Dataset Information

Electrocatalytic CO2 Reduction on CuOx Nanocubes: Tracking the Evolution of Chemical State, Geometric Structure, and Catalytic Selectivity using Operando Spectroscopy.

ABSTRACT: The direct electrochemical conversion of carbon dioxide (CO2 ) into multi-carbon (C2+ ) products still faces fundamental and technological challenges. While facet-controlled and oxide-derived Cu materials have been touted as promising catalysts, their stability has remained problematic and poorly understood. Herein we uncover changes in the chemical and morphological state of supported and unsupported Cu2 O nanocubes during operation in low-current H-Cells and in high-current gas diffusion electrodes (GDEs) using neutral pH buffer conditions. While unsupported nanocubes achieved a sustained C2+ Faradaic efficiency of around 60?% for 40?h, the dispersion on a carbon support sharply shifted the selectivity pattern towards C1 products. Operando XAS and time-resolved electron microscopy revealed the degradation of the cubic shape and, in the presence of a carbon support, the formation of small Cu-seeds during the surprisingly slow reduction of bulk Cu2 O. The initially (100)-rich facet structure has presumably no controlling role on the catalytic selectivity, whereas the oxide-derived generation of under-coordinated lattice defects, can support the high C2+ product yields.

SUBMITTER: Moller T

PROVIDER: S-EPMC7590092 | biostudies-literature | 2020 Jul

REPOSITORIES: biostudies-literature

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Electrocatalytic CO2 Reduction on CuOx Nanocubes: Tracking the Evolution of Chemical State, Geometric Structure, and Catalytic Selectivity using Operando Spectroscopy.

Möller Tim T Scholten Fabian F Thanh Trung Ngo TN Sinev Ilya I Timoshenko Janis J Wang Xingli X Jovanov Zarko Z Gliech Manuel M Roldan Cuenya Beatriz B Varela Ana Sofia AS Strasser Peter P

Angewandte Chemie (International ed. in English) 20200813 41

The direct electrochemical conversion of carbon dioxide (CO2 ) into multi-carbon (C2+ ) products still faces fundamental and technological challenges. While facet-controlled and oxide-derived Cu materials have been touted as promising catalysts, their stability has remained problematic and poorly understood. Herein we uncover changes in the chemical and morphological state of supported and unsupported Cu2 O nanocubes during operation in low-current H-Cells and in ...[more]

PMID: 32627953

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Project description:Copper-based catalysts are established catalytic systems for the electrocatalytic CO2 reduction reaction (CO2RR), where the greenhouse gas CO2 is converted into valuable industrial chemicals, such as energy-dense C2+ products, using energy from renewable sources. However, better control over the catalyst selectivity, especially at industrially relevant high current density conditions, is needed to expedite the economic viability of the CO2RR. For this purpose, bimetallic materials, where copper is combined with a secondary metal, comprise a promising and a highly tunable catalyst for the CO2RR. Nevertheless, the synergy between copper and the selected secondary metal species, the evolution of the bimetallic structural motifs under working conditions and the effect of the secondary metal on the kinetics of the Cu redox behavior require careful investigation. Here, we employ operando quick X-ray absorption fine structure (QXAFS) spectroscopy coupled with machine-learning based data analysis and surface-enhanced Raman spectroscopy (SERS) to investigate the time-dependent chemical and structural changes in catalysts derived from shape-selected ZnO/Cu2O nanocubes under CO2RR conditions at current densities up to -500 mA cm-2. We furthermore relate the catalyst transformations observed under working conditions to the catalytic activity and selectivity and correlate potential-dependent surface and subsurface processes. We report that the addition of Zn to a Cu-based catalyst has a crucial impact on the kinetics of subsurface processes, while redox processes of the Cu surface layer remain largely unaffected. Interestingly, the presence of Zn was found to contribute to the stabilization of cationic Cu(i) species, which is of catalytic relevance since Cu(0)/Cu(i) interfaces have been reported to be beneficial for efficient electrocatalytic CO2 conversion to complex multicarbon products. At the same time, we attribute the increase of the C2+ product selectivity to the formation of Cu-rich CuZn alloys in samples with low Zn content, while Zn-rich alloy phases result in an increased formation of CO paralleled by an increase of the parasitic hydrogen evolution reaction.

Project description:To control diesel vehicle NO x emissions, Cu-exchanged zeolites have been applied in the selective catalytic reduction (SCR) of NO using NH3 as reductant. However, the harsh hydrothermal environment of tailpipe conditions causes irreversible catalyst deactivation. The aggregation of isolated Cu2+ brings about unselective ammonia oxidation along with the main NH3-SCR reaction. An unusual 'dip' shaped NO conversion curve was observed in the steamed zeolite Cu-ZSM-5, resulting from the undesired NH3 oxidation that produced NO. Here we gain further insights into the NH3-SCR reaction and its deactivation by employing operando UV-vis diffuse reflectance spectroscopy (DRS) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) on fresh and steamed zeolite Cu-ZSM-5. We found that tetragonally distorted octahedral Cu2+ with associated NH3 preferentially forms during low temperature NH3-SCR (<250 °C) in fresh Cu-ZSM-5. The high coordination number of Cu2+ ensures the availability for high coverage of nitrate intermediates. Whilst in the steamed Cu-ZSM-5, [Cu x (OH)2x-1]+ oligomers/clusters in pseudo-tetrahedral symmetry with coordinated NH3 accumulated during the low-temperature NH3-SCR reaction. These clusters presented a strong adsorption of surface NH3 and nitrates/nitric acid at low temperatures and therefore limited the reaction between surface species in the steamed Cu-ZSM-5. Further release of NH3 with increased reaction temperature favors NH3 oxidation that causes the drop of NO conversion at ∼275 °C. Moreover, competitive adsorption of NH3 and nitrates/nitric acid occurs on shared Lewis-acidic adsorption sites. Prompt removal of surface nitrates/nitric acid by NO avoids the surface blockage and tunes the selectivity by alternating nitrate-nitrite equilibrium. The formation of adsorbed NO2 and HNO x points to the necessity of an acid adsorbent in practical applications. The structural similarity under the NH3-SCR reaction and unselective NH3 oxidation confirmed the entanglement of these two reactions above 250 °C.

Dataset Information

Electrocatalytic CO2 Reduction on CuOx Nanocubes: Tracking the Evolution of Chemical State, Geometric Structure, and Catalytic Selectivity using Operando Spectroscopy.

Publications

Electrocatalytic CO<sub>2</sub> Reduction on CuO<sub>x</sub> Nanocubes: Tracking the Evolution of Chemical State, Geometric Structure, and Catalytic Selectivity using Operando Spectroscopy.

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