Graphene-supported Fe, Co, Ni carbon nitride electrocatalysts for the ORR in alkaline environment

The development of advanced energy conversion systems characterized by a high efficiency and a low environmental impact is one of the most relevant targets of modern research.Very recently, viable OH--conducting membranes were developed, opening the possibility to devise efficient anion-exchange membrane fuel cells (AEMFCs). In these systems the ORR takes place in an alkaline environment; accordingly, AEMFCs can adopt “Pt-free” ORR ECs and still achieve a high performance level. In this work, new “Pt-free” ORR ECs are reported; the materials comprise a graphene support “core”, which is covered by a carbon nitride “shell” coordinating the ORR active sites. The proposed materials reap the benefits offered by graphene, including: (i) a high electrical conductivity; and (ii) a low microporosity, to facilitate the mass transport of reactants and products. The carbon nitride “shell” coordinates the bimetallic active sites, which include: (i) a 3d-“active metal” (i.e., Fe, Co, Ni); and (ii) an oxophilic “co-catalyst” (Sn). The ORR performance of the ECs proved very promising; in detail, “ex-situ” measurements in an alkaline environment demonstrated that the best material exhibits an ORR overpotential ca.70 mV higher with respect to a 10 wt.% Pt/C reference.