“Core-shell” carbon nitride electrocatalysts for the oxygen reduction reaction (ORR) based on graphene and related materials for application in low-temperature fuel cells

Fuel cells (FCs) are a family of advanced energy conversion systems characterized by an outstanding energy conversion efficiency, up to two-three times as high as typical internal combustion engines (ICEs). Furthermore, FCs show a number of other attractive features including a simple engineering of the power plant and a high compatibility with the environment. In particular, FCs operating at a low temperature (T<200°C) are typically characterized by a very high energy and power density. As a consequence, they are very promising candidates to provide power to a number of applications, ranging from portable electronic devices to light-duty vehicles. one important bottleneck in the operation of FCs functioning at a low temperature is the sluggishness of the ORR. Suitable ORR electrocatalysts (ECs) are needed to achieve a level of permormance compatible with applications. This contribution describes the preparation of innovative ORR ECs on the basis of the unique protocols developed in our laboratory. The proposed ECs are characterized by "core-shell" morphology. In detail, the "core" consists of sheets/nanoplatelets of graphene and related materials. The latter are covered by a carbon nitride "shell", which coordinates nanoparticles bearinf the ORR active sites through "nitrogen coordiantion nests". The chemical composition of the proposed "core-shell" ECs is determined by inductively-coupled plasma atomic emission spectroscopy (ICP-AES) and microanalysis. The structure of the materials is studied by powder X-ray diffraction (XRD); the morphology is inspected by high-resolution scanning electron microscopy (HR-SEM) and high-resolution transmission electron microscopy (HR-TEM). The electrochemical performance, reaction mechanism and selectivity of the ECs in the ORR is evaluated "ex situ" by cyclic voltammetry with the rotating ring-disk electrode (CV-TF-RRDE) method. Finally, the most promising ECs are used to fabricate membrane-electrode assemblies (MEAs), which are tested in single fuel cell in operating conditions.