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<p>This study explored the application of multi-walled carbon nanotube-based nanofluid electrolytes in vanadium redox flow batteries, focusing on low concentrations of carbon nanotubes (0.004–0.020 weight percent) to enhance electrochemical performance while minimizing adverse rheological and stability effects. Comprehensive characterization—including cyclic voltammetry, electrochemical impedance spectroscopy, viscosity measurements, scanning electron microscopy, and multi-cell vanadium redox flow battery stack testing—was performed. Among the tested formulations, the 0.012 weight percent carbon nanotube nanofluid demonstrated the most balanced and efficient behavior. In the three-electrode setup, this formulation achieved a 43% increase in peak current intensities, along with reductions in polarization (20–22%) and a substantial enhancement in diffusion kinetics (72%). The viscosity increase remained moderate at 6.98%, preserving suitable flow behavior. Electrochemical impedance spectroscopy confirmed improved ionic conductivity, with solution resistance decreasing from 5.65 Ω (bare) to 2.94 Ω. At the VRFB stack level, the optimized nanofluid used only in the positive side achieved a discharge capacity of 1229 mAh at 80&#xa0;mA cm⁻², compared to 1153 mAh for the bare electrolyte (6.6% improvement), and a higher peak power density of 1047.3 mW cm⁻² versus 1012.6 mW cm⁻² for the bare system (3.4% improvement). In contrast, higher carbon nanotube concentrations resulted in aggregation, increased internal resistance, and promotion of the hydrogen evolution reaction on the negative side. At the stack level, the selective use of the optimized nanofluid as the positive electrolyte improved long-term cycling stability. Conversely, applying the nanofluid on both sides degraded performance due to intensified hydrogen evolution activity. Electrolyte recovery tests—based on remixing the positive and negative electrolytes—demonstrated significant initial and peak discharge capacity improvements for the optimized positive-side electrolyte. These findings underscore the importance of selective carbon nanotube integration and offer strategic guidance for advancing nanofluid-enhanced vanadium redox flow batteries toward scalable, efficient, and durable grid-level energy storage systems.</p> Graphical Abstract <p></p>

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Engineering very low concentration MWCNT nanofluid electrolytes for enhanced performance in vanadium redox flow batteries

  • 期刊论文

  • 发表日期：

    2025年12月24日

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  • Mohammad Zarei-Jelyani,
  • Mohammad Reza Rahimpour,
  • Mohsen Babaiee

摘要

This study explored the application of multi-walled carbon nanotube-based nanofluid electrolytes in vanadium redox flow batteries, focusing on low concentrations of carbon nanotubes (0.004–0.020 weight percent) to enhance electrochemical performance while minimizing adverse rheological and stability effects. Comprehensive characterization—including cyclic voltammetry, electrochemical impedance spectroscopy, viscosity measurements, scanning electron microscopy, and multi-cell vanadium redox flow battery stack testing—was performed. Among the tested formulations, the 0.012 weight percent carbon nanotube nanofluid demonstrated the most balanced and efficient behavior. In the three-electrode setup, this formulation achieved a 43% increase in peak current intensities, along with reductions in polarization (20–22%) and a substantial enhancement in diffusion kinetics (72%). The viscosity increase remained moderate at 6.98%, preserving suitable flow behavior. Electrochemical impedance spectroscopy confirmed improved ionic conductivity, with solution resistance decreasing from 5.65 Ω (bare) to 2.94 Ω. At the VRFB stack level, the optimized nanofluid used only in the positive side achieved a discharge capacity of 1229 mAh at 80 mA cm⁻², compared to 1153 mAh for the bare electrolyte (6.6% improvement), and a higher peak power density of 1047.3 mW cm⁻² versus 1012.6 mW cm⁻² for the bare system (3.4% improvement). In contrast, higher carbon nanotube concentrations resulted in aggregation, increased internal resistance, and promotion of the hydrogen evolution reaction on the negative side. At the stack level, the selective use of the optimized nanofluid as the positive electrolyte improved long-term cycling stability. Conversely, applying the nanofluid on both sides degraded performance due to intensified hydrogen evolution activity. Electrolyte recovery tests—based on remixing the positive and negative electrolytes—demonstrated significant initial and peak discharge capacity improvements for the optimized positive-side electrolyte. These findings underscore the importance of selective carbon nanotube integration and offer strategic guidance for advancing nanofluid-enhanced vanadium redox flow batteries toward scalable, efficient, and durable grid-level energy storage systems.

Graphical Abstract