In order to have a good water balan

In order to have a good water balance and a hydrated membrane, normally the inlet gases are humidified. In PEM fuel cells, excessive amount of liquid water in the electrode can flood the backing and catalyst layers, which leads to poor fuel cell performance due to the blockage of gas diffusion paths. It is well known that cathode flooding is the main controlling factor in the performance of PEM fuel cells operating at medium-to-high-current densities. The simplest way to humidify a gas stream is either to pass the gas as a stream of fine bubbles through water called external humidification.