Green and Affordable Manufacturing Method for Multi-Scale Porous Carbon Nanofibers and Its Application in Vanadium Redox Flow Battery

Abstract

Carbon nanofibers with multi-scale pores have been easily constructed by synchronous water etching during the carbonization process of PAN nanofibers, reducing the additional consumption of energy and time. After etching by high-temperature water vapor, the fiber surface becomes more coarse, and large amounts of etched pits are formed, effectively increasing the electrode’s specific surface area and hydrophilicity. Oxygen content is also significantly increased, which may effectively increase the electrocatalytic active sites of the electrode. Electrochemical tests verified the improved electrocatalytic activity and increased effective surface area. As a result, the VRFB single cell with water vapor etched carbon nanofibers as its electrode shows higher battery efficiencies than that with pristine carbon nanofibers; the energy efficiency improves by nearly 9.4% at 200 mA·cm-2. After 100 charge/discharge cycles, the battery efficiency has no obvious attenuation, and the capacity attenuation rate of single cycle is nearly 0.26%，suggesting a satisfactory cycling stability. This green and simple method for constructing multi-scale porous carbon nanofibers electrode is expected to achieve large-scale production of high-performance electrode materials, and can be applied in various electrochemical energy storage systems.

Recent advances and perspectives of practical modifications of vanadium redox flow battery electrodes

“…The method is simple and energy-saving, and the etching agent can be used multiple times to avoid waste. 56,57 Kwon et al used benzoyl peroxide to etch graphite felt (GF) chemically (Fig. 3c), which can introduce powerful oxygen functional groups.…”

Review—Flow Batteries from 1879 to 2022 and Beyond

“…1.1 μm fibers with ca. 15 μm voids in between, 281 or 20 nm wide pits etched on the surface of 200 nm wide carbon fibers, 282 or carbon nanoribbons with 0.4 × 0.8 μm cross-section, 272 or carbon nanotubes grown on microfibers in commercial carbon felt [283][284][285] were less successful in improving the power-efficiency performance of a VRFB on the complete cell level at practically relevant current densities (i.e. over 0.2 A cm −12 ).…”

“…Fortunately, carbon nanofibers can usually be prepared (at carbonization temperature ⩾900 °C) with a fairly large electronic conductivity, e.g. in the range from 650 to 900 S m −1 , 244,282 which is ca. ten times larger than the peak conductivity of aqueous sulfuric acid (77.2 S m −1 at 29.5%w and 21 °C), thus making our conclusions relevant to many commercial systems.…”