhancing CO2-to-CO conversion kinetics. The partner metal to the Ni (denoted as M) catalyzes the Volmer step of the water/proton reduction to generate adsorbed *H, turning to H•, which reduces CO2 to carboxyl radicals (•COOH). The Ni partner then subsequently adsorbs the •COOH in an exothermic reaction, negating the usual high energy-penalty for the electrochemical hydrogenation of CO2. Tuning the H adsorption strength of the M site (with Cd, Pt, or Pd) allows for the optimization of H• formation, culminating in a markedly improved CO2 reduction rate toward CO production, offering 97.1% faradaic efficiency (FE) in aqueous electrolyte and up to 100.0% FE in an ionic liquid solution.

Rational Strategies for Preparing Highly Efficient Tin-, Bismuth- or Indium-Based Electrocatalysts for Electrochemical CO2 Reduction to Formic acid/Formate

Electrochemical carbon dioxide reduction reaction (CO2RR) is an environmentally friendly and economically viable approach to convert greenhouse gas CO2 into valuable chemical fuels and feedstocks. Among various products of CO2RR, formic acid/formate (HCOOH/HCOO-) is considered the most attractive one with its high energy density and ease of storage, thereby enabling widespread commercial applications in chemical, medicine, and energy-related industries. Nowadays, the development of efficient and financially feasible electrocatalysts with excellent selectivity and activity towards HCOOH/HCOO- is paramount for the industrial application of CO2RR technology, in which Tin (Sn), Bismuth (Bi), and Indium (In)-based electrocatalysts have drawn significant attention due to their high efficiency and various regulation strategies have been explored to design diverse advanced electrocatalysts. Herein, we comprehensively review the rational strategies to enhance electrocatalytic performances of these electrocatalysts for CO2RR to HCOOH/HCOO-. Specifically, the internal mechanism between the physicochemical properties of engineering materials and electrocatalytic performance is analyzed and discussed in details. Besides, the current challenges and future opportunities are proposed to provide inspiration for the development of more efficient electrocatalysts in this field.

Blended nexus molecules promote CO2 to l-tyrosine conversion

Using CO2 as the primary feedstock offers the potential for high-value utilization of CO2 while forging sustainable pathways for producing valuable natural products, such as l-tyrosine. Cascade catalysis is a promising approach but limited by stringent purity demands of nexus molecules. We developed an abiotic/biotic cascade catalysis using blended nexus molecules for l-tyrosine synthesis. Specifically, we begin by constructing a solid-state reactor to reduce CO2 electrochemically, yielding a mixture of acetic acid and ethanol, which serves as the blended nexus molecules. Subsequently, we use genetic engineering to introduce an ethanol utilization pathway and a tyrosine producing pathway to Escherichia coli to facilitate l-tyrosine production. The ethanol pathway synergistically cooperated with the acetic acid pathway, boosting l-tyrosine production rate (nearly five times higher compared to the strain without ethanol utilization pathway) and enhancing carbon efficiency. Our findings demonstrate that using blended nexus molecules could potentially offer a more favorable strategy for the cascade catalysis aimed at producing valuable natural products.

Multivalent Cu sites synergistically adjust carbonaceous intermediates adsorption for electrocatalytic ethanol production

Copper (Cu)-based catalysts show promise for electrocatalytic CO2 reduction (CO2RR) to multi-carbon alcohols, but thermodynamic constraints lead to competitive hydrocarbon (e.g., ethylene) production. Achieving selective ethanol production with high Faradaic efficiency (FE) and current density is still challenging. Here we show a multivalent Cu-based catalyst, Cu-2,3,7,8-tetraaminophenazine-1,4,6,9-tetraone (Cu-TAPT) with Cu2+ and Cu+ atomic ratio of about 1:2 for CO2RR. Cu-TAPT exhibits an ethanol FE of 54.3 ± 3% at an industrial-scale current density of 429 mA cm-2, with the ethanol-to-ethylene ratio reaching 3.14:1. Experimental and theoretical calculations collectively unveil that the catalyst is stable during CO2RR, resulting from suitable coordination of the Cu2+ and Cu+ with the functional groups in TAPT. Additionally, mechanism studies show that the increased ethanol selectivity originates from synergy of multivalent Cu sites, which can promote asymmetric C-C coupling and adjust the adsorption strength of different carbonaceous intermediates, favoring hydroxy-containing C2 intermediate (*HCCHOH) formation and formation of ethanol.

Selectivity of a Copper Oxide CO2 Reduction Electrocatalyst Shifted by a Bioinspired pH-Sensitive Polymer

A bioinspired polymeric membrane capable of shifting the selectivity of a copper oxide electrocatalyst in the CO2 reduction reaction is described. The membrane is deposited on top of copper oxide thin films from wet deposition techniques under controlled conditions of humidity and self-assembles into an arranged network of micrometer-sized pores throughout the polymer cross-section. The membrane was composed of a block copolymer with a precisely controlled ratio of poly-4-vinylpyridine and poly(methyl methacrylate) blocks (PMMA-b-P4VP). The intrinsic hydrophobicity, together with the porous nature of the membrane's surface, induces a Cassie-Baxter wetting transition above neutral pH, resulting in water repulsion from the catalyst surface. As a consequence, the catalyst's surface is shielded from surrounding water molecules under CO2 electroreduction reaction conditions, and CO2 molecules are preferentially located in the vicinity of the catalytically active area. The CO2 reduction reaction is therefore kinetically favored over the hydrogen evolution reaction (HER).

Strategies for overcoming challenges in selective electrochemical CO2 conversion to ethanol

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

Selective Increase in CO2 Electroreduction to Ethanol Activity at Nanograin-Boundary-Rich Mixed Cu(I)/Cu(0) Sites via Enriching Co-Adsorbed CO and Hydroxyl Species

Selective producing ethanol from CO2 electroreduction is highly demanded, yet the competing ethylene generation route is commonly more thermodynamically preferred. Herein, we reported an efficient CO2-to-ethanol conversion (53.5 % faradaic efficiency at -0.75 V versus reversible hydrogen electrode (vs. RHE)) over an oxide-derived nanocubic catalyst featured with abundant "embossment-like" structured grain-boundaries. The catalyst also attains a 23.2 % energy efficiency to ethanol within a flow cell reactor. In situ spectroscopy and electrochemical analysis identified that these dualphase Cu(I) and Cu(0) sites stabilized by grain-boundaries are very robust over the operating potential window, which maintains a high concentration of co-adsorbed *CO and hydroxyl (*OH) species. Theoretical calculations revealed that the presence of *OHad not only promote the easier dimerization of *CO to form *OCCO (ΔG~0.20 eV) at low overpotentials but also preferentially favor the key *CHCOH intermediate hydrogenation to *CHCHOH (ethanol pathway) while suppressing its dehydration to *CCH (ethylene pathway), which is believed to determine the remarkable ethanol selectivity. Such imperative intermediates associated with the bifurcation pathway were directly distinguished by isotope labelling in situ infrared spectroscopy. Our work promotes the understanding of bifurcating mechanism of CO2ER-to-hydrocarbons more deeply, providing a feasible strategy for the design of efficient ethanol-targeted catalysts.

Anion Modulation of Ag-Imidazole Cuboctahedral Cage Microenvironments for Efficient Electrocatalytic CO2 Reduction

How to achieve CO2 electroreduction in high efficiency is a current challenge with the mechanism not well understood yet. The metal-organic cages with multiple metal sites, tunable active centers, and well-defined microenvironments may provide a promising catalyst model. Here, we report self-assembly of Ag4L4 type cuboctahedral cages from coordination dynamic Ag+ ion and triangular imidazolyl ligand 1,3,5-tris(1-benzylbenzimidazol-2-yl) benzene (Ag-MOC-X, X=NO3, ClO4, BF4) via anion template effect. Notably, Ag-MOC-NO3 achieves the highest CO faradaic efficiency in pH-universal electrolytes of 86.1 % (acidic), 94.1 % (neutral) and 95.3 % (alkaline), much higher than those of Ag-MOC-ClO4 and Ag-MOC-BF4 with just different counter anions. In situ attenuated total reflection Fourier transform infrared spectroscopy observes formation of vital intermediate *COOH for CO2-to-CO conversion. The density functional theory calculations suggest that the adsorption of CO2 on unsaturated Ag-site is stabilized by C-H⋅⋅⋅O hydrogen-bonding of CO2 in a microenvironment surrounded by three benzimidazole rings, and the activation of CO2 is dependent on the coordination dynamics of Ag-centers modulated by the hosted anions through Ag⋅⋅⋅X interactions. This work offers a supramolecular electrocatalytic strategy based on Ag-coordination geometry and host-guest interaction regulation of MOCs as high-efficient electrocatalysts for CO2 reduction to CO which is a key intermediate in chemical industry process.

Oxygen Vacancy-Driven Heterointerface Breaks the Linear-Scaling Relationship of Intermediates toward Electrocatalytic CO2 Reduction

Smart metal-metal oxide heterointerface construction holds promising potentials to endow an efficient electron redistribution for electrochemical CO2 reduction reaction (CO2RR). However, inhibited by the intrinsic linear-scaling relationship, the binding energies of competitive intermediates will simultaneously change due to the shifts of electronic energy level, making it difficult to exclusively tailor the binding energies to target intermediates and the final CO2RR performance. Nonetheless, creating specific adsorption sites selective for target intermediates probably breaks the linear-scaling relationship. To verify it, Ag nanoclusters were anchored onto oxygen vacancy-rich CeO2 nanorods (Ag/OV-CeO2) for CO2RR, and it was found that the oxygen vacancy-driven heterointerface could effectively promote CO2RR to CO across the entire potential window, where a maximum CO Faraday efficiency (FE) of 96.3% at -0.9 V and an impressively high CO FE of over 62.3% were achieved at a low overpotential of 390 mV within a flow cell. The experimental and computational results collectively suggested that the oxygen vacancy-driven heterointerfacial charge spillover conferred an optimal electronic structure of Ag and introduced additional adsorption sites exclusively recognizable for *COOH, which, beyond the linear-scaling relationship, enhanced the binding energy to *COOH without hindering *CO desorption, thus resulting in the efficient CO2RR to CO.

Restructuring multi-phase interfaces from Cu-based metal-organic frameworks for selective electroreduction of CO2 to C2H4

Multi-phase interfaces are promising for surmounting the energy barriers of electrochemical CO2 reduction involving multiple electron transfer steps, but challenges still remain in constructing interfacial micro-structures and unraveling their dynamic changes and working mechanism. Herein, highly active Ag/Cu/Cu2O heterostructures are in situ electrochemically restructured from Ag-incorporating HKUST-1, a Cu-based metal-organic framework (MOF), and accomplish efficient CO2-to-C2H4 conversion with a high faradaic efficiency (57.2% at -1.3 V vs. RHE) and satisfactory stability in flow cells, performing among the best of recently reported MOFs and their derivatives. The combination of in/ex situ characterizations and theoretical calculations reveals that Ag plays a crucial role in stabilizing Cu(i) and increasing the CO surface coverage, while the active Cu/Cu2O interfaces significantly reduce the energy barrier of C-C coupling toward the boosted ethylene production. This work not only proves MOFs as feasible precursors to derive efficient electrocatalysts on site, but also provides in-depth understanding on the working interfaces at an atomic level.

Illustration of the Intrinsic Mechanism of Reconstructed Cu Clusters for Enhanced CO2 Electroreduction to Ethanol Production with Industrial Current Density

Copper-based catalysts have been attracting increasing attention for CO2 electroreduction into value-added multicarbon chemicals. However, most Cu-based catalysts are designed for ethylene production, while ethanol production with high Faradaic efficiency at high current density still remains a great challenge. Herein, Cu clusters supported on single-atom Cu dispersed nitrogen-doped carbon (Cux/Cu-N/C) show ethanol Faradaic efficiency of ∼40% and partial current density of ∼350 mA cm-2. Quasi in situ X-ray photoelectron spectroscopy and operando X-ray absorption spectroscopy results suggest the generation of surface asymmetrical sites of Cu+ and Cu0 as well as Cu clusters by electrochemical reduction and reconstruction during the CO2 electroreduction process. Density functional theory calculations indicate that the interaction between Cu clusters and the Cu-N/C support enhances *CO adsorption, facilitates the C-C coupling step, and favors the hydrogenation rather than dehydroxylation of the critical intermediate *CHCOH toward ethanol in the bifurcation.

Highly dispersed Cu-Cu2O-CeOx interfaces on reduced graphene oxide for CO2 electroreduction to C2+ products

The Cu0-Cu+ interfaces play a key role in the electrochemical CO2 reduction reaction (CO2RR) to produce multi-carbon products (C2+), however, it is difficult for Cu+ to exist stably under reducing conditions. Herein, we construct highly dispersed and stable Cu-Cu2O-CeOx interface on reduced graphene oxide (rGO) for CO2 electroreduction to C2+ products. During the synthesis process, utilizing strong electrostatic interactions, the complex ions of Cu2+ and Ce3+ are uniformly adsorbed on the surface of graphene oxide. Then, under the solvothermal reaction of ethylene glycol and thiourea, the two metal complex ions are converted into highly dispersed and ultrafine Cu2S-CeOx nanocomposites on rGO. Interestingly, CeOx and thiourea synergistically regulate the generation of only Cu+. Under the CO2RR process, the reconstruction of Cu2S promotes the formation of Cu0 and Cu2O species. CeOx stabilizes partial Cu+ species and promotes the formation of Cu-Cu2O-CeOx composite interface. With the help of synergistic effect of Cu0, Cu+ and CeOx, the optimized reaction interface achieves the Faradaic efficiency (FE) of 74.5 % for C2+ products with the current density of 230 mA cm-2 at -0.9 V versus the reversible hydrogen electrode. In situ attenuate total reflectance-infrared absorption spectroscopy (ATR-IRAS) spectra show that the composite interfaces promote the adsorption and activation of H2O and CO2, improve the surface coverage of CO intermediates (*CO), and thus accelerate the CC coupling process.

Efficient ammonia synthesis from the air using tandem non-thermal plasma and electrocatalysis at ambient conditions

While electrochemical N2 reduction presents a sustainable approach to NH3 synthesis, addressing the emission- and energy-intensive limitations of the Haber-Bosch process, it grapples with challenges in N2 activation and competing with pronounced hydrogen evolution reaction. Here we present a tandem air-NOx-NOx--NH3 system that combines non-thermal plasma-enabled N2 oxidation with Ni(OH)x/Cu-catalyzed electrochemical NOx- reduction. It delivers a high NH3 yield rate of 3 mmol h-1 cm-2 and a corresponding Faradaic efficiency of 92% at -0.25 V versus reversible hydrogen electrode in batch experiments, outperforming previously reported ones. Furthermore, in a flow mode concurrently operating the non-thermal plasma and the NOx- electrolyzer, a stable NH3 yield rate of approximately 1.25 mmol h-1 cm-2 is sustained over 100 h using pure air as the intake. Mechanistic studies indicate that amorphous Ni(OH)x on Cu interacts with hydrated K+ in the double layer through noncovalent interactions and accelerates the activation of water, enriching adsorbed hydrogen species that can readily react with N-containing intermediates. In situ spectroscopies and density functional theory (DFT) results reveal that NOx- adsorption and their hydrogenation process are optimized over the Ni(OH)x/Cu surface. This work provides new insights into electricity-driven distributed NH3 production using natural air at ambient conditions.

Fluorine Modification Promoted Water Dissociation into Atomic Hydrogen on a Copper Electrode for Efficient Neutral Nitrate Reduction and Ammonia Recovery

Electrocatalytic nitrate reduction to ammonia (NITRR) offers an attractive solution for alleviating environmental concerns, yet in neutral media, it is challenging as a result of the reliance on the atomic hydrogen (H*) supply by breaking the stubborn HO-H bond (∼492 kJ/mol) of H2O. Herein, we demonstrate that fluorine modification on a Cu electrode (F-NFs/CF) favors the formation of an O-H···F hydrogen bond at the Cu-H2O interface, remarkably stretching the O-H bond of H2O from 0.98 to 1.01 Å and lowering the energy barrier of water dissociation into H* from 0.64 to 0.35 eV at neutral pH. As a benefit from these advantages, F-NFs/CF could rapidly reduce NO3- to NH3 with a rate constant of 0.055 min-1 and a NH3 selectivity of ∼100%, far higher than those (0.004 min-1 and 9.2%) of the Cu counterpart. More importantly, we constructed a flow-through coupled device consisting of a NITRR electrolyzer and a NH3 recovery unit, realizing 98.1% of total nitrogen removal with 99.3% of NH3 recovery and reducing the denitrification cost to $5.1/kg of N. This study offers an effective strategy to manipulate the generation of H* from water dissociation for efficient NO3--to-NH3 conversion and sheds light on the importance of surface modification on a Cu electrode toward electrochemical reactions.

Cooperation of Different Active Sites to Promote CO2 Electroreduction to Multi-carbon Products at Ampere-Level

Electroreduction of CO2 to C2+ products provides a promising strategy for reaching the goal of carbon neutrality. However, achieving high selectivity of C2+ products at high current density remains a challenge. In this work, we designed and prepared a multi-sites catalyst, in which Pd was atomically dispersed in Cu (Pd-Cu). It was found that the Pd-Cu catalyst had excellent performance for producing C2+ products from CO2 electroreduction. The Faradaic efficiency (FE) of C2+ products could be maintained at approximately 80.8 %, even at a high current density of 0.8 A cm-2 for at least 20 hours. In addition, the FE of C2+ products was above 70 % at 1.4 A cm-2. Experiments and density functional theory (DFT) calculations revealed that the catalyst had three distinct catalytic sites. These three active sites allowed for efficient conversion of CO2, water dissociation, and CO conversion, ultimately leading to high yields of C2+ products.

Recent Advances in Electrocatalytic Hydrogenation Reactions on Copper-Based Catalysts

Hydrogenation reactions play a critical role in the synthesis of value-added products within the chemical industry. Electrocatalytic hydrogenation (ECH) using water as the hydrogen source has emerged as an alternative to conventional thermocatalytic processes for sustainable and decentralized chemical synthesis under mild conditions. Among the various ECH catalysts, copper-based (Cu-based) nanomaterials are promising candidates due to their earth-abundance, unique electronic structure, versatility, and high activity/selectivity. Herein, recent advances in the application of Cu-based catalysts in ECH reactions for the upgrading of valuable chemicals are systematically analyzed. The unique properties of Cu-based catalysts in ECH are initially introduced, followed by design strategies to enhance their activity and selectivity. Then, typical ECH reactions on Cu-based catalysts are presented in detail, including carbon dioxide reduction for multicarbon generation, alkyne-to-alkene conversion, selective aldehyde conversion, ammonia production from nitrogen-containing substances, and amine production from organic nitrogen compounds. In these catalysts, the role of catalyst composition and nanostructures toward different products is focused. The co-hydrogenation of two substrates (e.g., CO2 and NOx n, SO3 2-, etc.) via C─N, C─S, and C─C cross-coupling reactions are also highlighted. Finally, the critical issues and future perspectives of Cu-catalyzed ECH are proposed to accelerate the rational development of next-generation catalysts.

Steering the Reconstruction of Oxide-Derived Cu by Secondary Metal for Electrosynthesis of n-Propanol from CO

As fuel and an important chemical feedstock, n-propanol is highly desired in electrochemical CO2/CO reduction on Cu catalysts. However, the precise regulation of the Cu localized structure is still challenging and poorly understood, thus hindering the selective n-propanol electrosynthesis. Herein, by decorating Au nanoparticles (NPs) on CuO nanosheets (NSs), we present a counterintuitive transformation of CuO into undercoordinated Cu sites locally around Au NPs during CO reduction. In situ spectroscopic techniques reveal the Au-steered formation of abundant undercoordinated Cu sites during the removal of oxygen on CuO. First-principles accuracy molecular dynamic simulation demonstrates that the localized Cu atoms around Au tend to rearrange into disordered layer rather than a Cu (111) close-packed plane observed on bare CuO NSs. These Au-steered undercoordinated Cu sites facilitate CO binding, enabling selective electroreduction of CO into n-propanol with a high Faradaic efficiency of 48% in a flow cell. This work provides new insight into the regulation of the oxide-derived catalysts reconstruction with a secondary metal component.

Cd/Cd(OH)2 Nanosheets Enhancing the Electrocatalytic Activity of CO2 Reduction to CO

Electric-driven conversion of carbon dioxide (CO2 ) to carbon monoxide (CO) under mild reaction conditions offers a promising approach to mitigate the greenhouse effect and the energy crisis. Surface engineering is believed to be one of the prospective methods for enhancing the electrocatalytic activity of CO2 reduction. Herein, hydroxyl (OH) groups were successfully introduced to cadmium nanosheets to form cadmium and cadmium hydroxide nanocomposites (i. e. Cd/Cd(OH)2 nanosheets) via a facile two-step method. The as-prepared Cd/Cd(OH)2 /CP (CP indicates carbon paper) electrode displays excellent electrocatalytic activity for CO2 reduction to produce CO. The Faradaic efficiency of CO reaches 98.3 % and the current density achieves 23.8 mA cm-2 at -2.0 V vs. Ag/Ag+ in a CO2 -saturated 30 wt% 1-butyl-3-methylimidazole hexafluorophosphate ([Bmim]PF6 )-65 wt% acetonitrile (CH3 CN)-5 wt% water (H2 O) electrolyte. And the CO partial current density can reach up to 71.6 mA cm-2 with the CO Faradaic efficiency of more than 85 % at -2.3 V vs. Ag/Ag+ , which stands out against Cd/CP, Cd(OH)2 /CP, and Cd/CdO/CP electrodes. The excellent electrocatalytic performance of the Cd/Cd(OH)2 /CP electrode can be attributed to its unique structural properties, suitable OH groups, perfect interaction with electrolyte, abundant active sites and fast electron transfer rate.

Highly Efficient Electroreduction of CO2 to Ethanol via Asymmetric C-C Coupling by a Metal-Organic Framework with Heterodimetal Dual Sites

The electroreduction of CO2 into value-added liquid fuels holds great promise for addressing global environmental and energy challenges. However, achieving highly selective yielding of multi-carbon oxygenates through the electrochemical CO2 reduction reaction (eCO2RR) is a formidable task, primarily due to the sluggish asymmetric C-C coupling reaction. In this study, a novel metal-organic framework (CuSn-HAB) with unprecedented heterometallic Sn···Cu dual sites (namely, a pair of SnN2O2 and CuN4 sites bridged by μ-N atoms) was designed to overcome this limitation. CuSn-HAB demonstrated an impressive Faradic efficiency (FE) of 56(2)% for eCO2RR to alcohols, achieving a current density of 68 mA cm-2 at a low potential of -0.57 V (vs RHE). Notably, no significant degradation was observed over a continuous 35 h operation at the specified current density. Mechanistic investigations revealed that, in comparison to the copper site, the SnN2O2 site exhibits a higher affinity for oxygen atoms. This enhanced affinity plays a pivotal role in facilitating the generation of the key intermediate *OCH2. Consequently, compared to homometallic Cu···Cu dual sites (generally yielding ethylene product), the heterometallic dual sites were proved to be more thermodynamically favorable for the asymmetric C-C coupling between *CO and *OCH2, leading to the formation of the key intermediate *CO-*OCH2, which is favorable for yielding ethanol product.

Switching between C2+ Products and CH4 in CO2 Electrolysis by Tuning the Composition and Structure of Rare-Earth/Copper Catalysts

Rational regulation of the reaction pathway to produce the desired products is one of the most significant challenges in the electrochemical CO2 reduction reaction (CO2RR). Herein, we designed a series of rare-earth Cu catalysts with mixed phases. It was found that the products could be switched from C2+ to CH4 by tuning the composition and structure of the catalysts. Particularly at the Cu/Sm atomic ratio of 9/1 (Cu9Sm1-Ox), the Faradaic efficiency (FE) for C2+ products (FEC2+) could reach 81% at 700 mA cm-2 with negligible CH4. However, the FE of CH4 (FECH4) was 65% at 500 mA cm-2 over Cu1Sm9-Ox (Cu/Sm = 1/9), and the FEC2+ was extremely low. Experiments and theoretical studies indicated that the stable CuSm2O4 phase existed in all the catalysts within the Cu/Sm range of 9/1 to 1/9. At a high Cu content, the catalyst was composed of CuSm2O4 and Cu phases. The small amount of Sm could enhance the binding strength of *CO and facilitate C-C coupling. Conversely, at a high Sm content, the catalyst was composed of CuSm2O4 and Sm2O3 phases. Sm could effectively stabilize bivalent Cu and enrich proton donors, lowering the reaction energy of *CO for deep hydrogenation to generate CH4. In both pathways, the stable CuSm2O4 phase could cooperate with the Cu or Sm2O3 phases, which induced the formation of different microenvironments to generate different products. This strategy also had commonality with other Cu-rare-earth (La, Pr, and Eu) catalysts to boost the CO2RR for C2+ or CH4 production.

Designs of Tandem Catalysts and Cascade Catalytic Systems for CO2 Upgrading

Upgrading CO2 into multi-carbon (C2+) compounds through the CO2 reduction reaction (CO2 RR) offers a practical approach to mitigate atmospheric CO2 while simultaneously producing high value chemicals. The reaction pathways for C2+ production involve multi-step proton-coupled electron transfer (PCET) and C-C coupling processes. By increasing the surface coverage of adsorbed protons (*Had ) and *CO intermediates, the reaction kinetics of PCET and C-C coupling can be accelerated, thereby promoting C2+ production. However, *Had and *CO are competitively adsorbed intermediates on monocomponent catalysts, making it difficult to break the linear scaling relationship between the adsorption energies of the *Had /*CO intermediate. Recently, tandem catalysts consisting of multicomponents have been developed to improve the surface coverage of *Had or *CO by enhancing water dissociation or CO2 -to-CO production on auxiliary sites. In this context, we provide a comprehensive overview of the design principles of tandem catalysts based on reaction pathways for C2+ products. Moreover, the development of cascade CO2 RR catalytic systems that integrate CO2 RR with downstream catalysis has expanded the range of potential CO2 upgrading products. Therefore, we also discuss recent advancements in cascade CO2 RR catalytic systems, highlighting the challenges and perspectives in these systems.

Oxophilicity-Controlled CO2 Electroreduction to C2+ Alcohols over Lewis Acid Metal-Doped Cuδ+ Catalysts

Cu-based electrocatalysts have great potential for facilitating CO2 reduction to produce energy-intensive fuels and chemicals. However, it remains challenging to obtain high product selectivity due to the inevitable strong competition among various pathways. Here, we propose a strategy to regulate the adsorption of oxygen-associated active species on Cu by introducing an oxophilic metal, which can effectively improve the selectivity of C2+ alcohols. Theoretical calculations manifested that doping of Lewis acid metal Al into Cu can affect the C-O bond and Cu-C bond breaking toward the selectively determining intermediate (shared by ethanol and ethylene), thus prioritizing the ethanol pathway. Experimentally, the Al-doped Cu catalyst exhibited an outstanding C2+ Faradaic efficiency (FE) of 84.5% with remarkable stability. In particular, the C2+ alcohol FE could reach 55.2% with a partial current density of 354.2 mA cm-2 and a formation rate of 1066.8 μmol cm-2 h-1. A detailed experimental study revealed that Al doping improved the adsorption strength of active oxygen species on the Cu surface and stabilized the key intermediate *OC2H5, leading to high selectivity toward ethanol. Further investigation showed that this strategy could also be extended to other Lewis acid metals.

Multiscale CO2 Electrocatalysis to C2+ Products: Reaction Mechanisms, Catalyst Design, and Device Fabrication

Electrosynthesis of value-added chemicals, directly from CO2, could foster achievement of carbon neutral through an alternative electrical approach to the energy-intensive thermochemical industry for carbon utilization. Progress in this area, based on electrogeneration of multicarbon products through CO2 electroreduction, however, lags far behind that for C1 products. Reaction routes are complicated and kinetics are slow with scale up to the high levels required for commercialization, posing significant problems. In this review, we identify and summarize state-of-art progress in multicarbon synthesis with a multiscale perspective and discuss current hurdles to be resolved for multicarbon generation from CO2 reduction including atomistic mechanisms, nanoscale electrocatalysts, microscale electrodes, and macroscale electrolyzers with guidelines for future research. The review ends with a cross-scale perspective that links discrepancies between different approaches with extensions to performance and stability issues that arise from extensions to an industrial environment.

Enhanced CO Affinity on Cu Facilitates CO2 Electroreduction toward Multi-Carbon Products

Electrochemical CO2 reduction reaction (CO2 RR) is a promising strategy for waste CO2 utilization and intermittent electricity storage. Herein, it is reported that bimetallic Cu/Pd catalysts with enhanced *CO affinity show a promoted CO2 RR performance for multi-carbon (C2+) production under industry-relevant high current density. Especially, bimetallic Cu/Pd-1% catalyst shows an outstanding CO2 -to-C2+ conversion with 66.2% in Faradaic efficiency (FE) and 463.2 mA cm-2 in partial current density. An increment in the FE ratios of C2+ products to CO  for Cu/Pd-1% catalyst further illuminates a preferable C2+ production. In situ Raman spectra reveal that the atop-bounded CO is dominated by low-frequency band CO on Cu/Pd-1% that leads to C2+ products on bimetallic catalysts, in contrast to the majority of high-frequency band CO on Cu that favors the formation of CO. Density function theory calculation confirms that bimetallic Cu/Pd catalyst enhances the *CO adsorption and reduces the Gibbs free energy of the CC coupling process, thereby favoring the formation of C2+ products.

Regulated Surface Electronic States of CuNi Nanoparticles through Metal-Support Interaction for Enhanced Electrocatalytic CO2 Reduction to Ethanol

Developing stable catalysts with higher selectivity and activity within a wide potential range is critical for efficiently converting CO2 to ethanol. Here, the carbon-encapsulated CuNi nanoparticles anchored on nitrogen-doped nanoporous graphene (CuNi@C/N-npG) composite are designedly prepared and display the excellent CO2 reduction performance with the higher ethanol Faradaic effiency (FEethanol  ≥ 60%) in a wide potential window (600 mV). The optimal cathodic energy efficiency (47.6%), Faradaic efficiency (84%), and selectivity (96.6%) are also obtained at -0.78 V versus reversible hydrogen electrode (RHE). Combining with the density functional theory (DFT) calculations, it is demonstrated that the stronger metal-support interaction (Ni-N-C) can regulate the surface electronic structure effectively, boosting the electron transfer and stabilizing the active sites (Cu0 -Cuδ+ ) on the surface of CuNi@C/N-npG, finally realizing the controllable transition of reaction intermediates. This work may guide the designs of electrocatalysts with highly catalytic performance for CO2 reduction to C2+ products.

Modulating adsorbed hydrogen drives electrochemical CO2-to-C2 products

Electrocatalytic CO₂ reduction is a typical reaction involving two reactants (CO₂ and H₂O). However, the role of H₂O dissociation, which provides active *H species to multiple protonation steps, is usually overlooked. Herein, we construct a dual-active sites catalyst comprising atomic Cu sites and Cu nanoparticles supported on N-doped carbon matrix. Efficient electrosynthesis of multi-carbon products is achieved with Faradaic efficiency approaching 75.4% with a partial current density of 289.2 mA cm^-2 at -0.6 V. Experimental and theoretical studies reveal that Cu nanoparticles facilitate the C-C coupling step through *CHO dimerization, while the atomic Cu sites boost H₂O dissociation to form *H. The generated *H migrate to Cu nanoparticles and modulate the *H coverage on Cu NPs, and thus promote *CO-to-*CHO. The dual-active sites effect of Cu single-sites and Cu nanoparticles gives rise to the catalytic performance.

Guiding catalytic CO2 reduction to ethanol with copper grain boundaries

The grain boundaries (GBs) in copper (Cu) electrocatalysts have been suggested as active sites for CO₂ electroreduction to ethanol. Nevertheless, the mechanisms are still elusive. Herein, we describe how GBs tune the activity and selectivity for ethanol on two representative Cu-GB models, namely Cu∑3/(111) GB and Cu∑5/(100) GB, using joint first-principles calculations and experiments. The unique geometric structures on the GBs facilitate the adsorption of bidentate intermediates, *COOH and *CHO, which are crucial for CO₂ activation and CO protonation. The decreased CO-CHO coupling barriers on the GBs can be rationalized via kinetics analysis. Furthermore, when introducing GBs into Cu (100), the product is selectively switched from ethylene to ethanol, due to the stabilization effect for *CH₃CHO and inapposite geometric structure for *O adsorption, which are validated by experimental trends. An overall 12.5 A current and a single-pass conversion of 5.18% for ethanol can be achieved over the synthesized Cu-GB catalyst by scaling up the electrode into a 25 cm² membrane electrode assembly system.

Effects of Iron Species on Low Temperature CO2 Electrolyzers

Electrochemical energy conversion devices are considered key in reducing CO2 emissions and significant efforts are being applied to accelerate device development. Unlike other technologies, low temperature electrolyzers have the ability to directly convert CO2 into a range of value-added chemicals. To make them commercially viable, however, device efficiency and durability must be increased. Although their design is similar to more mature water electrolyzers and fuel cells, new cell concepts and components are needed. Due to the complexity of the system, singular component optimization is common. As a result, the component interplay is often overlooked. The influence of Fe-species clearly shows that the cell must be considered holistically during optimization, to avoid future issues due to component interference or cross-contamination. Fe-impurities are ubiquitous, and their influence on single components is well-researched. The activity of non-noble anodes has been increased through the deliberate addition of iron. At the same time, however, Fe-species accelerate cathode and membrane degradation. Here, we interpret literature on single components to gain an understanding of how Fe-species influence low temperature CO2 electrolyzers holistically. The role of Fe-species serves to highlight the need for considerations regarding component interplay in general.

Tunable CO2 electroreduction to ethanol and ethylene with controllable interfacial wettability

The mechanism of how interfacial wettability impacts the CO₂ electroreduction pathways to ethylene and ethanol remains unclear. This paper describes the design and realization of controllable equilibrium of kinetic-controlled *CO and *H via modifying alkanethiols with different alkyl chain lengths to reveal its contribution to ethylene and ethanol pathways. Characterization and simulation reveal that the mass transport of CO₂ and H₂O is related with interfacial wettability, which may result in the variation of kinetic-controlled *CO and *H ratio, which affects ethylene and ethanol pathways. Through modulating the hydrophilic interface to superhydrophobic interface, the reaction limitation shifts from insufficient supply of kinetic-controlled *CO to that of *H. The ethanol to ethylene ratio can be continuously tailored in a wide range from 0.9 to 1.92, with remarkable Faradaic efficiencies toward ethanol and multi-carbon (C₂₊) products up to 53.7% and 86.1%, respectively. A C₂₊ Faradaic efficiency of 80.3% can be achieved with a high C₂₊ partial current density of 321 mA cm^-2, which is among the highest selectivity at such current densities.

In Situ/Operando Characterization Techniques of Electrochemical CO2 Reduction

Electrocatalytic conversion of carbon dioxide to valuable chemicals and fuels driven by renewable energy plays a crucial role in achieving net-zero carbon emissions. Understanding the structure-activity relationship and the reaction mechanism is significant for tuning electrocatalyst selectivity. Therefore, characterizing catalyst dynamic evolution and reaction intermediates under reaction conditions is necessary but still challenging. We first summarize the most recent progress in mechanistic understanding of heterogeneous CO2/CO reduction using in situ/operando techniques, including surface-enhanced vibrational spectroscopies, X-ray- and electron-based techniques, and mass spectroscopy, along with discussing remaining limitations. We then offer insights and perspectives to accelerate the future development of in situ/operando techniques.

Over 2 A cm-2 CO2 -to-Ethanol Conversion by Alkali-Metal Cation Induced Copper With Dominant (200) Facets

The high-rate ethanol electrosynthesis from CO₂ is challenging due to the low selectivity and poor activity, which requires the competition with other reduction products and H₂ . Here, the electrochemical reconstruction of Cs₃ Cu₂ Cl₅ perovskite to form surface Cl-bonded, low-coordinated Cs modified Cu(200) nanocubes (CuClCs), is demonstrated. Density functional theory calculations reveal that the CuClCs structure possesses low Bader charges and a large coordination capacity; and thus, can promote the CO₂ -to-ethanol pathway via stabilizing C-O bond in oxygenate intermediates. The CuClCs catalyst exhibits outstanding partial current densities for producing ethanol (up to 2124 ± 54 mA cm^-2 ) as one of the highest reported values in the electrochemical CO₂ or CO reduction. This work suggests an attractive strategy with surface alkali-metal cations for ampere-level CO₂ -to-ethanol electrosynthesis.

Construction of 3D copper-chitosan-gas diffusion layer electrode for highly efficient CO2 electrolysis to C2+ alcohols

High-rate electrolysis of CO₂ to C₂₊ alcohols is of particular interest, but the performance remains far from the desired values to be economically feasible. Coupling gas diffusion electrode (GDE) and 3D nanostructured catalysts may improve the efficiency in a flow cell of CO₂ electrolysis. Herein, we propose a route to prepare 3D Cu-chitosan (CS)-GDL electrode. The CS acts as a "transition layer" between Cu catalyst and the GDL. The highly interconnected network induces growth of 3D Cu film, and the as-prepared integrated structure facilitates rapid electrons transport and mitigates mass diffusion limitations in the electrolysis. At optimum conditions, the C₂₊ Faradaic efficiency (FE) can reach 88.2% with a current density (geometrically normalized) as high as 900 mA cm^-2 at the potential of -0.87 V vs. reversible hydrogen electrode (RHE), of which the C₂₊ alcohols selectivity is 51.4% with a partial current density of 462.6 mA cm^-2, which is very efficient for C₂₊ alcohols production. Experimental and theoretical study indicates that CS induces growth of 3D hexagonal prismatic Cu microrods with abundant Cu (111)/Cu (200) crystal faces, which are favorable for the alcohol pathway. Our work represents a novel example to design efficient GDEs for electrocatalytic CO₂ reduction (CO₂RR).

CO2 electrolysis towards large scale operation: rational catalyst and electrolyte design for efficient flow-cell

The electrochemical CO₂ reduction reaction (CO₂RR) to renewable fuels/chemicals is a potential approach towards addressing the carbon neutral economy. To date, a comprehensive analysis of key performance indicators, such as an intrinsic property of catalyst, reaction environment and technological advancement in the flow cell, is limited. In this study, we discuss how the design of catalyst material, electrolyte and engineering gas diffusion electrode (GDE) could affect the CO₂RR in a gas-fed flow cell. Significant emphasis is given to scale-up requirements, such as promising catalysts with a partial current density of ≥100 mA cm^-2 and high faradaic efficiency. Additional experimental hurdles and their potential solutions, as well as the best available protocols for data acquisition for catalyst activity evaluation, are listed. We believe this manuscript provides some insights into the making of catalysts and electrolytes in a rational manner along with the engineering of GDEs towards CO₂RR.

A Review of Phosphorus Structures as CO2 Reduction Photocatalysts

Effective photocatalytic carbon dioxide (CO₂ ) reduction into high-value-added chemicals is promising to mitigate current energy crisis and global warming issues. Finding effective photocatalysts is crucial for photocatalytic CO₂ reduction. Currently, metal-based semiconductors for photocatalytic CO₂ reduction have been well reviewed, while review of nonmetal-based semiconductors is almost limited to carbon nitrides. Phosphorus is a promising nonmetal photocatalysts with various allotropes and tunable band gaps, which has been demonstrated to be promising non-metallic photocatalysts. However, no systematic review about phosphorus structures for photocatalytic CO₂ reduction reactions has been reported. Herein, the progresses of phosphorus structures as photocatalysts for CO₂ reduction are reviewed. The fundamentals of photocatalytic CO₂ reduction, corresponding properties of phosphorus allotropes, photocatalysts with phosphorus doping or phosphorus-containing ligands, research progress of phosphorus allotropes as photocatalysts for CO₂ reduction have been reviewed in this paper. The future research and perspective of phosphorus structures for photocatalytic CO₂ reduction are also presented.