Nanoclusters based on CoNC and FeNC for oxygen reduction reactions and their application at the cathode of a direct methanol fuel cell

Polymer electrolyte fuel cells (PEFCs) are attracting remarkable interest as an alternative power source with low environmental impact. Direct methanol fuel cells (DMFCs) are a subcategory of PEFCs well suited for portable applications. Nowadays, the widespread commercialization of a DMFC is hindered by the cost of the components. This cost is, in part, due to the precious metals, in particular Pt, used as the catalysts of the fuel cell. To solve this problem, the attention of many researchers is focused on the replacement of the expensive Pt catalyst with more abundant non precious metals. Here, in-house CoNC and FeNC have been prepared by, first, chelating the metals with ethylene diamine tetra acetic acid, known as EDTA (nitrogen precursor). UV-Visible (UV-Vis) spectrometry has been used to ensure the chelated metal formation. In the next step, the chelated metals have been deposited on a high surface area oxidized carbon support to increase the electrical conductivity. The latter composite material has been thermally treated at 800°C (CoNC8 and FeNC8) or 1000°C (CoNC10 and FeNC10) in nitrogen atmosphere in order to create the catalytic sites that will be able to perform the oxygen reduction reaction (ORR) in the acid medium. Electrochemical tests have been carried out to investigate the activity of the electro-catalysts for the ORR and the performance and durability in DMFCs. Moreover, some portions of the most performing electro-catalysts have been treated in HNO3 to leach out the unalloyed ions and, then, thermally treated a second time. Informations about the crystalline structure, size and morphologies have been obtained by X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques, whereas the elementary percentage composition has been studied with CHNS analyser and energy dispersive X-ray spectroscopy. Finally, the nature and the oxidation states of the nanoclusters have been related to the electrochemical results by using X-ray photoelectron spectroscopy (XPS).