The influence of three different transition metals (Me = Fe, Co, Cu) on the oxygen reduction reaction (ORR) kinetics in acidic medium of Me–N–C catalysts synthesized using Me­(II)-phthalocyanine as precursors is investigated in this work. Through a detailed electrochemical characterization using cyclic voltammetry and rotating ring-disk electrode, several kinetic parameters such as Tafel slope, reaction order for oxygen and proton, apparent activation energy, selectivity toward hydrogen peroxide production, and kinetics of reduction of adsorbed oxygen were determined. The behavior of these three catalysts is analyzed in detail. A comparison between each other of the catalysts, and with a Pt-based catalyst is done. The results obtained provide clear evidence of the important role played by each transition metal in the formation of more or less effective active sites. The ORR kinetics behavior can be well interpreted according to the occurrence of a redox-mediated coverage of the active sites at low overpotentials (close to the ORR onset), which has influence on the Tafel slope, as well as on the oxygen adsorption and activation energy of the process. The results clearly show that, among the other transition metals considered, Fe is the best performing one in carrying out the ORR.

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Platinum group metal (PGM)-free catalysts for oxygen reduction reaction (ORR) have attracted increasing interest as potential candidates to replace Pt, in the view of a future widespread commercialization of polymer electrolyte fuel cell (PEFC) devices, especially for automotive applications. Among different types of PGM-free catalysts, M–N–C materials appear to be the most promising ones in terms of activity. These catalysts can be produced using a wide variety of precursors containing C, N, and one (or more) active transition metal (mostly Fe or Co). The catalysts synthesis methods can be very different, even though they usually involve at least one pyrolysis step. In this review, five different synthesis methods are proposed, and described in detail. Several catalysts, produced approximately in the last decade, were analyzed in terms of performance in rotating disc electrode (RDE), and in H2/O2 or H2/air PEFC. The catalysts are subdivided in five different categories corresponding to the five synthesis methods described, and the RDE and PEFC performance is put in relation with the synthesis method.

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