Ferric ion substitution renders cadmium metal–organic framework derivatives for modulated Li storage based on local oxidation active centers

Abstract

In this work, a novel anionic Cd-MOF ([(CH₃)₂NH₂]_n[Cd(HL)DMF]_n·2nH₂O·nDMF, H₄L = 1,2,4,5-tetrakis[(4-carboxy)phenoxymethyl]benzene) was synthesized for the first time. As a precursor, it was utilized to obtain Fe@Cd-MOF crystals via the substitution of Fe³⁺ ions due to a negatively charged framework and free-coordinated carboxyl group. Fe₃O₄/Fe-embedded carbon-based materials (Fe@Cd-MOFD) were further constructed by deriving Fe@Cd-MOF at high temperatures. The derived Fe@Cd-MOFD showed a structure resembling a central city with metal redox centers embedded into a carbon matrix. The introduced Fe³⁺ ions formed a local nano-sized metal oxide upon annealing, and these derived carbon materials offered high electronic conductivity. These pushed Fe@Cd-MOFD to remarkable electrochemical performance with an initial discharge capacity of 1703.8 mA h g⁻¹. This work offers new insights into the fabrication of novel MOF-derived iron oxide hybrids for lithium storage.