Carbon paste electrodes: correlation between the electrochemical hydrogen storage capacity and the physicochemical properties of carbon blacks

The difficulties in the use of carbon paste electrodes to quantify the electrochemical adsorption of hydrogen in nanocarbon materials are described. Chronoamperometry studies using a Ferro/Ferri redox couple were performed to obtain the electrochemical active area of paste electrodes prepared by dispersion of differing samples of carbon blacks (CB) within silicon oil. This electrochemical active area was combined with the BET-surface area of the carbon blacks, to obtain the mass of superficial carbon involved in the electrochemical processes. To assure equal conditions for comparison, the electronic conductivity of the paste was equivalent in all the samples. From our results it appears that cyclic voltammetry, combined with carbon paste electrodes and nitrogen adsorption isotherms, provides a simple and less expensive route for the qualitative evaluation of the electrochemical hydrogen uptake of novel carbon materials. Still, for quantitative measurements, some issues remain unsolved in highly structured carbons, where the lack of penetration of the bulky Ferro/Ferri redox couple in the micropores of the CB and the occurrence of solid-state diffusion cause the underestimation of the mass involved in hydrogen adsorption.