Such operation is characterized by the production in the anode circuit of water, nitrogen diffusing through the membrane separating the anode compartment from the cathode compartment, as well as possibly impurities initially present in the hydrogen and which tend to concentrate.
So as to maintain optimum operating conditions, water, nitrogen and impurities are eliminated by proceeding generally to regular purges of the hydrogen circuit.
The frequency of the necessary purges depends on the characteristics of the cell as well as the operating cycles and can range from several seconds to several minutes.
One of the operating characteristic of such cells is also to leave, at the outlet of the anode circuit, a residual quantity of unconsumed hydrogen which is thus lost if the elimination of water, nitrogen and impurities is carried out by periodic purges.
So as to avoid a loss of hydrogen, the prior art ensured a recirculation of the mixture from the outlet of the anode compartment to reinject it at the inlet of the same compartment of the cell. Such a reinjection ensures continued mixing of the gases and improves the operation in the presence of impurities and nitrogen but however does not solve the problem of recovery of the water which is to be recovered so as to promote the hydraulic balance of the operation, particularly to ensure moistening and/or cooling of the cells.
The choice of proceeding with recirculation of the mixture requires using particular technical means and, particularly, the presence of a circulator which constitutes a rotary machine that is relatively complicated and subject to sensitive operating conditions, particularly in the presence of liquid water.
Such a rotary machine constitutes costly equipment, requiring substantial maintenance and, as a result, substantially increasing the purchase price as well as the operating cost of a fuel cell.
Moreover, it has been noted that the recirculation of mixture does not always improve the conditions effective to eliminate water, particularly when the speed of the principal gaseous mixture is not sufficient. This drawback could be overcome at least in part by subjecting the mixture to more rapid recirculation, but then the problems inherent in the presence of the circulator proportionately increase.
No matter what the operational conditions described above, it is moreover always necessary to have a particularly effective phase separator so as to be able to ensure the separation of the water. However, such a separator constitutes a relatively burdensome accessory, occupying a substantial volume and giving rise to problems of inertia in the case of stopping or starting the operation of a fuel cell.