Electric transport of sulfuric acid through anion-exchange membranes in aqueous solutions

The current efficiency of membrane electrolysis of sulfuric acid solution using two types of anion-exchange membranes (ACM and AAV) has been determined. The transport phenomena in the membrane surrounded by polarization layers have been described by the model based on the extended Nernst–Planck equation and the Donnan equilibria, applied locally. It has been found that in the case of ACM two fitting parameters – the concentration of fixed charges (c¯m=1.1 M) and the pore factor (kDVθ = 0.006) – are needed for a relatively good fitting of model to the experimental data. However, the weak-base membrane AAV should be characterized by three parameters—the maximum concentration of fixed charges which can be formed in that membrane (c¯m,max=1.2 M), the protonization constant (KH = 6) and kDVθ = 0.0025. For both membranes the optimal values of c¯m are much lower than the experimental ones. The probable reasons of that discrepancy have been discussed.The thickness of the polarization layer, lpol, necessary in the model fitting has been calculated from the experimentally determined limiting current density using the equation derived for sulfuric acid. Comparing the values of lpol determined for ACM in the H2SO4 and HNO3 solutions it was possible to find that only the sulfate anions carry the electric charge in that membrane in contact with dilute solutions of H2SO4.