Power-Dissipation Model for Water Dissociation in Bipolar Membranes: Model Extension to High Current Density and Experimental Validation

Water dissociation (WD) at the internal junction of bipolar membranes (BPMs) is the key process enabling acid/base generation under reverse bias, yet the physical origin of its strong enhancement remains debated. In our previous work, we proposed a power-dissipation model in which WD is enhanced by an intense electric field through local power dissipation by autoprotolysis ions. Here, we experimentally validate this model using three commercial BPMs under acid/base and neutral salt conditions and extend it to high current density by incorporating finite water supply to the BPM junction. Under acid/base conditions, two BPMs showed strong field-dominated quadratic behavior, while a catalyst-containing BPM displayed a predominantly linear response, indicating that heterogeneous interfacial catalysis can mask the purely field-driven signature. In neutral Na2SO4, all three BPMs exhibited excellent quadratic fits, confirming that the predicted JWD∝Uj2 behavior is robust. The fitted prefactor varied with membrane type and electrolyte configuration, reflecting differences in hydration, junction thickness, transport behavior, and catalysis effect. The model was extended at higher current density to include finite diffusive water supply to the junction. The resulting saturation law links the intrinsic quadratic WD current JWD to a water-transport-limited current Jlim,2, and predicts an inflection point at JWD,inf = 0.25 Jlim,2.