Diffusion simulations of proton concentrations in the vicinity of the protonator electrodes (WE2) were performed using Fick's second law. A model was designed to simulate the generation of protons at the protonator electrodes, and their subsequent diffusion from these electrodes, using finite element analysis software, Comsol Multiphysics 6.0 ™, in line with the galvanostatic model shown previously. The model boundary conditions were set at as a box 930 µm high by 5 mm wide, representing the experimental domain. Two sets of interdigitated 1 µm wide microband electrodes (34 protonator electrodes and 33 sensing electrodes), separated by 2 µm were defined at the bottom boundary layer.