Preparation and characterization of TiO2 filled sulfonated poly(ether ether ketone) nanocomposite membranes for direct methanol fuel cells - Hong, Ji-Sook.; Kalappa, Prashantha.; Kim, Han-Joo.; Kim, Hyun-Hoo.; Oshaka, Tetsuya.; Park, Jong-Eun.; Park, Soo-Gil.; Son, Won-Keun.