- Membranes containing crown ether were prepared. The membranes become positively charged by complexing alkali-metal ions. In these anion-exchange membranes, not containing amino groups, pH changes caused by above-limiting currents were very small in contrast to the substantial acid-base generation by conventional A membranes. This is consistent with Simons' model. It is suggested that both suppression of acidification and the dynamic nature of the positive charges may help to avoid fouling.