Types—Bipolar and Monopolar

Electrochemical cells, be they for electrolysis to generate products or for producing electricity (e.g., batteries, fuel cells), fall into two broad categories with respect to the electrode configuration, monopolar and bipolar cells. In a monopolar cell, there are typically many anode and cathode assembUes that are electrically in parallel with each other. Thus, a monopolar cell is typically a high current cell compared to most bipolar cells. In the typical DC circuit configuration, monopolar cells are connected in series by intercell conductors. 

On the other hand, in bipolar cells, only the terminal cells are connected by intercell conductors, and there are typically many unit cells electrically in series between the terminal cells (Fig. 5.2). The two basic types of bipolar cells are the flat plate cell and the finger type cell. A group of bipolar cells that have a common piping system for the fluids, via manifolds, is referred to as an electrolyzer or sometimes a series or a stack. Within a single bipolar electrolyzer, there are sometimes more than one set of terminal cells. Bipolar electrolyzers can be connected via an external bus within a DC circuit in series or in parallel, but usually not both. Furthermore, in the case of mercury-cell plant conversions to membrane cells, the electrolyzers are connected electrically in parallel as shown in Fig. 5.3. 

Historically, the concept of arranging the cells in bipolar and monopolar fashion was known before 1800, when Volta assembled batteries [3]. There are several advantages and disadvantages associated with the construction and operation of monopolar and bipolar cells [4,5]. They are noted in Table 5.1. 

Bipolar arrangement (filter-press type electrolyzer) FIGURE 5.2. Schematic of cell assemblies. 

Structure is shorter. Less busbar and fewer busbar connections for bipolar cells also save some voltage and some capital. 

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