The 8 µm PES had previously been shown to be capable of supplying liquid electrolyte to the electrodes at a sufficient rate to operate the cell continuously and at high current density. The 8 m PES separator membrane has a mildly asymmetric pore profile across its thickness. One side has fewer and smaller pores (the 'gloss' side) than the other side (the 'matt' side). As conventional alkaline electrolysis cells are generally known to produce smaller bubbles of hydrogen than oxygen, the gloss side of the separator membrane was placed facing the hydrogen-generating cathode with the matt side facing the oxygen-generating anode.