The zinc electrode (the anode) is a bed of zinc particles immersed in concentrated potassium hydroxide (KOH) in contact with a current collector. Zinc/air fuel cell showing electrodes. The anode reaction is as follows: As the zinc particles dissolve, the bed volume decreases, and unreacted particles fall from the fuel hopper into the electroactive area of the cell.
|Each cell has its own fuel hopper. This process continues until the hoppers are empty, at which point the cells are completely discharged and must be refueled. An important aspect of the fuel cell is that the bed of zinc particles in each cell is continually washed by a flow of recirculating KOH electrolyte. This removes the soluble zinc reaction product (zincate) and therefore reduces precipitation of discharge products in the electrode active area. Without this, the cell would quickly become clogged with a mixture of zinc and reaction products and would not be refuelable.
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The zincate is converted to ZnO in the electrolyte management unit and removed from the electrolyte via the reaction. At the air cathode, the reaction is where oxygen is supplied as air, passed up the backside of the electrode. The overall fuel cell reaction is therefore zinc plus oxygen reacting to form zinc oxide.
The recycling/refueling system uses electrolysis to convert the zinc oxide back to zinc metal in pellet form using AC electricity from the wall. The pellets are stored in a tank, and, when required, are pumped in a stream of flowing electrolyte into the fuel cell. Simultaneously, the zinc oxide is removed, also in a stream of flowing electrolyte, from the electrolyte management unit and transferred to the recycling/refueling system.
Alternatively the pellets are pumped into a container, which can be transported into the field and attached to the fuel cell, replacing a "spent" container filled with zinc oxide. The spent container is then transported back to the zinc recycling/refueling unit and flushed out and refilled. This alternative approach is superior for applications where it is inconvenient or impossible to bring the fuel cell and recycling unit close enough together to refuel via hoses.