To attend to this complication, EQCM was carried out to compliment these XRF studies and allow a complete mass and charge balance of the OMIEC films. Assuming a density of 1.0g/cm 3 and knowing the modulated cation concentration through XRF, the contribution to the mass change due to uptake of water molecules was calculated. The number of cations (injected/expelled) during cycling as quantified by XRF (Figure ) was used in the mass balance quantified by EQCM (Figure ) to calculate the amount of water that accompanies cation (injected/expelled). The combined experiments here indicate that on average ~11.6 H2O molecules accompany each Na + cation injected/expelled in to EG/GOPS-PEDOT:PSS. This is nearly three times the estimated accompanying water molecules previously reported using solely EQCM methods where the cation flux was equated with measured electrical current. This highlights the overestimate of cation content that can occur when measured currents are assumed to be purely cation flux. This ignores faradaic reactions that result in direct charge transfer, which can be especially large in aqueous environments in the presence of oxygen. These faradaic reactions arising from PEDOT based materials can in fact be harnessed as reported in PEDOT-based electrocatalysts. Our calculated cation-associated water content is more in line with near ambient pressure XPS measurements of water content (~8-10 per cation) associated with a metal halide counterbalanced PSS -functional group. It is intuitively reasonable that our cation-associated water uptake of a PSS containing film in contact with liquid electrolyte would exceed sorption measurements of PSS films in 100% relative humidity environments (but not in contact with liquid water). The experiments reported here indicate that cation transport into the film is accompanied by more than a single hydration shell. Figure 2 a) XRF spectra for pg2T-TT exposed and electrochemical cycled in 100mM at pH=7; b) Br (brown diamond) and Rb (violet square) to S ratio of pg2T-TT in different electrochemical doping level; c) Rb (brown diamond) or Br (violet square) to S elemental ratio for pg2T-TT after multiple electrochemical cycling (the doped states filled with green and the dedoped states filled with yellow) in acid (pH=3), neutral (pH=7) and basic (pH=11) conditions.