The properties and performance of linear and cross-linked KOH doped ABPBI membranes as electrolyte/separator for zero gap alkaline water electrolysis cells are evaluated and compared with a commercial Zirfon^® diaphragm. Stability in alkaline environment, swelling, thermal properties, water sorption, KOH uptake and conductivity of linear (L-ABPBI) and cross-linked (C-ABPBI) membranes doped with different concentrations of KOH are analyzed. Linear membranes show stability up to 3.0 mol·dm^-3 KOH doping, while cross-linked membranes are stable up to 4.2 mol·dm^-3 KOH doping. Both kinds of membranes exhibit good thermal stability and reasonable specific ionic conductivity at 22°C in the range between 7 and 25 mS·cm^-1, being slightly higher the conductivity of C-ABPBI membranes than that of L-ABPBI ones. In short-term electrolysis tests both L-ABPBI and C-ABPBI membranes show better performance than Zirfon diaphragm in the range from 50 to 70°C. A current density of 335 mA·cm^-2 at a cell voltage of 2.0 V is attained with C-ABPBI membranes doped in 3 mol·dm^-3 KOH at 70°C, a performance comparable with that of commercial units operating at temperatures ca. 80°C and 30 wt% KOH (6.7 mol·dm^-3) as electrolyte.