Selective CO2 Reduction to Ethylene Using Imidazolium-Functionalized Copper

Synthesis of ethane from CO2 by a methyl transferase-inspired molecular catalyst

Molecular catalysts with a single metal center are reported to reduce CO2 to a wide range of valuable single-carbon products like CO, HCOOH, CH3OH, etc. However, these catalysts cannot reduce CO2 to two carbon products like ethane or ethylene and the ability to form C-C from CO2 remains mostly limited to heterogeneous material-based catalysts. We report a set of simple iron porphyrins with pendant thiol group can catalyze the reduction of CO2 to ethane (C2H6) with H2O as the proton source with a Faradaic yield >40% the rest being CO. The mechanism involves a CO2-derived methyl group transfer to the pendant thiol akin to the proposal forwarded for methyl transferases and a follow-up C-C bond formation of the thioether thus formed and a Fe(II)-CH3 species generated by the reduction of a second molecule of CO2. The availability of a "parking space" in the molecular framework for the first reduced C1 product from CO2 reduction allows C-C bond formation resulting in a unique case where a component of natural gas can be generated from direct electrochemical reduction of CO2.

Tailoring Cu-Based Electrocatalysts for Enhanced Electrochemical CO2 Reduction to Alcohols: Structure-Selectivity Relationship

The use of CO2 as a feedstock for the production of carbon-based fuels and value-added chemicals offers a promising route toward carbon neutrality. In this study, two Cu-based electrocatalysts, namely, Cu24/N-C and Cu2/N-C, are successfully prepared by thermal treatment of Cu24 metal-organic polyhedron-loaded zeolitic imidazolate framework-8 (ZIF-8) nanocrystals (Cu24/ZIF-8) and Cu2 dinuclear compound-loaded ZIF-8 nanocrystals (Cu2/ZIF-8), respectively. Extensive structural and compositional analyses were conducted to confirm the formation of Cu nanocluster-loaded N-doped porous carbon supports in both Cu24/N-C and Cu2/N-C and Cu nanoparticles encapsulated by graphitic carbons in Cu2/N-C as well. These two Cu-based electrocatalysts exhibited different behaviors in the electrochemical CO2 reduction reaction (CO2RR). The Cu24/N-C electrocatalyst showed high selectivity for CO production, while Cu2/N-C showed a preference for alcohol generation. The excellent stability of Cu2/N-C over a 30 h continuous electrochemical reduction further highlights its potential for practical applications. The difference in electrocatalytic performance observed in the two catalysts for CO2RR was attributed to distinct catalytic sites associated with Cu nanoclusters and nanoparticles. This research reveals the significance of their structures and compositions for the development of highly selective electrocatalysts for CO2 reduction.

Electrocatalytic CO2 Reduction to Ethylene: From Advanced Catalyst Design to Industrial Applications

The value-added chemicals, monoxide, methane, ethylene, ethanol, ethane, and so on, can be efficiently generated through the electrochemical CO2 reduction reaction (eCO2 RR) when equipped with suitable catalysts. Among them, ethylene is particularly important as a chemical feedstock for petrochemical manufacture. However, despite its high Faradaic efficiency achievable at relatively low current densities, the substantial enhancement of ethylene selectivity and stability at industrial current densities poses a formidable challenge. To facilitate the industrial implementation of eCO2 RR for ethylene production, it is imperative to identify key strategies and potential solutions through comprehending the recent advancements, remaining challenges, and future directions. Herein, the latest and innovative catalyst design strategies of eCO2 RR to ethylene are summarized and discussed, starting with the properties of catalysts such as morphology, crystalline, oxidation state, defect, composition, and surface engineering. The review subsequently outlines the related important state-of-the-art technologies that are essential in driving forward eCO2 RR to ethylene into practical applications, such as CO2 capture, product separation, and downstream reactions. Finally, a greenhouse model that integrates CO2 capture, conversion, storage, and utilization is proposed to present an ideal perspective direction of eCO2 RR to ethylene.

Nickel oxide/copper nanocluster anchored in carbon-nitride nanosheets realizing ultrahigh stability and broad potential range for zero-gap membrane flow reactor towards CO2-into-CO electroreduction

CO2 electrochemical reduction is a sustainable approach to achieve chemical fixation of CO2 and storage of renewable energy. However, the catalyst which has the ability of mediating CO2 to a single product with a relatively high current density is highly demand. Herein, we reported a metallic nitrogen-carbon catalyst based on two kinds of metal phthalocyanines by a facile synthesis method. The synergistic effect of Cu and Ni and the active sites of nickel oxide/copper nanocluster endow the catalyst excellent performance towards CO2-into-CO electroreduction. Typically, the Cu-Ni bimetallic catalyst achieves high selectivity (85.2 %) at positive potential (-0.72 VRHE), with the stability of current density and product selectivity beyond 72 h. The volume ratio of CO/H2 can be effectively tuned (from 2:1, 1:1 to 1:2) by controlling the electrolysis potential, which is promising for synthesis gas in the Fischer-Tropsch reactions and methanol synthesis. Furthermore, the advantages are further amplified by applying it to zero-gap membrane flow reactor, which can enhance the selectivity over 90 % at a broad potential range (-2.5 ∼ -2.7 V) and achieve an current density of 9-fold of H-type cell. Our work proves a way for optimizing the CO2 electrocatalyst and electrolyzers.

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.

Ionomers Modify the Selectivity of Cu-Catalyzed Electrochemical CO2 Reduction

Electrochemical reduction of carbon dioxide (CO₂ RR) to produce energy-rich fuels using copper-based electrocatalysts is widely studied as a possible solution to CO₂ recycling. Ionomers are commonly used as binders to prepare catalyst-loaded electrodes, but their effects on the performance have not been fully investigated. In this study, electrochemical and operando Raman spectroscopic measurements are used to study the effects of three archetypical ionomers [Nafion, Sustainion-type XA-9, and poly(terphenyl piperidinium) (PTP)] on Cu-catalyzed CO₂ reduction at high current densities (up to 200 mA cm^-2 ). Nafion is found to have little influence, whereas XA-9 promotes the formation of CO over multicarbon products and PTP favors hydrogen and formate production. Charge and hydrophobicity/hydrophilicity are found to be important parameters of the ionomers. The observed effects are attributed to the charge transfer between Cu and XA-9 weakening the CO adsorption energy, whereas the hydrophilicity of PTP reduces M-H energy. This study reveals the structure-sensitive nature of the ionomer-catalyst interaction in CO₂ RR.