Flexible Iron-Ion Hybrid Capacitor Based on a MnO₂ Electrode

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Aqueous Fe-ion hybrid capacitors offer safe, low-cost, and eco-friendly energy storage.
• Existing Fe-ion systems face challenges like narrow voltage windows and limited energy density.

Purpose of the Study:

• To develop an improved aqueous Fe-ion hybrid capacitor with an expanded voltage window and enhanced energy density.
• To create a flexible Fe-ion capacitor for wearable electronics.

Main Methods:

• Fabrication of an aqueous Fe-ion hybrid capacitor using activated carbon (anode) and manganese dioxide (cathode) with an FeSO4 + NH4Cl electrolyte.
• Atomic molecular dynamics simulations to confirm MnO2's suitability as a cathode material.
• Assembly of a flexible device using a hydrogel soft-packaging material.

Main Results:

• Expanded voltage window to 0-1.2 V.
• Achieved a specific capacitance of 835 mF cm⁻² and areal energy density of 167 μWh cm⁻² with 97.2% capacitance retention after 3000 cycles.
• Developed a flexible device with excellent bending resistance, showing 682.4 mF cm⁻² specific capacitance and 136.48 μWh cm⁻² areal energy density, retaining 92.6% capacity after 3000 cycles.

Conclusions:

• The developed aqueous Fe-ion hybrid capacitor addresses limitations of previous systems, offering high performance and stability.
• The flexible Fe-ion supercapacitor demonstrates significant potential for wearable electronics due to its robust performance and durability.