Fuel Cell Design

Today we worked on the design of an individual fuel cell and its incorporation within a stack system:

Single Cell

Within a single cell, the electrolyte conducts ions between the cathode and anode, and serves as a gas separator and electronic insulator (Bruijn, The current status of fuel cell technology for mobile and stationary applications 2005). The electrochemical reactions occur at the electrodes, and thus need to contain the appropriate catalysts. In order to have high efficiency, it also needs to be designed such that the rate of transportation of reactants to and from the catalyst-electrolyte interfaces is maximized.

The power produced by a single cell is proportional to the surface area (SA), the current density of the cell (J), and the cell voltage (V_cell) (Bruijn, The current status of fuel cell technology for mobile and stationary applications 2005):

 Since the typical voltage under load conditions is only 0.7 V, a single cell design is unpractical.

Stack design

To overcome the low voltages of a single cell design, multiple cells are put in a series connected with flow plates, creating a fuel cell stack. The flow plates are highly conductive and connect the anode of one cell with the cathode of another, while separating the gases of the two cells. These plates contain “flow patterns” to evenly distribute the reactants across the cell, maximizing the surface area of the reaction (Bruijn, The current status of fuel cell technology for mobile and stationary applications 2005). The stack power and voltage are then proportional to the number of cells contained (n) and the power and voltage of the individual cell:

The current, at a much higher voltage than possible with a single cell, is then collected at the two end plates.