离子液体的合成及离子液体碳糊电极电催化性能研究

【作者】 佘奕奕；

【导师】 唐有根； 刘洪涛；

【作者基本信息】 中南大学 ， 有机化学， 2010， 硕士

【摘要】 本文用两步法合成了1-辛基-3-甲基咪唑六氟磷酸盐([Omim]PF6)和1-辛基-3-甲基咪唑二(三氟甲基磺酰)亚胺盐([Omim]Tf2N)两种离子液体,并用红外光谱和氢核磁共振谱进行了表征。随后用[Omim]PF6离子液体做稳定剂合成了纳米镍催化剂,并用X-射线衍射法分析了催化剂成分为纳米镍和纳米氢氧化镍的混合物。反应结束后将洗掉离子液体的催化剂和未洗掉离子液体的催化剂分别用扫描电镜观测其表面形貌,结果表明洗掉离子液体的催化剂团聚现象严重,而未洗掉离子液体的催化剂则分布均匀,成规则的球形或椭球形,显示了离子液体在纳米无机材料合成中良好的稳定作用。用[Omim]PF6完全或部分替代传统粘合剂液体石蜡与石墨粉混合分别制成了两种离子液体修饰碳糊电极IL-CPE和MIL-CPE。以亚铁氰化钾为电化学探针对IL-CPE和MIL-CPE的电化学行为进行了研究,并与传统碳糊电极M-CPE进行了比较。结果表明Fe(CN)64-在各种CPE上均为准可逆过程,但动力学控制机理不一样,M-CPE是表面吸附控制,MIL-CPE和IL-CPE是扩散控制。Fe(CN)64-在MIL-CPE和IL-CPE上的电流响应比在M-CPE上要大的多,分别接近在M-CPE上的8倍和10倍,这充分说明[Omim]PF6离子液体极大地加强了电极上电荷转移的能力。随后探讨了各种CPE在对苯二酚(H2Q)的磷酸氢二钠-磷酸二氢钠缓冲溶液(PBS)中的电化学行为,结果显示IL-CPE对H2Q显示了很好的电催化效果,各种CPE在H2Q的PBS溶液中均为准可逆过程。峰电流Ip和扫速平方根v1/2的关系及电化学阻抗谱分析均表明H2Q在IL-CPE上遵循扩散控制机理。由计时电流测试计算得出的扩散系数D约为5.05×10-4cm2／s,定量地证明了H2Q在[Omim]PF6 IL-CPE上良好的扩散能力。进一步分析氧化峰电流Ipa与H2Q浓度的关系得出,在0.01 mmol/L～10mmol/L的浓度范围内,Ipa与H2Q浓度线性相关,检出限为8.1×10-7mol／L(S/N=3)。最后将洗掉离子液体和未洗掉离子液体的催化剂分别复合于IL-CPE制成nanoNi/IL-CPE和IL-nanoNi/IL-CPE,探讨其在碱性条件下对甲醇的电催化效果。CV曲线表明,IL-nanoNi/IL-CPE比nanoNi/IL-CPE对甲醇有更好的催化效果,电极可逆性和反应动力学均有所提高,氧化峰形也更好,这可能是由于IL-nanoNi比单纯nanoNi在离子液体型碳糊电极中具有更高的相溶性。交流阻抗测试表明,当电位在0.4V时,整个体系可视为一个简单的扩散控制传荷电路,而当电位在0.6V和0.7V时,由于Ni(Ⅱ)电氧化为Ni(Ⅲ),并催化甲醇氧化,整个体系表现为双容抗特征。通过对计时电流曲线的分析得出甲醇在IL-nanoNi/IL-CPE上的扩散系数为扩散系数D为2.19×10-4 cm2/s,说明甲醇在该电极上良好的动力学反应特性。更多还原

【Abstract】 Two kinds of ionic liquids, namely 1-octyl-3-methylimidazolium hexafluorophsphate ([Omim]PF6) and 1-octyl-3-methylimidazolium bis(triflylmethyl-sulfonyl)imide ([Omim]Tf2N) were prepared and characterized by IR and 1H-NMR. Nano-Ni catalyst was synthesized using [Omim]PF6 as stabilizer. X-ray diffraction analysis showed the nanoNi catalyst is composed of elemental Ni and Ni(OH)2. It was found that the prepared nanoparticles agglomerated badly during storage or transportation if ionic liquid was removed while the catalyst distributed in ionic liquid showed spherical or ellipsoidal morphology. It implied that ionic liquids could play very important roles in synthesis of inorganic nano-materials.Two carbon paste electrodes named IL-CPE and MIL-CPE were fabricated by using IL to replace liquid paraffin totally or partly. K4Fe(CN)6 was adopted as probe to study the electrochemistry behavior of IL-CPE and MIL-CPE, and the traditional carbon paste electrode M-CPE was also investigated as a comparison. The different kinetic mechanisms were found at the CPEs. Fe(CN)64-/Fe(CN)63-redox reaction is controlled by surface charge transfer at M-CPE, but diffusion control at MIL-CPE and IL-CPE. The corresponding redox current is much larger at MIL-CPE and IL-CPE than at M-CPE, nearly 8 times and 10 times, respectively, which implies that [Omim]PF6 ionic liquid has the ability to enhance charge transfer. Subsequently electrochemical performances of all kinds of CPEs in hydroquinone (H2Q) PBS buffer solution were investigated. The results show that IL-CPE has the best electrocatalytic effect toward oxidation of H2Q. The relationship of peak current Ip and square root of sweep rate and the electrochemical impedance plots indicate the oxidation of H2Q is diffusion control at IL-CPE. Diffusion coefficient D is calculated as 5.05×10-4 cm2/s according to chronoamperometry measurement, quantitatively proves H2Q has good diffusion ability at [Omim]PF6 IL-CPE. Further study reveals that anodic peak current Ipa is linear correlation to the concentration of H2Q in the range of 0.01～10 mmol/L with detection limit as 8.1×10-7 mol/L(S/N=3).Finally, nanoNi/IL-CPE and IL-nanoNi/IL-CPE were fabricated with nanoNi and IL-nanoNi as catalyst, respectively. The electrocatalytic performance of the prepared electrodes on oxidation of methanol in alkaline solution was discussed. CV curves show IL-nanoNi/IL-CPE has better catalytic effect than nanoNi/IL-CPE by comparing reversibility, reaction kinetics and peak current. This good nature could be attributed to better compatibility for IL-nanoNi than nanoNi in IL-CPE. AC impedance measurements suggest that at 0.4V the whole system acted as a simple circuit controlled by diffusion, while at 0.6V and 0.7V the system becomes complex with two time constants. It is accounted for the reaction that Ni(Ⅱ) is oxidized to Ni(Ⅲ) which leads to the oxidation of methanol. Diffusion coefficient D of methanol at IL-nanoNi/IL-CPE is calculated as 2.19×10-4cm2/s according to chronoamperometry curve, which illustrates favorable kinetic reaction characteristic.更多还原