Method of operating a fuel cell

#Numerous other objects, features and advantages of the invention will become apparent from and/or are described in detail, along with the foregoing, in the following detailed description of preferred embodiments, taken in connection with the accompanying drawings, in which

#FIG. 1 is a diagrammatic sketch of fuel cell apparatus of the type described utilizing a combination of means for building up a pressure differential which can be used singly or in combination;

#FIG. 2 is a similar diagrammatic sketch of a fuel cell system which is operable in timed fill-drain sequence of anolyte and catholyte.

#Referring to FIG. 1, there is shown a preferred embodiment of the fuel cell 100 comprising anolyte and catholyte compartments 101 and 102, respectively, formed by separation of the cell into two compartments by an intermediate microporous diffusion barrier 103--an electrochemical grade separator with pores on the order of 0.1 .mu. diameter and a thickness of 1-10 mils. The cell has an anode 111 and cathode 112 in the anolyte and catholyte compartments, respectively. The cell is formed by stacking the electrodes and barrier with separating spacer elements 113 having integral feed channels, and cover plates 115. A reservoir of anolyte 121 supplies anolyte compartment 101 via a feed line 123 and the anolyte compartment is drained by a drain line 125 and the drained anolyte can be pumped through a pump 131 for return to the reservoir 121. The catholyte is fed from a catholyte reservoir 122 to catholyte compartment 102 via a feed line 124 and drained via a drain line 126 for recirculation to the reservoir via pump 132. A throttle valve 128 can be provided in an alternative catholyte drain line 126 for purposes hereafter described.

#The particulars of construction of the cell 100 in single cell form or in multi-cell form can be as described in the said application Ser. No. 256,924 or in the above cited copending application of Williams. It will be understood that while only a single cell is shown here, the invention can be practiced on some or all of the unit cells of a multi-cell array.

#In accordance with this preferred and distinctly advantageous embodiment of the present invention, the cell constructions of the above referenced disclosures are modified by means for inducing a pressure gradient to bias the anolyte/catholyte interface. One such means is the establishment of a pressure differential by providing differing vertical heights for the lines 123 and 124. This height differential .DELTA.H can be as little as a few inches difference or several feet. Another such means which can be used where the interface biasing is done by establishing higher pressure in catholyte than anolyte is to provide a throttle valve 128 in the alternative catholyte drain line 126, which, together with feed line 124 and a positive displacement pump 132, forms a closed loop recirculating system with fixed volumetric flow throughout. Still further methods of creating such pressure differential would include appropriate sizing of drain lines 125, 126 and/or feed lines 123, 124 or of the compartments 101, 102. If centrifugal pumps are used at 131, 132, they can be regulated to create such a pressure differential.