Porous carbon-coated graphite electrodes for energy production from salinity gradient using reverse electrodialysis

Performance of graphite foil electrodes coated by porous carbon black (i.e., Vulcan) was investigated in comparison with metal electrodes for reverse electrodialysis (RED) application. The electrode slurry that was used for fabrication of the porous carbon-coated graphite foil is composed of 7.2 wt% of carbon black (Vulcan X-72), 0.8 wt% of a polymer binder (polyvinylidene fluoride, PVdF), and 92.0 wt% of a mixing solvent (dimethylacetamide, DMAc). Cyclic voltammograms of both the porous carbon (i.e., Vulcan)-coated graphite foil electrode and the graphite foil electrode without Vulcan showed good reversibility in the hexacyanoferrate(III) (i.e., Fe(CN)(6)(3-)) and hexacyanoferrate(II) (i.e., Fe(CN)(6)(4-)) redox couple and 1 M Na2SO4 at room temperature. However, anodic and cathodic current of the Vulcan-coated graphite foil electrode was much higher than those of the graphite foil electrode. Using a bench-scale RED stack, the current-voltage polarization curve of the Vulcan-coated graphite electrode was compared to that of metal electrodes such as iridium (Ir) and platinum (Pt). From the results, it was confirmed that resistance of four different electrodes increased with the following order: the Vulcan-coated graphite foil < the Ir-coated titanium (Ti) mesh < the Pt-coated Ti plate < the graphite foil. Moreover, the Vulcan-coated graphite foil showed 5-10% higher power density than the metal mesh electrodes. From the polarization curve of the Vulcan-coated graphite foil electrode, it was found that total resistance decreased as thickness and geometric surface area of the electrode increased. (C) 2015 Elsevier Ltd. All rights reserved.