Nafion®/介孔二氧化矽複合材料之質子交換膜應用於直接甲醇燃料電池

Nafion®/Mesoporous Silica Composite Membranes as Proton Exchange Membrane for DMFC

楊巧薇(Ciao-Wei Yang)

指導教授 ： 鄭淑芬

國立臺灣大學/理學院/化學研究所/博士(2017年)

https://doi.org/10.6342/NTU201700272

摘要

本研究合成介孔二氧化矽奈米顆粒分別為SBA-15和MSN，且利用溶劑揮發法將這些奈米顆粒材料混入Nafion®中形成複合膜。我們用粉末X光繞射、氮氣吸脫附、熱重分析、元素分析和掃描式電子顯微鏡鑑定這些材料的物理化學性質，且為了比較奈米顆粒含量、有無孔洞引導試劑和有無磺酸官能基對複合膜的影響，並測量其複合膜的甲醇穿透、質子傳導和電池性能。本研究發現孔洞引導試劑存在於孔洞中會阻擋甲醇穿透到陰極，但是不同的孔洞引導試劑 (P123和CTMABr)對於質子傳導會有不同的效果。至於帶有磺酸官能基的介孔奈米顆粒材料混入Nafion®中，則可以有效的幫助質子傳導。
為了觀察孔洞引導試劑對複合膜的影響，分別合成含有界面活性劑 SBA-15奈米顆粒 (S-SBA-15n) 和萃取過不含界面活性劑的SBA-15奈米顆粒 (Ex-SBA-15n) 兩種，所合成的複合膜命名為x%-S-SBA-15n和x%-Ex-SBA-15n (x%：材料對Nafion®的重量百分比；S：界面活性劑在孔洞中；Ex：界面活性劑被萃取)。此研究觀察到P123的醚官能基可以幫助質子傳導，因此含介面活性劑的S-SBA-15n系列的複合膜擁有較高的質子傳導和較低的甲醇穿透，尤其將其組裝成單電池時，發現5% S-SBA-15n複合膜擁有最高的功率密度大約為117 mW cm-2，比recasting膜高出80%並且比商業用的膜Nafion® 117高出23%。
我們也合成介孔二氧化矽奈米粒子 (MSNs)，且將此材料混入Nafion®中形成複合膜，一樣是為了觀察孔洞引導試劑對複合膜的影響，所合成的複合膜命名為x%-S-MSN和x%-Ex-MSN。結果顯示S-MSN複合膜的甲醇穿透會低於Ex-MSN複合膜是由於CTMA+存在於S-MSN的孔洞中，但是CTMA+為四級銨鹽會降低質子傳導率，所以S-MSN系列複合膜比Ex-MSN系列複合膜擁有較低的質子傳導，其中5%-Ex-MSN複合膜擁有較高的功率密度約131 mW cm-2，比recasting膜高出2倍並且比商用Nafion® 117高出36%。
我們將SBA-15n 和MSN所形成的複合膜做比較，我們發現含有介面活性劑存在於孔洞中皆可有效地降低甲醇穿透，其中更發現Ex-MSN擁有最高的質子傳導和功率密度，因Ex-MSN含有較多的矽醇基(silanol group)於材料表面。
將Ex-SBA-15n的樣品官能基化，分別帶有5%和10%的丙基磺酸官能基，並將其混入Nafion®中後，觀察磺酸官能基對複合膜的影響。複合膜含有低負載量的磺酸Ex-SBA-15n可以幫助質子傳導但也增加甲醇穿透，其中5%-Ex-SBA-15n-10% -SO3H擁有最高的功率密度約為133 mW cm-2，比recasting膜約高出2倍並且比商用Nafion® 117高出39%。
也將Ex-MSN的樣品官能基化，分別帶有4%和10%的丙基磺酸官能基，並將其混入Nafion®中後，希望能更有效的提升質子傳導並提升功率密度。但卻無法有效地提質子傳導和功率密度，仍然是5%-Ex-MSN複合膜擁有較高的功率密度約131 mW cm-2。
同時也將S-SBA-15n的樣品官能基化，分別帶有4%和12%的丙基磺酸官能基，並將其混入Nafion®中後，希望能提高質子傳導也同時能降低甲醇穿透。複合膜含有低負載量的磺酸S-SBA-15n可以幫助質子傳導但也降低甲醇穿透，其中1%-Ex-SBA-15n-4%-SO3H擁有最高的功率密度約為120 mW cm-2，比recasting膜約高出1.8倍並且比商用Nafion® 117高出25%。

關鍵字

直接甲醇燃料電池 ； SBA-15 ； MSN ； Nafion ； 甲醇穿透 ； 質子傳導 ； 電池特性

並列摘要

Nanoparticles of mesoporous silica including SBA-15 and MSN were prepared and loaded into Nafion® to form composite membranes by solvent casting method. The physico-chemical properties of these nanoparticles were examined with powder-XRD, N2 sorption, TGA, EA and SEM. The methanol permeability, proton conductivity, and cell performance of the resultant composite membranes were compared in terms of the amount of nanoparticles, whether the pore-directing agents were removed and the influence of extra sulfonic acid groups. The pore-directing agents in the pores of mesoporous silica were found to resist methanol crossover to cathode. However, mesoporous silicas with different kinds of pore-directing agents (P123 and CTMABr) had different influences on proton conductivity.
The SBA-15 nanoparticles containing P123 surfactants (S-SBA-15n) and that extracted with ethanol (Ex-SBA-15n) are used in order to see the effect of pore-directing agent on the performance of resultant composite membranes. The as-prepared membranes were denoted as x%-S-SBA-15n, and x%-Ex-SBA-15n (x%: weight percentage of material relative to NafionⓇ; S: surfactant within mesopores; Ex: surfactant extracted). The ether groups on P123 were found to assist proton transfer. Consequently, higher proton conductivity and lower methanol penetration were obtained on the composite membranes with S-SBA-15n than Ex-SBA-15n. The single cell assembled with 5%-S-SBA-15n composite membrane gave higher power density of 117 mW cm-2 at 60˚C than 5 wt%-Ex-SBA-15n, which was about 80% higher than the cell with recasting membrane and 23% higher than that with Nafion® 117.
Mesoporous silica nanoparticles (MSNs) were also prepared and mixed in Nafion® to form composite membranes. The MSNs containing CTMA+ surfactants (S-MSN) and that extracted with ethanol (Ex-MSN) are used in order to also see the effect of pore-directing agent on the performance of resultant composite membranes. The result showed that methanol permeability of S-MSN composite membranes was lower than Ex-MSN, attributing to that the mesopores of S-MSN was filled with CTMA+. However, CTMA+ was a quaternary ammonium salt, which would resist proton transfer. Consequently, lower proton conductivity was obtained for the S-MSN composite membranes than Ex-MSN. The single cell assembled with 5 wt%-Ex-MSN/Nafion composite membrane gave highest power density of 131 mW cm-2 at 60˚C, which was about 2 times higher than the cell with recasting membrane and 36% higher than that with Nafion® 117.
The composite membranes of SBA-15n and MSN were compared. Our lab found that both of pore-directing agents in the mesopores (P123 and CTMA+) can effectively improve the methanol permeability and Ex-MSN composite membranes have the highest proton conductivity and power density due to a large amount of silanol group on the surface of Ex-MSN.
The S-SBA-15n samples were also functionalized with 4% and 12% propylsulfonic acid groups to form composite membranes in order to examine the influence of sulfonic acid groups. The sulfonic acid groups can assist proton transferring and P123 decrease the methanol permeability at low loading of inorganic fillers. The composite membrane of 1%-S-SBA-15n-4%SO3H had the highest power density of 120 mW cm-2 at 60˚C, which was about 1.8 times higher than the cell with recasting membrane and 25% higher than that with Nafion® 117.
The Ex-SBA-15n samples were functionalized with 5% and 10% propylsulfonic acid groups to form composite membranes in order to examine the influence of sulfonic acid groups. The sulfonic acid groups can assist proton transferring but increase the methanol permeability at low loading of inorganic fillers. The composite membrane of 5%-Ex-SBA-15n-10%-MPTMS-SO3H had the highest power density of 133 mW cm-2 at 60˚C, which was about 2 times higher than the cell with recasting membrane and 39% higher than that with Nafion® 117.
The Ex-MSN samples were also functionalized with 4% and 10% propylsulfonic acid groups to form composite membranes in order to examine the influence of sulfonic acid groups, expecting that the sulfonic acid groups could assist proton transferring. However, the highest proton conductivities and power density was obtained by 5%-Ex-MSN composite membrane.

並列關鍵字

DMFC ； SBA-15 ； MSN ； NafionR ； methanol permeability ； proton conductivity ； cell performance

參考文獻

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