双电层

Introduction
In the discussion of electron transfer reactions so far there has been no mention of the nature of the electrode/electrolyte interface. It is clear that any interface will disrupt the electrolyte solution since the interactions between the solid and the electrolyte will be considerably different to those in solution. For electrodes which are under potentiostatic control there will also be the additional influence of the charge held at the electrode. These different factors result in strong interactions occurring between the ions/molecules in solution and the electrode surface. This gives rise to a region called the electrical double layer. Many models have been put forward to explain the behaviour observed when electrochemical measurements are performed in electrolyte solutions. Below we introduce two of the models which have been used to explain the effects occurring in this region.
The electrical double layer
The model which gave rise to the term 'electrical double layer' was first put forward in the 1850's by Helmholtz. In this model he assumed that no electron transfer reactions occur at the electrode and the solution is composed only of electrolyte. The interactions between the ions in solution and the electrode surface were asssumed to be electrostatic in nature and resulted from the fact that the electrode holds a charge density (q m)which arises from either an excess or deficiency of electrons at the electrode surface. In order for the interface to remain neutral the charge held on the electrode is balanced by the redistribution of ions close to the electrode surface. Helmholtz's view of this region is shown in the figure below
The attracted ions are assumed to approach the electrode surface and form a layer balancing the electrode charge, the distance of approach is assumed to be limited to the radius of the ion and a single sphere of solvation round each ion. The overall result is two layers of charge (the double layer) and a potential drop which is confined to only this region (termed the outer Helmholtz Plane, OHP) in solution. The result is absolutely analogous to an electrical capacitor which has two plates of charge separated by some distance (d)
with the potential drop occurring in a linear manner between the two plates. It is perhaps no surprise that when impedance analysis is performed on electrochemical systems the response due to the electrolyte redistribution is modelled in terms of capacitative elements.
The model of Helmholtz while providing a basis for rationalising the behaviour of this region does not account for many factors such as, diffusion/mixing in solution, the possibility of absorption on to the surface and the interaction between solvent dipole moments and the electrode. A later model put forward by Stern begins to address some of these limitations
now the ions are assumed to be able to move in solution and so the electrostatic interactions are in competition with Brownian motion. The result is still a region close to the electrode surface (100x10-10 m) containing an excess of one type of ion but now the potential drop occurs over the region called the diffuse layer.
Many modifications and improvements have been made to these early models with the latest approaches using numerical modelling to follow the redistribution effects as the electrode potential is varied.
在电子转移反应的讨论介绍，到目前为止，一直没有提到的电极/电解液界面的性质。

很显然任何接口会破坏电解质溶液，因为溶液中的固体和电解质之间的相互作用，将大大不同。

电极电位控制下，也将是充电电极举行的额外影响。

这
些不同的因素导致在溶液中的离子/分子与电极表面之间发生强相互作用。

这就产生了一个区域，称为双电层。

许多车型已提出了解释的行为观察时在电解质溶液中进行电化学测量。

下面我们介绍两个模型已被用来解释发生在这一地区的影响。

双电层
模型，引起了“双电层”，首次提出在1850年由亥姆霍兹。

在这个模型中，他假设没有电子转移反应发生在电极和电解质组成的解决方案是。

溶液中的离子与电极表面之间的相互作用asssumed静电的性质和，从电极持有电荷密度（ q米），从过剩或缺乏在电极表面的电子产生。

为了让界面保持中立举行的电极上的电荷是平衡的离子在电极表面的再分配。

亥姆霍兹本地区的看法是，如下图所示
假定吸引离子接近电极表面形成一层平衡电极充电，距离的方法是假设是有限的离子半径和溶剂轮每个离子的单圈。

总的结果是两层电荷（双层），和一个潜在的下降，这是只限于只有这个地区在解决方案（被称为亥姆霍兹外层飞机，OHP）。

其结果是绝对类似于有两个充电板隔开一段距离（D）电力电容器
在两个板块之间的线性方式发生的潜在下降。

这也许是没有，阻抗电化学系统进行分析时，由于电解质再分配的回应库容元素为蓝本的惊喜。

亥姆霍兹模型，同时提供本地区的行为合理化的基础并不如许多因素帐户，扩散/混合溶液中，吸收表面和溶剂的偶极矩和电极之间的相互作用的可能性。

斯特
恩提出一个后来的模型开始，以解决某些限制
现在，假定离子能够移动解决方案等的静电相互作用，在与布朗运动的竞争。

结果仍是一个含有超过一种类型的离子在电极表面（100x10 -10米），但现在的潜在下降，该地区被称为扩散层发生的地区。

已作出许多修改和改进这些早期模型与最新的使用数值模拟的方法，按照再分配的影响，作为电极电位是多种多样的。