Polyoxometalate-pillared metal–organic frameworks synthesized by surfactant-assisted strategy and incorporated with carbon nanotubes for energy storage

Abstract

The application of surfactant or surfactant-assisted media to grow polyoxometalate (POM)-based MOFs (POMOFs) is extremely scarce. In this work, for the first time, we use water-polyethylene glycol (PEG) 400 mixed media to synthesize two new crystalline POM-pillared three-dimensional porous arrays, [Co₇(Trz)₁₂(H₂O)₈][HPX₁₂O₄₀(VO)₂]·12H₂O (X = Mo for Co-PMo and X = W for Co-PW, Trz = 1,2,4-triazole). By employing a simple sonication-driven functionalization strategy, Co-PMo/CNTs (PCNT-n) nanocomposites with increased effective sites, enhanced specific surface area and excellent conductivity are fabricated. The resulting PCNT-2 nanocomposite shows an excellent reversible capacity of 820 mA h g⁻¹ after 100 cycles and outstanding rate capability as an anode for lithium batteries. After the initial decay, the PCNT-2 electrode can bear a current density of 2000 mA g⁻¹ over 450 cycles without obvious capacity loss. Meanwhile, the mechanism of lithium storage in PCNT-2 is discussed using X-ray photoelectron spectroscopy (XPS). Moreover, the PCNT-2 nanocomposite exhibits the hybrid behavior of battery and supercapacitor according to the electrochemical kinetic analyses. This might open new avenues for the design of crystalline POM-based materials or their nanocomposites to achieve high-performance energy storage.