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Surface chemistry on a polarizable surface: Coupling of CO with KTaO₃(001).

ABSTRACT: Polarizable materials attract attention in catalysis because they have a free parameter for tuning chemical reactivity. Their surfaces entangle the dielectric polarization with surface polarity, excess charge, and orbital hybridization. How this affects individual adsorbed molecules is shown for the incipient ferroelectric perovskite KTaO₃. This intrinsically polar material cleaves along (001) into KO- and TaO₂-terminated surface domains. At TaO₂ terraces, the polarity-compensating excess electrons form a two-dimensional electron gas and can also localize by coupling to ferroelectric distortions. TaO₂ terraces host two distinct types of CO molecules, adsorbed at equivalent lattice sites but charged differently as seen in atomic force microscopy/scanning tunneling microscopy. Temperature-programmed desorption shows substantially stronger binding of the charged CO; in density functional theory calculations, the excess charge favors a bipolaronic configuration coupled to the CO. These results pinpoint how adsorption states couple to ferroelectric polarization.

SUBMITTER: Wang Z

PROVIDER: S-EPMC9390988 | biostudies-literature | 2022 Aug

REPOSITORIES: biostudies-literature

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Surface chemistry on a polarizable surface: Coupling of CO with KTaO3(001).

Wang Zhichang Z Reticcioli Michele M Jakub Zdenek Z Sokolović Igor I Meier Matthias M Boatner Lynn A LA Schmid Michael M Parkinson Gareth S GS Diebold Ulrike U Franchini Cesare C Setvin Martin M

Science advances 20220819 33

Polarizable materials attract attention in catalysis because they have a free parameter for tuning chemical reactivity. Their surfaces entangle the dielectric polarization with surface polarity, excess charge, and orbital hybridization. How this affects individual adsorbed molecules is shown for the incipient ferroelectric perovskite KTaO3. This intrinsically polar material cleaves along (001) into KO- and TaO2-terminated surface domains. At TaO2 terraces, the po ...[more]

PMID: 35984882

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Project description:Any substantial move of energy sources from fossil fuels to renewable resources requires large scale storage of excess energy, for example, via power to fuel processes. In this respect electrochemical reduction of CO2 may become very important, since it offers a method of sustainable CO production, which is a crucial prerequisite for synthesis of sustainable fuels. Carbon dioxide reduction in solid oxide electrolysis cells (SOECs) is particularly promising owing to the high operating temperature, which leads to both improved thermodynamics and fast kinetics. Additionally, compared to purely chemical CO formation on oxide catalysts, SOECs have the outstanding advantage that the catalytically active oxygen vacancies are continuously formed at the counter electrode, and move to the working electrode where they reactivate the oxide surface without the need of a preceding chemical (e.g., by H2) or thermal reduction step. In the present work, the surface chemistry of (La,Sr)FeO3-δ and (La,Sr)CrO3-δ based perovskite-type electrodes was studied during electrochemical CO2 reduction by means of near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) at SOEC operating temperatures. These measurements revealed the formation of a carbonate intermediate, which develops on the oxide surface only upon cathodic polarization (i.e., under sufficiently reducing conditions). The amount of this adsorbate increases with increasing oxygen vacancy concentration of the electrode material, thus suggesting vacant oxygen lattice sites as the predominant adsorption sites for carbon dioxide. The correlation of carbonate coverage and cathodic polarization indicates that an electron transfer is required to form the carbonate and thus to activate CO2 on the oxide surface. The results also suggest that acceptor doped oxides with high electron concentration and high oxygen vacancy concentration may be particularly suited for CO2 reduction. In contrast to water splitting, the CO2 electrolysis reaction was not significantly affected by metallic particles, which were exsolved from the perovskite electrodes upon cathodic polarization. Carbon formation on the electrode surface was only observed under very strong cathodic conditions, and the carbon could be easily removed by retracting the applied voltage without damaging the electrode, which is particularly promising from an application point of view.

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Surface chemistry on a polarizable surface: Coupling of CO with KTaO₃(001).

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Surface chemistry on a polarizable surface: Coupling of CO with KTaO<sub>3</sub>(001).

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Surface chemistry on a polarizable surface: Coupling of CO with KTaO3(001).

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Surface chemistry on a polarizable surface: Coupling of CO with KTaO&lt;sub&gt;3&lt;/sub&gt;(001).

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Surface chemistry on a polarizable surface: Coupling of CO with KTaO₃(001).

Surface chemistry on a polarizable surface: Coupling of CO with KTaO<sub>3</sub>(001).