Selective electro-oxidation of dopamine on Co or Fe supported onto N-doped ketjenblack

Abstract

Herein, we report the synthesis of Co and Fe supported onto N-doped ketjenblack (Co/KB-N and Fe/KB-N) electrocatalysts via a template-free synthesis method, using EDTA nitrogen precursor and oxidized carbon, and their examination for dopamine electrooxidation reaction. The as-fabricated electrocatalysts initially were physicochemically characterized using the transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS) and carbon, hydrogen, nitrogen, sulfur (CHNS), techniques. Afterwards, they were electrochemically evaluated using cyclic voltammetry, chronoamperometric and potentiometric methods. Both electrocatalysts were examined in alkaline environment (pH=13). Co/KB-N was also tested at a pH value close to human's serum (pH=7.25), exhibiting much higher performance in terms of activity, sensitivity, stability and selectivity. The lower pH values favored the dopamine electrooxidation reaction, specifically increasing the Co/KB-N current response from ca. 7 to 50 μA and its sensitivity at high concentration range from 571.3 to 1185.7 μA mM−1 cm−2. This performance improvement could be attributed to the fact that the neutral environment favors the formation of the Co3+/Co4+ redox pair, which is not presented in the alkaline medium, and, in combination with the presence of N, is responsible for the high rate of electron transfer as well as the Co/KB-N high selectivity.