Selectivity of CO<sub>2</sub> Reduction on Copper Electrodes: The Role of the Kinetics of Elementary Steps

Nie, Xiaowa; Esopi, Monica R.; Janik, Michael J.; Asthagiri, Aravind

doi:10.1002/anie.201208320

Cited by 861 publications

(802 citation statements)

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“…Here we expect CO@Cu + and H@Cu 0 . Interestingly, the COH pathway previously proposed by us (17,33) is an unreasonable option, because COH@Cu + is higher than CHO@Cu + by ∆G = 1.86 eV. This also eliminates the CO-COH pathway for C2 products we previously proposed (17).…”

Section: Pathwaysmentioning

confidence: 74%

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.

491

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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Section: Pathwaysmentioning

confidence: 74%

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.

491

429

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“…Such calculations with constant N e admit large variations in μ e , 14 which introduces significant deviations through the μ e N e contribution to free energies. Such inconsistency precludes quantitative predictions.…”

Section: ■ Introductionmentioning

confidence: 99%

Atomistic Mechanisms Underlying Selectivities in C₁ and C₂ Products from Electrochemical Reduction of CO on Cu(111)

2016

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Practical environmental and energy applications of the electrochemical reduction of CO 2 to chemicals and fuels require far more efficient and selective electrocatalysts beyond the only working material Cu, but the wealth of experimental data on Cu can serve to validate any proposed mechanisms. To provide design guidelines, we use quantum mechanics to predict the detailed atomistic mechanisms responsible for C 1 and C 2 products on Cu. Thus, we report the pH dependent routes to the major products, methane and ethylene, and identify the key intermediates where branches to methanol, ketene, ethanol, acetylene, and ethane are kinetically blocked. We discovered that surface water on Cu plays a key role in the selectivity for hydrocarbon products over the oxygencontaining alcohol products by serving as a strong proton donor for electrochemical dehydration reductions. We suggest new experiments to validate our predicted mechanisms.

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“…A suitable catalyst for CO 2 reduction is essential to achieve a cost-effective process with high efficiency and selectivity 9 . In the past two decades, electrocatalytic CO 2 reduction has attracted much attention because the required electricity may be obtained at a low cost from renewable energy sources, such as wind, solar, and wave [10][11][12][13][14] . Researchers have identified several potential catalysts that are able to reduce CO 2 electrochemically in aqueous electrolytes [15][16][17][18][19][20] .…”

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confidence: 99%

A selective and efficient electrocatalyst for carbon dioxide reduction

et al. 2014

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Converting carbon dioxide to useful chemicals in a selective and efficient manner remains a major challenge in renewable and sustainable energy research. Silver is an interesting electrocatalyst owing to its capability of converting carbon dioxide to carbon monoxide selectively at room temperature; however, the traditional polycrystalline silver electrocatalyst requires a large overpotential. Here we report a nanoporous silver electrocatalyst that is able to electrochemically reduce carbon dioxide to carbon monoxide with approximately 92% selectivity at a rate (that is, current) over 3,000 times higher than its polycrystalline counterpart under moderate overpotentials of o0.50 V. The high activity is a result of a large electrochemical surface area (approximately 150 times larger) and intrinsically high activity (approximately 20 times higher) compared with polycrystalline silver. The intrinsically higher activity may be due to the greater stabilization of CO 2 À intermediates on the highly curved surface, resulting in smaller overpotentials needed to overcome the thermodynamic barrier.

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Selectivity of CO₂ Reduction on Copper Electrodes: The Role of the Kinetics of Elementary Steps

Cited by 861 publications

References 20 publications

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

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

Atomistic Mechanisms Underlying Selectivities in C₁ and C₂ Products from Electrochemical Reduction of CO on Cu(111)

A selective and efficient electrocatalyst for carbon dioxide reduction

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Selectivity of CO2 Reduction on Copper Electrodes: The Role of the Kinetics of Elementary Steps

Cited by 861 publications

References 20 publications

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

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

Atomistic Mechanisms Underlying Selectivities in C1 and C2 Products from Electrochemical Reduction of CO on Cu(111)

A selective and efficient electrocatalyst for carbon dioxide reduction

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Selectivity of CO₂ Reduction on Copper Electrodes: The Role of the Kinetics of Elementary Steps

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

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

Atomistic Mechanisms Underlying Selectivities in C₁ and C₂ Products from Electrochemical Reduction of CO on Cu(111)