Highly Performing Supercapacitor Monometallic Cobalt - Layered Double Hydroxide with Local Structure Uncovered by X-Ray Diffraction and Absorption, Pair Distribution Function and X-Ray Photoelectron Spectroscopy Cross Study
Résumé
Through a topochemical oxidative reaction (TOR) under air, a β-Co(OH)2 brucite type structure is converted into a monometallic CoIICoIII–CO3 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 fine structure, X-ray absorption near-edge structure, and pair distribution function analysis. The chemical composition of pristine material and its derivatives (electrochemically treated) are identified by thermogravimetry analysis for the bulk and X-ray photoelectron spectroscopy for the surface. The electrochemical behavior is investigated on deposited thin films 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 CoIICoIII–CO3 LDH at a current density of 0.5 A g−1. The performances of these materials are described using Ragone plots, which finally 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.