Plasma Surface Modification of Carbon Electrodes for Polymer Electrolyte Fuel Cells (EFC 2005-86319)

Carbon electrodes are one of the key materials in polymer electrolyte fuel cells (PEFC), or proton exchange membrane fuel cells (PEMFC). The electrodes should allow water or water vapor, which is produced by the redox reactions, to flow out of the cells efficiently. In the meantime, the catalysis reactions are not interfered. In this study, the carbon electrodes for PEMFC have been modified in terms of the hydrophobic and hydrophilic properties by plasma irradiation. The process utilized inductively coupled plasma (ICP) driven by applying radio frequency (rf) power on an induction coil. A pure Ar, $O2$⁠, and $Ar∕O2$ gas mixture were used as the plasma gas. Only one side of the sample has been treated. The material properties of the plasma treated and untreated carbon electrodes were investigated by Raman spectroscopy, Fourier transformed infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). FTIR results show the plasma treatments effectively modified the functional groups on the carbon surface, and therefore the hydrophilic and hydrophobic properties of the surface. SEM and Raman spectra data suggested that the ion bombardment during plasma treatments alters the surface morphology and carbon bonding structures of the samples, which also result in a hydrophilic surface. The treated carbon electrodes were used as cathodes and have been packed with commercial carbon anodes and catalyst coated membrane to form $5cm×5cm$ fuel cells. The current-voltage polarization curves of these fuel cells were measured and compared. The test results show the feasibility of improving the cell performance by plasma treated electrodes. The feasibility of altering the hydrophobic and hydrophilic properties by plasma treatment has been demonstrated. The capillary effect due to the unbalanced hydrophilicity between the treated and untreated electrode surfaces may be responsible for the improved cell performance.