Electrospinning Equipment: ZnO-MnO₂ Co-Modified Porous Carbon Nanofiber Electrodes for Supercapacitors

Introduction

Supercapacitors are widely recognized for their high power density, rapid charge/discharge capabilities, and long cycle life, making them a key focus in energy storage research. However, their limited energy density restricts broader applications. To enhance energy density, optimizing the pore structure of carbon materials and incorporating metal oxides have been common strategies. Among metal oxides, manganese dioxide (MnO₂) is a promising material due to its high capacitance, low cost, and environmental friendliness. However, its low conductivity and high charge transfer resistance limit its 

performance. This study explores the synthesis of ZnO and MnO₂ co-modified hierarchical porous carbon nanofiber (ZnMnO-HPC) electrodes using an electrospinning machine and hydrothermal methods to enhance supercapacitor performance.

Schematic of the fabrication procedure of ZnO-HPC and ZnMnO-HPC.

Abstract

This research develops a composite hierarchical porous carbon nanofiber film modified with ZnO and MnO₂ for high-energy-density supercapacitors. The nanofibers are prepared using an electrospinning machine, forming a porous structure that enhances energy density due to the synergistic effects of ZnO and MnO₂. The ZnMnO-HPC electrode demonstrates excellent electrochemical properties, achieving a high specific capacity of 401.77 C/g at 0.5 A/g and 201.29 C/g at 5 A/g. When assembled into an asymmetric capacitor with an activated carbon electrode, it delivers an energy density of 38.37 Wh/kg at 407 W/kg and 19.5 Wh/kg at 12,800 W/kg, highlighting its potential for high-performance energy storage.

Research Content and Results

This study focuses on the fabrication and performance evaluation of ZnO and MnO₂ co-modified hierarchical porous carbon nanofiber (ZnMnO-HPC) electrodes for high-energy-density supercapacitors. The research integrates electrospinning and hydrothermal methods to enhance the structural and electrochemical properties of supercapacitor electrodes.

• Material Synthesis and Structural Analysis

ZnMnO-HPC electrodes were synthesized using an electrospinning machine, followed by hydrothermal treatment. The electrospinning process allowed precise control over the morphology and porosity of the nanofibers, leading to an optimized pore structure that enhances ion transport and charge storage. By adjusting the polyacrylonitrile (PAN) and polymethyl methacrylate (PMMA) ratio, a hierarchical porous structure was developed, facilitating better electrolyte penetration and increased surface area for electrochemical reactions.

Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) confirmed the formation of well-preserved nanofiber structures with hollow interiors, which became more pronounced as the PMMA content increased. X-ray diffraction (XRD) analysis verified the successful incorporation of ZnO and MnO₂ into the nanofibers, while X-ray photoelectron spectroscopy (XPS) confirmed the presence of key elements, including Zn, Mn, and O, evenly distributed throughout the material.

DSC (a) and TG (b) data of ZnO-HCPs, (c) Raman spectra of ZnO-HCPs, (d) N2 adsorption isotherms of ZnO-HCPs, (e) schematic diagram illustrates of ZnO-HCPs.

• Electrochemical Performance Evaluation

The ZnMnO-HPC electrodes demonstrated outstanding electrochemical performance, exhibiting:

High Specific Capacity: Achieved 401.77 C/g at 0.5 A/g, maintaining 201.29 C/g at 5 A/g, indicating excellent charge storage capability.

Enhanced Energy Density: Delivered an energy density of 38.37 Wh/kg at a power density of 407 W/kg, and 19.5 Wh/kg at a high power density of 12,800 W/kg, outperforming many previously reported ZnO-MnO₂-based materials.

Superior Rate Capability: Maintained a stable capacity even at increasing current densities, demonstrating rapid ion transport and high charge storage efficiency.

Long-Term Cycle Stability: Retained 92.61% of its initial capacity after 10,000 charge-discharge cycles, proving its durability and reliability for long-term applications.

The fabricated ZnMnO-HPC electrodes were assembled into an asymmetric supercapacitor with an activated carbon (AC) electrode. The assembled ZnMnO-HPC//AC supercapacitor exhibited excellent coulombic efficiency, reversible charge-discharge characteristics, and low internal resistance. Electrochemical impedance spectroscopy (EIS) analysis further confirmed minimal resistance change after cycling, reinforcing the material's structural stability.

• Comparative Analysis

Compared to conventional carbon-based and ZnO-MnO₂ electrode materials, ZnMnO-HPC demonstrated superior electrochemical performance due to its hierarchical porous architecture and synergistic effects between ZnO and MnO₂. The study also highlighted how the balance between structural optimization, conductivity enhancement, and charge transfer efficiency contributed to the electrode’s high energy and power density.

Capacity matching of ZnMnO-HCP electrode and AC electrode at the current density 1 A/g, (b) CV curves of ZnMnO-HCP//AC at different scan rates, (c) galvanostatic charge and discharge profiles of ZnMnO-HCP//AC at different current densities, (d) cycle performance of ZnMnO-HCP//AC at the current density of 2 A/g, (e) EIS profiles of ZnMnO-HCP//AC before and after cycles, (f) Ragone plots based on ZnMnO-HCP//AC

Conclusion

The ZnMnO-HPC electrode, synthesized via electrospinning and hydrothermal treatment, demonstrates outstanding electrochemical properties due to its hierarchical porous structure and the synergistic effects of ZnO and MnO₂. The material exhibits high specific capacity, excellent energy density, and long-term stability, making it a promising candidate for next-generation high-energy-density supercapacitors.

Electrospinning Nanofibers Article Source: 

https://doi.org/10.1038/s41598-025-90747-0