Abstract
In this work, Ni-Co oxides coatings were produced using electrochemical techniques (chronopotentiometry and/or linear voltammetry) and solutions containing Ni2+ and Co2+ ions in the molar ratio 1: 2, sodium citrate as the ligand, and different pH values (7.5 and 10.5). Energy dispersive spectrometry (EDS), scanning electron microscopy (SEM), Raman spectroscopy (LRS) and electrochemical impedance spectroscopy (EIS) were used to characterize these coatings. The results showed that both pH values favored the production of Ni-Co oxide phases, independent of the electrochemical technique used. The EDS analysis indicated that it was possible to produce of oxides coating presenting different Ni:Co ratios using electrodeposition process. However, the morphology, the microstructure and the electrocatalytic ability of the coatings depended on both the pH and on the electrochemical technique used to produce them. The coatings produced using pH 10.5 were suitable to be used as electrocatalysts for the oxygen evolution reaction (OER).
Highlights
Electrochemical deposition techniques allow the production of functional metallic, ceramics or composites coatings of excellent quality
All the electrochemical experiments were conducted in order to find the appropriate conditions for the electrodeposition of Ni-Co (1: 2 ratio) mixed oxide
The chemical characterization results show that the coatings producing using Solution 1 (Coatings 1, 2 and 3, for those produced under the conditions of Experiments 1, 2 and 3, respectively) presented approximately 1:4 Ni:Co ratio, independent of the experiment conditions uses
Summary
Electrochemical deposition techniques allow the production of functional metallic, ceramics or composites coatings of excellent quality. By using these techniques, it is possible to produce very thin and homogeneous films with specific chemical and morphological properties. There is a great interest in those useful to enhance the O2 and H2 evolution reactions (respectively, oxygen evolution reaction - OER, and hydrogen evolution reaction - HER), which are important in several technological processes, such as water electrolysis, fuel cells, batteries and sensors[1,10,11,12,13,14,15,16,17]. HER and OER are directly related to the demand for sustainable clean energy and concerns about climate change and global warming
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