Hierarchical oxygen reduction reaction electrocatalysts based on FeSn0.5 species embedded in carbon nitride-graphene based supports

This work reports the synthesis, the physicochemical characterization and the electrochemical studies of new electrocatalysts (ECs) for the oxygen reduction reaction (ORR) that: (i) exhibit a hierarchical architecture; and (ii) do not comprise platinum. The active sites of the ECs consist of Fe and Sn species stabilized in "coordination nests" of a carbon nitride (CN) matrix. The latter exhibits a rough, microporous morphology and acts as a "shell" covering a graphene "core". This paper: (i) discusses the role played by Fe as the "active metal" in this family of ECs; and (ii) examines in detail how the physicochemical properties and, correspondingly, the electrochemical performance are affected by a suitable activation procedure A meant to boost the ORR kinetics. The results lead to an improved fundamental understanding on the features of the active sites, including the impact of both A and the pH of the environment in their performance and ORR mechanism. These insights clarify the most desirable features to be included in high-performing ECs belonging to this family, paving the way to the synthesis of next-generation, efficient ECs for the ORR that do not comprise platinum. (C) 2018 Elsevier Ltd. All rights reserved.