The Problem of Air-Breathing Cathodes

The task of building such freely breathing cells is complicated by the fact that in most versions of fuel cells, water as a reaction product is evolved on the cathode, and a circulating stream of air is needed to remove it. Often, this airflow is also used to eliminate the heat of reaction. For plants of large power output (and large dimensions), it is usually more profitable to use actively injected air rather than solving all the problems associated with passive air supply. When building plants of low power and small size, however, it will be practically unavoidable to use a passive air supply. 

Despite the importance of this problem, little research was done to examine passive air supply in detail. The main condition for the passive use of air is a sufficiently large contact surface area between the cathode and the surrounding atmosphere. In fuel batteries of flat design, one of the sides may be left completely open. In fuel batteries designed for notebooks, the back side of the monitor in the lid housing the battery could be left almost completely open. 

A large contact surface area between the fuel cell and the surrounding atmosphere has a large defect, however, inasmuch as the ambient conditions (e.g., temperature, relative humidity, the presence of pollutants) are unstable and variable 

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