The role of electric current in the redox-sorption of oxygen by copper-containing nanocomposites
In order to explain the limiting stage of the redox-sorption of oxygen on a cathode-polarised copper-containing nanocomposite based on an ion exchange matrix and the regulation of the rate of the process, we need to determine the maximum current and study the influence of the polarisation current on the absorption rate of oxygen in the limiting polarization region of the thin granular layer of the nanocomposite. To obtain the maximum current, we placed a fraction of the granular nanocomposite material into the cathode section of the adsorption-membrane electrochemical cell. The cell had two anode sections with platinum anodes separated from the cathode section by cation exchange membranes MK-40. The cathode was a granular layer of the porous copper-ion-exchange nanocomposite Cu° Lewatit K2620 in the sodium ion form with the current leads made of thin copper wire. The anode sections contained a Lewatit K2620 sulfonic acid cation exchanger. MK-40 sulfonic acid cation exchanger membranes ensured the electrical conductivity and directional transport of hydrogen ions from the anode sections to the cathode. The kinetics of oxygen electroreduction from water was studied during the polarisation with direct current I for 5 hours. After that, the slices of the nanocomposite granules were studied under a microscope. We determined the geometric boundaries of the intermediate ξ<sub>1</sub>(Cu/Cu<sub>2</sub>О) and final ξ<sub>2</sub>(Cu/Cu<sub>2</sub>О)) stages of the successive oxidation reaction of the nanocomposite’s metal component. We also studied the redox-sorption of molecular oxygen from water on a thin granular layer of the copper-acid cation exchanger nanocomposite at different currents. The study determined the oxygen diffusion current for the new material Cu<sup>0</sup> Lewatit K2620. It also revealed a strong dependence of the maximum current on the degree of oxidation of copper nanoparticles, which indicates their high chemical activity. After several successive volt-ampere cycles, we reached stable activation of nanoparticles corresponding to the maximum value of the effective maximum current. The study determined that in the limiting region with a low current, the most oxygen is absorbed by the chemical component: the amount of oxygen is reduced by means of reduction by copper nanoparticles. The process is limited by the internal diffusion stage. When we increase the current, the amount of absorbed oxygen also grows, with the electrochemical component playing the key role: the reduction of oxygen by the current is observed. The process is forced from the internal diffusion limiting region to the external diffusion, which ensures a faster rate. The current is partly used for the electroreduction of copper oxides.