直接甲醇燃料电池用新型质子交换膜的研究
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摘要
燃料电池是一种将燃料和氧化剂的化学能不经燃烧直接转化为电能的发电装置。直接甲醇燃料电池(DMFC)以甲醇为燃料,具有比能量密度高、结构简单、使用方便灵活等特点,在手机、笔记本电脑等可移动电源领域具有广阔的应用前景。
质子交换膜是DMFC的关键材料之一,它起着分隔阴、阳极室和传导质子的双重作用,本论文工作以降低膜的甲醇渗透率和提高膜的使用温度为目标,围绕用于DMFC的新型质子交换膜材料的制备与表征,取得了如下主要进展:
1.采用浓硫酸作磺化剂,通过控制反应时间和温度,制得不同磺化度的磺化聚醚醚酮(SPEEK),磺化度为45～50%的SPEEK在机械稳定性和质子传导率方面能基本满足DMFC的性能要求。电化学研究结果表明,与Nafion~(?) 115膜相比,SPEEK膜的甲醇渗透率明显降低。
2.采用浸渍-烘烤方法制备了新型Nafion/SPEEK/Nafion复合膜,该膜的SPEEK层具有较强的阻甲醇渗透功能,两侧的Nafion层增强了膜与电极催化层的物理化学相溶性,有利于质子在膜与催化层界面传输,降低了膜与催化层的接触电阻。
3.用聚偏氟乙烯(PVdP)和SPEEK共混制膜,所得膜水热稳定性较高。实验表明共混膜的质子传导率随PVdF的含量增大而下降。虽然组成为SPEEK/PVdF=9/1的共混膜质子传导率约为Nafion~(?) 115膜传导率的1/10,但其甲醇渗透量仅是在相同测试条件下Nafion~(?) 115膜渗透量的1/20。
4.制备了Nafion/硅烷和PVdF/硅烷两种有机/无机复合膜,研究结果表明:(1)Nafion/硅烷复合膜有较高的质子传导率。其中,硅掺杂量为5%的由Nafion/正硅酸乙酯(TEOS)-巯基硅烷(SCA-902)制备的复合膜性能良好,由该膜组装的DMFC放电性能在120℃测试时好于Nafion~(?) 117膜组装的DMFC性能。(2)PVdF/硅烷复合膜的质子传导率随温度的变化关系表明,在90～100℃时,质子传导率最高。
A fuel cell is an electrochemical device that converts the chemical energy of the fuel and oxidant directly into electrical energy. Direct methanol fuel cell (DMFC) using liquid methanol as fuel, is promising for portable application such as cell phone, laptop computer and other electronics because of its high energy density, simplicity of structure (no additional equipment such as fuel reformer) and maintenance.The proton-exchange membrane in DMFC is one of the key materials, which plays the roles of separating the fuel from the oxidant and conducting proton. In this paper, the efforts are mainly focused on the preparation and characterization of novel proton-exchange membranes, reducing methanol crossover and increasing the tolerance of temperature for DMFC. The results obtained are mainly as follows:1 Sulfonated poly(ether ether ketone) (SPEEK) samples with different degrees sulfonation have been prepared in concentrated sulfuric acid by controlling the reaction time and temperature. With degrees sulfonation of 45~50%, the SPEEK membranes exhibit higher mechnical stabilities and proton conductivity. Electrochemical voltammetric studies show that these SPEEK membranes have significant lower methanol crossover than Nafion ~(?)115 membrane.2 The Nafion/SPEEK/Nafion (NSN) composite membranes are prepared by immersing the selected SPEEK into the Nafion-containing casting solution in which the SPEEK polymer is used as barrier layer of methanol. The Nafion layeres of both sides of NSN membrane improve the physical and chemical compatibility between the membrane and catalyst layer, facilitating proton transfer in the membrane-electrode interface. As a result, the resistance of MEA is lowed obviously.3 The blend membranes of SPEEK and polyvinylidene fluoride (PVdF) have been prepared. These membranes exhibit desirable thermal stability in the hot water. The proton conductivity of the blend membranes reduces with the concentration of PVdF increasing. Although the proton conductivity of the SPEEK/PVdF (weight fraction is 9/1) blend membrane is about 1/10 of that of Nafion ~(?)115, the methanol permeability
of the blend membrane is about 1/20 of that of Nafion 115 under the same test condition.4 Two kinds of organo-inorganic membranes Nafion/S-SiO2 and PVdF/ S-S1O2 have been prepared for the operation of DMFC at temperatures higher than 90°C. (1) The Nafion/S-SiC>2 membrane has good proton conductivity, and the one with the weight composition of 5% Sid prepared from Nafion-TEOS-SCA902 materials shows better performance than Nafion?117 membrane at 120°C. (2) The proton conductivity of PVdF/ S-SiC>2 composite membrane is the highest at 90-100cC among the test temperature range.
质子交换膜是DMFC的关键材料之一,它起着分隔阴、阳极室和传导质子的双重作用,本论文工作以降低膜的甲醇渗透率和提高膜的使用温度为目标,围绕用于DMFC的新型质子交换膜材料的制备与表征,取得了如下主要进展:
1.采用浓硫酸作磺化剂,通过控制反应时间和温度,制得不同磺化度的磺化聚醚醚酮(SPEEK),磺化度为45～50%的SPEEK在机械稳定性和质子传导率方面能基本满足DMFC的性能要求。电化学研究结果表明,与Nafion~(?) 115膜相比,SPEEK膜的甲醇渗透率明显降低。
2.采用浸渍-烘烤方法制备了新型Nafion/SPEEK/Nafion复合膜,该膜的SPEEK层具有较强的阻甲醇渗透功能,两侧的Nafion层增强了膜与电极催化层的物理化学相溶性,有利于质子在膜与催化层界面传输,降低了膜与催化层的接触电阻。
3.用聚偏氟乙烯(PVdP)和SPEEK共混制膜,所得膜水热稳定性较高。实验表明共混膜的质子传导率随PVdF的含量增大而下降。虽然组成为SPEEK/PVdF=9/1的共混膜质子传导率约为Nafion~(?) 115膜传导率的1/10,但其甲醇渗透量仅是在相同测试条件下Nafion~(?) 115膜渗透量的1/20。
4.制备了Nafion/硅烷和PVdF/硅烷两种有机/无机复合膜,研究结果表明:(1)Nafion/硅烷复合膜有较高的质子传导率。其中,硅掺杂量为5%的由Nafion/正硅酸乙酯(TEOS)-巯基硅烷(SCA-902)制备的复合膜性能良好,由该膜组装的DMFC放电性能在120℃测试时好于Nafion~(?) 117膜组装的DMFC性能。(2)PVdF/硅烷复合膜的质子传导率随温度的变化关系表明,在90～100℃时,质子传导率最高。
A fuel cell is an electrochemical device that converts the chemical energy of the fuel and oxidant directly into electrical energy. Direct methanol fuel cell (DMFC) using liquid methanol as fuel, is promising for portable application such as cell phone, laptop computer and other electronics because of its high energy density, simplicity of structure (no additional equipment such as fuel reformer) and maintenance.The proton-exchange membrane in DMFC is one of the key materials, which plays the roles of separating the fuel from the oxidant and conducting proton. In this paper, the efforts are mainly focused on the preparation and characterization of novel proton-exchange membranes, reducing methanol crossover and increasing the tolerance of temperature for DMFC. The results obtained are mainly as follows:1 Sulfonated poly(ether ether ketone) (SPEEK) samples with different degrees sulfonation have been prepared in concentrated sulfuric acid by controlling the reaction time and temperature. With degrees sulfonation of 45~50%, the SPEEK membranes exhibit higher mechnical stabilities and proton conductivity. Electrochemical voltammetric studies show that these SPEEK membranes have significant lower methanol crossover than Nafion ~(?)115 membrane.2 The Nafion/SPEEK/Nafion (NSN) composite membranes are prepared by immersing the selected SPEEK into the Nafion-containing casting solution in which the SPEEK polymer is used as barrier layer of methanol. The Nafion layeres of both sides of NSN membrane improve the physical and chemical compatibility between the membrane and catalyst layer, facilitating proton transfer in the membrane-electrode interface. As a result, the resistance of MEA is lowed obviously.3 The blend membranes of SPEEK and polyvinylidene fluoride (PVdF) have been prepared. These membranes exhibit desirable thermal stability in the hot water. The proton conductivity of the blend membranes reduces with the concentration of PVdF increasing. Although the proton conductivity of the SPEEK/PVdF (weight fraction is 9/1) blend membrane is about 1/10 of that of Nafion ~(?)115, the methanol permeability
of the blend membrane is about 1/20 of that of Nafion 115 under the same test condition.4 Two kinds of organo-inorganic membranes Nafion/S-SiO2 and PVdF/ S-S1O2 have been prepared for the operation of DMFC at temperatures higher than 90°C. (1) The Nafion/S-SiC>2 membrane has good proton conductivity, and the one with the weight composition of 5% Sid prepared from Nafion-TEOS-SCA902 materials shows better performance than Nafion?117 membrane at 120°C. (2) The proton conductivity of PVdF/ S-SiC>2 composite membrane is the highest at 90-100cC among the test temperature range.
引文
[1] Lemons R A. Fuel cells for transportation. Journal of Power Sources, 1990, 29:251～264.
[2] Surampudi S, Narayanan S R, Vamos E, et al. Advances in direct oxidation methanol fuel cells. Journal of Power Sources, 1994, 47(3): 377～385.
[3] Steele B C H, Heinzel A. Materials for fuel-cell technologies. Nature, 2001, 414:345～352.
[4] Ren X M, Zelenay P, Thomas S, et al. Recent advances in direct methanol fuel cells at Los Alamos National Laboratory. Journal of Power Sources, 2000, 86:111～116.
[5] 衣宝廉.燃料电池—原理·技术·应用,北京:化学工业出版社,2003年8月.
[6] Jung D H, Lee C H, Kim C S, et al. Performance of a direct methanol polymer electrolyte fuel cell. Journal of Power Sources, 1998, 71:169～173.
[7] Banerjee S, Curtin D E. Nafion perfluorinated membranes in fuel cells. Journal of Fluorine Chemistry, 2004, 125:1211-1216.
[8] Surampudi S, Narayanan S R, Vamos E, et al. Advances in direct oxidation methanol fuel cells. Journal of Power Sources, 1994, 47:371～385.
[9] Qi Z, Kaufman A. Open circuit voltage and methanol crossover in DMFCs. Journal of Power Sources, 2002,110(1): 177-185.
[10] Ravikumar M K, Shukla A K. Effect of methanol crossover in a liquid-feed polymer-electrolyte direct methanol fuel cell. Journal of The Electrochemical Society, 1996,143(8): 2601-2606.
[11] Heinzel A, Barrag'an V M. A review of the state-of-the-art of the methanol crossover in direct methanol fuel cells. Journal of Power Sources, 1999, 84(1): 70-74.
[12] Scott K, Taama W M, Argyropoulos P, et al. The impact of mass transport and methanol crossover on the direct methanol fuel cell. Journal of Power Sources, 1999, 83(1-2): 204-216.
[13] Cruickshank J, Scott K. The degree and effect of methanol crossover in the direct methanol fuel cell. Journal of Power Sources, 1998,70(1): 40-47.
[14] Guraua B, Smotkin E S. Methanol crossover in direct methanol fuel cells: a link between power and energy density. Journal of Power Sources, 2002, 112(2): 339-352.
[2] Surampudi S, Narayanan S R, Vamos E, et al. Advances in direct oxidation methanol fuel cells. Journal of Power Sources, 1994, 47(3): 377～385.
[3] Steele B C H, Heinzel A. Materials for fuel-cell technologies. Nature, 2001, 414:345～352.
[4] Ren X M, Zelenay P, Thomas S, et al. Recent advances in direct methanol fuel cells at Los Alamos National Laboratory. Journal of Power Sources, 2000, 86:111～116.
[5] 衣宝廉.燃料电池—原理·技术·应用,北京:化学工业出版社,2003年8月.
[6] Jung D H, Lee C H, Kim C S, et al. Performance of a direct methanol polymer electrolyte fuel cell. Journal of Power Sources, 1998, 71:169～173.
[7] Banerjee S, Curtin D E. Nafion perfluorinated membranes in fuel cells. Journal of Fluorine Chemistry, 2004, 125:1211-1216.
[8] Surampudi S, Narayanan S R, Vamos E, et al. Advances in direct oxidation methanol fuel cells. Journal of Power Sources, 1994, 47:371～385.
[9] Qi Z, Kaufman A. Open circuit voltage and methanol crossover in DMFCs. Journal of Power Sources, 2002,110(1): 177-185.
[10] Ravikumar M K, Shukla A K. Effect of methanol crossover in a liquid-feed polymer-electrolyte direct methanol fuel cell. Journal of The Electrochemical Society, 1996,143(8): 2601-2606.
[11] Heinzel A, Barrag'an V M. A review of the state-of-the-art of the methanol crossover in direct methanol fuel cells. Journal of Power Sources, 1999, 84(1): 70-74.
[12] Scott K, Taama W M, Argyropoulos P, et al. The impact of mass transport and methanol crossover on the direct methanol fuel cell. Journal of Power Sources, 1999, 83(1-2): 204-216.
[13] Cruickshank J, Scott K. The degree and effect of methanol crossover in the direct methanol fuel cell. Journal of Power Sources, 1998,70(1): 40-47.
[14] Guraua B, Smotkin E S. Methanol crossover in direct methanol fuel cells: a link between power and energy density. Journal of Power Sources, 2002, 112(2): 339-352.