Geometrically deformed iron-based single-atom catalysts for high-performance acidic proton exchange membrane fuel cells

Lei Shi, Xuanni Lin, Feng Liu, Yongde Long, Ruyi Cheng, Chunhui Tan, Liu Yang, Chuangang Hu, Shenlong Zhao*, Dong Liu*
ACS Catalysis 12(9), 5397–5406, (2022)
DOI:https://doi.org/10.1021/acscatal.2c00915

Abstract

Atomically dispersed metal–nitrogen–carbon (M–N–C) catalysts have emerged as the promising alternative to replace platinum-based catalysts for oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). However, their practical applications are restricted by the relatively low intrinsic activity, low utilization rate, and poor stability of atomic metal sites. Herein, we propose a simple but efficient strategy to synthesize a geometrically deformed single Fe site catalyst (d-SA-FeNC) by trace NaCl-coating-assisted pyrolysis of Fe-containing zeolitic imidazolate frameworks. Benefiting from the significantly exposed Fe-N4 active sites and enhanced mass transport by the hierarchically porous structure, the newly developed catalysts exhibit improved ORR performance in acidic media. Remarkably, the as-constructed membrane electrode assemblies achieve high peak power densities of 0.904 and 0.502 W cm–2 in H2–O2 and H2–air PEMFCs even at a low catalyst loading of 1 mg cm–2, respectively, revealing ultrahigh mass activity density. Both experimental and theoretical results reveal that the enhanced intrinsic activity is attributed to the synergy of deformed Fe-N4 moieties and the surrounding graphitic N dopant. In addition, the locally increased graphitization of the carbon matrix can efficiently reduce carbon corrosion, thereby promoting catalyst stability. This work provides useful guidance for the development of highly efficient ORR catalysts for PEMFCs.