Toward Pt-Free Anion-Exchange Membrane Fuel Cells:\nFe–Sn Carbon Nitride–Graphene Core–Shell Electrocatalysts\nfor the Oxygen Reduction Reaction

Abstract

We report on the\ndevelopment of two new <i>Pt-free</i> electrocatalysts (ECs)\nfor the oxygen reduction reaction (ORR) process\nbased on graphene nanoplatelets (GNPs). We designed the ECs with a <i>core–shell</i> morphology, where a GNP <i>core</i> support is covered by a carbon nitride (CN) <i>shell.</i> The proposed ECs present ORR active sites that are not associated\nwith nanoparticles of metal/alloy/oxide but are instead based on Fe\nand Sn subnanometric clusters bound in <i>coordination nests</i> formed by carbon and nitrogen ligands of the CN <i>shell</i>. The performance and reaction mechanism of the ECs in the ORR are\nevaluated in an alkaline medium by cyclic voltammetry with the thin-film\nrotating ring-disk approach and confirmed by measurements on gas-diffusion\nelectrodes. The proposed GNP-supported ECs present an ORR overpotential\nof only ca. 70 mV higher with respect to a conventional Pt/C reference\nEC including a XC-72R carbon black support. These results make the\nreported ECs very promising for application in anion-exchange membrane\nfuel cells. Moreover, our methodology provides an example of a general\nsynthesis protocol for the development of new <i>Pt-free</i> ECs for the ORR having ample room for further performance improvement\nbeyond the state of the art.