Structural Transformation and Degradation of Cu Nanocatalysts during Electrochemical CO2 Reduction Reaction

Abstract

Abstract 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 under realistic working conditions, which can dictate the overall device performance, is needed. In this work, we report the structural dynamics and degradation pathway of Cu nanoparticles (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 Cu 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. Other reaction parameters, including reaction intermediates and bubble generation, induce changes in the agglomeration process and final morphology of the Cu NPs electrode, supported by post-mortem ex situ microscopic analysis. The in situ XAS analysis suggests that the majority of the Cu NPs detached from the electrode as soon as the reaction began, and the remaining Cu 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 Cu 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.