Controllable Cu 0 ‐Cu + Sites for Electrocatalytic Reduction of Carbon Dioxide

High-Power CO2-to-C2 Electroreduction on Ga-Spaced, Square-like Cu Sites

The electrochemical conversion of CO2 into multicarbon (C2) products on Cu-based catalysts is strongly affected by the surface coverage of adsorbed CO (*CO) intermediates and the subsequent C-C coupling. However, the increased *CO coverage inevitably leads to strong *CO repulsion and a reduced C-C coupling efficiency, thus resulting in suboptimal CO2-to-C2 activity and selectivity, especially at ampere-level electrolysis current densities. Herein, we developed an atomically ordered Cu9Ga4 intermetallic compound consisting of Cu square-like binding sites interspaced by catalytically inert Ga atoms. Compared to Cu(100) previously known with a high C2 selectivity, the Ga-spaced, square-like Cu sites presented an elongated Cu-Cu distance that allowed to reduce *CO repulsion and increased *CO coverage simultaneously, thus endowing more efficient C-C coupling to C2 products than Cu(100) and Cu(111). The Cu9Ga4 catalyst exhibited an outstanding CO2-to-C2 electroreduction, with a peak C2 partial current density of 1207 mA cm-2 and a corresponding Faradaic efficiency of 71%. Moreover, the Cu9Ga4 catalyst demonstrated a high-power (∼200 W) electrolysis capability with excellent electrochemical stability.

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.

Insight into the Electrochemical CO2-to-Ethanol Conversion Catalyzed by Cu2S Nanocrystal-Decorated Cu Nanosheets

Ethanol (C₂H₅OH) is an economically ideal C₂ product in electrochemical CO₂ reduction. However, the CO₂-to-C₂H₅OH conversion yield has been rather low and the underlying catalytic mechanism remains vague or unexplored in most cases. Herein, by decorating small Cu₂S nanocrystals uniform ly on Cu nanosheets, three desirable features are integrated into the electrocatalyst, including a relatively high positive local charge on Cu (Cu^δ+), abundant interfaces between Cu^δ+ and zero-valence Cu⁰, and a non-flat, stepped catalyst surface, leading to the promoted affinity of *CO, decreased *COCO formation barrier, and thermodynamically preferred *CH₂CHO-to-*CH₃CHO conversion. As a result, a high partial current density of ∼20.7 mA cm^-2 and a Faraday efficiency of 46% for C₂H₅OH are delivered at -1.2 V vs reversible hydrogen electrode in an H-cell containing a 0.1 M KHCO₃ solution. This work proposes an efficient strategy for the high-yield CO₂-to-C₂H₅OH conversion, emphasizing the promise for the industrial production of alcohol and related products from CO₂.

Continuous synthesis of 2,2,6,6-tetramethyl-4-piperidinol over CuCrSr/Al2O3: effect of Sr promoter

A continuous process was developed for catalytic hydrogenation of triacetoneamine (TAA) to 2,2,6,6-tetramethyl-4-piperidinol (TMP), both of which are indispensable raw materials of hindered amine light stabilizers. A series of promoter-modified CuCr/Al2O3 catalysts were prepared by co-precipitation method and evaluated by the above reaction. The effect of promoter on the catalytic performance was explored by characterization tools, in which, CuCrSr/Al2O3 exhibited excellent catalytic performance with nearly complete conversion of TAA and over 97% selectivity of TMP at 120 °C. The characterization results indicated that the doped Sr could decrease the size of Cu nanoparticles to provide more active sites, improve the ratio of Cu+/Cu0 to promote the adsorption of substrates, and reduce the surface acidity to depress side reactions, thus remarkably enhancing catalytic performance. This work provides a low-cost, reliable and efficient strategy for the continuous industrial production of TMP.

Organic Additive-derived Films on Cu Electrodes Promote Electrochemical CO2 Reduction to C2+ Products Under Strongly Acidic Conditions

Electrochemical CO₂ reduction (CO₂ R) at low pH is desired for high CO₂ utilization; the competing hydrogen evolution reaction (HER) remains a challenge. High alkali cation concentration at a high operating current density has recently been used to promote electrochemical CO₂ R at low pH. Herein we report an alternative approach to selective CO₂ R (>70 % Faradaic efficiency for C₂₊ products, FE_C2+ ) at low pH (pH 2; H₃ PO₄ /KH₂ PO₄ ) and low potassium concentration ([K⁺ ]=0.1 M) using organic film-modified polycrystalline copper (Modified-Cu). Such an electrode effectively mitigates HER due to attenuated proton transport. Modified-Cu still achieves high FE_C2+ (45 % with Cu foil /55 % with Cu GDE) under 1.0 M H₃ PO₄ (pH≈1) at low [K⁺ ] (0.1 M), even at low operating current, conditions where HER can otherwise dominate.

Copper-Based Catalysts for Electrochemical Reduction of Carbon Dioxide to Ethylene

Electrochemical reduction of CO₂ into high energy density multi-carbon chemicals or fuels (e. g., ethylene) via new renewable energy storage has extraordinary implications for carbon neutrality. Copper (Cu)-based catalysts have been recognized as the most promising catalysts for the electrochemical reduction of CO₂ to ethylene (C₂ H₄ ) due to their moderate CO adsorption energy and moderate hydrogen precipitation potential. However, the poor selectivity, low current density and high overpotential of the CO₂ RR into C₂ H₄ greatly limit its industrial applications. Meanwhile, the complex reaction mechanism is still unclear, which leads to blindness in the design of catalysts. Herein, we systematically summarized the latest research, proposed possible conversion mechanisms and categorized the general strategies to adjust of the structure and composition for CO₂ RR, such as tip effect, defect engineering, crystal plane catalysis, synergistic effect, nanoconfinement effect and so on. Eventually, we provided a prospect of the future challenges for further development and progress in CO₂ RR. Previous reviews have summarized catalyst designs for the reduction of CO₂ to multi-carbon products, while lacking in targeting C₂ H₄ alone, an important industrial feedstock. This Review mainly aims to provide a comprehensive understanding for the design strategies and challenges of electrocatalytic CO₂ reduction to C₂ H₄ through recent researches and further propose some guidelines for the future design of copper-based catalysts for electroreduction of CO₂ to C₂ H₄ .

Controllable States and Porosity of Cu-Carbon for CO2 Electroreduction to Hydrocarbons

The electrocatalytic carbon dioxide reduction reaction (CO₂ RR) to value-added chemical products is an effective strategy for both greenhouse effect mitigation and high-density energy storage. However, controllable manipulation of the oxidation state and porous structure of Cu-carbon based catalysts to achieve high selectivity and current density for a particular product remains very challenging. Herein, a strategy derived from Cu-based metal-organic frameworks (MOFs) for the synthesis of controllable oxidation states and porous structure of Cu-carbon (Cu-pC, Cu₂ O-pC, and Cu₂ O/Cu-pC) is demonstrated. By regulating oxygen partial pressure during the annealing process, the valence state of the Cu and mesoporous structures of surrounding carbon are changed, leads to the different selectivity of products. Cu₂ O/CuO-pC with the higher oxidation state exhibits FE_C2H4 of 65.12% and a partial current density of -578 mA cm^-2 , while the Cu₂ O-pC shows the FE_CH4 over 55% and a partial current density exceeding -438 mA cm^-2 . Experimental and theoretical studies indicate that porous carbon-coated Cu₂ O structures favor the CH₄ pathway and inhibit the hydrogen evolution reaction. This work provides an effective strategy for exploring the influence of the various valence states of Cu and mesoporous carbon structures on the selectivity of CH₄ and C₂ H₄ products in CO₂ RR.

Synergistic effect of Cu/Cu2O surfaces and interfaces for boosting electrosynthesis of ethylene from CO2 in a Zn–CO2 battery

We constructed Cu/Cu2O hybrid catalysts with highly active surfaces/interfaces to realize a synergistic effect, thus improving the selectivity and efficiency of C2H4 production.

The Crystal Plane is not the Key Factor for CO2 -to-Methane Electrosynthesis on Reconstructed Cu2 O Microparticles

Cu₂ O microparticles with controllable crystal planes and relatively high stability have been recognized as a good platform to understand the mechanism of the electrocatalytic CO₂ reduction reaction (CO₂ RR). Herein, we demonstrate that the in situ generated Cu₂ O/Cu interface plays a key role in determining the selectivity of methane formation, rather than the initial crystal plane of the reconstructed Cu₂ O microparticles. Experimental results indicate that the methane evolution is dominated on all three different crystal planes with similar Tafel slopes and long-term stabilities. Density functional theory (DFT) calculations further reveal that *CO is protonated via a similar bridge configuration at the Cu₂ O/Cu interface, regardless of the initial crystal planes of Cu₂ O. The Gibbs free energy changes (ΔG) of *CHO on different reconstructed Cu₂ O planes are close and more negative than that of *OCCOH, indicating the methane formation is more favorable than ethylene on all Cu₂ O crystal planes.

Predesign of Catalytically Active Sites via Stable Coordination Cluster Model System for Electroreduction of CO2 to Ethylene

Purposefully designing the well-defined catalysts for the selective electroreduction of CO₂ to C₂ H₄ is an extremely important but challenging work. In this work, three crystalline trinuclear copper clusters (Cu₃ -X, X=Cl^- , Br^- , NO₃ ^- ) have been designed, containing three active Cu sites with the identical coordination environment and appropriate spatial distance, delivering high selectivity for the electrocatalytic reduction of CO₂ to C₂ H₄ . The highest faradaic efficiency of Cu₃ -X for CO₂ -to-C₂ H₄ conversion can be adjusted from 31.90 % to 55.01 % by simply replacing the counter anions (NO₃ ^- , Cl^- , Br^- ). The DFT calculation results verify that Cu₃ -X can facilitate the C-C coupling of identical *CHO intermediates, subsequently forming molecular symmetrical C₂ H₄ product. This work provides an important molecular model system and a new design perspective for electroreduction of CO₂ to C₂ products with symmetrical molecular structure.

Imparting CO2 Electroreduction Auxiliary for Integrated Morphology Tuning and Performance Boosting in a Porphyrin-based Covalent Organic Framework

Strategies that enable simultaneous morphology-tuning and electroreduction performance boosting are much desired for the exploration of covalent organic frameworks in efficient CO₂ electroreduction. Herein, a kind of functionalizing exfoliation agent has been selected to simultaneously modify and exfoliate bulk COFs into functional nanosheets and investigate their CO₂ electroreduction performance. The obtained nanosheets (Cu-Tph-COF-Dct) with large-scale (≈1.0 μm) and ultrathin (≈3.8 nm) morphology enable a superior FE_CH4 (≈80 %) (almost doubly enhanced than bare COF) with large current-density (-220.0 mA cm^-2 ) at -0.9 V. The boosted performance can be ascribed to the immobilized functionalizing exfoliation agent (Dct groups) with integrated amino and triazine groups that strengthen CO₂ absorption/activation, stabilize intermediates and enrich the CO concentration around the Cu active sites as revealed by DFT calculations. The point-to-point functionalization strategy for modularly assembling Dct-functionalized COF catalyst for CO₂ electroreduction will open up the attractive possibility of developing COFs as efficient CO₂ RR electrocatalysts.