Inorganic-anion-modulated synthesis of 2D nonlayered aluminum-based metal-organic frameworks as carbon precursor for capacitive sodium ion storage

Metal-organic frameworks (MOFs) have been widely employed as the precursors to obtain functional carbon with tuneable composition and structure. However, the design of 2D carbon nanostructures directly from two-dimensional (2D) nonlayered MOFs is still very scarce, which is mainly hindered by the synthesis of 2D nonlayered MOFs. Herein, 2D nonlayered NH2-MIL-53 (Al) is synthesized via inorganic anion modulation for 2D S, N, O-rich hard carbon nanosheets (SNO-HCN) precursor. Due to the introduction of S-doping, more open edge sites generate, which accordingly promote the formation of pyridinic N and C=O carbonyl groups. When adopted as the anode for the sodium ion batteries, the SNO-HCN electrode delivers high reversible capacity of 522 mAh g(-1) and 185 mAh g(-1) at 50 mA g(-1) and 15000 mA g(-1), respectively. The enlarged interlayer spacing, unique 2D structure, heteroatom-rich active sites, and high surface area lead to the improved electrochemical performance. Furthermore, the galvanostatic intermittent titration technique (GITT) test indicates the superior electrochemical kinetics of the SNO-HCN electrode and the quantitative analysis reveals the capacitance contribution dominates during sodium-ion storage process. This represents an universal approach for the preparation of various 2D carbon nanomaterials derived from 2D nonlayered MOFs.