Vanadium redox flow battery working even at a high current density by the adoption of tris(hydroxymethyl) aminomethane functionalized acidified carbon nanotube catalyst

Highlights: • Tris(hydroxymethyl) aminomethane functionalized carbon nanotube (Tris-CNT) is suggested as catalyst. • Tris-CNT is synthesized by condensation reaction. • Tris-CNT containing abundant oxygen groups promotes V²⁺/V³⁺ and VO²⁺/VO₂⁺ reactions. • VRFB using Tris-CNT works well even at high current density of 250 mA cm⁻². • VRFB using Tris-CNT shows capacity of 19.1 Ah L⁻¹ and energy efficiency of 69%. Tris(hydroxymethyl) aminomethane (Tris) functionalized carbon nanotube (Tris-CNT) is newly suggested as a catalyst promoting the redox reactivity of vanadium ions in vanadium redox flow battery (VRFB). This Tris-CNT is synthesized by a condensation reaction between the carboxyl group of carboxylic acid functionalized carbon nanotube (CA-CNT) and the amine group of Tris. Since one Tris molecule has three hydroxyl groups, the surface of Tris-CNT consists of abundant oxygen functional groups that play a key role in facilitating the redox reaction of vanadium ions. To confirm the viability of Tris-CNT as a catalyst for VRFB, its chemical and electrochemical properties are evaluated. As a result, the reactivity of Tris-CNT increases by 136 and 159% for V²⁺/V³⁺ and VO²⁺/VO₂⁺ reactions when compared to those of CA-CNT. Besides, at a high current density of 250 mA cm⁻², VRFB using Tris-CNT shows a capacity of 19.1 Ah L⁻¹ and energy efficiency of 69%, while those of VRFB using CA-CNT are 13.0 Ah L⁻¹ and 63%. The above results show that the use of the new Tris-CNT catalyst has a strong influence on the improvement in the performance of VRFB.