What question did this study set out to answer?

The research aims to enhance the performance of zinc ion capacitors by developing a novel porous carbon material from Zn-MOF microspheres.

February 26, 2026

Urea-Assisted Dual-Shell Hollow Zn-MOF Microsphere-Derived Carbon for a Zinc Ion Capacitor

Key Points

The research aims to enhance the performance of zinc ion capacitors by developing a novel porous carbon material from Zn-MOF microspheres.
Synthesis of double-shell hollow Zn-MOF microspheres using a one-step solvothermal method.
Utilization of urea as an additional carbon source during carbonization.
Characterization of the resulting porous carbon for surface area and capacitive properties.
U-MPC showcases a specific surface area of 1695.66 m2 g–1.
The zinc ion capacitor with U-MPC achieves a specific capacitance of 199.0 F g–1.
Demonstrated an energy density of 70.8 Wh kg–1 at 0.1 A g–1.
Showed a low self-discharge rate of 3.1 mV h–1 over 300 h and maintained 59.7% of initial capacitance after testing.
Maintained good cyclic stability over 20,000 cycles with 90% Coulombic efficiency.

Abstract

In the zinc ion capacitors (ZICs), Zn2+ storage is limited by the common carbon-based cathodes due to the sluggish kinetics of zinc ion diffusion. Porous carbon derived from metal–organic frameworks (MOFs) is a good candidate with the abundant micropores and mesopores. By using a one-step template-free solvothermal method, double-shell hollow Zn-MOF microspheres were directly synthesized, eliminating the traditional multistep activation process using KOH/HCl. During the carbonization procedure, urea has been used to provide an additional carbon source and activate the derived carbon, which is due to urea pyrolysis products, such as NH3, cyanuric acid, and ammelide. The derived porous carbon (U-MPC) exhibits a high specific surface area of 1695.66 m2 g–1. The ZIC device assembled with U-MPC as the cathode has a high specific capacitance of 199.0 F g–1 and a high energy density of 70.8 Wh kg–1 at 0.1 A g–1. The Zn//U-MPC ZICs demonstrate a good antiself-discharge performance, with a low self-discharge rate of only 3.1 mV h–1 over 300 h, and can maintain 59.7% of the initial capacitance. Moreover, the ZICs exhibit good cyclic stability, showing a slight decrease after 20,000 cycles at 5 A g–1, and the Coulombic efficiency is 90%.

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