Nanoarchitectonics with redox active site modulation in bimetallic MIL-125(Ti, Mn) MOF for enhanced supercapacitor performance

Abstract

Metal-organic frameworks (MOFs) with dual metal centres have received considerable attention as electrode materials for supercapacitor applications due to their redox-active sites and unique structural architecture. Herein, we present a simple one-step solvothermal approach to synthesize and optimize bimetallic MIL-125(Ti,Mn) MOF, where redox active site modulation enhances its electrochemical performance in asymmetric supercapacitors. The unique structure of MIL-125(Ti,Mn), featuring a spindle-like morphology anchored by flake-like sheets, facilitates interaction between active sites and electrolyte ions and modulates the redox active sites, leading to improved electrochemical performance. As such, the optimized MIL-125(Ti)-Mn-2 electrode demonstrates a high specific capacity of 137.2 mAhg⁻¹ at 1 A g^–1 and a capacity retention of more than 76.3 % after 5000 cycles. Furthermore, an asymmetric supercapacitor built with Mn-MIL-125(Ti)-2 and activated carbon achieved a high specific energy of 22.74 Wh kg^–1 at a specific power of 996 W kg^–1, while also demonstrating excellent stability with 71.2 % capacitance retention over 10,000 cycles at 10 Ag⁻¹. This one-pot incorporation strategy offers a novel route to modulate the structure of MIL-125(Ti) via Mn²⁺ doping for enhanced supercapacitor performance.