Monitoring of the phosphoric acid concentration in a fuel cell membrane production line


In fuel cells, hydrogen and oxygen react in a controlled manner to efficiently generate electrical power and heat.

The picture below shows the fuel (e.g. natural gas) entering the reformer, where it is transformed into hydrogen (orange spheres). At the anode catalyst, hydrogen is split into protons (H+) and electrons (e-).

The membrane of a fuel cell is permeable for protons, but not for electrons. Thus, the electrons flow through the external circuit - including a power consumer such as a motor - and return to the cathode side of the fuel cell. On the cathode, oxygen gas (blue spheres) takes up electrons and protons to form water - the primary exhaust emission of a fuel cell. In order to achieve a reasonable power level, many separate membrane electrode assemblies must be combined to form a fuel-cell stack.

The ProcessLab analysis system described here records and documents the concentration of the phosphoric acid in the reservoir. The concentration has to be kept within a defined range (± 2% of a target value). This guarantees a constant quality of the membrane. During the stretching of the membrane this concentration will increase, so the solution in the reaction trough has to be diluted with water to reach a specified concentration. The combination of analytical method, control of the production line, as well as the intuitive handling via the user interface allows complete process control.