Atomic-Level Control of Graphitic Carbon Shell Thickness on Pt–Co Nanoparticles for Efficient and Durable Oxygen Reduction Reaction

Carbon shell encapsulation of platinum (Pt)-based catalysts has shown promise in enhancing the activity and durability of oxygen reduction reaction (ORR) in proton exchange membrane fuel cells. Achieving optimal performance, however, requires precise control of carbon layer thickness to balance activity and durability effectively. Here, we present an integrated theoretical and experimental study that elucidates the impact of carbon shell thickness on the ORR catalytic performance of Pt–Co nanoparticles. Density functional theory calculations reveal that coating Pt–Co nanoparticles with a monolayer of N-doped porous graphitic carbon optimizes the electronic structure of active sites and modulates the adsorption energy of key reaction intermediates, thereby enhancing ORR kinetics. Inspired by these insights, we develop a scalable ligand-mediated carbonization strategy by precisely controlling the ratio of oleylamine to sec-butylamine. This approach enables the formation of N-doped porous carbon shells with precise control over layer thickness, ranging from submonolayer to multilayer architectures. Comprehensive characterization confirms that the monolayer-coated catalyst (Pt–Co@N-MonoC) exhibits minimized particle agglomeration, enhanced graphitization, and reduced metal leaching. Accelerated durability testing shows that Pt–Co@N-MonoC exhibits much higher activity retention in both regular (0.6–1.0 V vs RHE) and high (1.0–1.5 V vs RHE) potential windows than the pristine uncoated catalysts. Additionally, under realistic operating conditions in membrane electrode assembly, Pt–Co@N-MonoC also exhibits superior ORR activity and durability compared to uncoated counterparts. These findings underscore the dual role of the monolayer carbon coating in both protecting active sites and modulating electronic interactions, ultimately providing a straightforward, scalable pathway for enhancing the stability and performance of commercial fuel cell catalysts.