Current and potential distributions enable rational design and scale-up of electro-deoxidation reactors where geometric similarity is sacrificed for current and potential similarity. Calculation of primary current distribution and resistance represents the first step towards reactor analysis and optimization and is determined by geometric factors. The Maxwell equation ∂tP + curl(P × v) = j P for the polarization charge, where P denotes the vector of polarization, v is the barycentric velocity vector and j is the current density vector, defines the normal current on the cathode boundary: