The role of carbon additives in improving the electronic conductivity of composite porous electrodes is well understood. However, there has been little work studying the effect of various carbon additives on effective ionic transport in porous electrodes. This work determines effective ionic conductivities and associated tortuosities of composite cathodes with various types of carbon additive and porosities in an alkaline system. A two-compartment direct-current method was developed to make these measurements and was validated with multiple electrolyte solutions. This experimental method was modeled using COMSOL Multiphysics in order to understand the effect of design parameters on the polarization curve. Empirical correlations were developed to predict the effect of porosity and various carbon additives on tortuosity. As expected, the results show that tortuosity decreases with porosity and increases with carbon amount. Cathodes containing BNB90 and KS6 carbon additives have the highest and the lowest tortuosity, respectively. Furthermore, for cathodes containing BNB90, tortuosity in the direction orthogonal to the direction of compression (in-plane tortuosity) was found to be less than tortuosity in the direction parallel to compression (out-of-plane tortuosity). (C) The Author(s) 2017. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives 4.0 License (CC BY-NC-ND, http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial reuse, distribution, and reproduction in any medium, provided the original work is not changed in any way and is properly cited. For permission for commercial reuse, please email: [email protected]. All rights reserved.