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

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 mu m 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 mu m 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. The vanadium(IV/V) redox reaction is probed at relevant carbon substrate electrodes by a pulse profile creating a feedback mode experiment of scanning electrochemical microscopy. Kinetic constants are extracted from the evaluation of approach curve data. image