Synthesis of Platinum Nanocrystals Dispersed on Nitrogen-Doped Hierarchically Porous Carbon with Enhanced Oxygen Reduction Reaction Activity and Durability.

Abstract

Platinum-based catalysts are widely used for efficient catalysis of the acidic oxygen reduction reaction (ORR). However, the agglomeration and leaching of metallic Pt nanoparticles limit the catalytic activity and durability of the catalysts and restrict their large-scale commercialization. Therefore, this study aimed to achieve a uniform distribution and strong anchoring of Pt nanoparticles on a carbon support and improve the ORR activity and durability of proton-exchange membrane fuel cells. Herein, we report on the facile one-pot synthesis of a novel ORR catalyst using metal-nitrogen-carbon (M-N-C) bonding, which is formed in situ during the ion exchange and pyrolysis processes. An ion-exchange resin was used as the carbon source containing R-N+(CH3)3 groups, which coordinate with PtCl62- to form nanosized Pt clusters confined within the macroporous framework. After pyrolysis, strong M-N-C bonds were formed, thereby preventing the leaching and aggregation of Pt nanoparticles. The as-synthesized Pt supported on the N-doped hierarchically porous carbon catalyst (Pt/NHPC-800) showed high specific activity (0.3 mA cm-2) and mass activity (0.165 A mgPt-1), which are approximately 2.7 and 1.5 times higher than those of commercial Pt/C, respectively. The electrochemical surface area of Pt/NHPC-800 remained unchanged (~1% loss) after an accelerated durability test of 10,000 cycles. The mass activity loss after ADT of Pt/NHPC-800 was 18%, which is considerably lower than that of commercial Pt/C (43%). Thus, a novel ORR catalyst with highly accessible and homogeneously dispersed Pt-N-C sites, high activity, and durability was successfully prepared via one-pot synthesis. This facile and scalable synthesis strategy for high-efficiency catalysts guides the further synthesis of commercially available ORR catalysts.