Morphology Matters: Tuning the Product Distribution of CO<sub>2</sub> Electroreduction on Oxide-Derived Cu Foam Catalysts

Dutta, Abhijit; Rahaman, Motiar; Luedi, N.; Mohos, Miklós; Broekmann, Peter

doi:10.1021/acscatal.6b00770

Cited by 389 publications

(490 citation statements)

References 56 publications

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“…9,15,16,20,36 All catalysts were tested for 70 min at -0.7, -0. Table S4, summary of C2 product generation for all catalysts; Tables S18-S33, current density and FE for major products; Tables S34-S49, FE for minor products.…”

Section: Overview Of Co2 Reduction Measurementsmentioning

confidence: 99%

Optimizing C–C Coupling on Oxide-Derived Copper Catalysts for Electrochemical CO₂ Reduction

Lum¹,

Yue

Lobaccaro³

et al. 2017

J. Phys. Chem. C

284

272

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Copper electrodes, prepared by reduction of oxidized metallic copper have been reported to exhibit higher activity for the electrochemical reduction of CO2 and better selectivity towards C2 and C3 (C2+) products than metallic copper that has not been pre-oxidized. We report here an investigation of the effects of four different preparations of oxide-derived electrocatalysts on their activity and selectivity for CO2 reduction, with particular attention given to the selectivity to C2+ products. All catalysts were tested for CO2 reduction in 0.1 M KHCO3 and 0.1 M CsHCO3 at applied voltages in the range of -0.7 V to -1.0 V vs RHE. The best performing oxide-derived catalysts show up to ~70% selectivity to C2+ products and only ~3% selectivity to C1 products at -1.0 V vs RHE when CsHCO3 is used as the electrolyte. In contrast, the selectivity to C2+ products decreases to ~56% for the same catalysts tested in KHCO3. By studying all catalysts under identical conditions, the key factors affecting product selectivity could be discerned. These efforts reveal that the surface area of the oxide-derived layer is a critical parameter affecting selectivity. A high selectivity to C2+ products is attained at an overpotential of -1 V vs RHE by operating at a current density sufficiently high to achieve a moderately high pH near the catalyst surface but not so high as to cause a significant reduction in the local concentration of CO2. Based on recent theoretical studies, a high pH suppresses the formation of C1 relative to C2+ products. At the same time however, a high local CO2 concentration is necessary for the formation of C2+ products.3

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Section: Overview Of Co2 Reduction Measurementsmentioning

confidence: 99%

Optimizing C–C Coupling on Oxide-Derived Copper Catalysts for Electrochemical CO₂ Reduction

Lum¹,

Yue

Lobaccaro³

et al. 2017

J. Phys. Chem. C

284

272

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“…Because Cu2O is subject to reduction (back to Cu metal) under CO2RR conditions, the improved performance was initially attributed to Cu metal surface morphology (8,16). But a more recent experiment (15) showed that Cu + sites can survive on the Cu surface for the course of CO2RR.…”

mentioning

confidence: 99%

Cu metal embedded in oxidized matrix catalyst to promote CO ₂ activation and CO dimerization for electrochemical reduction of CO ₂

Xiao

Goddard

Cheng

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

461

429

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We propose and validate with quantum mechanics methods a unique catalyst for electrochemical reduction of CO 2 (CO 2 RR) in which selectivity and activity of CO and C 2 products are both enhanced at the borders of oxidized and metallic surface regions. This Cu metal embedded in oxidized matrix (MEOM) catalyst is consistent with observations that Cu 2 O-based electrodes improve performance. However, we show that a fully oxidized matrix (FOM) model would not explain the experimentally observed performance boost, and we show that the FOM is not stable under CO 2 reduction conditions. This electrostatic tension between the Cu + and Cu 0 surface sites responsible for the MEOM mechanism suggests a unique strategy for designing more efficient and selective electrocatalysts for CO 2 RR to valuable chemicals (HCOx), a critical need for practical environmental and energy applications.electrochemical reduction of CO 2 | Cu metal embedded in oxidized matrix | density functional theory | CO 2 activation | CO dimerization E lectrochemical reduction of CO2 (CO2RR) to valuable chemicals is an essential strategy to achieve industrial-scale reduction of the carbon footprint under mild conditions and to provide a means of storing electrical power from intermittent renewable sources into stable chemical forms (1). Cu is the prototype electrocatalyst for CO2RR, because it is the only pure metal that delivers appreciable amounts of methane and ethylene plus minor alcohol products (2-7), but it suffers from high overpotentials and very significant hydrogen evolution reactions (HERs). Consequently, tremendous efforts are being made to develop more efficient and selective electrocatalysts, for example by surface modification (8) and by nanoparticle (9, 10) and nanowire (11) engineering.We examine here the mechanism by which Cu2O-based electrodes are observed to improve both efficiency and selectivity for C2 products (12-15), which also suppresses HERs by severalfold. Because Cu2O is subject to reduction (back to Cu metal) under CO2RR conditions, the improved performance was initially attributed to Cu metal surface morphology (8,16). But a more recent experiment (15) showed that Cu + sites can survive on the Cu surface for the course of CO2RR. Importantly, a Cu sample that is first oxidized and then reduced using an H2 plasma leads to performance substantially worse than that of the oxidized sample, despite both having similarly roughened surfaces. This provides solid evidence that surface Cu + plays an essential role in promoting the efficiency and selectivity of CO2RR. However, experiments have provided no clue about how surface Cu + affects the mechanisms of CO2RR. Moreover, no previous theoretical efforts have elucidated its role.To understand the promising results achieved with Cu2O-based electrodes, we investigated three distinct models aimed at unraveling the role of surface Cu + in shaping the free energy profiles of two key steps for CO2RR. Here we carry out quantum mechanics (QM) calculations at constant potential by using our ...

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“…6,7 However, the explanation becomes more complicated when dealing with nanostructured copper materials derived from oxidized precursors, which show both higher activity and greatly enhanced selectivity towards multicarbon products. [8][9][10][11][12][13][14][15][16] It has been hypothesized that this could be related for instance to an increase of local pH, [17][18][19] grain boundaries, 20 undercoordinated sites, 21 or residual oxides. [22][23][24] Several groups have shown the existence of sites with higher CO binding energy in oxidederived copper.…”

mentioning

confidence: 99%

Subsurface Oxygen in Oxide-Derived Copper Electrocatalysts for Carbon Dioxide Reduction

Eilert

Cavalca

Roberts

et al. 2016

J. Phys. Chem. Lett.

388

396

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Copper electrocatalysts derived from an oxide have shown extraordinary electrochemical properties for the carbon dioxide reduction reaction (CO 2 RR). Using in situ Ambient Pressure Xray Photoelectron Spectroscopy (APXPS) and quasi in situ Electron Energy Loss Spectroscopy (EELS) in a Transmission Electron Microscope (TEM), we show that there is a substantial amount of residual oxygen in nanostructured, oxide-derived copper electrocatalysts, but no residual copper oxide. Based on these findings in combination with Density Functional Theory (DFT) simulations, we propose that residual subsurface oxygen changes the electronic structure of the catalyst and creates sites with higher carbon monoxide binding energy. If such sites are stable under the strongly reducing conditions found in CO 2 RR, these findings would explain the high efficiencies of oxide-derived copper in reducing carbon dioxide to multi-carbon compounds such as ethylene.

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Morphology Matters: Tuning the Product Distribution of CO₂ Electroreduction on Oxide-Derived Cu Foam Catalysts

Cited by 389 publications

References 56 publications

Optimizing C–C Coupling on Oxide-Derived Copper Catalysts for Electrochemical CO₂ Reduction

Optimizing C–C Coupling on Oxide-Derived Copper Catalysts for Electrochemical CO₂ Reduction

Cu metal embedded in oxidized matrix catalyst to promote CO ₂ activation and CO dimerization for electrochemical reduction of CO ₂

Subsurface Oxygen in Oxide-Derived Copper Electrocatalysts for Carbon Dioxide Reduction

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Morphology Matters: Tuning the Product Distribution of CO2 Electroreduction on Oxide-Derived Cu Foam Catalysts

Cited by 389 publications

References 56 publications

Optimizing C–C Coupling on Oxide-Derived Copper Catalysts for Electrochemical CO2 Reduction

Optimizing C–C Coupling on Oxide-Derived Copper Catalysts for Electrochemical CO2 Reduction

Cu metal embedded in oxidized matrix catalyst to promote CO 2 activation and CO dimerization for electrochemical reduction of CO 2

Subsurface Oxygen in Oxide-Derived Copper Electrocatalysts for Carbon Dioxide Reduction

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Product

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Morphology Matters: Tuning the Product Distribution of CO₂ Electroreduction on Oxide-Derived Cu Foam Catalysts

Optimizing C–C Coupling on Oxide-Derived Copper Catalysts for Electrochemical CO₂ Reduction

Optimizing C–C Coupling on Oxide-Derived Copper Catalysts for Electrochemical CO₂ Reduction

Cu metal embedded in oxidized matrix catalyst to promote CO ₂ activation and CO dimerization for electrochemical reduction of CO ₂