Abstract
Oxygen reduction electrode is one of the important electrode materials for energy technologies because of the technical importance of oxygen reduction reaction (ORR) in the development of fuel cells and batteries. In this work, a fast, simple and applicable electrodeposition process has been used to modify the oxygenated functionalized carbon nanotubes (FCNTs) with cobalt oxide nanoparticles (CoOx) for use as an active catalyst electrode for ORR in alkaline medium. The prepared electrodes were characterized with structural techniques (XRD and TEM) to confirm the deposition of CoOx nanoparticle on FCNTs surface. The electrocatalytic activity of the prepared electrodes towards ORR was evaluated using different electrochemical methods such as cyclic voltammetry, linear sweep voltammetry combined with rotating disk electrode technique and chronoamperometry. Based on RDE measurements, the CoOx/FCNTs showed higher electrocatalytic activity and the mechanism of ORR proceeds via the four-electron mechanism, the favourable mechanism shown by the noble metal catalysts. However, the CoOx electrode exhibited only the two-electron mechanism with formation of hydrogen peroxide, rather than the four-electron mechanism, while the FCNTs electrode exhibited the two parallel mechanisms favouring four-electron mechanism only at higher overpotential. These results indicate the synergistic effect of the coupling between FCNTs and CoOx nanoparticles catalyzing the ORR via the direct four-electron mechanism. Such a synergistic effect is assumed to be attributed to the formation of an active interface between the FCNTs and CoOx resulting in highly catalytic active sites that allow the adsorption of oxygen and simultaneous reduction and/or the chemical decomposition of the intermediates, mainly the peroxide intermediate formed during the two-electron pathway mechanism. Moreover, compared to the benchmarked catalyst (Pt/C), the non-precious CoOx/FCNTs electrode showed both the higher stability under continuous ORR at a fixed potential for 6 h and higher tolerance for methanol poisoning. The results reported in this work could contribute to the development of high stable and fuel poisoning tolerance cathode electrodes for direct alkaline alcohol fuel cells.