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Molybdenum carbide catalysts supported on carbon nanofibers (β-Mo 2 C/CNF) were synthetized employing different carburization parameters: five temperatures (550-750 ºC) and four heating rates (1-10 ºC/min) were tested. The carburization process of the Mo precursor in the catalysts was studied by thermogravimetric analysis, X-ray diffraction, X-ray photoelectron spectroscopy, N 2 physisorption, inductively coupled plasma optical emission spectrometry and transmission electron microscopy. The formation of the carbide phase was confirmed by the presence of the oxycarbide and carbide phases which were observed on the surface of all catalysts. Higher carburization temperatures resulted in an increase of the carbide phase content and crystal size at the expenses of the oxycarbide phase disappearance. High carburization temperatures and low heating rates were needed in order to obtain well-defined β-Mo 2 C crystals over the

The catalytic layers of a low temperature fuel cell must present a sufficient electronic conductivity for a high overall performance and, in this sense, the electrocatalyst support plays an important role. However, regarding carbon nanofibers as support, it is necessary to chemically treat their surface to improve both metal deposition and anchorage, which unfortunately affects negatively the electronic conductivity. The effects of functionalization of carbon nanofibers (CNFs) on their electronic conductivity, in addition with their physicochemical properties have been studied. Oxygen surface groups have been created on the surface of three CNFs with different properties, following three oxidation treatments with diverse severity. Whereas some important properties for their application as electrocatalyst support are not significantly modified after functionalization (texture, crystalline structure, etc.), other properties like the electronic conductivity are affected depending on the extent of the process. Refluxing at boiling temperature causes the largest reduction of electronic conductivity, of ca. 80% when using a mixture of nitric and sulfuric acids and of ca. 50-60% when using nitric acid. On the other hand, the electronic conductivity of certain CNFs is not negatively influenced after treatment at room temperature with the mixture of nitric and sulfuric acids.

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