Fe(III) ions substituted at Ni2 site in Ni-TDC with defect-rich for high-performance asymmetric supercapacitors

Abstract

The Ni-TDC material exhibits high specific capacity and rate capability as a supercapacitor anode, yet suffers from poor intrinsic conductivity. To address this limitation, Fe(III) ions were introduced to substitute Ni2 site at specific sites within the Ni-TDC nanoflowers, enabling the controlled generation of lattice defects and oxygen vacancies. In the resulting NixFe1-x-TDC materials, the oxygen vacancies enhanced the conductivity by introducing additional charge carriers and creating localized charge deficiencies. Moreover, these defects facilitate electron migration by providing pathways or channels, thereby improving the overall electrical conductivity of the materials. The optimized Ni0.67Fe0.33-TDC demonstrated exceptional electrochemical performance, with its specific capacitance increasing from 985 F g-1 for pristine Ni-TDC to 1306 F g-1 at a current density of 1 A g-1. Furthermore, an asymmetric supercapacitor assembled with Ni0.67Fe0.33-TDC as the anode and activated carbon (AC) as the cathode achieved an impressive energy density of 67 Wh kg-1 at a power density of 819 W kg-1. This device also exhibited remarkable cycling stability, retaining 74% of its initial capacitance after 10000 cycles. Density functional theory (DFT) calculations indicate that substituting Fe at specific Ni2 site exhibits low substitution energy, favoring its incorporation, while oxygen vacancy defects are instrumental in promoting electron transport, leading to enhanced intrinsic conductivity. This study provides an effective strategy for optimizing the conductivity of MOF-based electrode materials.