Integrating sulfur-doped atomically dispersed FeNx sites with small-sized Fe3C nanoparticles for PEMFCs and beyond

Abstract

Developing highly efficient and robust oxygen reduction reaction (ORR) catalysts with low cost is essential to accelerate their widespread application in proton exchange membrane fuel cells (PEMFCs) and metal–air batteries. Herein, we in situ encapsulate Fe₃C nanoparticles (NPs), decorated with a thin carbon shell, into porous S-doped Fe–NC two-dimensional carbon nanosheets. The membrane electrode assembly (MEA) with the hybrid Fe–S–NC/Fe₃C catalyst in the cathode could achieve high power densities of 0.836 W cm⁻² and 0.535 W cm⁻² in H₂–O₂ and H₂–air PEMFCs, respectively. Moreover, the catalyst exhibits excellent durability when applied as the cathode of H₂–O₂ PEMFCs with 75% of its original performance recovered after 68 h of lifespan testing. Experimental results and density functional theory calculations indicate that the improvement of electrochemical activity and durability could be ascribed to the synergistic catalysis between porous S-doped Fe–NC and Fe₃C NPs in the hybrid construction with lower energy barriers for the rate-determining step of the ORR. This work provides an avenue for improving the performance of PEMFCs by synergistic catalysis between single-atom sites and nanoparticles.