Dynamic Characterization of Inter- and Intralamellar Domains of Cobalt-Based Layered Double Hydroxides upon Electrochemical Oxidation
Résumé
This work investigated in situ changes in the structure of the layered double hydroxides (LDH) during electrochemical processes as well as followed the ion motion related to the charge balancing process. Electrogravimetric measurements, using an electrochemical quartz crystal microbalance (EQCM), allowed one to monitor simultaneously changes in current and in microbalance frequency when electroactive films of Co2Al–NO3 LDH were subjected to voltammetry potential cycling in alkaline solutions (0.1 M COH, C = Li+, Na+, and K+). EQCM results showed a strong dependence of the electrochemical process on the nature of electrolyte cations. Operando X-ray diffraction measurements, carried out during potential cycling of Co2Al–NO3 films in KOH electrolyte, showed the diffusion of OH– species gradually replacing NO3–. Total X-ray scattering experiments recorded ex situ on Co2Al–NO3 after successive oxidation and reduction revealed the presence of a high level of structural disorders even in the pristine material. A quantitative analysis of the local distribution of the cations by the analysis of the pair distribution functions highlighted the presence of different Co sites with distinct modification of Co–OH distances in the first coordination shells after oxidation/reduction.
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