Effects of Surface Roughening of Nafion® on Electrode Plating, Mechanical Strength, and Cell Performances for SPE Water Electrolysis

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Abstract
The most suitable conditions for surface‐roughening Nafion membranes used as solid polymer electrolytes (SPE) were examined for their effect on electrode plating, mechanical strength, and cell performance for water electrolysis. Though the surface roughening by sand‐blasting caused a considerable lowering of mechanical strength and had no influence on the roughness factor of the platinum electrode plated on the membrane surface, it was very effective for enlarging the reaction interface between SPE and the electrode and for forming a porous structure of the electrode, which facilitated the release of evolving gases from the electrode. The formation of porous structure was very important for the electrolysis at higher current density, because it prevented decrease in mechanical strength of the SPE‐electrode composite due to void formation at the interface, increase in resistance due to gas bubbles, and decrease in current efficiency due to permeation of produced gases through the membrane. In addition, surface roughening by sputteretching was conducted. The etching at 400W for 30s under a mixed gas gave a fine roughness of ca. 6000Å, on which metal particles with almost the same dimensions as the roughness were deposited. The finely controlled roughening also caused a decrease in mechanical strength but could not improve the cell voltage, because the reaction interface between the SPE and the electrode was not enlarged, showing that a roughness of 3–5 μm was more suitable.

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