Ion sieving effects in the electrical double layer of porous carbon electrodes: Estimating effective ion size in electrolytic solutions
Ion sieving effects in the electrical double layer of porous carbon electrodes: Estimating effective ion size in electrolytic solutions
复制标题
DOI：
10.1021/jp010086y
复制
发表时间：
2001-07-26
影响因子：
3.3
通讯作者：
Aurbach, D
中科院分区：
文献类型：
--
作者：
Eliad, L;Salitra, G;Aurbach, D
某些微孔碳具有分子尺寸的孔，其尺寸可以在很宽的范围内调节以适应多种分子的尺寸。了解这些分子的尺寸后，可以生产尺寸校准的多孔碳。在这项工作中，我们利用碳的电子导电性，将其用作电解溶液中的电极。通过改变电极电位，我们可以诱导不同尺寸的离子电吸附和电吸附到孔径校准的碳中，从而使我们能够估计有效离子尺寸。一些基本问题可以得到解决，例如电极孔隙中的离子是否处于溶剂化状态，这对于新型电化学储能装置和微生物系统很重要。结果分析表明，所使用的所有阳离子均以水合状态电吸附在电极孔中。与一价阳离子相比，二价阳离子的尺寸几乎是一价阳离子的两倍。一价阴离子基本上以非水合状态被吸附。带双电荷的硫酸根阴离子以水合状态被吸附。根据对许多活性炭中的孔是狭缝形的观察，硝酸根是多原子平面阴离子，其有效尺寸比单原子卤素阴离子更小。对结果的分析使我们能够建立水介质中离子有效尺寸的尺度，如下所示（MTBE 代表甲基叔丁基醚）： 阳离子，[3.62 埃，N-2] < Cs+ < K+ < Na+ < Li+ < [4.21 埃，CF4] < [5.05 埃，SF6] < [5.8 埃，MTBE] < Ba2+， Ca2+、Mg2+；阴离子，[3.62 埃，N-2] < NO3- < Cl- < F- < Br- < [4.21 埃，CF4] < ClO4- < [5.05 埃，SF6] < [5.8 埃，MTBE] < SO2-。我们发现，只要孔径远大于离子尺寸，中等浓度下的双电层容量就与溶液中离子的尺寸和电荷无关。
Certain microporous carbons have pores of molecular dimensions, the size of which can be adjusted over a wide range to fit the dimensions of a large variety of molecules. With knowing the dimensions of these molecules, size-calibrated porous carbons can be produced. In this work, we took advantage of the electronic conductivity of carbon in using it as an electrode in electrolytic solutions. By changing the electrode potential, we could induce electroadsorption and electrodesorption of ions of different dimensions into pore-calibrated carbons, thus enabling us to estimate effective ion sizes. A few fundamental questions such as whether ions accommodated in the electrodes' pores are in a solvated state, which is important for novel electrochemical energy storage devices and for microbiological systems, could be addressed. Analysis of the results indicates that all the cations that are employed are electroadsorbed in the electrode pores in hydrated states. Compared with the monovalent cations, the bivalent cations exhibit dimensions that make them almost twice as big. Monovalent anions are basically adsorbed in a nonhydrated state. The doubly charged sulfate anion is adsorbed in the hydrated state. The nitrate, a multiatom planar anion, has a smaller effective dimension than the monoatomic halogen anions, in accordance with the observation that the pores in many activated carbons are slit-shaped. The analysis of the results enabled us to establish a scale of ionic effective dimensions in aqueous media, as presented below (MTBE stands for methyl tert-butyl ether): cations, [3.62 Angstrom, N-2] < Cs+ < K+ < Na+ < Li+ < [4.21 Angstrom, CF4] < [5.05 Angstrom, SF6] < [5.8 Angstrom, MTBE] < Ba2+, Ca2+, and Mg2+; anions, [3.62 Angstrom, N-2] < NO3- < Cl- < F- < Br- < [4.21 Angstrom, CF4] < ClO4- < [5.05 Angstrom, SF6] < [5.8 Angstrom, MTBE] < SO2-. We discovered that as long as the pore size is considerably greater than the ion size, the electric double-layer capacity at moderate concentrations is independent of both the size and charge of the ions in solutions.