Metal-N-C electrocatalysts (where the Metal is Fe or Co) have been investigated for mitigating the dependence on platinum-group-metals (PGM), when catalyzing the oxygen reduction reaction (ORR) in acidic or alkaline for fuel cell technologies. This thesis relates the activity, durability and poisoning resistance with the physicochemical properties of such electrocatalysts with iron and cobalt. The investigated materials contain two main active groups: (i) atomicallydispersed metals attached to nitrogen-doped carbon networks (M-NxCy active sites) and (ii) metal nanoparticles encased on nitrogen-doped carbon shells (M@N-C active sites). Regarding the activity, Fe-N-C is more active than the Co-based catalysts, either at low and high pHs. Fe-NxCy sites present the highest ORR activity in acid media, amplified by an adequate energy binding between the metallic center and oxygenated reaction intermediates. In contrast, Fe@N-C core-shell sites present maximum ORR mass activity in alkaline media, promoted by a synergistic effect involving catalyst particles with metallic iron in the core and nitrogen-doped carbon in the shell. The durabilities tests have shown two main degrading processes that may occur on the catalyst: (i) oxygenated and nitrogen functional groups interconversion and/or oxidation and (ii) demetallation of the metallic center. Iron nanoparticulated catalyst centers undergo more severe carbon degradation and nitrogen/oxygenated functional groups interconversion (and/or oxidation) than the atomically dispersed iron centers. But, this latter catalyst losses metal severely, which is re-deposited growing in situ Fe-based nanoparticles after accelerated stressing tests under O2 atmosphere, more at 25 °C than at 60 °C. As a consequence, the atomically dispersed iron-based nanoparticles drop the ORR mass activities less intensely. Further, the atomically dispersed Fe-and Co-containing electrocatalysts have better BH4 −-tolerance than bare Fe and Co nanoparticles. The atomically dispersed iron electrocatalysts, the material with the highest micropores area, present slight advantage of ORR mass activity in the presence of BH4anions. Finally, these features place the atomicallydispersed iron as a promising candidate for the investigations in direct borohydride fuel cell (DBFC) and as an excellent candidate for application in the cathode of anion-exchange membrane fuel cell (AEMFC).

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