Lithium Vacancy-Tuned [CuO4 ] Sites for Selective CO2 Electroreduction to C2+ Products

Synthesis of n-Propanol from CO2 Electroreduction on Bicontinuous Cu2O/Cu Nanodomains

n-propanol is an important pharmaceutical and pesticide intermediate. To produce n-propanol by electrochemical reduction of CO2 is a promising way, but is largely restricted by the very low selectivity and activity. How to promote the coupling of *C1 and *C2 intermediates to form the *C3 intermediate for n-propanol formation is challenging. Here, we propose the construction of bicontinuous structure of Cu2O/Cu electrocatalyst, which consists of ultra-small Cu2O nanodomains, Cu nanodomains and large amounts of grain boundaries between Cu2O and Cu nanodomains. The n-propanol current density is as high as 101.6 mA cm-2 at the applied potential of -1.1 V vs. reversible hydrogen electrode in flow cell, with the Faradaic efficiency up to 12.1 %. Moreover, the catalyst keeps relatively stable during electrochemical CO2 reduction process. Experimental studies and theoretical calculations reveal that the bicontinuous structure of Cu2O/Cu can facilitate the *CO formation, *CO-*CO coupling and *CO-*OCCO coupling for the final generation of n-propanol.

Advances and challenges in the electrochemical reduction of carbon dioxide

The electrocatalytic carbon dioxide reduction reaction (ECO2RR) is a promising way to realize the transformation of waste into valuable material, which can not only meet the environmental goal of reducing carbon emissions, but also obtain clean energy and valuable industrial products simultaneously. Herein, we first introduce the complex CO2RR mechanisms based on the number of carbons in the product. Since the coupling of C-C bonds is unanimously recognized as the key mechanism step in the ECO2RR for the generation of high-value products, the structural-activity relationship of electrocatalysts is systematically reviewed. Next, we comprehensively classify the latest developments, both experimental and theoretical, in different categories of cutting-edge electrocatalysts and provide theoretical insights on various aspects. Finally, challenges are discussed from the perspectives of both materials and devices to inspire researchers to promote the industrial application of the ECO2RR at the earliest.

(111) Facet-oriented Cu2Mg Intermetallic Compound with Cu3-Mg Sites for CO2 Electroreduction to Ethanol with Industrial Current Density

The efficient ethanol electrosynthesis from CO2 is challenging with low selectivity at high CO2 electrolysis rates, due to the competition with H2 and other reduction products. Copper-based bimetallic electrocatalysts are potential candidates for the CO2-to-ethanol conversion, but the secondary metal has mainly been focused on active components (such as Ag, Sn) for CO2 electroreduction, which also promote selectivity of ethylene or other reduction products rather than ethanol. Limited attention has been given to alkali-earth metals due to their inherently active chemical property. Herein, we rationally synthesized a (111) facet-oriented nano Cu2Mg (designated as Cu2Mg(111)) intermetallic compound with high-density ordered Cu3-Mg sites. The in situ Raman spectroscopy and density function theory calculations revealed that the Cu3 -δ $_{^{\rm{{\rm \delta} }} }$ --Mg-δ $_{^{\rm{{\rm \delta} }} }$ + active sites allowed to increase *CO surface coverage, decrease reaction energy for *CO-CO coupling, and stabilize *CHCHOH intermediates, thus promoting the ethanol formation pathway. The Cu2Mg(111) catalyst exhibited a high FEC2H5OH of 76.2±4.8 % at 600 mA⋅cm-2, and a peak value of |jC2H5OH| of 720±34 mA⋅cm-2, almost 4 times of that using conventional Cu2Mg with (311) facets, comparable to the best reported values for the CO2-to-ethanol electroreduction.

Modulating the Cu2O Photoelectrode/Electrolyte Interface with Bilayer Surfactant Simulating Cell Membranes for Boosting Photoelectrochemical CO2 Reduction

The low solubility of CO₂ molecules and the competition of the hydrogen evolution reaction (HER) in aqueous electrolytes pose significant challenges to the current photoelectrochemical (PEC) CO₂ reduction reaction. In this study, inspired by the bilayer phospholipid molecular structure of cell membranes, we developed a Cu₂O/Sn photocathode that was modified with the bilayer surfactant DHAB for achieving high CO₂ permeability and suppressed HER. The Cu₂O/Sn/DHAB photocathode stabilizes the *OCHO intermediate and facilitates the production of HCOOH. Our findings show that the Faradaic efficiency (FE) of HCOOH by the Cu₂O/Sn/DHAB photoelectrode is 83.3%, significantly higher than that achieved with the Cu₂O photoelectrode (FE_HCOOH = 30.1%). Furthermore, the FE_H2 produced by the Cu₂O/Sn/DHAB photoelectrode is only 2.95% at -0.6 V vs RHE. The generation rate of HCOOH by the Cu₂O/Sn/DHAB photoelectrode reaches 1.52 mmol·cm^-2·h^-1·L^-1 at -0.7 V vs RHE. Our study provides a novel approach for the design of efficient photocathodes for CO₂ reduction.

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.

Coupling Value-Added Anodic Reactions with Electrocatalytic CO2 Reduction

Electrocatalytic CO₂ reduction features a promising approach to realize carbon neutrality. However, its competitiveness is limited by the sluggish oxygen evolution reaction (OER) at anode, which consumes a large portion of energy. Coupling value-added anodic reactions with CO₂ electroreduction has been emerging as a promising strategy in recent years to enhance the full-cell energy efficiency and produce valuable chemicals at both cathode and anode of the electrolyzer. This review briefly summarizes recent progresses on the electrocatalytic CO₂ reduction, and the economic feasibility of different CO₂ electrolysis systems is discussed. Then a comprehensive summary of recent advances in the coupled electrolysis of CO₂ and potential value-added anodic reactions is provided, with special focus on the specific cell designs. Finally, current challenges and future opportunities for the coupled electrolysis systems are proposed, which are targeted to facilitate progress in this field and push the CO₂ electrolyzers to a more practical level.

Surface Co-Modification of Halide Anions and Potassium Cations Promotes High-Rate CO2 -to-Ethanol Electrosynthesis

The high-rate electrochemical CO₂ conversion to ethanol with high partial current density is attractive but challenging, which requires competing with other reduction products as well as hydrogen evolution. This work demonstrates the in situ reconstruction of KCuF₃ perovskite under CO₂ electroreduction conditions to fabricate a surface fluorine-bonded, single-potassium-atom-modified Cu(111) nanocrystal (K-F-Cu-CO₂ ). Density functional theory calculations reveal that the co-modification of both F and K atoms on the Cu(111) surface can promote the ethanol pathway via stabilization of the CO bond and selective hydrogenation of the CC bond in the CH₂ CHO* intermediate, while the single modification of either F or K is less effective. The K-F-Cu-CO₂ electrocatalyst exhibits an outstanding CO₂ -to-ethanol partial current density of 423 ± 30 mA cm^-2 with the corresponding Faradaic efficiency of 52.9 ± 3.7%, and a high electrochemical stability at large current densities, thus suggesting an attractive means of surface co-modification of halide anions and alkali-metal cations on Cu catalysts for high-rate CO₂ -to-ethanol electrosynthesis.

Plasmonic Ag-decorated Cu2O nanowires for boosting photoelectrochemical CO2 reduction to multi-carbon products

The generation of multi-carbon products on the Cu₂O photocathode remains a great challenge. Herein, effective charge separation and surface catalytic reaction are achieved for photoelectrochemical CO₂ reduction through plasmon metal (Ag) decoration on Cu₂O nanowires. The Cu₂O/Ag composite photocathode achieves a 47.7% faradaic efficiency for CH₃COOH and the generation rate is 212.7 μmol cm^-2 h^-1 under illumination, which is about five times that in dark (44.4 μmol cm^-2 h^-1) at -0.7 V vs. RHE.

Recent Advances in Heterogeneous Electroreduction of CO2 on Copper-Based Catalysts

Facing greenhouse effects and the rapid exhaustion of fossil fuel, CO2 electrochemical reduction presents a promising method of environmental protection and energy transformation. Low onset potential, large current density, high faradaic efficiency (FE), and long-time stability are required for industrial production, due to economic costs and energy consumption. This minireview showcases the recent progress in catalyst design and engineering technology in CO2 reduction reaction (CO2RR) on copper based-catalysts. We focus on strategies optimizing the performance of copper-based catalysts, such as single-atom catalysts, doping, surface modification, crystal facet engineering, etc., and reactor design including gas diffusion layer, membrane electrode assembly, etc., in enhancing target electroreduction products including methane, methanol, ethylene, and C2+ oxygenates. The determination of the correlation and the developed technology might be helpful for future applications in the industry.