The effect of pore structural properties (porosity and pore diameter) of current collectors in proton exchange membrane (PEM) electrolyzers on electrolysis performance was experimentally evaluated by using various titanium (Ti)-felt substrates with different porosities and pore diameters (measured by capillary flow porometry) as the anode current collectors. The current-potential (j similar to Delta V) characteristics were measured, and overpotential analysis was performed based on the j similar to Delta V characteristics and the cell resistance (R-cell) data. The results showed that (1) the effect of the decrease in water supply on the membrane resistance due to produced gas bubbles is limited when the mean pore diameter of the anode current collector is less than 50 imn, but might appear at the concentration overpotential, and (2) enhancing the uniform and sufficient contact between the current collector and the electrode reduces not only the contact resistance but also the activation overpotential. (C) 2012 Elsevier Ltd. All rights reserved.