Dielectric and electrical conduction behavior of carbon paste electrochemical electrodes, with decoupling of carbon, electrolyte and interface contributions

The electrical conduction and dielectric (capacitive) properties of electrolyte-filled carbon paste electrochemical electrodes are reported, with the carbon, electrolyte (15% H2SO4), carbon-electrolyte interface and carbon-contact(metal) interface contributions fully decoupled for the first time. Without full decoupling and with the carbon contributions neglected, the carbon-electrolyte specific interfacial capacitance would be much overestimated and the carbon-electrolyte interfacial resistivity would be much underestimated. The carbons and electrolyte are comparable in both dielectric constant and resistivity. The specific contact capacitance is increased and the contact resistivity is decreased by adding the electrolyte to a carbon. The electrolyte is more effective than water in enhancing carbon-liquid and paste-contact interfaces. Conductivity is attractive for batteries and supercapacitors; strong dielectric properties are attractive for supercapacitors but not batteries. Exfoliated graphite provides handleability and excellent volumetric and interfacial conductivities. It gives low carbon dielectric constant, but contributes to the interfacial capacitances. Activated graphite nanoplatelet (GNP) gives high carbon and paste dielectric constants and high specific contact capacitance. Activated carbon gives poor volumetric and interfacial conductivities. Exfoliated graphite is even better than carbon black for batteries; GNP is even better than activated carbon for supercapacitors; an exfoliated-graphite/GNP mixture is suitable for both; natural graphite is not competitive for either. (C) 2014 Elsevier Ltd. All rights reserved.