Influence of DC Hollow Cathode H_2 and CH_4/H_2 Plasma Processing Conditions on the Hydrophobic Behavior of Carbon Fiber Paper used as Gas Diffusion Barrier Layer

摘要

Significant improvement on the hydrophobicity of the Carbon Fiber Paper (CFP) Gas Diffusion Barrier Layer used in PEM Fuel Cell was achieved using DC Hollow Cathode Plasma Technique. Influence of the plasma processing conditions such as H_2 and CH_4 /H_2 gas mixture, gas flow rates, processing time, and discharge current were identified. To quantify the hydrophobicity, water contact angle (θ_w) measurements via sessile drop method were conducted. As-received untreated CFP and vacuum treated CFP formed no contact angle and both exhibited θ w =0. After H_2 plasma treatment at 50 sccm and 26 mA discharge, the CFP yield θ_w= 108.45°. At 50 sccm H_2 flow rate and varying CH_4 flow rate (5 sccm-20 sccm), measured θ_w values range from 107.71° to 137.25°. SEM images revealed etching of the CFP surface for the H_2 treated samples. Partial etching and deposition effects were observed upon addition of CH_4. This was attributed to the polymerization of hydrocarbon compounds accompanied by ion etching. AFM analysis revealed a significant difference between the surface rms roughness of the etched surfaces obtained with H_2 only and CH_4 /H_2 plasma. Using Micro-Raman Spectroscopy, intensity, position and FWHM of the D band peak at 1350 cm~(-1) and G band peak at 1585 cm~(-1) of the untreated CFP were compared against the plasma processed CFP substrates.