Hydrophilic treatment of carbon paper for anodic porous transport layer in proton exchange membrane water electrolyzer

Abstract

We have studied a method to lower a price and to enhance an electric contact of proton exchange membrane (PEM) water electrolyzer by using hydrophilic carbon paper as anodic porous transport layer (PTL). Hydrophobized carbon papers owing to an anti-oxidation process were turned hydrophilic by facile plasma treatment-1% Nafion solution impregnation in order to use a carbon paper as an excellent anodic PTL. We introduced two step hot-pressing process to strengthening the adhesion between catalyst layer and Nafion membrane when we manufactured membrane electrode assembly (MEA) by hot-pressing carbon papers as anodic and cathodic PTLs on catalyst coated membrane. A total charge transfer resistance of electrolyzer with hydrophilic carbon paper was 0.182Ω cm², and that was 0.035Ω cm² smaller than one with hydrophobic carbon paper. The cell voltages of PEM water electrolyzers with hydrophobic and hydrophilic carbon paper as an anodic PTL at the current density of 1 A cm⁻² were 1.755 V and 1.716 V. The water flow rate played an important role in the performance of PEM water electrolyzer in case of hydrophobic carbon paper, but water was sufficiently supplied even at a low flow rate (20 mL/min) to stabilize the cell voltage which was changed within the range of ± 0.025 V in case of hydrophilic one. Prepared PEM water electrolyzer with the hydrophilic anodic PTL displayed desirable performance; initial voltage at 1.2 A cm⁻² of current density, at 80 °C was 1.76 ± 0.02 V, and finally measured voltage 1.84 ± 0.02 V after 6270 h of testing.