Through a topochemical oxidative reaction (TOR) under air, a β-Co(OH) 2 brucite type structure is converted into a monometallic Co II Co III -CO 3 layered double hydroxide (LDH). The structural and morphological characterizations are performed using powder X-ray diffraction, Fourier-transformed IR spectroscopy, and scanning and transmission electron microscopy. The local structure is scrutinized using an extended X-ray absorption fi ne structure, X-ray absorption near-edge structure, and pair distribution function analysis. The chemical composition of pristine material and its derivatives (electrochemically treated) are identifi ed by thermogravimetry analysis for the bulk and X-ray photoelectron spectroscopy for the surface. The electrochemical behavior is investigated on deposited thin fi lms in aqueous electrolyte (KOH) by cyclic voltammetry and electrochemical impedance spectroscopy, and their capacitive properties are further investigated by Galvanostatic cycling with potential limitation. The charge capacity is found to be as high as 1490 F g −1 for Co II Co III -CO 3 LDH at a current density of 0.5 A g −1 . The performances of these materials are described using Ragone plots, which fi nally allow us to propose them as promising supercapacitor materials. A surface-to-bulk comparison using the above characterization techniques gives insight into the cyclability and reversibility limits of this material.

International audienceThis 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