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”

Abstract 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–CN l T f /ST p , consist of a “core” of pyrolyzed polyketone nanoballs (indicated as ST p “core” support) covered by a carbon nitride (CN) “shell” matrix embedding PtNi x alloy NPs (indicated as PtNi x -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 ST p “core” supports and the details of the preparation procedure, such as pyrolysis temperature, T f , and treatment with H 2 O 2 , 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–CN l T f /ST p systems: (a) including a ST p “core” support with a high porosity; and (b) obtained at T f  = 600 °C. It is demonstrated that in general, the treatment with H 2 O 2 of electrocatalysts is detrimental for the ORR performance. Nevertheless, in particular conditions, the treatment in H 2 O 2 improves the ORR performance of PtNi-CN l T f /ST p . The results presented in this work allow to elucidate the complex correlation existing between: (a) the composition; (b) the interactions in PtNi x -CN; (c) the morphology of ST p and PtNi–CN l T f /ST p ; and (d) the ORR performance of the electrocatalysts.