Sugar-based iron-doped N-carbons for oxygen reduction reaction

Fuel cells for low temperature applications are the subject of intensive research because they could reduce consumption of primary fossil fuels and greenhouse gas emissions. However, performances of these devices are severely limited by the kinetics of the oxygen reduction reaction (ORR) at the cathode, so that the use of high-cost catalysts, such as Pt, is so far mandatory. Although catalytically optimal, Pt catalysts suffer drawbacks such as formation of poisoning surface Pt-oxides and particle coarsening (by dissolution/re-precipitation, Ostwald ripening), that cause loss of both active surface area and activity. Other negative aspects have economic origin due to the metal natural scarcity and cost. A very interesting research challenge is to find an alternative non-precious, though less catalytically performing, catalyst. Among others, nitrogen-modified carbons doped with non-precious transition metal centres, typically iron, are of interest because of reduced costs of precursors and easiness by which composition and morphology can be modulated by preparation. In this work we present some results on oxygen reduction reaction by a series of Pt-free catalysts obtained by pyrolysis of guanidine-based nitrogen compounds/sugar mixtures in the presence of a metal salt and a templating agent. Catalysts were characterized by physical, chemical and electrochemical methods. Results are presented in terms of the influence that precursors nature exerts on oxygen reduction onset potential, presence of defined limiting current and reaction mechanism. They are characterized by a well-defined limiting current, an onset potential approaching Pt ORR starting potential and a number of exchanged electrons n>3.9. An attempt of explanation of different electrocatalytic behavior obtained varying the nature of precursor is also done.