Two new 2D POMOFs based on octamolybdate/copper substituted keggin polymolybdate for enhancing electrochemical capacitor performance

Abstract

The multi-electron redox properties of polyoxometalates (POMs) and the high surface area and diverse structures of metal-organic frameworks (MOFs) have led to the attracted much attention of polyoxometalate-based metal-organic frameworks (POMOFs) as supercapacitor electrode materials. To investigate the relationship between the structure and catalytic performance of POMOF electrode materials, two novel 2D POMOF crystalline materials were synthesized by a one-step hydrothermal method, namely (H2bipy)[CuI2(bipy)2(H3PMo11CuO40)] (1) and H[CuI2(bipy)2CuI(bipy)(β-Mo8O26] (2) (bipy = 4,4′-bipyridine). Compound 1 shows a Cu-substituted Keggin-based 2D POMOF layer, and compound 2 shows a novel 2D + 1D hydrotalcite-like architecture. Compound 1 exhibits better electrochemical performance, and the prepared electrode material has a specific capacitance of 407.7 F g−1 at 3 A g−1 and maintains cycling stability of 89.5% of the initial capacitance after 1000 cycles at a current density of 10 A g−1. The compounds 1–2 have the potential in optimizing electrode materials for POMOF-based capacitors applications.