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1 Jurnal f the Krean Ceramic Sciety Vl. 45, N. 2, pp. 119~125, Synthesis f Inrganic-Organic Cmpsite Electrlyte Membranes fr DMFCs Eun Hyung Kim, Gug-H Yn, Sung Bum Park, Myung-Hn Oh, Sungjin Kim, and Yng-il Park Schl f Advanced Materials & Systems Engineering, Kumh Natinal Institute Technlgy, Gumi , Krea (Received January 14, 2008; Accepted February 22, 2008) DMFC»-» w w w ½ xá yá Á zá½ Á œ w lœw ( ; ) ABSTRACT The FAS(Fluralkylsilane)/Nafin inrganic-rganic cmpsite electrlyte membrane was successfully fabricated thrugh sl-gel methd. The FAS having hydrphbic functinal grup and silanl ligands is impregnated in Nafin F membrane t reduce methanl crssver. The prepared FAS/Nafin inrganic-rganic cmpsite electrlyte membrane cnsist f the hydrphbic FAS-derived silicate nan-particles and Nafin F matrix shwed decrease f methanl crssver and reductin f humidity dependence withut large sacrifice f prtn cnductivity. The micrstructural analysis f the cmpsite membranes was perfrmed using FESEM and FT- IR. And the effect f the incrpratin f the hydrphbic FAS-derived silicate nan-particles int Nafin F membrane was investigated via slvent uptake, membrane expansin rate, humidity dependency f prtn cnductivity and cntact angle measurement. Key wrds : Direct methanl fuel cell, Methanl crssver, Sl-gel methd, FAS(Fluralkylsilane) 1. { y, p ful {»» ƒwš š» y» e w ƒ ù š, ƒ š { w» rw w š x œ e v w. k w k (Direct Methanl Fuel Cell, DMFC) k ƒ, š w ƒ. w œ v ƒ x y» l g w v k (ande) œ w» w œ ƒ, l e w { x œ e w. 1,2) w x { œ e k y j» w ƒ w w w. k»yw y ƒ û k y j v w šƒ (Pt) Crrespnding authr : Yng-il Park yipark@kumh.ac.kr Tel : Fax : š w (Plymer Electrlyte Membrane Fuel Cell, PEMFC) w, k y w COù HCO w v x w» y» w l (Ru) w g w w. 3,4) w, w š mw (ande) k œ» (cathde) w k j (methanl crssver) x w g w jš ƒ. x 3~5wt% 5-7) k û w. k j j» w Nafin F š w matrix w w ƒ wy mw p š, ƒ t silica - (sl-gel) w Nafin» ü en k ü w ù mw k n w j ƒ w š. Nafin/silica w w Nafin slutin w Nafin/silica w w w Nafin F (mdificatin) w ù. Nafin w silica en k n w 119

2 김은형 윤국호 박성범 오명훈 김성진 박용일 120 Fig. 1. Suggested chemical reactin and prperties f the FAS additive. 성능 증가의 긍정적인 효과를 나타내었으나 고농 도 메탄올 연료 적용 시에는 여전히 심각한 전위차의 감 소를 나타내며 게다가 silica의 투입량에 비례하여 프로톤 전도도가 급속히 저하하는 문제점이 지적되고 있다. Jung 등 은 tetraethxysilane(teos)을 사용하여 졸-겔법을 통해 Nafin/silican xide hybrid 막을 제조하여 DMFC에 응용 한 결과, 100 C 이하의 실사용 온도영역에서 Nafin 막 중에 침투한 silica에 의한 프로톤 전도성의 저하현상을 보고하였다. 본 연구에서는 메탄올 크로스오버 현상을 감소시키기 위해 직접 메탄올 연료전지의R전해질 막으로 일반적으로 사용되는 Dupnt사의 Nafin 112 막을 모재로 기존의 연구에서 silica의 침투원료로 사용되어 오던 silicnalkxide계열 대신에, 강한 발수성 작용기를 가지는 FAS(fluralkylsilane)계열의 (Heptadecaflur-1,1,2,2-tetrahydrdecyl)triethxysilane 를 졸-겔법을 이용해 합성하여 FAS/Nafin 복합막을 제조하였다. FAS는 NafinR 막 내 부의 in cluster와 같은 빈 공간에 우선적으로 침투하여 가수분해 및 중축합반응을 거쳐 FAS로부터 유도된 silicate 나노입자를 형성시킴으로써, 무기재료의 안정성과 유기재 료의 기능성을 함께 갖춘 무기-유기 나노복합체가 제조된 다. 침투한 FAS 용액의 기본 반응과 형성되는 작용기의 특성을 Fig. 1에서 나타내었다. NafinR 막의 in cluster 내에 형성된 silicate 나노입자는 고체 입자 자체로 in cluster 내부 공간을 부분적으로 막음으로써 공기극으로의 메탄올 이동을 억제하는 장애물로 작용한다. 동시에 나노 입자 표면에 강력한 발수성 작용기를 유지함으로써 메탄 올의 이동을 더욱 효과적으로 저하시키며, 나노입자 표면 에 생성된 hydrxyl grup 즉, silanl(si-oh) 작용기는 저 습도 환경에서도 막의 건조를 방지하는 역할을 하기 때 문에 100 C 이상의 고온 환경에서 사용할 수 있는 가능 성을 확보할 수 있다. 본 연구에서는 제조된 복합막의 미 DMFC 8) 세구조 및 결합구조, 용매 함유율(slvent uptake)과 막 팽 창률(membrane expansin rate) 등을 측정하였으며, 상대 습도 변화에 따른 이온 전도도 변화를 측정하여 막의 습 도의존성을 확인하였다. 2. 실험 방법 복합 전해질 막의 제조 막은 보관을 목적으로 일반적으로 Na 의 형태로 공급되므로 불순물 제거 및 이온 전도도 향상을 위해 H 를 갖는 술폰산기(-SO H)로 변환시켜주는 전처리 과정이 필요하다. 먼저 90 C의 5 wt% H O 수용액에서 2.1. NafinR ) 한국세라믹학회지 Fig. 2. Flw diagram fr the preparatin f the FAS/Nafin cmpsite membrane.

3 DMFC»-» w w w z wš 90 C 1 w z 0.5 M H 2 SO 4 90 C 1 wš x z 90 C 1 w. 10,11) FAS/ Nafin w w Fig. 2 ùkü. FAS 1:5 (v/v) (heptadecaflur-1,1,2,2-tetrahydrdecyl)triethxysilane (GELEST, INC.) : prpanl Nafin F z 1:2 (v/v) water: methanl 3 «Nafin F ü in cluster FASƒ ƒ w w mw silicate ù x j w. 80 C 24 1 z 110 C 2 2 jš 0.2 M H 2 SO 4 1 y k q w 50 C k w. 8) FAS/Nafin w w FAS w wt%, w p w z FAS we j Nafin F 112 p x w w w p sƒ w FAS/Nafin w FESEM(Field Emissin Scanning Electrn Micrscpy, JSM-6500F, JEOL Ltd.) EDS(Energy Dispersive X-ray Spectrmeter, INCA Energy, OXFORD) mw w Si(silicn) s d w FAS l silicate s y w š, FT-IR(Furier Transfrm Infrared Spectrmeter, VERTEX-70, ERUKER OPTICS) w Nafin F 112 FAS/Naifn w ü w y w. t y w» w ƒd Cntact Angle Meter (DM 700, Kywa Interface Science C. Ltd.) w d w. š w w e»(-so ÃH+ 3 )ƒ š š», ü nx w t x ¼. ü (interstitial phase) w» Nafin F 112 FAS/Nafin w w q d w k en w. w q d, w ( ) k k j y w k 1.56 M(5 wt%) k 12) š k 20 M(50 ml%) k w. ƒ w w y w» w w Nafin F 112 w ƒƒ «w q (W wet ) d 70 C» 24 k k (W dry ) d w w w (slvent uptake) w. Slvent uptake (%) = W wet W dry W dry», W wet q k š W dry k. q w d w ƒ w w q (A wet ) d w w q (membrane expansin rate) w. Expansin rate (%) = A wet A dry A dry», A wet q k š A dry k. ƒ y yw, Nafin F 112 w FAS/Nafin w 70 C š k k y g d w. AC Impedance analyzer(slartrn, SI 1287, SI 1260, ULVAC KIKO Inc.) w š g 0.1 ~ 10 Hz q 7 10 mv ƒ ¼ w w Nyquist plt l w. 3. š Nafin F 112 w FAS/Nafin w SEM EDS d Fig. 3 ùkü. Fig. 3. SEM images and EDS mapping images fr the element Si (represented by white dts) f the membranes crsssectin (a) Nafin F membrane, (b) FAS/Nafin cmpsite membrane (FAS cntent = wt%). 45«2y(2008)

4 122 ½ xá yá Á zá½ Á Fig. 5. Cntact angles f membranes measured by water drplet. Fig. 4. FT-IR spectra f Nafin F membrane and FAS/Nafin cmpsite membrane. FAS Si, O, C, H, F š Nafin F C, F, O, S, H. ƒ w FAS Si ƒ û š, Si w mapping w FAS l ƒ ü ³ w x. Si ƒ p r š ³ w s, Nafin F ü w 1nm j» channel 4nm j» in cluster ü FAS l 13) silicate ù ƒ œ. (H + ) v m k m in cluster ü ƒ w w k j» w ƒ. Fig. 4 Nafin F 112 FAS/Nafin w FT-IR rp. 1200, 1147, 1060, 980, 970 cm 1 e peak Nafin F ùkù x peak 14) FAS/Nafin w w ùkû. FAS ƒw ƒ peak Nafin F 1 e15) š, FAS/Nafin w d. 780 cm 1060 ~ 1120 cm e16,17) 1 ùkù silxane(si-o-si) peak mw w ü silicate y w, 870 cm 1 e8) ùkù C-H w» FAS peak. 900 cm 1 e16) FAS alkyl grup (-OC 2 H 5 ) ƒ w z hydrxyl grup(-oh) y ü (H 2 O) ww g w w. Fig. 5 t y w» w wwš 30 ƒ w z t w ƒ d. ƒ 0 < θ<90 t e (hydrphilic), θ>90 (hydrphbic) p. Nafin F ƒ 72 t e w FAS/Nafin w ƒ 120 e ƒ j ƒ. w t k n ü t w j d. w k p sƒ w, MEA w w š, š ( inmer) š w. Nafin w j» w 5 wt% Nafin slutin w w w yw w. w ƒ» ƒ w FAS/Nafin w t p k n j» w Nafin š w. Nafin slutin w MEA w, w w w w Nafin F w w w d w w yw ƒ œ v w. Nafin F 112 w FAS/Nafin w uptake w ( ) k w d w. Fig. 6 Nafin F FAS/ Nafin w w ƒw 1 z y w. ƒƒ w w Nafin F w FAS/Nafin w û ƒ š, k ƒ ƒw w Nafin F w w ƒ ù kû. Nafin F» w w 17.35%, FAS/Nafin w 0.6 ù û» w w wz

5 DMFC»-» w w w 123 Fig. 6. Slvent uptake f Nafin F membrane by incrpratin f FAS in (a) water, (b) 1.56 M methanl slutin, (c) 20 M methanl slutin. ƒ M k w Nafin F» w 22.45% w 0.24 û. 20 M k w Nafin F 78.74% w w 0.46 û w ƒ. w wew z 24 ù w y z w Nafin F w Fig. 7. Membrane expansin rate f Nafin F membrane by incrpratin f FAS in (a) water, (b) 1.56 M methanl slutin, (c) 20 M methanl slutin. FAS/Nafin w ƒƒ w û w ƒ. in cluster ü FAS» ƒ silicate ù k w, silicate ù ƒ cluster œ 45«2y(2008)

6 124 ½ xá yá Á zá½ Á k ww w w» d. Fig. 7 Nafin F 112 FAS/Nafin w ( ), 1.56 M k, 20 M k ƒƒ w y y, q d w w w w. Nafin F» q ƒ w ƒƒ 14.67%, 24.67%, 74.32% q ƒ, wt% FAS we ƒ FAS/Nafin w Nafin F w w 0.85, 1.56 M k w 0.23, 20 M k w 0.35 û» q ƒ. w q we 5 w š, k ƒ ƒw ƒ w. w FAS/Nafin w w Nafin F w ƒ w û q ƒ. mw Nafin F FAS ƒ k n wz ƒ. Nafin F 112 FAS/Nafin w w d Fig. 8 ùkü. 70 C, 99% d Nafin F S/cm ƒ w Nafin F 0.1 S/cm w. Nafin F ƒ FAS w k FAS/Nafin w û ùkþ. Nafin F ü w in cluster m k m w š š. 18) cluster ü silicate ù ƒ k w w w k n Fig. 8. Cnductivity f Naifn F membrane and FAS/Nafin cmpsite membrane under different relative humidity at 70 ± 1 C. w z ƒ ù, ww» FAS/Nafin w ƒ w. k w w w z w mw w û k n w w ƒ. w ƒ w y, Nafin F FAS/Nafin w û, ƒ 50%» û Nafin F w ƒ. in cluster ü x FAS l ù p ƒ., ù» FAS alkyl grup(-oc 2 H 5 ) ƒ w z hydrxyl grup(-oh), silanl(si-oh)» ƒ hydrxyl» (H 2 O) ww g w w.» Nafin F w ƒ j w» š w w w 80 C w w w w wš 100 C š y w ƒ y w. 4. k k j x j» w w Nafin F 112 w» ƒ silane FAS sl-gel mw Nafin F ü we g FAS/ Nafin»-» w w w. FAS l silicate ù ƒ ³ w y w., 1.56 M(5 wt%) k, 20 M(50 ml%) k w q d, FAS/Nafin w Nafin F 112 w û ùkü. Nafin F in cluster ü silicate ù ƒ š cluster œ k ww w t FAS» w p k n w j w ƒ». w 50% w w ƒ silicate ù t hydrxyl grup, silanl(si-oh)»ƒ w k. š (> 100 C) p k n z w. w FAS ƒw FAS/Nafin w w w wz

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