Thin films of Co, Ni, and CoNi oxide composites with carbon were successfully prepared using the sol-gel method. Three synthesis methods were investigated: the citric acid method, the classical Pechini method, and a modified Pechini method with EDTA. The influence of pH, PVA and calcination temperatures (350 °C and 450 °C) on the film morphology was studied.
Raman spectroscopy confirmed the presence of partially ordered carbon, with a higher degree of ordering at the film surface compared to its interior. The electrochemical properties of the samples were analyzed by cyclic voltammetry, evaluating the effect of calcination temperature, synthesis method, Co/Ni ratio, and cycling stability (comparison between the first and third cycle).
XRD analysis showed that calcination at 350 °C does not result in sufficient crystallization, although the morphology is favorable. Samples calcined at 450 °C exhibited higher electrochemical activity, pseudocapacitive behavior, and improved cycling stability at lower potentials. Oxidation peaks (M²⁺ → M³⁺ → M⁴⁺) were reduced or disappeared in the third cycle. Higher crystallinity was found to be more important than the presence of carbon for enhancing the electrochemical activity of the films.
The main objective of the thesis was to determine the influence of the synthesis parameters on the morphology, degree of crystallinity, and electrochemical activity of the prepared thin films.
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