Alkaline fuel cell stack design

Alkaline fuel cell stack design involves working out the details of optimum configuration of the individual module, array or pack to develop the required output. The basic concept in the design being the assembly of pair of electrodes, provision of hydrogen and oxygen gases to the appropriate electrodes and supply of electrolyte into the individual cell assemblies. Cascading the electrode pairs is possible in many different ways. The basic configuration can be either mono or bipolar with either internal or external manifolding. Also electrolyle supply by matrixing or stagnant boundary or by circulation are the various possibilities. The technique to be adopted in the stack boundary or by circulation are the various possibilities. The technique to be adopted in the stack fabrication mainly depends on the limitation in materials to be used.
Stack design concepts
Various possibilities of stack disign are possible, The options for air electrode of hydrophilic and hydrophobic nature with electrolyte circulation by pump / fan or by natural respiration are possible.
Internal manifolding where electrolyte and gas manifolds arranged internally or external manifolding is possible..
The choice of internal or external manifolding have their inherent problems. The external type has all plumbing works done externally which are amenable for easy maintenance, while the choice of polarity and coupling depends on the capacity. In the internal type cell reliability of fluid transfer depends on seals and O rings and the maintenance requires dismantling of cell assembly.
Stack designs
The stack design adopted by various investigators are described below:
Filter press type: Hydrogen - oxygen fuel cell have circular frame and electrodes. The frame consists of rooms for KOH, H2 and O2. There are six passages two each for entry and exit of electrolyte, hydrogen and oxygen and the frame was clamped by six bolt holes. The electrolyte and gas diffuse radially inwards and leave radially out. This design akins to Grove's design concept.
Monocell construction: The monocell of the actual design contains seven structural components. The central matrix of 20.4 x 20.4 x 0.025cm is connected by means of film gluing with an epoxy frame layer, with the later supported with Teflon mesh screen. Adjacent nickel collectors of the electrodes consist of galvanised screens which are soldered and filled with tin at two opposite edges and sealed in the frame zone after having been charged with catalyst.
Bipolar alkaline fuel cell battery: This consists of bipolar cells, separator packages, electrolyte frame and end plate assembly. The electrodes are rectangular size and framed with suitable slots for gas and electrolyte entry.