Improving the Stability of Non‐Noble‐Metal M–N–C Catalysts for Proton‐Exchange‐Membrane Fuel Cells through M–N Bond Length and Coordination Regulation

Abstract

An effective and universal strategy is developed to enhance the stability of the non‐noble‐metal M–Nx/C catalyst in proton exchange membrane fuel cells (PEMFCs) by improving the bonding strength between metal ions and chelating polymers, i.e., poly(acrylic acid) (PAA) homopolymer and poly(acrylic acid–maleic acid) (P(AA‐MA)) copolymer with different AA/MA ratios. Mössbauer spectroscopy and X‐ray absorption spectroscopy (XAS) reveal that the optimal P(AA‐MA)–Fe–N catalyst with a higher Fe3+–polymer binding constant possesses longer FeN bonds and exclusive Fe–N4/C moiety compared to PAA–Fe–N, which consists of ≈15% low‐coordinated Fe–N2/N3 structures. The optimized P(AA‐MA)–Fe–N catalyst exhibits outstanding ORR activity and stability in both half‐cell and PEMFC cathodes, with the retention rate of current density approaching 100% for the first 37 h at 0.55 V in an H2–air fuel cell. Density functional theory (DFT) calculations suggest that the Fe–N4/C site could optimize the difference between the adsorption energy of the Fe atoms on the support (Ead) and the bulk cohesive energy (Ecoh) relative to Fe–N2/N3 moieties, thereby strongly stabilizing Fe centers against demetalation.

Deciphering the Precursor–Performance Relationship of Single‐Atom Iron Oxygen Electroreduction Catalysts via Isomer Engineering

“…Usually, longer bond lengths are conducive to maintaining the structural integrity of the catalyst. [55] Wavelet-transform (WT) EXAFS is prone to distinguishing the backscattering atoms because of its high-resolution in both k space and R space. [56] The WT of Fe-PpPD-800 is shown in Figure 3c, the intensity maximum is observed at k = 5 Å −1 , which is very close to FePc and can be designated as the contribution of FeN bonds.…”

Research Progress and Application of Single-Atom Catalysts: A Review

“…A mono-atomic catalyst has the characteristics of stability and high efficiency, which can be used in various batteries and electrochemical storage devices, can drive the research of a series of energy conversion and storage devices, and accelerate the exploration and development of green energy [94]. The highly stable non-precious metal M-NX/C singleatom catalyst has application prospects in proton-exchange-membrane fuel cells and promotes the development of the transportation industry [95].…”

Exploring Durable Single-Atom Catalysts for Proton Exchange Membrane Fuel Cells

“…Li and co-workers regulated the Fe−N coordination and bond length by tuning the binding constant between metal ions and chelating polymers in the catalyst precursor. 69 As shown in Figure 4a and b, XAS and 57 Fe Mossbauer spectroscopy analyses revealed that the higher binding constant resulted in a longer Fe−N bond. The optimized catalyst with longer Fe−N bonds exhibited outstanding stability in a H 2 -air fuel cell, with near 100% current retention for the first 37 h at 0.55 V (Figure 4c).…”