Enhancing the stability of Pt/C catalysts for oxygen reduction reaction in PEMFCs via Fe-N-C-mediated 5d-3d/2p orbital hybridization

doi:10.1016/S1872-2067(26)64985-6

Abstract

Abstract:

Pt/C catalysts are widely used for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs) but suffer from limited stability. Herein, we demonstrate that the introduction of Fe-N-C layers onto the surface of Pt/C catalysts can significantly bolster both the ORR stability and activity of Pt/C in the harsh working environment of PEMFCs. Whilst Fe-N-C catalysts typically exhibit poor ORR activity and durability in acidic media, the obtained PtFe/C@Fe-N-C catalyst exhibits a very high peak power density of 2.03 W cm^-2 and an excellent mass activity (MA) of 0.75 A mg_Pt^-1 in a H₂-O₂ fuel cell, with only 2.7% decay after 30000 cycles, far superior to the Pt/C (0.176 A mg_Pt^-1 and 54.0% decay) and the U.S. Department of Energy 2025 targets. Experimental and density functional theory investigations unequivocally confirm that the Pt coated with optimized Fe-N-C layer contributes to a more delocalized electronic structure and stronger bonding between Pt and FeN_x via strong hybridization of 5d-3d/2p orbitals, resulting in the excellent activity and stability of the PtFe/C@Fe-N-C catalyst.

Key words: Pt/C catalysts, Fe-N-C layers, Orbital hybridization, Acid oxygen reduction reaction, Proton exchange membrane fuel cells

Yujuan Zhuang, Qingjun Chen, Xingen Lin, Lingwei Meng, Fuwang Hu, Xintao Yu, Geoffrey I. N. Waterhouse, Lishan Peng. Enhancing the stability of Pt/C catalysts for oxygen reduction reaction in PEMFCs via Fe-N-C-mediated 5d-3d/2p orbital hybridization[J]. Chinese Journal of Catalysis, 2026, 83: 308-318.

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URL: https://www.cjcatal.com/EN/10.1016/S1872-2067(26)64985-6

https://www.cjcatal.com/EN/Y2026/V83/I4/308

Figures/Tables 5

Fig. 1. (a) Schematic representation of PtFe/C@Fe-N-C from a commercial Pt/C catalyst. (b) HAADF-STEM image and nanoparticle size distribution (inset) of PtFe/C@Fe-N-C. (c) XRD patterns for PtFe/C@Fe-N-C, PtFe/C, and Pt/C. (d) HRTEM image of PtFe/C@Fe-N-C. (e,f) HAADF-STEM image of PtFe/C@Fe-N-C showing the presence of PtFe nanoparticles covered by a thin Fe-N-C layer containing Fe single atoms. (g) HAADF-STEM micrographs along with EDS mapping images for PtFe/C@Fe-N-C.

Fig. 2. (a) Fe 2p XPS spectra with high resolution. (b) High-resolution Pt 4f XPS spectra for various PtFe/C@Fe-N-C catalysts with different Fe-N-C contents. (c) XPS binding energy gap for Fe2+ and Pt0 peaks relative to Fe-N-C/C and PtFe/C, respectively, with Fe-N-C layers of varying thicknesses. XANES spectra at Pt L3-edge (d) and Fe K-edge (e) for different catalysts. Corresponding FT-EXAFS spectra at Pt L3-edge (f) and Fe K-edge (g) in R-space. Difference XANES spectra at Pt L3-edge (h) and Fe K-edge (i). For better visualization, the intensity of the conventional XANES spectra was scaled by a factor of 0.2.

Fig. 3. (a) Relationship between the MA of PtFe/C@Fe-N-C catalysts with Fe-N-C layers of varying thicknesses and the XPS binding energy gap for Fe 2p (Fe2+) and Pt 4f (Pt0) peaks relative to Fe-N-C/C and PtFe/C, respectively. (b) ORR polarization curves for various catalysts collected in O2-saturated. (c) Mass activity and specific activity. (d) Polarization curves for PtFe/C@Fe-N-C, PtFe/C and Pt/C before and after undergoing different cycles. (e) Mass activity comparison of PtFe/C@Fe-N-C, PtFe/C and Pt/C before and after different cycles. (f) The change in average particle diameter for PtFe/C@Fe-N-C, PtFe/C and Pt/C after different cycles.

Fig. 4. Polarization curves and power density plots of PtFe/C@Fe-N-C and Pt/C under the conditions of H2-O2 (a) and H2-air (b). (c) H2-O2 fuel cell polarization curves and power density plots of PtFe/C@Fe-N-C prior to and post ADTs. (d) H2-O2 fuel cell polarization curves and power density plots of Pt/C prior to and post ADTs. MA (e) and cell voltage (f) at 0.8 A cm-2 for PtFe/C@Fe-N-C and Pt/C prior to and post ADTs. (g) Comparative analysis of BOL MA and MA retention post 30k ADT cycles versus recently reported advanced Pt-based catalysts. (h) The relative current of Pt/C and PtFe/C@Fe-N-C during the ADTs.

Fig. 5. (a) Charge density difference diagrams for Pt@C and PtFe@Fe-N-C, areas of charge depletion and accumulation are illustrated in cyan and yellow respectively. (b) The PDOS of PtFe@Fe-N-C. (c) Schematic diagram of the band structures of Pt@C, PtFe@Fe-N-C and Fe-N-C. (d) Gibbs free energy diagram (U = 1.23 V). (e) The dissolution energy of Fe and theoretical models for Fe-N-C and PtFe@Fe-N-C. The concentration of Pt (f) and Fe (g) collected in the electrolyte during ADTs. Color code: Pt (grey), Fe (purple), C (white), N (blue).

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