continuing concentration and dilution of electrolyte at opposite ends of an array of unit cells with single positives fig2 can be prevented by several practical arrangements for example a tubular conduit for oxygen gas can be provided between the ends of the cell array practical implementation is facilitated by the absence of a pressure difference between the interior and the exterior of the conduit also hermeticity is not required alternatively the cell stack can terminate with a catalyst electrode such as used for the anode in this case the oxygen will react with the hydrogen environment at the catalyst to yield water which will dilute the electrolyte the excess water can be returned via a conduit e g wick to the opposite end of the cell array the same types of materials that are suitable as reservoir structures can also be used for wick arrangements this configuration is schematically shown in fig3 it shows the array of the following components gas distribution screen 52 anode 53 separator matrix 54 cathode 55 reservoir structure 56 cover membrane 57 and wick for water return 58 if the ni h 2 cell is operated only under mild conditions low rate limited amount of overcharge a special oxygen or water return conduit need not be provided at all since the common hydrogen atmosphere acts as such for example the more dilute electrolyte has an increased partial pressure of water.