Fuel cells are electrochemical cells in which a free energy change resulting from a fuel oxidation reaction is converted into electrical energy. A typical fuel cell consists of a fuel electrode (anode) and an oxidant electrode (cathode), separated by an ion-conducting polymer electrolyte. The electrodes are connected electrically to a load (such as an electronic circuit) by an external circuit conductor. In the circuit conductor, electric current is transported by the flow of electrons, whereas in the electrolyte it is transported by the flow of ions, such as the hydrogen ion (H.sup.+) in acid electrolytes, or the hydroxyl ion (OH.sup.-) in alkaline electrolytes. Gaseous hydrogen is the fuel of choice for most applications, because of its high reactivity in the presence of suitable catalysts and because of its high energy density. Similarly, the most common oxidant is gaseous oxygen, which is readily and economically available from the air. At the anode, incoming hydrogen gas ionizes to produce hydrogen ions and electrons. Since the electrolyte is a non-electronic conductor, the electrons flow away from the anode via the metallic external circuit. At the cathode, oxygen gas reacts with the hydrogen ions migrating through the electrolyte and the incoming electrons from the external circuit to produce water as a byproduct. The byproduct water is typically extracted as vapor. The overall reaction that takes place in the fuel cell is the sum of the anode and cathode reactions, with part of the free energy of reaction released directly as electrical energy. Some of the energy is produced as heat.
In practice, a number of unit cells are normally stacked or `ganged` together to form a fuel cell assembly. The individual cells are typically electrically connected in series. Fuel and oxidant are introduced through manifolds into respective chambers. One style of fuel cell is a side-by-side air breathing configuration in which a number of individual cells are placed next to each other in a planar arrangement (see, for example, U.S. Pat. No. 5,783,324). Air breathing fuel cells do not rely on forced flow of oxidant or air past the cathodes, but instead utilize the ambient air and rely on natural convection in the surrounding environment. A classical problem with air breathing planar fuel cells is water management. Since the byproduct water is produced at the cathode (air side), it normally evaporates away during operation. However, under heavy loads, the evaporation rate lags the rate of formation and water tends to migrate back through the polymer electrolyte to the anode side. Some spots on the planar fuel cell are cooler than others, and the H.sub.2 O condenses at these locations into liquid water, flooding both the anode and the cathode, impeding the reactions at the catalyst sites and impeding the flow of hydrogen gas to the anode. Thus, although air breathing fuel cells continue to hold technological promise, they remain a dream that has so far proven to be elusive to the skilled artisan. An improved planar fuel cell that is less complex and less prone to failure would be a significant addition to the field.