Role of ion hydration for the differential capacitance of an electric double layer.
Role of ion hydration for the differential capacitance of an electric double layer.
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DOI：
10.1039/c6cp04199j
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发表时间：
2016-10
期刊：
影响因子：
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通讯作者：
D. Caetano;G. Bossa;Vinicius M de Oliveira;M. A. Brown;S. J. de Carvalho;S. May
中科院分区：
文献类型：
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作者：
D. Caetano;G. Bossa;Vinicius M de Oliveira;M. A. Brown;S. J. de Carvalho;S. May
用蒙特卡罗方法研究了软的、水合作用的离子-离子和离子-表面相互作用对双电层微分电容的影响，并与不同的平均场模型进行了比较。在均匀的介电背景下，我们研究了一价离子生理浓度下的平面电极表面。水合作用是在汤川势的基础上模拟的，汤川势增加了库仑，排除了离子之间的体积相互作用。我们提出了一个平均场模型，该模型包括水合作用介导的阴离子-阴离子、阴离子-阳离子和任意强度的阳离子-阳离子相互作用。此外，有限离子大小是通过排除的体积相互作用来解释的，这种相互作用是基于卡纳汉-斯塔林状态方程或使用晶格气体模型来描述的。我们的蒙特卡罗模拟和平均场方法都预测了微分电容的特征双峰(所谓的驼峰形状)；它的减少反映了反离子在电极表面附近的堆积。水合作用介导的离子表面斥力的存在导致靠近表面的一个薄的电荷耗竭区域，这让人想起斯特恩层。我们分析了排除体积和水合作用对微分电容的影响，并证明了在小表面电荷密度下，基于Carnhan-Starling方程的平均场模型能够模拟蒙特卡罗模拟结果。相反，对于较大的表面电荷密度，基于晶格气体模型的平均场方法是可取的。
The influence of soft, hydration-mediated ion-ion and ion-surface interactions on the differential capacitance of an electric double layer is investigated using Monte Carlo simulations and compared to various mean-field models. We focus on a planar electrode surface at physiological concentration of monovalent ions in a uniform dielectric background. Hydration-mediated interactions are modeled on the basis of Yukawa potentials that add to the Coulomb and excluded volume interactions between ions. We present a mean-field model that includes hydration-mediated anion-anion, anion-cation, and cation-cation interactions of arbitrary strengths. In addition, finite ion sizes are accounted for through excluded volume interactions, described either on the basis of the Carnahan-Starling equation of state or using a lattice gas model. Both our Monte Carlo simulations and mean-field approaches predict a characteristic double-peak (the so-called camel shape) of the differential capacitance; its decrease reflects the packing of the counterions near the electrode surface. The presence of hydration-mediated ion-surface repulsion causes a thin charge-depleted region close to the surface, which is reminiscent of a Stern layer. We analyze the interplay between excluded volume and hydration-mediated interactions on the differential capacitance and demonstrate that for small surface charge density our mean-field model based on the Carnahan-Starling equation is able to capture the Monte Carlo simulation results. In contrast, for large surface charge density the mean-field approach based on the lattice gas model is preferable.