The metabolism of electroactive microorganisms enables the use of an external electrode as an electron source or sink. Usually, these microorganisms form an electroactive biofilm (EAB) on the electrode surface. Porous 3D electrodes provide a large habitat for the EAB and can thus facilitate high metabolic rates and high current densities, which are necessary for the commercialization of bioelectrochemical systems. On the other hand, the biofilm limits the diffusive transport of nutrients and reaction products. In current research, porous electrodes are developed considering the biofilm density, its metabolism and the occuring transport phenomena. In this context models and simulations help to better understand the processes in the electrode-biofilm composite structure. Direct and spatially resolved measurement of parameters such as biofilm density or diffusion coefficients are essential to improve the existing models and evaluate the effectiveness of the porous electrodes. However, the predominant optical methods used at this time fail due to the opacity of the electrodes. Therefore, tools that do not rely on optical transparency are required.