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Experimental study on proton exchange membrane (PEM) electrolyzer was carried out focusing on the effect of pore structural properties of current collectors, such as porosity and pore diameter. Various titanium (Ti)-felt substrates with different porosities and 2 pore diameters (measured by capillary flow porometry) were used as the anode current collector. Results show that when the mean pore diameter of the current collector was larger than 10 μm, the electrolysis performance improved with decreasing pore diameter. In contrast, changes in porosity had no significant effect on the cell performance when the porosity exceeded 0.50. The flow pattern of two-phase flow in the flow channel was discussed in terms of its relationship to bubble size and to pore diameter of the current collector. Finally, correlation between the calculated membrane resistance and the measured pore diameter of the current collectors suggest that larger bubbles generated from larger pores tend to become long bubbles in the channel, thus hindering the water supply to the membrane.

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Polymer electrolyte-based unitized reversible fuel cells (URFCs) combine the functionality of a fuel cell and an electrolyzer in a single device. In a URFC, titanium (Ti)-felt is used as a gas diffusion layer (GDL) of the oxygen electrode, whereas typical carbon paper is used as a GDL of the hydrogen electrode. Different samples of Ti-felt with different structural properties (porosity and fiber diameter) and PTFE content were prepared for use as GDLs of the oxygen electrode, and the relation between the properties of the GDL and the fuel cell performance was examined for both fuel cell and electrolysis operation modes. Experimental results showed that the cell with a Ti-felt GDL of 80μm fiber diameter had the highest round-trip efficiency due to excellent fuel cell operation under relatively high-humidity conditions despite degradation in performance in the electrolysis mode.