The electrical properties of an activated carbon packed bed were studied for its potential application as a 3D cathode in electrochemical processes. In this way, different levels of carbon compaction and their electrical properties were evaluated in an electrochemical reactor using electrochemical impedance spectroscopy (EIS) and the four-point conductivity measurement technique. The results showed that by increasing the compaction from 0.39 to 0.52 g cm(-3), it is possible to improve the conductivity of the material by a factor between 17 and 28 times. The effect of carbon chemistry on this property was also explored; showing that increasing the number of oxygenated functional groups results in an increase of the electrical conductivity of the packed carbon bed by a factor of 1.7. As expected, the conductivity promoted by carbon compaction also resulted in an improved performance of the material as a cathode. Finally, studies using EIS were carried out and analyzed with an equivalent circuit for porous electrodes. These experiments showed that along the packed carbon bed, two charge transfer processes can be detected: the first, at high frequencies, was associated with charge transfer at the carbon particles, and the second, at low frequencies, was associated with ion diffusion phenomena. (C) 2018 The Electrochemical Society.