Eco-conscious one-step treatment for oxygen-containing group functionalization on CNTs using TAEA and its use in vanadium redox flow batteries

A one-step eco-friendly approach for the large-scale production of oxygen-functionalized carbon nanotubes (CNTs) without fragmentation was successfully developed using tris (2-aminoethyl) amine (TAEA). This method resulted in an increase in the surface oxygen content of the CNT to over 10 % through sequential and consecutive five-step processes, enhancing their hydrophilicity and catalytic activity for vanadium ion redox reactions on both sides. Various characterization techniques have confirmed the structural and chemical stability of TAEAtreated CNT (CNT/TAEA), indicating that TAEA facilitates the formation of carbonyl groups without damaging the graphitic structure. The CNT/TAEA catalyst demonstrated superior catalytic activity, reduced charge transfer resistance, and increased peak current density in both positive and negative electrolytes. In practical vanadium redox flow batteries (VRFBs), electrodes using CNT/TAEA showed enhanced energy efficiency (65.8 %) and discharge capacity (27.1 Ah L-1) under high current densities (400 mA cm(- 2)), outperforming those using commercial heat-treated graphite felt (H-GF) and other GFs using similar treatment applied catalysts. Vanadium redox flow batteries using CNT/TAEA also maintained high stability and performance over extended cycling (500 cycles), suggesting its feasibility for commercial VRFB applications.