Holey Aligned Electrospun Carbon Electrodes for High-Performance Redox Flow Batteries
Authors: Sun Jing , Jiang Haoran , Zhang Cheng , Fan Xinzhuang , Liu Bin , Zhao Tianshou 
Published: May 2020

Recently, the electrospinning method has been employed to fabricate fibrous carbon electrodes in redox flow batteries, due to the large specific surface area of the nano-scale electrospun carbon fibers[1-3]. However, the poor transport properties of the densely packed electrospun carbon electrodes cause a large flow resistance, and hence a large concentration overpotential, which limited the battery’s performances [4,5]. The vanadium redox flow battery (VRFB) is one of the most-studied redox flow battery systems. However, the state-of-art VRFB that employed electrospun carbon fibers as the electrode can only be operated a realtively small current density (~ 100 mA cm-2), which is mainly hindered by the poor transport properties of the electrode material. Hence, the geometric structures of the electrospun carbon materials should be tailored so that the battery with the electrospun carbon fibers can be operated at a much elevated current density with high energy efficiency. Currently, several strategies have been proposed to improve the transport properties of the electrospun material, which include increasing the fiber diameter and expanding the pore sizes. However, the enhancement in the transport properties is always at the cost of sacrificing the active surface area[6].
Here we report an approach to effectively enhancing the transport of the electrolyte inside the porous media while ensuring a large specific surface area of the material. Aligned electrospun polymer fiber bundles are successfully produced by properly adjusting the electrospinning conditions. By applying self-etching methods, highly holey aligned fiber bundles were fabricated. In this structure, the aligned large fiber bundles provide the pathway for the electrolyte and the large surface area enabled by the holey fibers provides sufficient active sites for the redox reactions to take place. We compared the single-cell employed with the as-prepared highly holey aligned fibers on both sides with the battery assembled with conventional electrospun materials as well as thermal-treated commercial carbon felts. The results show that the novel structure can enable an energy efficiency of around 79.3% at the current density of 400 mA cm-2.
Details of fabricating and characterization of the holey aligned electrospun electrodes and more data relating to the battery tests will be disclosed at the meeting.

Acknowledgement

The work described in this paper was fully supported by a grant from the Research Grants Council of the Hong Kong Special Administrative Region, China (Project No. T23-601/17-R)

References

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