Stack Design with Anion-Exchange Membranes

Stack Design with Anion-Exchange Membranes 

The most recent AFC design uses AEMs. Because of this solid-state electrolyte membrane, stack designs based on AEMs are similar to the stack designs for PEFCs. The electrolyte loop is eliminated, which simplifies the cell design from a systems perspective, and the cooling is instead similar to that of PEFCs. The AFC can still be credited with a reduced need for expensive noble metals. 

At present, only a few materials are available for AEMs (stability requirements are demanding) therefore, this type of stack has been used in laboratories but is not yet commercially available. 

One recent example is notable for its iimovative application and has already been mentioned here. A new stack concept from the University of Applied Science in Offenburg (Germany), included a new catalyst from the Italian company ACTA and an AEM membrane from the Japanese membrane producer Tokuyama. This consortium developed an AEM-based ethanol-powered AFC and successfully inserted it into an electric vehicle. This stack was not able to work for an extended time because the system was built without an ethanol loop and without a KOH re-concentrator, but it is an impressive demonstration of AEM technology and the direct use of ethanol. DLR together with the University of Diisseldorf are working with laboratory-scale fuel cells to understand the ethanol oxidation mechanism in detail. 

Alkaline Direct Ethanol Fuel Cells Assembled with a Non-Platinum Catalyst 

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Stack Design with Anion-Exchange Membranes... 

Stack design in bipolar membrane electrodialysis The key component is the stack which in general has a sheet-flow spacer arrangement. The main difference between an electrodialysis desalination stack and a stack with bipolar membranes used for the production of acids and bases is the manifold for the distribution of the different flow streams. As indicated in the schematic diagram in Figure 5.10 a repeating cell unit in a stack with bipolar membranes is composed of a bipolar membrane and a cation- and an anion-exchange membrane and three flow streams in between, that is, a salt... 

Yet another stack design utilizes unit cells. Unit-cell stacks were specifically developed for concentrating solutions. Each concentrating cell consists of one cation-exchange membrane and one anion-exchange membrane sealed at the edges to form an envelope with a spacer screen inside. The envelopes also have... 

The gaskets not only separate the membranes but also contain manifolds to distribute the process fluids in the different compartments. The supply ducts for the diluate and the brine are formed by matching holes in the gaskets, the membranes, and the electrode cells. The distance between the membrane sheets, i.e. the cell thickness, should be as small as possible to minimize the electrical resistance. In industrial size electrodialysis stacks membrane distances are typically between 0.5 to 2 mm. A spacer is introduced between the individual membrane sheets both to support the membrane and to help control the feed solution flow distribution. The most serious design problem for an electrodialysis stack is that of assuring uniform flow distribution in the various compartments. In a practical electrodialysis system, 200 to 1000 cation- and anion-exchange membranes are installed in parallel to form an electrodialysis stack with 100 to 500 cell pairs. 

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