THE ELECTROCHEMICAL FACING OF POWDER IRON FOR THERMOGALVANIC ELEMENTS
Background. The oxygen impact for electrochemical formation of surface structures on iron particles is not sufficiently taken into account in the production technology of composite electrodes for thermogalvanic energy sources; the main conditions of the performance improvement are considered.
Objective. The aim of the paper is to define the electrochemical conditions of oxide layers formation on the surface of the iron powder composite electrode with the presence of oxygen in neutral and basic media.
Methods. For better performance of the oxygen impact the study of composite electrodes was conducted in open air and inert atmosphere, the assembly of cells with composite electrodes was carried out on air in two versions: hermetic and perforated. Electrochemical studies were carried out on the electrochemical module Autolab 30 PGSTAT301N Metrohm Autolab using 3-electrode cells. The microtexture of the iron powder during redox reactions was examined using a high resolution scanning electron microscope Mira 3 FESEM Tescan USA Inc. on a cathode with field emission at SEM HV-10 KeV and automatic measurement on the image. The analytical regime of the scanning microscope was used to determine the surface components distribution and their degrees of oxidation.
Results. It was determined that with a low oxygen partial pressure in potential range from - 0.23 to - 0.88 V surface iron structure has two stages of organization: 1 – mosaic stage with partial covering of iron surface FeO and Fe2O3 ; 2 – transformation of mosaic structure into core–shell structure. Under a high oxygen partial pressure and cathodic potential > - 0.88 V thick iron oxide layers have been formed on the surface structure of iron particles. Thus, the oxygen partial pressure has a key role in electrochemical formation of nanolayers on the surface of iron particles and realizes the thermoelectrochemical activity of composite electrodes.Conclusions. The study found that thermoelectric parameters of an electrode based on iron powder are determined as a function of the pH of the medium and the oxygen content. In the neutral medium electrodes lose ability to reversible processes needed for the formation of the thermogalvanic properties. The ability of a powdered iron-composite electrode to a thermo-galvanic element is formed in an alkaline medium.
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