Fe-Doped MnO 2 Catalysts for Li–O 2 Batteries: Mechanistic Insights into Durability Enhancement via Operando XAFS

Le résumé fourni par la source

Fe-doped MnO 2 (Fe–MnO 2 ) was prepared to address the low conductivity of MnO 2 and applied as an electrocatalyst for lithium–oxygen batteries. MnO 2 was hydrothermally synthesized by using sacrificial single-walled carbon nanotubes (SWCNTs, consumed during the reaction) and subsequently blended with fresh SWCNTs to fabricate electrodes. Fe–MnO 2 was obtained by the same method with the addition of FeSO 4 ·7H 2 O. Scanning and transmission electron microscopies, X-ray diffraction, and X-ray absorption fine structure (XAFS) confirmed the formation of uniformly distributed nanosheets with low crystallinity. Compared with the MnO 2 /SWCNT electrode, the Fe–MnO 2 /SWCNT electrode exhibited lower resistance, delivered higher discharge capacity, and maintained stable operation over 100 cycles. Time-resolved operando Mn K-edge XAFS revealed that Fe–MnO 2 sustains a higher average Mn valence (about +0.2 relative to undoped MnO 2 ) and suppresses the discharge-induced loss of the second-shell Fourier-transformed magnitude associated with the cleavage of edge-sharing MnO 6 octahedra, followed by substantial recovery upon charging. These findings indicate that Fe doping strengthens Mn–O bonding and mitigates Jahn–Teller-driven distortions, thereby enhancing durability. Long-term cycling tests nevertheless showed, through post-test XAFS measurements, that both Mn and Fe were reduced. The results were consistent with the possible formation of metallic nanoparticles with low coordination numbers after 311 cycles. Thus, while it was primarily introduced to improve conductivity, Fe doping was also found to enhance catalytic durability.

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.