Electrochemical Oxygen Reduction on Modified Carbon Nanotubes in Alkaline Electrolyte

The electrochemical characteristics of carbon nanotubes subjected to various types of modification, to increase their activity and stability, in the oxygen reduction reaction in alkaline electrolyte are determined by cyclic voltammetry on a rotating disk and rotating ring-disk electrodes. The measurements were performed on the carbon nanotubes after their functionalization, doping with nitrogen, and subsequent modification with platinum in an amount of up to 20 wt %. The resulting dispersed material in the form of an extremely thin layer was applied to a disk electrode, and the effect of carbon nanotubes’ pretreatment on their efficiency in the oxygen reduction reaction in alkaline electrolyte is studied. The activity is shown to be higher, and the degree of degradation, lower, as the selectivity in the oxygen reduction to water increased. When oxygen was reduced through the intermediate formation of hydrogen peroxide, the degradation of the system under study increased. According to the rotating ring-disk electrode data, the greatest contribution of the reaction with the intermediate Н 2 О 2 formation is observed on the carbon nanotubes after their functionalization, whereas the doping with nitrogen increased the activity and the contribution of the four-electron reaction; the value of n is 3.2. After the modification with platinum, the oxygen reduction reaction proceeds predominantly with the breaking of the O–O-bond and the reduction of oxygen to water. The influence of the support on the platinum-modified nanotubes’ characteristics displays itself in the potential range below 0.70 V, where the electroreduction of oxygen on the platinum-free surface proceeds with the transfer of two electrons and contributes to the overall process. The less hydrogen peroxide formed during the oxygen reduction reaction, the less is the degradation of the catalyst. Further increase in the activity of the carbon nanotubes is required; to this purpose, the number of certain types of nitrogen-containing surface groups facilitating the contribution of the four-electron reaction path of the oxygen reduction reaction must be elevated.