Efficient CO2 Electroreduction to Multicarbon Products at CuSiO3/CuO Derived Interfaces in Ordered Pores

Tuning catalyst-support interactions enable steering of electrochemical CO2 reduction pathways

Tuning of catalyst-support interactions potentially offers a powerful means to control activity. However, rational design of the catalyst support is challenged by a lack of clear property-activity relationships. Here, we uncover how the electronegativity of a support influences reaction pathways in electrochemical CO2 reduction. This was achieved by creating a model system consisting of Cu nanoparticles hosted on a series of carbon supports, each with a different heteroatom dopant of varying electronegativity. Notably, we discovered that dopants with high electronegativity reduce the electron density on Cu and induce a selectivity shift toward multicarbon (C2+) products. With this design principle, we built a composite Cu and F-doped carbon catalyst that achieves a C2+ Faradaic efficiency of 82.5% at 400 mA cm-2, with stable performance for 44 hours. Using simulated flue gas, the catalyst attains a C2+ FE of 27.3%, which is a factor of 5.3 times higher than a reference Cu catalyst.

Ag Stabilized Cu+/Cu0 Interface Catalysts for Enhanced CO2 Electroreduction to C2+ Products at Ampere Level Current Density

Electrochemical carbon dioxide reduction reaction (CO2RR) to yield multicarbon (C2+) products still suffers from a great hardship, which requires high current density and Faradaic efficiency (FE) accompanied by favorable stability for the purpose of industrial applications. Herein, we display 5.6 atom % Ag/Cu2O-Cu catalyst with abundant and steady Ag/Cu+/Cu0 interfaces for the efficient conversion of CO2-to-C2+ at ampere level current density. 5.6 atom % Ag/Cu2O-Cu catalyst attains a desirable FE of 76.5 ± 1.2% toward C2+ products at 1.0 A/cm2 in 1 M KOH electrolyte and remains stable CO2 electrolysis at 0.50 A/cm2 for 20 h using a flow cell apparatus. In situ Raman spectrometry and density functional theory calculations indicate that a steady Ag/Cu+/Cu0 interface can promote CO2-to-C2+ conversion through adjusting the energy barrier for the formation and dimerization of *CO intermediates. The synergistically heterogeneous interfaces promote the activity, selectivity, and stability of CO2 electroreduction to C2+ products via a tandem route of *COOH, *CO, and *OCCO intermediates over Ag/Cu+/Cu0 cooperative sites.

Rational Construction of Cu Active Sites for CO2 Electrolysis to C2+ Product

Electrocatalytic CO2 reduction reaction (CO2RR) has emerged as a promising approach in advancing towards carbon neutrality and addressing renewable energy intermittency. Copper-based catalysts have received much attention due to their high catalytic activity to convert CO2 into high value-added C2+ products. However, CO2RR exhibits a diversity of reduction products and unavoidable hydrogen precipitation side reactions due to the moderate adsorption strength of *CO on the copper surface and the fact that the electrode potential for CO2 reduction is very close to that for hydrogen precipitation reduction. Here, we summarize recent advances in the structural design and active site construction of copper-based catalysts for CO2RR, and investigate their effects on the improvement of CO2RR performance, with the aim of deepening the understanding of catalyst structure and active sites, thereby facilitating the design of more efficient copper-based catalysts for the sustainable production of value-added chemicals.

Ultralow Coordination Copper Sites Compartmentalized within Ordered Pores for Highly Efficient Electrosynthesis of n-Propanol from CO2

Coordinatively unsaturated copper (Cu) has been demonstrated to be effective for electrifying CO2 reduction into C3 products by adjusting the coupling of C1-C2 intermediates. Nevertheless, the intuitive impacts of ultralow coordination Cu sites on C3 products are scarcely elucidated due to the lack of synthetic recipes for Cu with low coordination numbers and its vulnerability to aggregation under reductive potentials. Herein, computational predictions revealed that Cu sites with higher levels of coordinative unsaturation favored the adsorption of C1 and C2 intermediates. Building upon the correlations, we constructed an ultralow coordination Cu catalyst from the in situ reduction of copper oxide nanoparticles (CuO NPs) compartmentalized within an ordered porous matrix, achieving a remarkable Faradaic efficiency (FE) for n-propanol (n-PrOH) from CO2 electroreduction, reaching up to 27.4% in the H-cell at -0.8 VRHE and 11.8% at 300 mA cm-2 in the flow cell. The presence and maintenance of ultralow coordination Cu sites during the rigorous electrolysis process contributed to the outstanding performances, as verified by the combination of in situ spectroscopy techniques, disclosing that the formed ultralow coordination Cu sites featured strong adsorption for *C1 and *C2 intermediates that lead to n-PrOH.

In-situ Reduced Cu3N Nanocrystals Enable High-Efficiency Ammonia Synthesis and Zinc-nitrate Batteries

Nitrate reduction reaction (NO3RR) involves an 8-electron transfer process and competes with the hydrogen evolution reaction process, resulting in lower yields and Faraday efficiency (FE) in the process of NH3 synthesis. Especially, Cu-based catalysts (Cu0 and Cu+) have been investigated in the field of NO3RR due to the energy levels of d-orbital and the least unoccupied molecular orbital (LUMO) π* of nitrate's orbital. Based on the above, we synthesized a Cu-based compound containing Cu3N (Cu+) through a simple one-step pyrolysis method, applied it to electrocatalytic NO3RR, and tested the performance of the Zn-NO3 - battery. Through various characterization analyses, Cu-based catalysts (Cu+) are the key active sites in reduction reactions, making Cu3N a potential catalyst for ammonia synthesis. The research results indicate the application of Cu3N catalyst in NO3RR shows the best NH3 yield of 173.7 μmol h-1 cm-2 with FENH3 reaching 91.0 % at -0.3 V vs. RHE, which is much higher than that of Cu catalyst without N. In addition, the Zn-NO3 - battery based on Cu3N electrode also exhibits an NH3 yield of 39.8 μmol h-1 cm-2 63.0 % FENH3, and a power density of 2.7 mW cm-2 as well as stable cycling charge-discharge stability for 5 hours. This work guides the application of Cu3N enhanced regulation of the active site in the electrocatalytic synthesis of NH3 from NO3RR.

Crown ether functionalization boosts CO2 electroreduction to ethylene on copper-based MOFs

The electroconversion of CO2 into ethylene (C2H4) offers a promising solution to environmental and energy challenges. Crown ether (CE) modification significantly enhances the C2H4 selectivity of copper-based MOFs, improving C2H4 faradaic efficiency (FE) in CuBTC, CuBDC, and CuBDC-NH2 by 3.1, 1.7, and 2.4 times, respectively. Among these, CuBTC achieves the highest FE for C2H4, reaching ca. 52% at 120 mA cm-2. Control experiments and in situ Fourier transform infrared spectroscopy (FTIR) reveal that CE stabilizes Cu+ during the catalyst's in situ reconstruction, promoting the formation of Cu2O, which is more favorable for C2H4 production. Furthermore, CE increases the local concentration of K+ at the catalyst-electrolyte interface, enhancing *CO adsorption and facilitating C-C coupling reactions. This process promotes the formation of key intermediates, such as *CO*CO, *CO*COH and *COCHO, ultimately boosting C2H4 production.

Br, O-Modified Cu(111) Interface Promotes CO2 Reduction to Multicarbon Products

Electrochemical reduction of CO2 to multicarbon (C2+) products with added value represents a promising strategy for achieving a carbon-neutral economy. Precise manipulation of the catalytic interface is imperative to control the catalytic selectivity, particularly toward C2+ products. In this study, a unique Cu/UIO-Br interface is designed, wherein the Cu(111) plane is co-modified simultaneously by Br and O from UIO-66-Br support. Such Cu/UIO-Br catalytic interface demonstrates a superior Faradaic efficiency of ≈53% for C2+ products (ethanol/ethylene) and the C2+ partial current density reached 24.3 mA cm-2 in an H-cell electrolyzer. The kinetic isotopic effect test, in situ attenuated total reflection Fourier transform infrared spectroscopy and density functional theory calculations have been conducted to elucidate the catalytic mechanism. The Br, O co-modification on the Cu(111) interface enhanced the adsorption of CO2 species. The hydrogen-bond effect from the doped Br atom regulated the kinetic processes of *H species in CO2RR and promoted the formation of *COH intermediate. The formed *COH facilitates the *CO-*COH coupling and promotes the C2+ selectivity finally. This comprehensive investigation not only provides an in-depth study and understanding of the catalytic process but also offers a promising strategy for designing efficient Cu-based catalysts with exceptional C2+ products.

Convergence of Tandem Catalysis and Nanoconfinement Promotes Electroreduction of CO2 to C2 Products

An efficient electrocatalytic conversion of CO2 into valuable multicarbon (C2+) products requires enhanced C-C coupling of C1 intermediates. Herein, we combine a tandem effect with a confinement strategy to construct a hollow Cu2O@Ag nanoshell electrocatalyst with a well-defined porous structure to improve the *CO intermediate coverage on the catalyst surface. In CO2 electroreduction, in situ Raman spectroscopy shows that the introduction of Ag can not only promote the CO intermediate production but also improve the stability of Cu+ to capture the *CO intermediate due to a CO-tandem effect, and the fine-tuned hollowness degree and pore size of Cu2O@Ag create a spatially confined microenvironment for trapping CO2 as well as the enrichment of CO, which greatly facilitate subsequent C-C coupling for C2+ product. The optimized Cu2O@Ag-45 with a specific nanoconfinement exhibits an enhanced ethylene (C2H4) production under the wide potential range from -0.4 to -1.2 V (vs RHE), and a Faradaic efficiency of 55.4% for C2+ products could be achieved at -1.2 V (vs RHE). This study highlights a promising strategy for the electrochemical reduction of CO2 to C2+ products on efficient C-C coupling catalysts.

Ni-Electrocatalytic CO2 Reduction Toward Ethanol

The electroreduction of CO2 offers a sustainable route to generate synthetic fuels. Cu-based catalysts have been developed to produce value-added C2+ alcohols; however, the limited understanding of complex C-C coupling and reaction pathway hinders the development of efficient CO2-to-C2+ alcohols catalysts. Herein, a Cu-free, highly mesoporous NiO catalyst, derived from the microphase separation of a block copolymer, is reported, which achieves selective CO2 reduction toward ethanol with a Faradaic efficiency of 75.2% at -0.6 V versus RHE. The dense mesopores create a favorable local reaction environment with CO2-rich and H2O-deficient interfaces, suppressing hydrogen evolution and maximizing catalytic activity of NiO for CO2 reduction. Importantly, the C1-feeding experiments, in situ spectroscopy, and theoretical calculations consistently show that the direct coupling of *CO2 and *COOH is responsible for C-C bond formation on NiO, and subsequent reduction of *CO2-COOH to ethanol is energetically facile through the *COCOH and *OC2H5 pathway. The unconventional C-C coupling mechanism on NiO, in contrast to the *CO dimerization on Cu, is triggered by strong CO2 adsorption on the polarized Ni2+-O2- sites. The work not only demonstrates a highly selective Cu-free Ni-based alternative for CO2-to-C2+ alcohols transformation but also provides a new perspective on C-C coupling toward C2+ synthesis.

Highly Tensile Strained Cu(100) Surfaces by Epitaxial Grown Hexagonal Boron Nitride for CO2 Electroreduction to C2+ Products

Copper (Cu) has been considered as the most promising catalyst for the electrochemical conversion of CO2 to multicarbon (C2+) products. However, insufficient coverage of the *CO intermediate on the C2+ formation Cu(100) facet largely hinders the C-C coupling process and thus the C2+ conversion efficiency. Herein, we developed an epitaxial growth strategy to generate highly tensile-strained Cu(100) facets via the epitaxial growth of hexagonal boron nitride (hBN) on Cu(100) facets to promote *CO coverage for efficient CO2 to C2+ conversion. The highest ∼6% tensile strain on the Cu(100) facets was obtained by lattice mismatch between the Cu(100) and hBN(002) facets. Theory calculations indicated that tensile-strained Cu(100) facets deliver a notable d-band center upshift to enhance *CO adsorption. As a result, the obtained highly tensile-strained Cu(100) facets enabled an 8-fold improvement of *CO coverage and thus a 83.4% C2+ Faradaic efficiency at 1.2 A cm-2 in strongly acidic electrolyte (pH = 1).

Mg-Doped Cu Catalyst for Electroreduction of CO2 to Multicarbon Products: Lewis Acid Sites Simultaneously Promote *CO Adsorption and Water Dissociation

The electroreduction of CO2 to valuable fuels or high-value chemicals by using sustainable electric energy provides a promising strategy for solving environmental problems dominated by the greenhouse effect. Copper-based materials are the only catalysts that can convert CO2 into multicarbon products, but they are plagued by high potential, low selectivity, and poor stability. The key factors to optimize the conversion of CO2 into multicarbon products are to improve the adsorption capacity of intermediates on the catalyst surface, accelerate the hydrogenation step, and improve the C-C coupling efficiency. Herein, we successfully doped Lewis acid Mg into Cu-based materials using a simple liquid-phase chemical method. In situ Raman and FT-IR tracking show that the Mg site enhances the surface coverage of the *CO intermediate, simultaneously promoting water dissociation. Under an industrial current density of 0.7 A cm-2, the FEC2+ reaches 73.9 ± 3.48% with remarkable stability. Density functional theory studies show that doping the Lewis acid Mg site increases the coverage of *CO and accelerates the splitting of water, thus promoting the C-C coupling efficiency, reducing the reaction energy barrier, and greatly improving the selectivity of C2+ products.

Tensile-Strained Cu Penetration Electrode Boosts Asymmetric C-C Coupling for Ampere-Level CO2-to-C2+ Reduction in Acid

The synthesis of multicarbon (C2+) products remains a substantial challenge in sustainable CO2 electroreduction owing to the need for sufficient current density and faradaic efficiency alongside carbon efficiency. Herein, we demonstrate ampere-level high-efficiency CO2 electroreduction to C2+ products in both neutral and strongly acidic (pH=1) electrolytes using a hierarchical Cu hollow-fiber penetration electrode (HPE). High concentration of K+ could concurrently suppress hydrogen evolution reaction and facilitate C-C coupling, thereby promoting C2+ production in strong acid. By optimizing the K+ and H+ concentration and CO2 flow rate, a faradaic efficiency of 84.5 % and a partial current density as high as 3.1 A cm-2 for C2+ products, alongside a single-pass carbon efficiency of 81.5 % and stable electrolysis for 240 h were demonstrated in a strong acidic solution of H2SO4 and KCl (pH=1). Experimental measurements and density functional theory simulations suggested that tensile-strained Cu HPE enhances the asymmetric C-C coupling to steer the selectivity and activity of C2+ products.

Regulating the Critical Intermediates of Dual-Atom Catalysts for CO2 Electroreduction

Electrocatalysis is a very attractive way to achieve a sustainable carbon cycle by converting CO2 into organic fuels and feedstocks. Therefore, it is crucial to design advanced electrocatalysts by understanding the reaction mechanism of electrochemical CO2 reduction reaction (eCO2RR) with multiple electron transfers. Among electrocatalysts, dual-atom catalysts (DACs) are promising candidates due to their distinct electronic structures and extremely high atomic utilization efficiency. Herein, the eCO2RR mechanism and the identification of intermediates using advanced characterization techniques, with a particular focus on regulating the critical intermediates are systematically summarized. Further, the insightful understanding of the functionality of DACs originates from the variable metrics of electronic structures including orbital structure, charge distribution, and electron spin state, which influences the active sites and critical intermediates in eCO2RR processes. Based on the intrinsic relationship between variable metrics and critical intermediates, the optimized strategies of DACs are summarized containing the participation of synergistic atoms, engineering of the atomic coordination environment, regulation of the diversity of central metal atoms, and modulation of metal-support interaction. Finally, the challenges and future opportunities of atomically dispersed catalysts for eCO2RR processes are discussed.

Activating Inert Perovskite Oxides for CO2 Electroreduction via Slight Cu2+ Doping in B-Sites

Perovskite oxides are proven as a striking platform for developing high-performance electrocatalysts. Nonetheless, a significant portion of them show CO2 electroreduction (CO2RR) inertness. Here a simple but effective strategy is reported to activate inert perovskite oxides (e.g., SrTiO3) for CO2RR through slight Cu2+ doping in B-sites. For the proof-of-concept catalysts of SrTi1-xCuxO3 (x = 0.025, 0.05, and 0.1), Cu2+ doping (even in trace amount, e.g., x = 0.025) can not only create active, stable CuO6 octahedra, increase electrochemical active surface area, and accelerate charge transfer, but also significantly regulate the electronic structure (e.g., up-shifted band center) to promote activation/adsorption of reaction intermediates. Benefiting from these merits, the stable SrTi1-xCuxO3 catalysts feature great improvements (at least an order of magnitude) in CO2RR activity and selectivity for high-order products (i.e., CH4 and C2+), compared to the SrTiO3 parent. This work provides a new avenue for the conversion of inert perovskite oxides into high-performance electrocatalysts toward CO2RR.

Synthesis and Electrocatalytic Applications of Layer-Structured Metal Chalcogenides Composites

Featured with the attractive properties such as large surface area, unique atomic layer thickness, excellent electronic conductivity, and superior catalytic activity, layered metal chalcogenides (LMCs) have received considerable research attention in electrocatalytic applications. In this review, the approaches developed to synthesize LMCs-based electrocatalysts are summarized. Recent progress in LMCs-based composites for electrochemical energy conversion applications including oxygen reduction reaction, carbon dioxide reduction reaction, oxygen evolution reaction, hydrogen evolution reaction, overall water splitting, and nitrogen reduction reaction is reviewed, and the potential opportunities and practical obstacles for the development of LMCs-based composites as high-performing active substances for electrocatalytic applications are also discussed. This review may provide an inspiring guidance for developing high-performance LMCs for electrochemical energy conversion applications.