Nitrogen-Doped Ptni Catalysts on Polybenzimidazole-Functionalized Carbon Support for the Oxygen Reduction Reaction in Pemfcs

Abstract

The increasing consumption of fossil fuels and the consequent environmental issues have promoted development in novel technologies for sustainable and renewable energy conversion. Among them, the polymer electrolyte membrane fuel cell (PEMFC) is a promising technology for its high energy conversion efficiency, zero carbon emission, and abundant fuel resources. However, many obstacles still exist on the road of PEMFC commercialization. The sluggish kinetics of the oxygen reduction reaction (ORR) require the use of platinum group metals (PGMs), especially Pt as the most effective ORR catalysts, which are very scarce and expensive element in the earth crust. PtM (M = 3d transition metals) alloys are known as the promising oxygen reduction reaction catalysts and have been considered as the replacement of pure Pt catalysts for the PEMFC commercialization. Although great progress has been made in the past three decades, the performance and durability of PtM catalysts still face stringent challenges from practical applications. Functionalization of a catalyst carbon support with nitrogen-contained groups can add charges onto its surface, which can be utilized to build a more complete ionomer/catalyst interface, to reduce the catalyst particle size, and to improve particle size distribution. Nitriding PtNi catalysts can effectively improve the catalyst activity and stability by the modification of lattice strain. Hereby, we report a synergistic approach of combining polybenzimidazole (PBI)-grafted Vulcan XC72 carbon as the catalyst support and the nitriding of PtNi to develop PtNiN/ XC72-polybenzimidazole catalysts from Pt seeds on the support. Such PtNiN/XC72-PBI catalysts exhibit the excellent performance of fuel cell membrane electrode assembly (MEA) (i.e., mass activity, 440 mA mgPt −1 ; electrochemical surface area, 51 m 2 gPt −1 ; and rated power density, 836 mW cm −2 ) as well as promising catalyst stability. Employing the seed-Pt/XC-PBI for PtNiN synthesis effectively reduced the PtNiN catalyst particle size, and narrowed size distribution, which consequently leads to significantly improved MEA performance. Additionally, the grafted-PBI can efficiently dope N atoms onto carbon support after thermal annealing, leading to the formation of a better ionomer/catalyst interface because of the electrostatic attraction between N-doped CCS and the ionomer, which in turn results in the increased ECSA and catalyst utilization. Moreover, the nitriding can effectively enhance the stability of the PtNiN/ XC72-PBI catalyst, making it a promising potential electrocatalyst for PEMFCs in practical transportation applications.