Gorska B, Timperman L, Anouti M, Béguin F
Institute of Chemistry and Technical Electrochemistry, Poznan University of Technology, Berdychowo 4, 60-965 Poznan, Poland.
Phys Chem Chem Phys. 2017 May 10;19(18):11173-11186. doi: 10.1039/c7cp00398f.
The effect of low water content (<20, 150, 1000, 10 000 ppm) in triethylammonium bis[(trifluoromethyl)sulfonyl]imide - [(CH)NH][TFSI] - protic ionic liquid (PIL) on the performance of activated carbon (AC) electrodes as well as AC/AC electrochemical capacitors (ECs) is reported. Under negative polarization, hydrogen electrosorption onto carbon is enhanced along with the increase of water content in PIL, whereas the resulting desorption peaks are shifted to lower potential values, evidencing lower sorption energy when hydrogen is stored from moisture containing PIL. Cyclic voltammetry (CV) investigations on PIL-based ECs demonstrated that the evolution of the Stern layer nanostructure at positive and negative potentials is asymmetrical. The results revealed comparable electrochemical performance for PIL containing 150 and 1000 ppm of HO, due to similar operation of the positive electrode, where [TFSI] anions are adsorbed in the outer Helmholtz plane, and the negative one, where hydrogen is stored through the reduction of the intermediate hydronium cation. By contrast, a cell with "dry" PIL (<20 ppm of water) displayed a distinctive operation due to hydrogen electrosorption directly through reduction of the protonated cation, and selective adsorption of [TFSI] anions, which occurs thanks to the high polarizability and image force (IF) created by their induced charge. Galvanostatic cycling with potential limitation (GCPL) showed comparable capacitance values whatever the water content in PILs up to 1000 ppm, yet electrochemical impedance spectroscopy (EIS) revealed higher capacitance as well as better retention at higher frequencies with the PIL containing 150 ppm of water. Hence, 150 ppm is reasoned to be an optimal value for diffusion and adsorption of ions. The nature of current collectors (aluminum or stainless steel) has a determining role in their polarization behavior, and consequently the potential range of electrodes as well as ion diffusion into the activated carbon porosity, influencing the observed capacitance values (C: 170 vs. 128 F g, for Al and SSt, respectively).
报道了三乙铵双[（三氟甲基）磺酰基]亚胺 - [（CH）NH][TFSI] - 质子离子液体（PIL）中低含水量（<20、150、1000、10000 ppm）对活性炭（AC）电极以及AC/AC电化学电容器（EC）性能的影响。在负极极化下，随着PIL中含水量的增加，碳上的氢电吸附增强，而产生的解吸峰向更低的电位值移动，这表明当从含水分的PIL中储存氢时吸附能更低。基于PIL的EC的循环伏安法（CV）研究表明，在正电位和负电位下斯特恩层纳米结构的演变是不对称的。结果显示，含有150和1000 ppm HO的PIL具有可比的电化学性能，这是由于正电极和负电极的运行相似，在正电极中，[TFSI]阴离子吸附在亥姆霍兹外平面，在负电极中，氢通过中间水合氢离子的还原而储存。相比之下，具有“干燥”PIL（含水量<20 ppm）的电池表现出独特的运行方式，这是由于氢通过质子化阳离子的直接还原进行电吸附，以及[TFSI]阴离子的选择性吸附，这是由于它们的诱导电荷产生的高极化率和镜像力（IF）所致。恒电流电位限制循环（GCPL）表明，无论PIL中的含水量高达1000 ppm，电容值都具有可比性，但电化学阻抗谱（EIS）显示，含有150 ppm水的PIL在较高频率下具有更高的电容以及更好的保持率。因此，150 ppm被认为是离子扩散和吸附的最佳值。集流体（铝或不锈钢）的性质在其极化行为中起决定性作用，因此也影响电极的电位范围以及离子扩散到活性炭孔隙中，进而影响观察到的电容值（对于铝和不锈钢，C分别为170和128 F g）。
