Ternary Cross-Vanadium Tetra-Capped POMOFs@PPy/RGO Nanocomposites with Hybrid Battery-Supercapacitor Behavior for Enhancing Lithium Battery Storage
Xiya Yang, Jingquan Sha, Wenjing Li, Zenglong Tan, Liran Hou, Jianzhuang Jiang
Abstract
To improve the electrochemical performances and to understand the mechanism of lithium storage of polyoxometalate-based metal–organic frameworks (POMOFs), a generic strategy to construct nanocomposites based on POMOFs and reduced graphene oxide (RGO) assisted by polypyrrole (PPy) as an adhesive, and a conductive additive is demonstrated for the first time in this work. Here, two fascinating vanadium-capped POMs-encapsulating MOFs, [Cu12(Trz)8Cl][PMo12O42V2] (Trz = 1,2,4 triazole) (POMOF-1, and -2), were explored in detail. Although POMOF-1 and -2 have different cell parameters and morphologies caused by the different stacking directions, both are the same compound. Using PPy as an adhesive, POMOF-2 was successfully anchored on RGO, resulting in a new type of POMOF@PPy/RGO (PPG-n, n = 1, 2, 3) nanocomposites. The resulting PPG-3 nanocomposite exhibits excellent reversible capacity (985 mA h g–1 at 50 mA g–1 after 100 cycles) and outstanding rate capabilities, which is much better than those of most nanocomposite electrodes based on POMs. Meanwhile, the lithium storage mechanism of PPG-3 has been discussed by analyzing X-ray photoelectron spectroscopy and powder X-ray diffraction patterns. Moreover, the PPG-3 nanocomposite exhibits the hybrid supercapacitor-battery behavior confirmed by the analysis results of cyclic voltammetry and electrochemical impedance spectroscopy. This might open a new avenue for designing other multifunctional POMOF-based nanocomposites as high-performance electrode materials for lithium storage.