Transport properties of separating membranes MF-4SK during alkaline electrolysis of water

Abstract

The transport properties of separating membranes MF-4SK are studied during electrolysis of H2O in solutions of KOH. The effective diffusion coefficients of molecules of KOH and H2O and the transfer coefficients of ions K+ and OH− and molecules of H2O are measured at KOH concentrations reaching 11 M, currents reaching 0.31 A cm−2, at ambient temperature and at 80°C. In contact with a KOH solution in the concentration interval 0.1 to 11 M, the membranes that initially swelled in H2O lose a considerable fraction of water that was present in them and the overall volume of clusters and solution-filled channels in them noticeably decreases. The coefficients of transfer by current of ions K+ out of anodic compartment into cathodic and the OH− ions in the reverse direction, respectively, happen to be equal to about 0.6 and 0.4 at ambient temperature and 0.8 and 0.2 at 80°C. The coefficients of transfer of water molecules out of the anodic volume into the cathodic volume in the process of electrolysis happen to be in the limits 1.6–1.9 at ambient temperature and in the limits 2.2–2.8 at 80°C. The effective diffusion coefficients of molecules of KOH and H2O at moderate concentrations of KOH (5.6 M) amount to ∼2.6 × 10−7 and 30 × 10−7 cm2s−1 at ambient temperature and ∼4 × 10−7 and 61 × 10−7 cm2s−1 at 80°C, respectively. At a high concentration of KOH (∼10 M) these quantities substantially diminish.