Neutron Radiography of PEM Water Electrolysis Cells

In the past neutron radiography has been successfully applied to investigate the water transport behavior in polymer electrolyte fuel cells and its influence on overall cell performance [1-2]. The same technique can be also used to visualize the gas and water transport inside working polymer electrolyte membrane (PEM) electrolyzers.

                While it is obvious that under operating conditions, a two phase flow of water and its gaseous splitting products occurs inside the porous layers and the flow channels, it is not clear to what extent this can influence overall electrolysis cell performance. In theory gas bubble formation can block the catalyst surface on the anode, decreasing the overall efficiency In addition, the resulting inhomogeneity of the current density over the active area can lead to a local overheating and membrane damage. Strong attenuation of the neutron beam inside liquid water, as compared to typical electrolyzer materials like steel and titanium, makes neutron radiography a perfect technique to investigate these phenomena.

                Neutron radiograms of PEM electrolysis cells (1 cm² active area) were obtained at varying working parameters. Our experimental setup is designed to provide maximal imaging capabilities at simulated local conditions which can occur in real scale devices. Special attention will be put to the water – gas transport perpendicular to the porous layer. Figure 1 shows the typical patterns with gradients of water thickness being little dependent on the operating conditions.

                This presentation is intended to provide the fundamentals about both the experimental possibilities as well as the water/gas transport behavior during PEM electrolysis cell operation, stimulating the development of numerical models describing this complex system.

References

[1] P. Boillat, P. Oberholzer, A. Kaestner, R. Siegrist, E.  H. Lehmann, G. G. Scherer and A. Wokaun, J. Electrochem. Soc. 159, F210-F218 (2012).

[2] P. Boillat, G. Frei, E.H. Lehmann, G.G. Scherer,  A. Wokaun, Electrochem. Solid-State Lett. 13(3), B25-B27 (2010).

Figure 1. Image recorded for the dry cell (section A) and the cell with flooded anode (section B). The difference in horizontal and vertical scales results from the use of a tilted detector setup [1].

Section C shows images of cells taken at increasing current density (denoted in bottom - right corner [A cm^-2]) with the same configuration as in section A and B. The pixel values have been divided by reference values of the cell with flooded anode – white pixels on anode side corresponds to gas, while black on the cathode side to water.