Hydrogen Redox in Protic Ionic Liquids and a Direct Measurement of Proton Thermodynamics
Hydrogen Redox in Protic Ionic Liquids and a Direct Measurement of Proton Thermodynamics
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DOI：
10.1021/jp902762c
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发表时间：
2009-07-16
影响因子：
3.7
通讯作者：
Friesen, C.
中科院分区：
文献类型：
--
作者：
Bautista-Martinez, J. A.;Tang, L.;Friesen, C.
室温离子液体由于具有良好的热稳定性、宽的电化学窗口和低的蒸气压等优异的物理化学性能，近年来引起了人们的广泛关注。离子液体的一个亚类，质子离子液体（PIL），通过质子从布朗斯台德酸转移到布朗斯台德碱而形成，并且是包括燃料电池在内的几种应用中作为电解质的良好候选者，因为它们将高离子性和质子交换动力学与低蒸气压结合在一起。在这里，我们提出了一些氢饱和PIL的氢氧化还原结果。具体而言，我们研究了系统二乙基甲基铵双三氟甲烷磺酰亚胺，二乙基甲基铵氯铝酸盐，三乙基铵三氟甲磺酸盐，二乙基甲基铵三氟甲磺酸盐，二甲基乙基铵三氟甲磺酸盐，乙基铵硝酸盐，吡啶乙酸盐，三乙基铵甲烷磺酸盐，二乙基甲基铵甲烷磺酸盐，和α-甲基吡啶三氟甲磺酸盐。我们观察到一个显着的电位之间的差距，在质子还原发生的电位和电位，在这一点上，容易氢氧化物（与半乳糖）范围从约。0至800 mV）。我们发现，这一观察与质子提取的阴离子（酸的形式HA）和阳离子（酸的形式BH+），这是由质子的布朗斯台德夫妇HA/H-和BH+/B之间的自由能的差异定义的能量学的差异。该能隙和滴定曲线中的相关等效点固定这些系统中的质子活性，并确定当在电极附近没有较低能量位点可用时激活质子所需的电化学电势。
Room temperature ionic liquids have attracted a great deal of interest in recent years due to their remarkable physicochemical properties including high thermal stability, wide electrochemical window, and low vapor pressure. A subclass of ionic liquids, protic ionic liquids (PILs), are formed by proton transfer from a Bronsted acid to a Bronsted base, and are good candidates as electrolytes in several applications, including fuel cells, because they integrate high ionicity and proton exchange kinetics with low vapor pressure. Here we present hydrogen redox results for a number of hydrogen-saturated PILs. Specifically we study the systems diethylmethylammonium bistrifluoromethanesulfonimide, diethylmethylammonium chloroaluminate, triethylammonium triflate, diethylmethylammonium triflate, dimethylethylammonium triflate, ethylammonium nitrate, pyridinium acetate, triethylammonium methane sulfonate, diethylmethylammonium methane sulfonate, and alpha-picolinium triflate. We observe a significant potential gap between the potential at which proton reduction occurs and the potential at which facile hydrogen oxidation Occurs (with the gal) ranging from ca. 0 to 800 mV). We show that this observation correlates with differences in the energetics for proton extraction from the anion (acid with the form HA) and from the cation (acid with the form BH+), which is defined by the differences in proton free energy between the Bronsted couples HA/H- and BH+/B. This energy gap and the associated equivalence point in the titration curve fix the proton activity in these systems and determine the electrochemical potential needed to activate a proton when no lower energy sites are available in the vicinity of the electrode.