A new stack design for closed loop fuel cell applications

Kurzfassung

In mobile and portable applications electrical energy is normally supplied by secondary batteries since the use of electricity from stationary power plants required grid connection. Unfortunately the specific energy and the energy density of those energy storage systems are rather low. Therefore fuel cells are an interesting option to overcome the limitation of energy density. However fuel cells need a continuous supply with fuel and oxidant. At some special applications, like space crafts, autonomous long distance aircrafts or stand-alone power supplies, an external refuelling is not possible or feasible. In that case the reactants must be regenerated by water electrolysis and a reversible fuel cell system is needed. Two different designs of reversible fuel cell systems are known. First a reversible fuel cell system which has two separate stacks for both electrolysis and fuel cell mode. The second type is the unitized reversible fuel cell using only one stack for both. While the first system is characterized by high masses and volumes the second one shows lower performance because of the reduced activity of the catalyst mixture and the compromises required to accommodate two functions in one reactor. The new stack design uses features of both systems simplifying the set-up. Only one stack is used but the electrolysis cells and fuel cells are galvanically separated. The commonly used cooling compartments of generic fuel cell stacks are used for integrating cells for electrolysis. Therefore in each working mode the best performance can be reached and the overall efficiency can be increased without the need for additional stacks.