Efficient electroreduction of CO2 to C2-C3 products on Cu/Cu2O@N-doped graphene

Boosting multi-carbon products selectivity of carbon dioxide reduction via bifunctional cyclodextrin-modification on copper/copper(I) oxide electrocatalysts

Electrochemical carbon dioxide reduction to multi-carbon (C2+) products presents a significant opportunity for converting greenhouse gases into valuable fuels and feedstocks. The development of highly active and stable catalysts remains a critical challenge. In this study, we report the design and synthesis of cyclodextrin-modified Cu/Cu2O electrocatalysts, which exhibit remarkable efficiency in driving the CO2 electroreduction process towards C2+ products. Our optimized catalyst achieves a C2+ Faradaic efficiency exceeding 50 % at a high current density of over 200 mA cm-2. Experimental findings, supported by density functional theory (DFT) calculations, reveal that cyclodextrin plays a dual role in stabilizing Cu+ and increasing the surface density of hydroxyl radicals. This dual function greatly benefits for enhancing *CO intermediate adsorption and promotes *CHO formation, thereby facilitating the crucial dimerization step for the formation of C2+ products. This work provides valuable insights into the development of highly active and selective electrocatalysts by carefully tuning the local catalytic environment, potentially opening new avenues for functionalizing electrocatalysts for future research in this area.

Efficient electrocatalytic CO2 reduction to ethylene using cuprous oxide derivatives

Copper-based materials play a vital role in the electrochemical transformation of CO2 into C2/C2+ compounds. In this study, cross-sectional octahedral Cu2O microcrystals were prepared in situ on carbon paper electrodes via electrochemical deposition. The morphology and integrity of the exposed crystal surface (111) were meticulously controlled by adjusting the deposition potential, time, and temperature. These cross-sectional octahedral Cu2O microcrystals exhibited high electrocatalytic activity for ethylene (C2H4) production through CO2 reduction. In a 0.1 M KHCO3 electrolyte, the Faradaic efficiency for C2H4 reached 42.0% at a potential of -1.376 V vs. RHE. During continuous electrolysis over 10 h, the FE (C2H4) remained stable around 40%. During electrolysis, the fully exposed (111) crystal faces of Cu2O microcrystals are reduced to Cu0, which enhances C-C coupling and could serve as the main active sites for catalyzing the conversion of CO2 to C2H4.

Proton-Coupled Electron Transfer on Cu2O/Ti3C2Tx MXene for Propane (C3H8) Synthesis from Electrochemical CO2 Reduction

Electrochemical CO2 reduction reaction (CO2RR) to produce value-added multi-carbon chemicals has been an appealing approach to achieving environmentally friendly carbon neutrality in recent years. Despite extensive research focusing on the use of CO2 to produce high-value chemicals like high-energy-density hydrocarbons, there have been few reports on the production of propane (C3H8), which requires carbon chain elongation and protonation. A rationally designed 0D/2D hybrid Cu2O anchored-Ti3C2Tx MXene catalyst (Cu2O/MXene) is demonstrated with efficient CO2RR activity in an aqueous electrolyte to produce C3H8. As a result, a significantly high Faradaic efficiency (FE) of 3.3% is achieved for the synthesis of C3H8 via the CO2RR with Cu2O/MXene, which is ≈26 times higher than that of Cu/MXene prepared by the same hydrothermal process without NH4OH solution. Based on in-situ attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) and density functional theory (DFT) calculations, it is proposed that the significant electrocatalytic conversion originated from the synergistic behavior of the Cu2O nanoparticles, which bound the *C2 intermediates, and the MXene that bound the *CO coupling to the C3 intermediate. The results disclose that the rationally designed MXene-based hybrid catalyst facilitates multi-carbon coupling as well as protonation, thereby manipulating the CO2RR pathway.

Integrating hydrogen utilization in CO2 electrolysis with reduced energy loss

Electrochemical carbon dioxide reduction reaction using sustainable energy is a promising approach of synthesizing chemicals and fuels, yet is highly energy intensive. The oxygen evolution reaction is particularly problematic, which is kinetically sluggish and causes anodic carbon loss. In this context, we couple CO2 electrolysis with hydrogen oxidation reaction in a single electrochemical cell. A Ni(OH)2/NiOOH mediator is used to fully suppress the anodic carbon loss and hydrogen oxidation catalyst poisoning by migrated reaction products. This cell is highly flexible in producing either gaseous (CO) or soluble (formate) products with high selectivity (up to 95.3%) and stability (>100 h) at voltages below 0.9 V (50 mA cm-2). Importantly, thanks to the "transferred" oxygen evolution reaction to a water electrolyzer with thermodynamically and kinetically favored reaction conditions, the total polarization loss and energy consumption of our H2-integrated CO2 reduction reaction, including those for hydrogen generation, are reduced up to 22% and 42%, respectively. This work demonstrates the opportunity of combining CO2 electrolysis with the hydrogen economy, paving the way to the possible integration of various emerging energy conversion and storage approaches for improved energy/cost effectiveness.

Converting CO2 into Value-Added Products by Cu2 O-Based Catalysts: From Photocatalysis, Electrocatalysis to Photoelectrocatalysis

Converting CO₂ into value-added products by photocatalysis, electrocatalysis, and photoelectrocatalysis is a promising method to alleviate the global environmental problems and energy crisis. Among the semiconductor materials applied in CO₂ catalytic reduction, Cu₂ O has the advantages of abundant reserves, low price and environmental friendliness. Moreover, Cu₂ O has unique adsorption and activation properties for CO₂ , which is conducive to the generation of C₂₊ products through CC coupling. This review introduces the basic principles of CO₂ reduction and summarizes the pathways for the generation of C₁ , C₂ , and C₂₊ products. The factors affecting CO₂ reduction performance are further discussed from the perspective of the reaction environment, medium, and novel reactor design. Then, the properties of Cu₂ O-based catalysts in CO₂ reduction are summarized and several optimization strategies to enhance their stability and redox capacity are discussed. Subsequently, the application of Cu₂ O-based catalysts in photocatalytic, electrocatalytic, and photoelectrocatalytic CO₂ reduction is described. Finally, the opportunities, challenges and several research directions of Cu₂ O-based catalysts in the field of CO₂ catalytic reduction are presented, which is guidance for its wide application in the energy and environmental fields is provided.

Integrated carbon capture and conversion: A review on C2+ product mechanisms and mechanism-guided strategies

The need to reduce atmospheric CO₂ concentrations necessitates CO₂ capture technologies for conversion into stable products or long-term storage. A single pot solution that simultaneously captures and converts CO₂ could minimize additional costs and energy demands associated with CO₂ transport, compression, and transient storage. While a variety of reduction products exist, currently, only conversion to C₂₊ products including ethanol and ethylene are economically advantageous. Cu-based catalysts have the best-known performance for CO₂ electroreduction to C₂₊ products. Metal Organic Frameworks (MOFs) are touted for their carbon capture capacity. Thus, integrated Cu-based MOFs could be an ideal candidate for the one-pot capture and conversion. In this paper, we review Cu-based MOFs and MOF derivatives that have been used to synthesize C₂₊ products with the objective of understanding the mechanisms that enable synergistic capture and conversion. Furthermore, we discuss strategies based on the mechanistic insights that can be used to further enhance production. Finally, we discuss some of the challenges hindering widespread use of Cu-based MOFs and MOF derivatives along with possible solutions to overcome the challenges.

Use of Chitosan as Copper Binder in the Continuous Electrochemical Reduction of CO2 to Ethylene in Alkaline Medium

This work explores the potential of novel renewable materials in electrode fabrication for the electrochemical conversion of carbon dioxide (CO₂) to ethylene in alkaline media. In this regard, the use of the renewable chitosan (CS) biopolymer as ion-exchange binder of the copper (Cu) electrocatalyst nanoparticles (NPs) is compared with commercial anion-exchange binders Sustainion and Fumion on the fabrication of gas diffusion electrodes (GDEs) for the electrochemical reduction of carbon dioxide (CO₂R) in an alkaline medium. They were tested in membrane electrode assemblies (MEAs), where selectivity to ethylene (C₂H₄) increased when using the Cu:CS GDE compared to the Cu:Sustainion and Cu:Fumion GDEs, respectively, with a Faradaic efficiency (FE) of 93.7% at 10 mA cm^-2 and a cell potential of -1.9 V, with a C₂H₄ production rate of 420 µmol m^-2 s^-1 for the Cu:CS GDE. Upon increasing current density to 90 mA cm^-2, however, the production rate of the Cu:CS GDE rose to 509 µmol/m²s but the FE dropped to 69% due to increasing hydrogen evolution reaction (HER) competition. The control of mass transport limitations by tuning up the membrane overlayer properties in membrane coated electrodes (MCE) prepared by coating a CS-based membrane over the Cu:CS GDE enhanced its selectivity to C₂H₄ to a FE of 98% at 10 mA cm^-2 with negligible competing HER. The concentration of carbon monoxide was below the experimental detection limit irrespective of the current density, with no CO₂ crossover to the anodic compartment. This study suggests there may be potential in sustainable alernatives to fossil-based or perfluorinated materials in ion-exchange membrane and electrode fabrication, which constitute a step forward towards decarbonization in the circular economy perspective.