Carbon nitride-based oxygen reduction reaction nano-electrocatalysts for PEM fuel cells.

(POSTER) The oxygen reduction reaction (ORR) is one of the fundamental electrochemical processes involved in the operation of fuel cells (FCs). The ORR is a very sluggish process and bottlenecks the performance of FCs working at T < 250°C, e.g. proton-exchange membrane fuel cells (PEMFCs). The latter systems are of a high scientific and technological relevance for their exceptional energy conversion efficiency, remarkable power density and environment-friendly operation. To achieve a performance level compatible with the applications, PEMFCs must mount suitable ORR electrocatalyts (ECs). Typical state-of-the-art ORR ECs for application in PEMFCs comprise Pt nanocrystals supported on active carbons with a large surface area. The performance and durability of these ECs is still insufficient; furthermore, the high loading of Pt raises the costs to unacceptable levels. One approach to address the above issues consists in the development of carbon nitride (CN)-based ECs. These systems are characterized by a porous conductive CN support, coordinating the metal alloy nanoparticles bearing the ORR active sites in “nitrogen coordination nests”. This contribution overviews the development of this family of ECs [1]. Early unsupported materials were studied to identify the best preparation route and the chemical composition yielding the best ORR performance. A major breakthrough was achieved by devising “core-shell” CN-based ECs; in these systems, the CN “shell” embedding the ORR active sites is supported on a conductive carbonaceous “core”. It was shown that the morphology of the “core” plays a crucial role to modulate the performance of the CN-based EC. The performance in the ORR of the best “core-shell” CN-based ECs is outstanding. With respect to the reference ECs, the intrinsic ORR activity is no less than twice larger (>300 A/cm2Pt at 0.9 V vs. ca. 150 A/cm2Pt of the reference) [2], while the Pt loading to achieve 1 kW or power is as little as ca. 1/3 (0.3 gPt/kW vs. 1.1 gPt/kW of the reference) [3]. References [1] Di Noto, V.; Negro, E. Electrochim. Acta 2010, 55, 7564. [2] Negro, E.; Polizzi, S.; Vezzù, K.; Toniolo, L.; Cavinato, G.; Di Noto, V. Int. J. Hydrogen Energy 2014, 39, 2828. [3] Di Noto, V.; Negro, E. Fuel Cells 2010, 10, 234.