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.
Zhengpei MiaoXiaoming WangZhonglong ZhaoWenbin ZuoShaoqing ChenZhiqiang LiYanghua HeJiashun LiangFeng MaHsing-Lin WangGang LuYunhui HuangGang WuQing LiPublished in: Advanced materials (Deerfield Beach, Fla.) (2021)
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 FeN 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.
Keyphrases
- metal organic framework
- aqueous solution
- density functional theory
- visible light
- high resolution
- induced apoptosis
- ionic liquid
- molecular dynamics
- highly efficient
- room temperature
- dna methylation
- oxidative stress
- gene expression
- computed tomography
- single molecule
- magnetic resonance
- gold nanoparticles
- cell death
- signaling pathway
- pi k akt