Correlation between Precursor Properties and Performance in the Oxygen Reduction Reaction of Pt and Co Core-shell Carbon Nitride-Based Electrocatalysts

This report shows the synthesis of a new family of core-shell carbon nitride (CN)-based electrocatalysts (ECs) for the oxygen reduction reaction (ORR) in acid medium. The ECs comprise cores of carbon black nanoparticles (NPs) that are covered by a CN shell embedding the active sites. The latter include Pt as the active metal and Co as the co-catalyst. The interplay between the synthesis parameters, the chemical composition, and the ORR performance of the final ECs is elucidated. In particular, the ORR performance and reaction mechanism are studied both in an: (i) ex-situ setup, by means of cyclic voltammetry with thin-film rotating ring-disk electrode (CV-TF-RRDE) measurements; and (ii) in-situ experiment, i.e., in single proton exchange membrane fuel cells (PEMFCs) tested under operating conditions. A structural hypothesis is proposed that explains both the ex situ and the in situ ORR results on the basis of: (i) the relative amounts of the reactants used in the precursor synthesis; and (ii) the main temperature of the pyrolysis process (T-f) adopted in the preparation of the ECs. It is shown that the understanding of the fundamental features of the physicochemical processes involved in the preparation of the ECs is crucial in order to improve the proposed synthesis route and to yield ORR ECs exhibiting a performance level beyond the state of the art.