Adenosine-Derivative Functionalized Carbon Nanotubes Considered as Catalysts for Vanadium Flow Batteries

Vanadium flow battery (VFB) is one of the various candidates considered for energy storage systems. To further improve the performance of VFBs, adding functional groups to the surface of carbon nanotube (CNT) to provide more active sites for promoting redox reactions of vanadium ions is one desirable way. For the purpose, adenosine (AD) and adenosine monophosphate (AMP) attached carboxylic acid functionalized CNTs (CACNT) (ADCNT and AMPCNT) are used as the catalysts. Furthermore, proper co-doping of N, O or N, P, O atoms included in AD and AMP may increase diversity of active sites. In this regard, ADCNT and AMPCNT are considered better catalysts than CACNT for increasing the reaction rate of vanadium ions because a large number of hydrophilic groups belonged to ADCNT and AMPCNT can maximize contact between catalyst and electrolyte. Quantitatively, charge transfer resistance is decreased by ~ 37.6% (ADCNT) and ~ 42.3% (AMPCNT), while peak reversibility is ~ 5.8% improved with the new catalysts. Regarding performance evaluations, voltage and energy efficiencies of VFBs using AMPCNT are best even at 250 mA cm⁻², proving the above benefits of AMPCNT catalyst. Conclusively, this study confirms that larger functional groups compared to those traditionally used can act as effective catalysts, while multi-atom co-doped catalysts can be used for the performance improvement of VFBs.