  In this report, the preparation of Fe-carbon nitride (CN)-based
electrocatalysts (ECs) with a 'core-shell' morphology for the oxygen reduction
reaction (ORR) is described. The ECs consist of spherical XC-72R carbon
nanoparticles, the 'cores', that are covered by a CN matrix, the 'shell',
embedding Fe species in 'coordination nests'. The latter is formed by the
presence of carbon and nitrogen ligands on the surface of the CN matrix, the
'shell'. Two families of CN-based ECs are prepared, which are grouped on the
basis of the concentration of N atoms in the CN 'shell'. Each group comprises
of both a 'pristine' and an 'activated' EC; the latter is obtained from the
'pristine' EC by a suitable series of treatments (A) devised to improve the ORR
performance. The chemical composition of the CN-based ECs is determined by
Inductively-Coupled Plasma Atomic Emission Spectroscopy (ICP-AES) and
microanalysis. The surface area of the CN-based ECs is determined by nitrogen
physisorption techniques, and the surface composition is probed by X-ray
Photoelectron Spectroscopy (XPS). The electrochemical performance and reaction
mechanism of the CN-based ECs in the ORR is investigated in both acid and
alkaline environments by cyclic voltammetry with the Thin-Film Rotating
Ring-Disk Electrode setup (CV-TF-RRDE). The influence of the preparation
parameters and of the treatments on the physicochemical properties, the ORR
performance, and reaction mechanism is studied in detail. In the alkaline
environment the FeFe2-CNl 900/CA 'core-shell' EC shows a remarkable ORR onset
potential of 0.908 V vs. RHE which, with respect to the value of 0.946 V vs.
RHE of the Pt/C ref., classifies the proposed materials as very promising
'Platinum Group Metal-free' ECs for the ORR.
