Filter-press battery

Figure 16.3. Fuel-cell components, (a) Bipolar electrode and (b) filter-press battery (1) bipolar electrode (2) separator (3) gaskets (4) air supply (5) fuel supply (6) end plate (7) tie bolts (8) positive current collector.

When assembling a filter-press battery from individual fuel cells of any type, considerable compression must be applied in order to minimize the contact... 

The products of reaction are pumped to a filter press for separation into a sodium sulfate solution and a filter cake having a low moisture content. The filter cake is then ready to be processed for the recovery of lead. The filtrate from the process contains an excess of sodium carbonate, and can be neutralized using the sulfuric acid drained from the batteries. 

In either version, cells of the bipolar type assembled to batteries of the filter-press t5q)e can be used. The version with circulating electrolyte is also feasible for building monopolar ( jai -type) cells that are cheaper than bipolar types (as they do not require expensive bipolar plates) and offer a highly flexible series-parallel switching within the battery to accommodate specific user needs. 

The Allis-Chalmers battery had a filter-press design. It contained a 5 M KOH solntion in asbestos diaphragms 0.75 mm thick. The working temperature was 65°C, much lower than that in the batteries described above. At a current density of 200 mA/cm and a gas pressure of 1.35 bar, the voltage per cell was 0.75 V, which is somewhat lower fiian in battery types working at higher temperatures. 

The MCFC components have thicknesses as follows the anode, 0.8 to 1.5 mm the cathode, 0.4 to 1.5 mm and the matrix, 0.5 to 1 mm. In a battery of the filter-press type, the individual cells are separated by bipolar plates made of nickel-plated stainless steel contacting the anode with their nickel side, and the cathode with their steel side. All structural parts are made of nickel or nickel-plated steel. In a working battery, the temperature of the outer part of the matrix electrolyte is lower than that of the inner part, so that in the outer part the electrolyte is solidified. This provides tight sealing around the periphery of the individual battery cells. 

The most convenient way to establish a series connection of individual fuel cells in stacks and batteries is to use the filter-press design with bipolar electrodes and bipolar plates between two adjacent individual cells (as described in Section 1.2.2). 

The active material of the positive electrode (1) consisting of mercury oxide HgO and 5-15% fine purified graphite is pressed into the nickel-plated steel case (6). Zinc powder (2) is pressed into the steel cover (4) and amalgamated. The separator (3) consists of several layers of a special alkali-resistant filter paper. The separator and the powdered zinc electrode are impregnated with a 40% KOH solution saturated with zincate. After assembly the battery is sealed by bending the edges of the case (6). The terminals (case and cover) are insulated by a mbber or plastic spacer (5). 

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