Synthesis and electrochemical properties of two cobalt(II) and nickel(II) metal-organic frameworks for excellent performance supercapacitors

Abstract

Two novel metal-organic frameworks, [Co(HNTB)(bif)]·3H2O·DMA (1) and [(Ni2(μ2O)(HNTB)2(bif)2]·2H2O·2H3O·2DMA (2), were obtained with a tripod-type carboxylic ligand (4,4′,4″-Nitrilotrisbenzoic acid, H3NTB) and a rigid N-donor ligand (2,7-bis(1-imidazoly)fluorene, bif) by solvothermal method. Complex 1 exhibits a 2D layered structure and 2 is a 3D microporous structure with an anionic skeleton. Significantly, their electrochemical tests show that both of them own excellent capacitive performance. Complex 1 has a relatively high specific capacitance (301.2 F g−1 at 1 A g−1) with favorable cycling durability (retained 73.2 % over 3000 cycles). Complex 2 presents a high specific capacitance (329.6 F g−1 at 1 A g−1) with a relatively poor cycling durability (retained 58.9 % over 3000 cycles). Additionally, complex 1 // activates carbon (AC) as an asymmetrical ultra-capacitor exhibits a maximum energy density of 20.9 Wh kg−1 at 800.0 W kg−1 and a high cycle stability (retained 89.2 % over 8000 cycles). Complex 2 // AC owns an energy density of 19.3 Wh kg−1 at 750.0 W kg−1 and a satisfactory cycle stability (retained 88.6 % over 8000 cycles).