Understanding the phase structure evolution and charge storage mechanism of FeCoNi-MOFs as electrodes for asymmetric supercapacitors.

Metal-organic frameworks (MOFs) due to abundant apertures, adjustable components, and multi-purpose structures have broad application prospects in supercapacitors. However, its low conductivity, poor stability, and difficulty growing evenly on the conductive substrate limit the electrochemical energy storage performance. Herein, with FeCoNi-OH nanosheets serving as the precursors, the trimetallic FeCoNi-MOF (FCNM) multilayer structure is successfully synthesized on activated carbon cloth (AC), and its optimal growth state (FCNM/AC-12 h) is achieved by regulating the reaction time. The FCNM/AC-12 h with enhanced kinetics and multi-metal synergies achieve an excellent capacitance (13.02 F/cm at 1 mA/cm) and a good cycle stability (the capacity is 83.33 % of the initial value after 10,000 cycles). Its phase structural evolution and charge storage mechanism during the electrode process are investigated through in-depth electrochemical testing and ex-situ characterization. Furthermore, when the power density is 1.6 mW/cm, the FCNM/AC-12 h//AAC device exhibits a high energy density of 1.134 mWh/cm, and its capacity retains 97.89 % of the initial value after 10,000 cycles at 50 mA/cm. This work provides reliable experimental guidance for synthesizing multi-metal MOFs on carbon cloth and revealing its energy storage mechanism.