Abstract:Under
ambient conditions, copper with oxygen near the surface displays
strengthened CO2 and CO adsorption energies. This finding
is often used to rationalize differences seen in product distributions
between Cu-oxide and pure Cu electrodes during electrochemical CO2 reduction. However, little evidence exists to confirm the
presence of oxygen within first few layers of the Cu matrix under
relevant experimental reducing conditions. Using density functional
theory calculations, we discuss the stability of subsurf… Show more
“…1 – 12 ). (for details, see the “Methods”) Previous research has shown that O below the third layer had little effect on the adsorption behavior of adsorbates 24 , therefore we believe that our OD-Cu surface models are consistent with the current experimental research that metallic copper is the active phase for CO 2 R over OD-Cu rather than the oxide phase 25 . Fig.…”
The active sites for CO2 electroreduction (CO2R) to multi-carbon (C2+) products over oxide-derived copper (OD-Cu) catalysts are under long-term intense debate. This paper describes the atomic structure motifs for product-specific active sites on OD-Cu catalysts in CO2R. Herein, we describe realistic OD-Cu surface models by simulating the oxide-derived process via the molecular dynamic simulation with neural network (NN) potential. After the analysis of over 150 surface sites through NN potential based high-throughput testing, coupled with density functional theory calculations, three square-like sites for C–C coupling are identified. Among them, Σ3 grain boundary like planar-square sites and convex-square sites are responsible for ethylene production while step-square sites, i.e. n(111) × (100), favor alcohols generation, due to the geometric effect for stabilizing acetaldehyde intermediates and destabilizing Cu–O interactions, which are quantitatively demonstrated by combined theoretical and experimental results. This finding provides fundamental insights into the origin of activity and selectivity over Cu-based catalysts and illustrates the value of our research framework in identifying active sites for complex heterogeneous catalysts.
“…1 – 12 ). (for details, see the “Methods”) Previous research has shown that O below the third layer had little effect on the adsorption behavior of adsorbates 24 , therefore we believe that our OD-Cu surface models are consistent with the current experimental research that metallic copper is the active phase for CO 2 R over OD-Cu rather than the oxide phase 25 . Fig.…”
The active sites for CO2 electroreduction (CO2R) to multi-carbon (C2+) products over oxide-derived copper (OD-Cu) catalysts are under long-term intense debate. This paper describes the atomic structure motifs for product-specific active sites on OD-Cu catalysts in CO2R. Herein, we describe realistic OD-Cu surface models by simulating the oxide-derived process via the molecular dynamic simulation with neural network (NN) potential. After the analysis of over 150 surface sites through NN potential based high-throughput testing, coupled with density functional theory calculations, three square-like sites for C–C coupling are identified. Among them, Σ3 grain boundary like planar-square sites and convex-square sites are responsible for ethylene production while step-square sites, i.e. n(111) × (100), favor alcohols generation, due to the geometric effect for stabilizing acetaldehyde intermediates and destabilizing Cu–O interactions, which are quantitatively demonstrated by combined theoretical and experimental results. This finding provides fundamental insights into the origin of activity and selectivity over Cu-based catalysts and illustrates the value of our research framework in identifying active sites for complex heterogeneous catalysts.
“…Defect sites such as grain boundaries, step sites, and vacancies that result in under-coordinated atoms on the surface of Cu are known to promote C–C coupling 33 , 34 . In addition, Cu + and subsurface oxygen are proposed to promote the adsorption of CO 2 and C–C coupling 12 , 35 – 38 , although the stability of subsurface oxygen remains controversial 34 , 35 , 39 , 40 .…”
Development of efficient catalysts for selective electroreduction of CO 2 to high-value products is essential for the deployment of carbon utilization technologies. Here we present a scalable method for preparing Cu electrocatalysts that favor CO 2 conversion to C 2+ products with faradaic efficiencies up to 72%. Grazing-incidence X-ray diffraction data confirms that anodic halogenation of electropolished Cu foils in aqueous solutions of KCl, KBr, or KI creates surfaces of CuCl, CuBr, or CuI, respectively. Scanning electron microscopy and energy dispersive X-ray spectroscopy studies show that significant changes to the morphology of Cu occur during anodic halogenation and subsequent oxide-formation and reduction, resulting in catalysts with a high density of defect sites but relatively low roughness. This work shows that efficient conversion of CO 2 to C 2+ products requires a Cu catalyst with a high density of defect sites that promote adsorption of carbon intermediates and CC coupling reactions while minimizing roughness.
“…This would potentially help stabilize the residual bulk Cu 4 O 3 which then acts as a support oxide layer for the surface‐active Cu 0 phase. As for the Cu 2 O particles present in the PrC powder, from previous work, it clear that the Cu + species also undergo a reduction and form a surface‐active Cu 0 phase …”
Section: Resultsmentioning
confidence: 82%
“…The role of copper oxidation state and subsurface oxygen in hydrocarbon formation during CO 2 RR has been a topic of a wide debate . However, based on the most recent theoretical and experimental work, it now seems clear that surface copper oxides are unstable under CO 2 RR conditions and that existence of any near‐surface residual oxides, which would actually have an effect on the CO 2 RR, is highly improbable. By employing CV studies and postelectrolysis, ex situ XPS measurements of PrC samples, we were also able to observe the reduction of surface oxide species after exposure to negative potentials at the cathode, suggesting that Cu 0 is the active phase during electrolysis.…”
Section: Resultsmentioning
confidence: 99%
“…Currently, oxide‐derived copper (OD‐Cu) catalysts are in the spotlight due to their high ethylene selectivity and CO 2 RR activity, which has been attributed to the formation of numerous grain boundaries during oxidative/reductive treatment, increased surface roughness, oxidation state of the surface layer, residual bulk oxides and subsurface oxygen . Although it has been suggested that presence of Cu + surface species during CO 2 RR plays an important role in achieving high ethylene selectivity, recent experimental and theoretical work has pointed out that these surface species are unstable under the reducing potentials that occur during cell operation. Even though it is unlikely that Cu + and Cu 2+ surface species are present during CO 2 RR, looking back on the previous work done on copper‐oxide‐based catalysts, it is clear that the initial oxidation state of the catalyst's surface has an effect on the CO 2 RR product distribution .…”
A copper‐oxide‐based catalyst enriched with paramelaconite (Cu4O3) is presented and investigated as an electrocatalyst for facilitating electroreduction of CO2 to ethylene and other hydrocarbons. Cu4O3 is a member of the copper‐oxide family and possesses an intriguing mixed‐valance nature, incorporating an equal number of Cu+ and Cu2+ ions in its crystal structure. The material is synthesized using a solvothermal synthesis route and its structure is confirmed via powder X‐ray diffraction, transmission electron microscope based selected area electron diffraction, and X‐ray photoelectron spectroscopy. A flow reactor equipped with a gas diffusion electrode is utilized to test a copper‐based catalyst enriched with the Cu4O3 phase under CO2 reduction conditions. The Cu4O3‐rich catalyst (PrC) shows a Faradaic efficiency for ethylene over 40% at 400 mA cm−2. At −0.64 versus reversible hydrogen electrode, the highest C2+/C1 product ratio of 4.8 is achieved, with C2+ Faradaic efficiency over 61%. Additionally, the catalyst exhibits a stable performance for 24 h at a constant current density of 200 mA cm−2.
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