Probing Carbon Materials Towards the Vanadium(IV)/(V) Reaction by Scanning Electrochemical Microscopy

Abstract

Abstract A method is presented to quantitatively analyze the reduction of vanadium(V) to vanadium(IV) over two flat carbon substrates (glassy carbon and graphite foil) using the feedback mode of scanning electrochemical microscopy. A pulse profile is validated and applied during approach curve experiments of a 10 μm Pt microelectrode. By fitting the approach curve data, electron transfer constants are calculated for various potentials and k0 is extracted from the corresponding Tafel plot. Furthermore, surface functional groups were introduced to the carbon substrates by acid treatment; however, kinetic parameters of the sluggish reduction reaction were only influenced to a minor extent. Finally, the same approach, combined with in situ‐Raman microscopy, is applied to a single graphene layer using a 2.7 μm Pt microelectrode. In this case, increased activity for both, the vanadium(V) reduction and vanadium(IV) oxidation reaction, was found close to the graphene edge sites by means of electrochemical microscopy for the first time.

Keywords

• scanning electrochemical microscopy
• Raman microscopy
• vanadium redox flow battery
• graphene
• carbon materials