Maintaining desired level of relative humidity throughout a fuel cell with spatially variable heat removal rates

A concept of using the product water to internally humidify the air stream in a PEM fuel cell without external humidification is investigated by a simple, pseudo 2-D model along a single channel. This model takes into account the mass and energy balance, water and heat generation rates, heat removal, and water transport through the membrane. The model and thus the concept were confirmed experimentally using a 5-segment fuel cell. The temperature of each segment could be individually controlled, and the temperature and humidity of air could be measured between each segment. A temperature profile has been established, by applying spatially variable heat removal rates along the cathode channel, that results in relative humidity being close to 100% throughout the cell without any external humidification. The concept may be applied to a fuel cell stack resulting in simplification of the suporting system by avoiding external humidification.

► We ran a PEM fuel cell without external humidification.
► We maintained the desired temperature along the cathode channel.
► Relative humidity was close to 100% along the channel.
► Performance was 70 mV better at 0.5 A cm−2 than when isothermal hardware was used.