Interplay between morphology and electrochemical performance of “core–shell” electrocatalysts for oxygen reduction reaction based on a PtNix carbon nitride “shell” and a pyrolyzed polyketone nanoball “core”

The interplay between morphology and electrochemical performance of a new class of "core-shell" electrocatalysts for the oxygen reduction reaction (ORR) is studied. The electrocatalysts, labelled PtNi-CN1 T-f/STp, consist of a "core" of pyrolyzed polyketone nanoballs (indicated as STp "core" support) covered by a carbon nitride (CN) "shell" matrix embedding PtNix alloy NPs (indicated as PtNix-CN). The electrocatalysts are characterized by means of: (a) high-resolution transmission electron microscopy (HR-TEM); and (b) cyclic voltammetry with the thin-film rotating ring-disk electrode (CV-TF-RRDE) method. The structure of the STp, "core" supports and the details of the preparation procedure, such as pyrolysis temperature, T-f, and treatment with H2O2, play a crucial role on modulating: (a) the morphology; and (b) the ORR performance of the electrocatalysts. In particular, the best results are achieved for PtNi-CN1 T-f/STp systems: (a) including a STp, "core" support with a high porosity; and (b) obtained at T-f = 600 degrees C. It is demonstrated that in general, the treatment with H2O2 of electrocatalysts is detrimental for the ORR performance. Nevertheless, in particular conditions, the treatment in H2O2 improves the ORR performance of PtNi-CN1 T-f/STp. The results presented in this work allow to elucidate the complex correlation existing between: (a) the composition; (b) the interactions in PtNix-CN; (c) the morphology of STp and PtNi-CN1 T-f/STp; and (d) the ORR performance of the electrocatalysts.