Fast screening of carbon-based nanostructured materials as potential electrode materials for vanadium redox flow battery

•Fast method for evaluation of electrochemical activity of nanostructured carbon materials.•The method based on a fixed bed of carbon materials creating a virtual 3D electrode.•Various carbon nanotubes exhibit very different electrochemical activities toward vanadium species.•Geometry of the nanostructured bed affects the overall performance. Carbon-based nanostructured materials possess good electrochemical activity toward vanadium species employed in vanadium redox flow batteries (VRFB). However, fast screening and testing their electrochemical activity are challenging due to unreliable methods, depositing the nanomaterials onto solid current collectors. We show that creating a nanomaterial fixed bed on a planar current collector in a specifically designed electrochemical cell overcomes these problems. The fixed bed preserves the nanomaterial intrinsic large interfacial area, which reflects in the electric currents reaching up to two orders higher values when compared to flat electrodes. Using the concept of the fixed bed, we screened selected carbon-based materials for their electrochemical activity in a working solution of vanadium. Cyclic voltammograms measured on various carbon nanotubes and fibers of thermally treated graphite felt possessed the well-defined peaks pertinent to vanadium electrochemical reactions. Surprisingly, nickel-doped carbon nanotubes, similarly to fibers of pristine graphite felt or graphene, failed to produce such peaks, rendering them unusable for VRFB. Our screening method can be modified to characterize and test carbon materials for other electrochemical applications. [Display omitted]