Gas-phase functionalization of macroscopic carbon nanotube fiber fabrics: reaction control, electrochemical properties and use for flexible supercapacitors

TL;DR

This study introduces a gas-phase ozone functionalization method for carbon nanotube fibers that preserves their morphology, enhances hydrophilicity, and improves their performance in flexible supercapacitors.

Contribution

It presents a novel gas-phase functionalization technique for CNTF that maintains morphology and enhances electrochemical properties for flexible energy storage devices.

Findings

Gas-phase ozone functionalization increases CNTF hydrophilicity.

Functionalized CNTF enables electrochemical testing in aqueous media.

The material performs effectively in flexible supercapacitors.

Abstract

The assembly of aligned carbon nanotubes (CNT) into fibers (CNTF) is a convenient approach to exploit and apply the unique physico-chemical properties of CNTs in many fields. CNT functionalization has been extensively used for their implementation into composites and devices. However, CNTF functionalization is still in its infancy, due to the challenges associated with preservation of CNTF morphology. Here, we report a thorough study of the gas-phase functionalization of CNTF fabrics using ozone that was generated in situ from a UV-source. By contrast with liquid-based oxidation methods, this gas-phase approach preserves CNTF morphology, whilst notably increasing its hydrophilicity. The functionalized material is thoroughly characterized by Raman, XPS, TEM and SEM. Its newly acquired hydrophilicity enables CNTF electrochemical characterization in aqueous media, which was not possible for the pristine material. Through comparison of electrochemical measurements in aqueous electrolyte and ionic liquid we decouple the effects of functionalization on pseudocapacitive reactions and quantum capacitance. The functionalized CNTF fabric is successfully used as active material and current collector in all-solid supercapacitor flexible devices with ionic liquid-based polymer electrolyte.