Elektrochemická charakterizace redoxních reakcí železa a jeho sloučenin na pevných a pastových elektrodách

Abstract

The dissertation deals with the electrochemical characterization of redox reactions of iron and its compounds on solid and carbon paste electrodes and applying the obtained knowledge to the electrochemical reactions of leached blast furnace sludge (BFSL). For this purpose, polyamide split-holder of the carbon paste electrode with exchangeable tips was designed and modified, and its geometrical parameters' influence on the electrochemical response was investigated. In the first phase of the research, the electrochemical characterization of BFSL in acidic (1M HCl) and alkaline (1M NaOH) media was performed using the carbon paste electrode and cyclic voltammetry with emphasis on the reducing region. Hematite, magnetite, and solid iron electrode served as model systems. The reduction reactions of BFSL were found to be suppressed in acidic electrolytes. Whereas in alkaline media, a significant peak in the reduction region for BFSL was identified, corresponding to the complex reduction of iron oxides to nanostructured metallic Fe0. In the second phase of the research, attention was paid to the formation of oxide layers during voltammetric cycling in alkaline media. An iron electrode was used as a model system, and obtained results were applied to BFSL. Analytical methods (Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray Analysis (EDX)) together with Fourier Transform Infrared Spectroscopy (FTIR), Raman spectroscopy, and X-ray Diffraction (XRD) were used to analyze the oxidation products. The formation of nanostructured magnetite (Fe3O4) and, to a lesser extent, maghemite (γ-Fe203) was detected on the Fe-electrode surface. It was proven that evolving hydrogen strongly influences these oxidation processes during the initial voltammetric cycles. In addition, the charges corresponding to magnetite formation and reduction together with the hydrogen evolution reaction (HER) were found to depend on the number of cycles and appeared to follow a similar pattern. Repeated voltammetric cycling on a carbon paste electrode modified with BFSL showed a voltammetric waveform similar to that of the solid Fe electrode. It was shown that the same electrochemical processes occur on the surface of BFSL as on the surface of Fe-electrode. These processes result in the formation of a magnetite nanolayer on the surface of BFSL. Simultaneously, the transformation of hematite to magnetite occurs, where hydrogen is also involved in the first stages of the cycling.