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Despite, platinum supported on carbon (Pt/C) is the most used electro-catalyst for the Oxygen Reduction Reaction (ORR) in PEM fuel cells, problems such as sintering, dissolution of Pt in the electrolyte and oxidation of the carbon support during long-term operation ar e obstacles limiting the mass utilization of PEMFCs. The low abundance of Pt natural resources and its high cost are also limiting its utilization in high volume pr oduction of fuel cell cars (1, 2). Therefore, finding a new cheaper non-noble electro-catalyst with high activity and h igh stability in acidic condition becomes one of the mo st important topics in the PEMFC research. Development of transition metals oxy-nitride is an interesting app roach for new electro-catalysts development for the ORR. Due to its high abundance, titanium oxy-nitride (TiO xNy) is one the most appealing electro-catalysts for the ORR (3 -6). In this study, TiOxNy was prepared by a new in-situ urea-based sol-gel method. For comparison three oth r titanium oxide-nitrides were prepared using classic al solgel method without urea. This electro-catalyst show ed interesting activity for the ORR) with an onset pot ential of ca. 0.75 volts vs. NHE. As well, exchange curren t density of the electro-catalyst prepared by in-situ ureabased sol-gel method was one order of magnitude hig her than that of other electro catalyst obtained by ano ther method. In addition, SEM pictures and BET surface a rea characterization showed a very small particle size (ca. 20~60 nm) with a BET surface area of ca. 93 m /g. This value is higher than those obtained on some titaniu m oxides (ca.45 m/g). The relatively high surface area of these electro-catalysts might be responsible for th e improvement of their electro-catalytic performance for the ORR. The specific chemical composition of these ele ctrocatalysts which led to an optimized ionization pote ntial, work function and density of states of electrons mi ght be the key success to identify excellent electro-catal ys s for the ORR based on TiO xNy electrodes. The prepared electro-catalysts with different N/O ratios showed different properties from a semiconductor behavior in oxygen-rich materials to more conductive and stable electro-catalyst behavior in nitrogen-rich oxy-nitr ides, respectively. XRD and EDS results revealed that the in-situ ureabased sol-gel method might help to fabricate oxy ni tride more active for the ORR than the conventional metho ds because it allows the insertion of more nitrogen, i n the form of TiN phase, through the electro-catalyst str ucture. Considering the mass ratio of nitrogen, oxygen and titanium, EDS results show that the bulk electro-ca talyst was prepared based on a 24 wt. % of nitrogen. Howev er, results from XPS spectra showed only 11 % of nitrog en on the surface. Oxidation of the electrodes, specia lly, t a high anodic potential (ca. 1.5 volts vs. SCE) leads to a change of the surface chemical composition with a significant decrease of the nitrogen amount on the surface to 5 %. It affected the electro-catalytic propertie s of the electro-catalyst. Figure 1 shows the polarization c urves of the catalyst before and after oxidation at a high p otential. Figure 2 shows the first five cycles of Cyclic Voltammetry (CV) curves of the electrode in H 2SO4 0.5 M electrolyte at 25 °C between -2 to +2 V vs. SCE f or 100 cycles with a scan rate of 100 mV/s. An importa nt oxidation peak is seen around 1.5 volts vs. SCE. Th is might be related to the oxidation and/or dissolutio n of the electrode involving nitrogen and titanium. This is supported by evaluation of the dissolution of the T i into the electrolyte using ICP-TOF-MS methods. According ly Ti concentration was measured after each oxidizing scans (up to +2 volts vs. SCE) by ICP-TOF-MS. Results are depicted in figure 3. Maximum dissolute titanium concentration was less than 45 μg/L (~ 0.18 wt. %) after 100 cycles. This amount was less than 0.1 wt. % whe n there was no applied potential. In comparison, the concentration of the Pt dissolved in the same elect rolyte with the same conditions is more than 57 μg/L (more than 0.23 wt. %). Accordingly, the TiO xNy based electrocatalyst represents higher stability than the comme rcial Pt/C based electro-catalyst.

Electrochemical Stability Investigation of TiOxNy electro-Catalyst Produced By in-Situ Urea-Based Sol-Gel Method for PEM Fuel Cell Application