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Hydroxyl radicals dominate reoxidation of oxide-derived Cu in electrochemical CO₂ reduction.

ABSTRACT: Cu^δ+ sites on the surface of oxide-derived copper (OD-Cu) are of vital importance in electrochemical CO₂ reduction reaction (CO₂RR). However, the underlying reason for the dynamically existing Cu^δ+ species, although thermodynamically unstable under reductive CO₂RR conditions, remains uncovered. Here, by using electron paramagnetic resonance, we identify the highly oxidative hydroxyl radicals (OH^•) formed at room temperature in HCO₃^- solutions. In combination with in situ Raman spectroscopy, secondary ion mass spectrometry, and isotope-labelling, we demonstrate a dynamic reduction/reoxidation behavior at the surface of OD-Cu and reveal that the fast oxygen exchange between HCO₃^- and H₂O provides oxygen sources for the formation of OH^• radicals. In addition, their continuous generations can cause spontaneous oxidation of Cu electrodes and produce surface CuO_x species. Significantly, this work suggests that there is a "seesaw-effect" between the cathodic reduction and the OH^•-induced reoxidation, determining the chemical state and content of Cu^δ+ species in CO₂RR. This insight is supposed to thrust an understanding of the crucial role of electrolytes in CO₂RR.

SUBMITTER: Mu S

PROVIDER: S-EPMC9237086 | biostudies-literature | 2022 Jun

REPOSITORIES: biostudies-literature

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Hydroxyl radicals dominate reoxidation of oxide-derived Cu in electrochemical CO2 reduction.

Mu Shijia S Lu Honglei H Wu Qianbao Q Li Lei L Zhao Ruijuan R Long Chang C Cui Chunhua C

Nature communications 20220627 1

Cuδ+ sites on the surface of oxide-derived copper (OD-Cu) are of vital importance in electrochemical CO2 reduction reaction (CO2RR). However, the underlying reason for the dynamically existing Cuδ+ species, although thermodynamically unstable under reductive CO2RR conditions, remains uncovered. Here, by using electron paramagnetic resonance, we identify the highly oxidative hydroxyl radicals (OH•) formed at room temperature in HCO ...[more]

PMID: 35760802

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Project description:The electrochemical CO2 reduction reaction (CO2RR) holds enormous potential as a carbon-neutral route to the sustainable production of fuels and platform chemicals. The durability for long-term operation is currently inadequate for commercialization, however, and the underlying deactivation process remains elusive. A fundamental understanding of the degradation mechanism of electrocatalysts, which can dictate the overall device performance, is needed. In this work, we report the structural dynamics and degradation pathway of Cu oxide nanoparticles (CuOx NPs) during the CO2RR by using in situ small-angle X-ray scattering (SAXS) and X-ray absorption spectroscopy (XAS). The in situ SAXS reveals a reduction in the size of NPs when subjected to a potential at which no reaction products are detected. At potentials where the CO2RR starts to occur, CuOx NPs are agglomerated through a particle migration and coalescence process in the early stage of the reaction, followed by Ostwald ripening (OR) as the dominant degradation mechanism for the remainder of the reaction. As the applied potential becomes more negative, the OR process becomes more dominant, and for the most negative applied potential, OR dominates for the entire reaction time. The morphological changes are linked to a gradual decrease in the formation rate for multicarbon products (C2H4 and ethanol). Other reaction parameters, including reaction intermediates and local high pH, induce changes in the agglomeration process and final morphology of the CuOx NPs electrode, supported by post-mortem ex situ microscopic analysis. The in situ XAS analysis suggests that the CuOx NPs reduced into the metallic state before the structural transformation was observed. The introduction of high surface area carbon supports with ionomer coating mitigates the degree of structural transformation and detachment of the CuOx NPs electrode. These findings show the dynamic nature of Cu nanocatalysts during the CO2RR and can serve as a rational guideline toward a stable catalyst system under electrochemical conditions.

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Hydroxyl radicals dominate reoxidation of oxide-derived Cu in electrochemical CO₂ reduction.

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Hydroxyl radicals dominate reoxidation of oxide-derived Cu in electrochemical CO<sub>2</sub> reduction.

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