The BPM model employed here (described in detail in Section S1 of the SI) was designed to mimic the 4-probe experiments performed for direct BPM analysis (described in detail in Section S2.2), modeling the relevant domain as a 1-dimensional (1D) continuum consisting of an 80 µm CEL, and an 80 µm AEL sandwiching a 3.5 nm water dissociation CL, with a 25 µm diffusion boundary layer (Section S1.6) on either side of the BPM assembly (Figure ). Modeling the domain as such enables the capturing of all relevant concentration profiles and species fluxes.