In Situ Halogen-Ion Leaching Regulates Multiple Sites on Tandem Catalysts for Efficient CO2 Electroreduction to C2+ Products

Promoting CO2 Electroreduction to Ethane by Iodide-Derived Copper with the Hydrophobic Surface

Electrochemical reduction of CO2 to value-added products provides a feasible pathway for mitigating net carbon emissions and storing renewable energy. However, the low dimerization efficiency of the absorbed CO intermediate (*CO) and the competitive hydrogen evolution reaction hinder the selective electroreduction of CO2 to ethane (C2H6) with a high energy density. Here, we designed hydrophobic iodide-derived copper electrodes (I-Cu/Nafion) for reducing CO2 to C2H6. The Faradaic efficiency of C2H6 reached 23.37% at -0.7 V vs RHE over the I-Cu/Nafion electrode in an H-type cell, which was about 1.7 times higher than that of the I-Cu electrode. The hydrophobic properties of the I-Cu/Nafion electrodes led to an increase in the local CO2 concentration and stabilized the Cu+ species. In situ Raman characterizations and density functional theory calculations indicate that the enhanced performances could be ascribed to the strong *CO adsorption and decreased the formation energy of *COOH and *COCOH intermediates. This study highlights the effect of the hydrophobic surface on Cu-based catalysts in the electroreduction of CO2 and provides a promising way to adjust the selectivity of C2 products.

Electronic Structure Design of Transition Metal-Based Catalysts for Electrochemical Carbon Dioxide Reduction

With the increasingly serious greenhouse effect, the electrochemical carbon dioxide reduction reaction (CO2RR) has garnered widespread attention as it is capable of leveraging renewable energy to convert CO2 into value-added chemicals and fuels. However, the performance of CO2RR can hardly meet expectations because of the diverse intermediates and complicated reaction processes, necessitating the exploitation of highly efficient catalysts. In recent years, with advanced characterization technologies and theoretical simulations, the exploration of catalytic mechanisms has gradually deepened into the electronic structure of catalysts and their interactions with intermediates, which serve as a bridge to facilitate the deeper comprehension of structure-performance relationships. Transition metal-based catalysts (TMCs), extensively applied in electrochemical CO2RR, demonstrate substantial potential for further electronic structure modulation, given their abundance of d electrons. Herein, we discuss the representative feasible strategies to modulate the electronic structure of catalysts, including doping, vacancy, alloying, heterostructure, strain, and phase engineering. These approaches profoundly alter the inherent properties of TMCs and their interaction with intermediates, thereby greatly affecting the reaction rate and pathway of CO2RR. It is believed that the rational electronic structure design and modulation can fundamentally provide viable directions and strategies for the development of advanced catalysts toward efficient electrochemical conversion of CO2 and many other small molecules.

Efficient Lead Removal by Assembly of Bio-Derived Ellagate Framework, Which Enables Electrocatalytic Reduction of CO2 to Formate

Lead (Pb) poisoning and CO2-induced global warming represent two exemplary environmental and energy issues threatening humanity. Various biomass-derived materials are reported to take up Pb and convert CO2 electrochemically into low-valent carbon species, but these works address the problems separately rather than settle the issues simultaneously. In this work, cheap, natural ellagic acid (EA) extracted from common plants is adopted to assemble a stable metal-organic framework (MOF), EA-Pb, by effective capture of Pb2+ ions in an aqueous medium (removal rate close to 99%). EA-Pb represents the first structurally well-defined Pb-based MOF showing selective electrocatalytic CO2-to-HCOO- conversion with Faradaic efficiency (FE) of 95.37% at -1.08 V versus RHE. The catalytic mechanism is studied by 13CO2 labeling, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and theoretical calculation. The use of EA-Pb as an electrocatalyst for CO2 reduction represents a 2-in-1 solution of converting detrimental wastes (Pb2+) as well as natural resources (EA) into wealth (electrocatalytic EA-Pb) for addressing the global warming issue.

Unveiling pH-Dependent Adsorption Strength of *CO2 - Intermediate over High-Density Sn Single Atom Catalyst for Acidic CO2-to-HCOOH Electroreduction

The acidic electrochemical CO2 reduction reaction (CO2RR) for direct formic acid (HCOOH) production holds promise in meeting the carbon-neutral target, yet its performance is hindered by the competing hydrogen evolution reaction (HER). Understanding the adsorption strength of the key intermediates in acidic electrolyte is indispensable to favor CO2RR over HER. In this work, high-density Sn single atom catalysts (SACs) were prepared and used as catalyst, to reveal the pH-dependent adsorption strength and coverage of *CO2 - intermediatethat enables enhanced acidic CO2RR towards direct HCOOH production. At pH=3, Sn SACs could deliver a high Faradaic efficiency (90.8 %) of HCOOH formation and a corresponding partial current density up to -178.5 mA cm-2. The detailed in situ attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopic studies reveal that a favorable alkaline microenvironment for CO2RR to HCOOH is formed near the surface of Sn SACs, even in the acidic electrolyte. More importantly, the pH-dependent adsorption strength of *CO2 - intermediate is unravelled over the Sn SACs, which in turn affects the competition between HER and CO2RR in acidic electrolyte.

Construction of Cobalt Porphyrin-Modified Cu2 O Nanowire Array as a Tandem Electrocatalyst for Enhanced CO2 Reduction to C2 Products

Here, the molecule-modified Cu-based array is first constructed as the self-supporting tandem catalyst for electrocatalytic CO2 reduction reaction (CO2 RR) to C2 products. The modification of cuprous oxide nanowire array on copper mesh (Cu2 O@CM) with cobalt(II) tetraphenylporphyrin (CoTPP) molecules is achieved via a simple liquid phase method. The systematical characterizations confirm that the formation of axial coordinated Co-O-Cu bond between Cu2 O and CoTPP can significantly promote the dispersion of CoTPP molecules on Cu2 O and the electrical properties of CoTPP-Cu2 O@CM heterojunction array. Consequently, as compared to Cu2 O@CM array, the optimized CoTPP-Cu2 O@CM sample as electrocatalyst can realize the 2.08-fold C2 Faraday efficiency (73.2% vs 35.2%) and the 2.54-fold current density (-52.9 vs -20.8 mA cm-2 ) at -1.1 V versus RHE in an H-cell. The comprehensive performance is superior to most of the reported Cu-based materials in the H-cell. Further study reveals that the CoTPP adsorption on Cu2 O can restrain the hydrogen evolution reaction, improve the coverage of * CO intermediate, and maintain the existence of Cu(I) at low potential.

Alkyl sulfonate surfactant mediates electroreduction of carbon dioxide to ethylene or ethanol over hydroxide-derived copper catalysts

For CO2 electroreduction (CO2ER) to C2 compounds, it is generally accepted that the formation of ethylene and ethanol shares the same intermediate, *HCCOH. The majority of studies have achieved high faradaic efficiency (FE) towards ethylene, but faced challenges to get high ethanol FE. Herein, we present an alkyl sulfonate surfactant (e.g., sodium dodecyl sulfonate, SDS) mediated CO2ER to a C2 product over an in situ generated Cu catalyst (Cu@SDS) from SDS-modified Cu(OH)2. It achieves the CO2ER to ethylene as the sole C2 product at low applied voltages with a FE of 55% at -0.6 V vs. RHE and to ethanol as the main product at potentials ≥0.7 V with a maximum FE of 64% and a total C2 FE of 86% at -0.8 V, with a current density of 231 mA cm-2 in a flow cell. Mechanism investigation indicates that SDS modifies the oxidation state of the in situ formed Cu species in Cu@SDS, thus tuning the catalyst activity for CO2ER and lowering the C-C coupling energy barrier; meanwhile, it tunes the adsorption mode of the *HCCOH intermediates on the catalyst, thus mediating the selectivity of CO2ER towards C2 products.

Nano-Cu Derived from a Copper Nitride Precatalyst for Reductive Coupling of Nitroaromatics to Azo Compounds

The study of structural reconstruction is vital for the understanding of the real active sites in heterogeneous catalysis and guiding the improved catalyst design. Herein, we applied a copper nitride precatalyst in the nitroarene reductive coupling reaction and made a systematic investigation on the dynamic structural evolution behaviors and catalytic performance. This Cu3N precatalyst undergoes a rapid phase transition to nanostructured Cu with rich defective sites, which act as the actual catalytic sites for the coupling process. The nitride-derived defective Cu is very active and selective for azo formation, with 99.6% conversion of nitrobenzene and 97.1% selectivity to azobenzene obtained under mild reaction conditions. Density functional theory calculations suggest that the defective Cu sites play a role for the preferential adsorption of nitrosobenzene intermediates and significantly lowered the activation energy of the key coupling step. This work not only proposes a highly efficient noble-metal-free catalyst for nitroarenes coupling to valuable azo products but also may inspire more scientific interest in the study of the dynamic evolution of metal nitrides in different catalytic reactions.

Local reaction environment in electrocatalysis

Beyond conventional electrocatalyst engineering, recent studies have unveiled the effectiveness of manipulating the local reaction environment in enhancing the performance of electrocatalytic reactions. The general principles and strategies of local environmental engineering for different electrocatalytic processes have been extensively investigated. This review provides a critical appraisal of the recent advancements in local reaction environment engineering, aiming to comprehensively assess this emerging field. It presents the interactions among surface structure, ions distribution and local electric field in relation to the local reaction environment. Useful protocols such as the interfacial reactant concentration, mass transport rate, adsorption/desorption behaviors, and binding energy are in-depth discussed toward modifying the local reaction environment. Meanwhile, electrode physical structures and reaction cell configurations are viable optimization methods in engineering local reaction environments. In combination with operando investigation techniques, we conclude that rational modifications of the local reaction environment can significantly enhance various electrocatalytic processes by optimizing the thermodynamic and kinetic properties of the reaction interface. We also outline future research directions to attain a comprehensive understanding and effective modulation of the local reaction environment.

Hydrophobic Trinuclear Copper Cluster-Containing Organic Framework for Synergetic Electrocatalytic Synthesis of Amino Acids

Electrocatalytic synthesis of amino acids provides a promising green and efficient pathway to manufacture the basic substances of life. Herein, reaction of 2,5-perfluroalkyl-terepthalohydrazide and tris(4-µ2 -O-carboxaldehyde-pyrazolato-N, N')-tricopper affords a crystalline trinuclear copper cluster-containing organic framework, named F-Cu3 -OF. Incorporation of abundant hydrophobic perfluroalkyl groups inside the channels of F-Cu3 -OF is revealed to successfully suppress the hydrogen evolution reaction via preventing H+ cation with large polarity from the framework of F-Cu3 -OF and in turn increasing the adsorption of other substrates with relatively small polarity like NO3 - and keto acids on the active sites. The copper atoms with short distance in the trinuclear copper clusters of F-Cu3 -OF enable simultaneous activization of NO3 - and keto acids, facilitating the following synergistic and efficient C─N coupling on the basis of in situ spectroscopic investigations together with theoretical calculation. Combination of these effects leads to efficient electroproduction of various amino acids including glycine, alanine, leucine, valine, and phenylalanine from NO3 - and keto acids with a Faraday efficiency of 42%-71% and a yield of 187-957 µmol cm-2 h-1 , representing the thus far best performance. This work shall be helpful for developing economical, eco-friendly, and high-efficiency strategy for the production of amino acids and other life substances.

Enhancing Electroreduction CO2 to Hydrocarbons via Tandem Electrocatalysis by Incorporation Cu NPs in Boron Imidazolate Frameworks

Due to the higher value of deeply-reduced products, electrocatalytic CO2 reduction reaction (CO2 RR) to multi-electron-transfer products has received more attention. One attractive strategy is to decouple individual steps within the complicated pathway via multi-component catalysts design in the concept of tandem catalysts. Here, a composite of Cu@BIF-144(Zn) (BIF = boron imidazolate framework) is synthesized by using an anion framework BIF-144(Zn) as host to impregnate Cu2+ ions that are further reduced to Cu nanoparticles (NPs) via in situ electrochemical transformation. Due to the microenvironment modulation by functional BH(im)3 - on the pore surfaces, the Cu@BIF-144(Zn) catalyst exhibits a perfect synergetic effect between the BIF-144(Zn) host and the Cu NP guest during CO2 RR. Electrochemistry results show that Cu@BIF-144(Zn) catalysts can effectively enhance the selectivity and activity for the CO2 reduction to multi-electron-transfer products, with the maximum FECH4 value of 41.8% at -1.6 V and FEC2H4 value of 12.9% at -1.5 V versus RHE. The Cu@BIF-144(Zn) tandem catalyst with CO-rich microenvironment generated by the Zn catalytic center in the BIF-144(Zn) skeleton enhanced deep reduction on the incorporated Cu NPs for the CO2 RR to multi-electron-transfer products.

Potential Alignment in Tandem Catalysts Enhances CO2-to-C2H4 Conversion Efficiencies

The in-tandem catalyst holds great promise for addressing the limitation of low *CO coverage on Cu-based materials for selective C2H4 generation during CO2 electroreduction. However, the potential mismatch between the CO-formation catalyst and the favorable C-C coupling Cu catalyst represents a bottleneck in these types of electrocatalysts, resulting in low tandem efficiencies. In this study, we propose a robust solution to this problem by introducing a wide-CO generation-potential window nickel single atom catalyst (Ni SAC) supported on a Cu catalyst. The selection of Ni SAC was based on theoretical calculations, and its excellent performance was further confirmed by using in situ IR spectroscopy. The facilitated carbon dimerization in our tandem catalyst led to a ∼370 mA/cm2 partial current density of C2H4, corresponding to a faradic efficiency of ∼62%. This performance remained stable and consistent for at least ∼14 h at a high current density of 500 mA/cm2 in a flow-cell reactor, outperforming most tandem catalysts reported so far.

Steering CO2 Electroreduction Selectivity U-Turn to Ethylene by Cu-Si Bonded Interface

Copper (Cu), with the advantage of producing a deep reduction product, is a unique catalyst for the electrochemical reduction of CO2 (CO2RR). Designing a Cu-based catalyst to trigger CO2RR to a multicarbon product and understanding the accurate structure-activity relationship for elucidating reaction mechanisms still remain a challenge. Herein, we demonstrate a rational design of a core-shell structured silica-copper catalyst (p-Cu@m-SiO2) through Cu-Si direct bonding for efficient and selective CO2RR. The Cu-Si interface fulfills the inversion in CO2RR product selectivity. The product ratio of C2H4/CH4 changes from 0.6 to 14.4 after silica modification, and the current density reaches a high of up to 450 mA cm-2. The kinetic isotopic effect, in situ attenuated total reflection Fourier-transform infrared spectra, and density functional theory were applied to elucidate the reaction mechanism. The SiO2 shell stabilizes the *H intermediate by forming Si-O-H and inhibits the hydrogen evolution reaction effectively. Moreover, the direct-bonded Cu-Si interface makes bare Cu sites with larger charge density. Such bare Cu sites and Si-O-H sites stabilized the *CHO and activated the *CO, promoting the coupling of *CHO and *CO intermediates to form C2H4. This work provides a promising strategy for designing Cu-based catalysts with high C2H4 catalytic activity.

Cu-Based Materials for Enhanced C2+ Product Selectivity in Photo-/Electro-Catalytic CO2 Reduction: Challenges and Prospects

Carbon dioxide conversion into valuable products using photocatalysis and electrocatalysis is an effective approach to mitigate global environmental issues and the energy shortages. Among the materials utilized for catalytic reduction of CO2, Cu-based materials are highly advantageous owing to their widespread availability, cost-effectiveness, and environmental sustainability. Furthermore, Cu-based materials demonstrate interesting abilities in the adsorption and activation of carbon dioxide, allowing the formation of C2+ compounds through C-C coupling process. Herein, the basic principles of photocatalytic CO2 reduction reactions (PCO2RR) and electrocatalytic CO2 reduction reaction (ECO2RR) and the pathways for the generation C2+ products are introduced. This review categorizes Cu-based materials into different groups including Cu metal, Cu oxides, Cu alloys, and Cu SACs, Cu heterojunctions based on their catalytic applications. The relationship between the Cu surfaces and their efficiency in both PCO2RR and ECO2RR is emphasized. Through a review of recent studies on PCO2RR and ECO2RR using Cu-based catalysts, the focus is on understanding the underlying reasons for the enhanced selectivity toward C2+ products. Finally, the opportunities and challenges associated with Cu-based materials in the CO2 catalytic reduction applications are presented, along with research directions that can guide for the design of highly active and selective Cu-based materials for CO2 reduction processes in the future.

High stability copper clusters anchored on N-doped carbon nanosheets for efficient CO2 electroreduction to HCOOH

Cu-based nanomaterials is crucial for electrochemical CO2 reduction reaction (CO2RR), but they inevitably undergo performance degradation due to structural self-reconstruction at a large current density during CO2RR. Here, we developed a pre-synthetic atomically dispersed Cu source strategy to fabricate a catalyst of stable Cu clusters anchored on N-doped carbon nanosheets (c-Cu/NC), which exhibited an exceptional electroreduction for CO2 to HCOOH with a Faradaic efficiency of up to 96.2 % at current density of 276.4 mA cm-2 at - 0.96 V vs. RHE, which surpasses most reported catalysts. Especially, there was no any decay in stability during a 100 h continuous test, attributed to a strong interaction of Cu-C for restraining its self-reconstruction during CO2RR. DFT calculations indicated that N-doped carbon can strongly stabilize Cu clusters for keeping stability and cause the downshift of d-band center of Cu on c-Cu/NC for reducing the desorption energy between c-Cu/NC and OCHO* intermediates. This work provides an effective way to construct stable Cu clusters catalysts, and unveil the origin of catalyticmechanism over Cu clusters anchored on N-doped carbon towards electrochemical conversion ofCO2 to HCOOH.

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

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

Bromine-Enhanced Generation and Epoxidation of Ethylene in Tandem CO2 Electrolysis Towards Ethylene Oxide

The indirect electro-epoxidation of ethylene (C2 H4 ), produced from CO2 electroreduction (CO2 R), holds immense promise for CO2 upcycling to valuable ethylene oxide (EO). However, this process currently has a mediocre Faradaic efficiency (FE) due to sluggish formation and rapid dissociation of active species, as well as reductive deactivation of Cu-based electrocatalysts during the conversion of C2 H4 to EO and CO2 to C2 H4 , respectively. Herein, we report a bromine-induced dual-enhancement strategy designed to concurrently promote both C2 H4 -to-EO and CO2 -to-C2 H4 conversions, thereby improving EO generation, using single-atom Pt on N-doped CNTs (Pt1 /NCNT) and Br- -bearing porous Cu2 O as anode and cathode electrocatalysts, respectively. Physicochemical characterizations including synchrotron X-ray absorption, operando infrared spectroscopy, and quasi in situ Raman spectroscopy/electron paramagnetic resonance with theoretical calculations reveal that the favorable Br2 /HBrO generation over Pt1 /NCNT with optimal intermediate binding facilitates C2 H4 -to-EO conversion with a high FE of 92.2 %, and concomitantly, the Br- with strong nucleophilicity protects active Cu+ species in Cu2 O effectively for improved CO2 -to-C2 H4 conversion with a FE of 66.9 % at 800 mA cm-2 , superior to those in the traditional chloride-mediated case. Consequently, a single-pass FE as high as 41.1 % for CO2 -to-EO conversion can be achieved in a tandem system.

Breaking K+ Concentration Limit on Cu Nanoneedles for Acidic Electrocatalytic CO2 Reduction to Multi-Carbon Products

Electrocatalytic CO2 reduction reaction (CO2 RR) to multi-carbon products (C2+ ) in acidic electrolyte is one of the most advanced routes for tackling our current climate and energy crisis. However, the competing hydrogen evolution reaction (HER) and the poor selectivity towards the valuable C2+ products are the major obstacles for the upscaling of these technologies. High local potassium ions (K+ ) concentration at the cathode's surface can inhibit proton-diffusion and accelerate the desirable carbon-carbon (C-C) coupling process. However, the solubility limit of potassium salts in bulk solution constrains the maximum achievable K+ concentration at the reaction sites and thus the overall acidic CO2 RR performance of most electrocatalysts. In this work, we demonstrate that Cu nanoneedles induce ultrahigh local K+ concentrations (4.22 M) - thus breaking the K+ solubility limit (3.5 M) - which enables a highly efficient CO2 RR in 3 M KCl at pH=1. As a result, a Faradaic efficiency of 90.69±2.15 % for C2+ (FEC2+ ) can be achieved at 1400 mA.cm-2 , simultaneous with a single pass carbon efficiency (SPCE) of 25.49±0.82 % at a CO2 flow rate of 7 sccm.

Insight on Atomically Dispersed Cu Catalysts for Electrochemical CO2 Reduction

Electrochemical CO2 reduction (ECO2R) with renewable electricity is an advanced carbon conversion technology. At present, copper is the only metal to selectively convert CO2 into multicarbon (C2+) products. Among them, atomically dispersed (AD) Cu catalysts have received great attention due to the relatively single chemical environment, which are able to minimize the negative impact of morphology, valence state, and crystallographic properties, etc. on product selectivity. Furthermore, the completely exposed atomic Cu sites not only provide space and bonding electrons for the adsorption of reactants in favor of better catalytic activity but also provide an ideal platform for studying its reaction mechanism. This review summarizes the recent progress of AD Cu catalysts as a chemically tunable platform for ECO2R, including the atomic Cu sites dynamic evolution, the catalytic performance, and mechanism. Furthermore, the prospects and challenges of AD Cu catalysts for ECO2R are carefully discussed. We sincerely hope that this review can contribute to the rational design of AD Cu catalysts with enhanced performance for ECO2R.

Sequential *CO management via controlling in situ reconstruction for efficient industrial-current-density CO2-to-C2+ electroreduction

Sequentially managing the coverage and dimerization of *CO on the Cu catalysts is desirable for industrial-current-density CO2 reduction (CO2R) to C2+, which required the multiscale design of the surface atom/architecture. However, the oriented design is colossally difficult and even no longer valid due to unpredictable reconstruction. Here, we leverage the synchronous leaching of ligand molecules to manipulate the seeding-growth process during CO2R reconstruction and construct Cu arrays with favorable (100) facets. The gradient diffusion in the reconstructed array guarantees a higher *CO coverage, which can continuously supply the reactant to match its high-rate consumption for high partial current density for C2+. Sequentially, the lower energy barriers of *CO dimerization on the (100) facets contribute to the high selectivity of C2+. Profiting from this sequential *CO management, the reconstructed Cu array delivers an industrial-relevant FEC2+ of 86.1% and an FEC2H4 of 60.8% at 700 mA cm-2. Profoundly, the atomic-molecular scale delineation for the evolution of catalysts and reaction intermediates during CO2R can undoubtedly facilitate various electrocatalytic reactions.

Less-Coordinated Atomic Copper-Dimer Boosted Carbon-Carbon Coupling During Electrochemical CO2 Reduction

This work reports a metal-organic framework (MOF) with less-coordinated copper dimers, which displays excellent electrochemical CO2 reduction (eCO2 RR) performance with an advantageous current density of 0.9 A cm-2 and a high Faradaic efficiency of 71% to C2 products. In comparison with MOF with Cu monomers that are present as Cu1 O4 with a coordination number of 3.8 ± 0.2, Cu dimers exist as O3 Cu1 ···Cu2 O2 with a coordination number of 2.8 ± 0.1. In situ characterizations together with theoretical calculations reveal that two *CO intermediates are stably adsorbed on each site of less-coordinated Cu dimers, which favors later dimerization via a key intermediate of *CH2 CHO. The highly unsaturated dual-atomic Cu provides large-quantity and high-quality actives sites for carbon-carbon coupling, achieving the optimal trade-off between activity and selectivity of eCO2 RR to C2 products.

Nanograin-Boundary-Abundant Cu2O-Cu Nanocubes with High C2+ Selectivity and Good Stability during Electrochemical CO2 Reduction at a Current Density of 500 mA/cm2

Surface and interface engineering, especially the creation of abundant Cu⁰/Cu⁺ interfaces and nanograin boundaries, is known to facilitate C₂₊ production during electrochemical CO₂ reductions over copper-based catalysts. However, precisely controlling the favorable nanograin boundaries with surface structures (e.g., Cu(100) facets and Cu[n(100)×(110)] step sites) and simultaneously stabilizing Cu⁰/Cu⁺ interfaces is challenging, since Cu⁺ species are highly susceptible to be reduced into bulk metallic Cu at high current densities. Thus, an in-depth understanding of the structure evolution of the Cu-based catalysts under realistic CO₂RR conditions is imperative, including the formation and stabilization of nanograin boundaries and Cu⁰/Cu⁺ interfaces. Herein we demonstrate that the well-controlled thermal reduction of Cu₂O nanocubes under a CO atmosphere yields a remarkably stable Cu₂O-Cu nanocube hybrid catalyst (Cu₂O(CO)) possessing a high density of Cu⁰/Cu⁺ interfaces, abundant nanograin boundaries with Cu(100) facets, and Cu[n(100)×(110)] step sites. The Cu₂O(CO) electrocatalyst delivered a high C₂₊ Faradaic efficiency of 77.4% (56.6% for ethylene) during the CO₂RR under an industrial current density of 500 mA/cm². Spectroscopic characterizations and morphological evolution studies, together with in situ time-resolved attenuated total reflection-surface enhanced infrared absorption spectroscopy (ATR-SEIRAS) studies, established that the morphology and Cu⁰/Cu⁺ interfacial sites in the as-prepared Cu₂O(CO) catalyst were preserved under high polarization and high current densities due to the nanograin-boundary-abundant structure. Furthermore, the abundant Cu⁰/Cu⁺ interfacial sites on the Cu₂O(CO) catalyst acted to increase the *CO adsorption density, thereby increasing the opportunity for C-C coupling reactions, leading to a high C₂₊ selectivity.

Eight-Electron Superatomic Cu31 Nanocluster with Chiral Kernel and NIR-II Emission

Owing to the inherent instability caused by the low Cu(I)/Cu(0) half-cell reduction potential, Cu(0)-containing copper nanoclusters are quite uncommon in comparison to their Ag and Au congeners. Here, a novel eight-electron superatomic copper nanocluster [Cu₃₁(4-MeO-PhC≡C)₂₁(dppe)₃](ClO₄)₂ (Cu₃₁, dppe = 1,2-bis(diphenylphosphino)ethane) is presented with total structural characterization. The structural determination reveals that Cu₃₁ features an inherent chiral metal core arising from the helical arrangement of two sets of three Cu₂ units encircling the icosahedral Cu₁₃ core, which is further shielded by 4-MeO-PhC≡C^- and dppe ligands. Cu₃₁ is the first copper nanocluster carrying eight free electrons, which is further corroborated by electrospray ionization mass spectrometry, X-ray photoelectron spectroscopy and density functional theory calculations. Interestingly, Cu₃₁ demonstrates the first near-infrared (750-950 nm, NIR-I) window absorption and the second near-infrared (1000-1700 nm, NIR-II) window emission, which is exceptional in the copper nanocluster family and endows it with great potential in biological applications. Of note, the 4-methoxy groups providing close contacts with neighboring clusters are crucial for the cluster formation and crystallization, while 2-methoxyphenylacetylene leads only to copper hydride clusters, Cu₆H or Cu₃₂H₁₄. This research not only showcases a new member of copper superatoms but also exemplifies that copper nanoclusters, which are nonluminous in the visible range may emit luminescence in the deep NIR region.

Localized Alkaline Environment via In Situ Electrostatic Confinement for Enhanced CO2-to-Ethylene Conversion in Neutral Medium

Electrocatalytic CO₂ reduction reaction (CO₂RR) is one of the most promising routes to facilitate carbon neutrality. An alkaline electrolyte is typically needed to promote the production of valuable multi-carbon molecules (such as ethylene). However, the reaction between CO₂ and OH^- consumes a significant quantity of CO₂/alkali and causes the rapid decay of CO₂RR selectivity and stability. Here, we design a catalyst-electrolyte interface with an effective electrostatic confinement of in situ generated OH^- to improve ethylene electrosynthesis from CO₂ in neutral medium. In situ Raman measurements indicate the direct correlation between ethylene selectivity and the intensities of surface Cu-CO and Cu-OH species, suggesting the promoted C-C coupling with the surface enrichment of OH^-. Thus, we report a CO₂-to-ethylene Faradaic efficiency (FE) of 70% and a partial current density of 350 mA cm^-2 at -0.89 V vs the reversible hydrogen electrode. Furthermore, the system demonstrated a 50 h stable operation at 300 mA cm^-2 with an average ethylene FE of ∼68%. This study offers a universal strategy to tune the reaction micro-environment, and a significantly improved ethylene FE of 64.5% was obtained even in acidic electrolytes (pH = 2).

Accelerated Transfer and Spillover of Carbon Monoxide through Tandem Catalysis for Kinetics-boosted Ethylene Electrosynthesis

Cu-based catalysts have been widely applied in electroreduction of carbon dioxide (CO₂ ER) to produce multicarbon (C₂₊ ) feedstocks (e.g., C₂ H₄ ). However, the high energy barriers for CO₂ activation on the Cu surface is a challenge for a high catalytic efficiency and product selectivity. Herein, we developed an in situ *CO generation and spillover strategy by engineering single Ni atoms on a pyridinic N-enriched carbon support with a sodalite (SOD) topology (Ni-SOD/NC) that acted as a donor to feed adjacent Cu nanoparticles (NPs) with *CO intermediate. As a result, a high C₂ H₄ selectivity of 62.5 % and an industrial-level current density of 160 mA cm^-2 at a low potential of -0.72 V were achieved. Our studies revealed that the isolated NiN₃ active sites with adjacent pyridinic N species facilitated the *CO desorption and the massive *CO intermediate released from Ni-SOD/NC then overflowed to Cu NPs surface to enrich the *CO coverage for improving the selectivity of CO₂ ER to C₂ H₄ .

Halogen-Incorporated Sn Catalysts for Selective Electrochemical CO2 Reduction to Formate

Electrochemically reducing CO₂ to valuable fuels or feedstocks is recognized as a promising strategy to simultaneously tackle the crises of fossil fuel shortage and carbon emission. Sn-based catalysts have been widely studied for electrochemical CO₂ reduction reaction (CO₂ RR) to make formic acid/formate, which unfortunately still suffer from low activity, selectivity and stability. In this work, halogen (F, Cl, Br or I) was introduced into the Sn catalyst by a facile hydrolysis method. The presence of halogen was confirmed by a collection of ex situ and in situ characterizations, which rendered a more positive valence state of Sn in halogen-incorporated Sn catalyst as compared to unmodified Sn under cathodic potentials in CO₂ RR and therefore tuned the adsorption strength of the key intermediate (*OCHO) toward formate formation. As a result, the halogen-incorporated Sn catalyst exhibited greatly enhanced catalytic performance in electrochemical CO₂ RR to produce formate.

Monitoring Electron Flow in Nickel Single-Atom Catalysts during Nitrogen Photofixation

An efficient catalytic system for nitrogen (N₂) photofixation generally consists of light-harvesting units, active sites, and an electron-transfer bridge. In order to track photogenerated electron flow between different functional units, it is highly desired to develop in situ characterization techniques with element-specific capability, surface sensitivity, and detection of unoccupied states. In this work, we developed in situ synchrotron radiation soft X-ray absorption spectroscopy (in situ sXAS) to probe the variation of electronic structure for a reaction system during N₂ photoreduction. Nickel single-atom and ceria nanoparticle comodified reduced graphene oxide (CeO₂/Ni-G) was designed as a model catalyst. In situ sXAS directly reveals the dynamic interfacial charge transfer of photogenerated electrons under illumination and the consequent charge accumulation at the catalytic active sites for N₂ activation. This work provides a powerful tool to monitor the electronic structure evolution of active sites under reaction conditions for photocatalysis and beyond.

Structural Reconstruction of Catalysts in Electroreduction Reaction: Identifying, Understanding, and Manipulating

Electroreduction transformation of small molecules (CO₂ , N₂ , and H₂ O) into chemical feedstocks offers a promising approach to eliminate carbon emissions and harness renewable energy. Most cathodic catalysts often undergo structural transformation under operating electroreduction conditions. These structural reconstructions are reflected in changes in their catalytic activity. In-depth understanding of the change of active sites and influence parameters of reconstruction behaviors is an essential precondition for the design of highly efficient catalysts. Despite the previous achievements, comprehensive insight toward the structural evolution mechanism in cathodic catalysts, compared to anode ones, under reaction conditions is still lacking. Herein, an overview of structural reconstruction for cathodic catalysts in terms of fundamental mechanisms, reconstruction process, advanced characterizations, and influencing parameters is provided. On this basis, the typical strategies for manipulating the structural reconfiguration of catalysts are also explicitly discussed from the catalyst structure and working environment. By delivering the mechanism, strategies, insights, and techniques, this review will provide a comprehensive understanding of the structural reconstruction of cathodic catalysts in electroreduction reactions and future guidelines for their rational development.