where 𝛽, 𝜏, and 𝜎 are lumped parameters discussed in more detail in Section S1.3. The dependence on E in equation ( ) is approximately exponential, as shown in previous work. The above dependence of the activity coefficient on the electric field ensures that macroscopic equilibrium is upheld (e.g., 𝜇 0 & + 𝜇 10 % = 𝜇 0 ! 1 for water dissociation or 𝜇 0 & + 𝜇 >1 ' !% = 𝜇 0>1 ' % for bicarbonate dissociation) (see Section S1.1 for consistency of macroscopic equilibrium), and results in the equilibrium constants of net-charge-generating reactions to be 𝐾 M6",!,+ (𝐸) = 𝐾 M (𝐸 = 0)𝑓(𝐸) (10) where 𝐾 M6",!,+ (𝐸) is the equilibrium constant, which is a function of local electric field, and 𝐾 M (𝐸 = 0) is the value of the equilibrium constant for no applied electric field. For neutral species (i.e., CO2) and ions that do not participate in buffer reactions (i.e., K + ), the activity coefficient is unaffected by the electric field. We note that ion-specific interactions likely impact ionic transport and concentrations in the BPM due to the high concentrations (> 1 M) in the BPM. However, these are likely second-order effects and mixed-interaction parameters are not available for the broad variety of ions in the polymer membranes studied herein.