DMFC용 분리막을 위한 광가교 가능 sPPO 적층막에 관한 연구

Abstract

본 연구에서는 poly(diallyl dimethyl ammonium chloride) (PDDA) 와 sulfonated polymer 혼합 전해질을 Nafion 212 표면에 LbL 기법으로 교대로 쌓아 LbL 다층 전해질막 (PEM)을 제작하였다. Sulfonated polymer 혼합 전해질은 높은 degree of sulfonation (DS)의 sulfonated poly (phenylene oxide) (sPPO)와 azide group을 포함한 polystyrene sulfonic acid가 추가적으로 이루어져 있다. sPPO는 trimethylsilyl chlorosulfonate를 sulfonation agent로 사용해서 합성되었다. Azide group을 포함한 polystyrene sulfonic acid copolymer는 styrene, styrene sulfonic acid, chloromethylstyrene 단량체를 이용해 중합했으며, azide group을 치환시키는 반응을 통해 제작하였다. 기계적, 화학적 안정성을 높이기 위해 UV 광가교로 LbL 전해질막을 가교시켰다. 다층막의 적층비를 FTIR로 확인했으며, 박막의 두께는 전해질 수용액에 첨가된 염의 농도가 증가할수록 두꺼워졌다. 메탄올 투과도는 0.5M NaCl이 첨가된 sPPO blend 막의 적층 횟수가 증가할수록 감소하였다. 수소 이온 전도도가 소량 감소하였지만, 메탄올 투과도가 40%이상 감소해서 LbL 전해질막의 상호 비교를 위한 선택도는 Nafion 117에 비해 2.63배 Nafion 212에 비해 1.5배 증가하였다. 비록 UV 광가교 과정 중 UV 광에 의해 수소 이온 전도도가 감소하는 것을 발견했지만 그럼에도 불구 하고 높은 선택도는 DMFC 용 전해질막으로의 성능향상 가능성을 보여주었다.|Multilayered composite polyelectrolyte membrane (PEM), we prepared by LbL method by alternating deposition of poly(diallyl dimethyl ammonium chloride) and sulfonated polymer mixture on the surface of Nafion212. The sulfonated polymer mixture contains highly sulfonated poly(phenylene oxide) (sPPO) and additional polystyrenesulfonic acid copolymer containing azide moiety. sPPO was synthesized by sulfonation of PPO with trimethylsilyl chlorosulfonate. And the polystyrenesulfonic acid copolymer with azide moiety was prepared by terpolymerization of styrene, styrenesulfonic acid, and chloromethylstyrene, and the following azide replacement reaction of the resultant terpolymer. Crosslinked composite membrane was prepared by photochemical crosslinking using UV to give the mechanical and chemical durability to the LbL composite film. The composition ratios of polymer layers were identified using FTIR. Also the layer thickness was shown to increase with the concentration of NaCl in the bath. Methanol permeability of sPPO blend membrane with 0.5M NaCl added was shown to decrease with number of bilayers. Selectivity, a relative comparison value of PEM, was 2.63 fold greater than Nafion 117 and 1.5 times greater than Nafion212. Although the proton conductivity was slightly lower than that of Nafion, a 40% reduction of methanol permeability ultimately leads to an increased overall selectivity. Also it has been found that proton conductivity decreases with UV crosslinking. Nevertheless, this proves that the UV crosslinking method can be applied to other LbL composite films as well as flat fuel cell membranes.; Multilayered composite polyelectrolyte membrane (PEM), we prepared by LbL method by alternating deposition of poly(diallyl dimethyl ammonium chloride) and sulfonated polymer mixture on the surface of Nafion212. The sulfonated polymer mixture contains highly sulfonated poly(phenylene oxide) (sPPO) and additional polystyrenesulfonic acid copolymer containing azide moiety. sPPO was synthesized by sulfonation of PPO with trimethylsilyl chlorosulfonate. And the polystyrenesulfonic acid copolymer with azide moiety was prepared by terpolymerization of styrene, styrenesulfonic acid, and chloromethylstyrene, and the following azide replacement reaction of the resultant terpolymer. Crosslinked composite membrane was prepared by photochemical crosslinking using UV to give the mechanical and chemical durability to the LbL composite film. The composition ratios of polymer layers were identified using FTIR. Also the layer thickness was shown to increase with the concentration of NaCl in the bath. Methanol permeability of sPPO blend membrane with 0.5M NaCl added was shown to decrease with number of bilayers. Selectivity, a relative comparison value of PEM, was 2.63 fold greater than Nafion 117 and 1.5 times greater than Nafion212. Although the proton conductivity was slightly lower than that of Nafion, a 40% reduction of methanol permeability ultimately leads to an increased overall selectivity. Also it has been found that proton conductivity decreases with UV crosslinking. Nevertheless, this proves that the UV crosslinking method can be applied to other LbL composite films as well as flat fuel cell membranes.