武汉大学电化学课件 陈胜利 Chaper 6 Double layer.ppt

phase
The Gauss law: if we enclose a volume with an imaginary surface ( a Gaussian surface), we will find that the net charge “q” inside the surface is given by an integral of the electric field over the surface:
The potential is uniform within conductors
The conductors usually contains abundance of charge carriers. When no current passes through a conducting phase, there is no net movement of charge carriers. This implies that the electric field at all interior points within a conducting phase must be zero. Therefore, the potential difference between any two points in the interior of the phase must also be zero.
—— the work required to bring a unit positive charge from point 1
to point 2.Leabharlann 212 2
1



1
Edl
(E - - - the electric field, l - - - the path from point 1to point 2)
The electric double layer is the core of the electrode/electrolyte interface, which is formed by the charges reside in the interfacial region, and in which the interfacial potential difference is distributed.
a
b
c
A relatively detailed view of potentials and interfacial potential differences
1. The equi-potential nature of conductors
The potential difference between two points within a phase
The formation of charged layers at the interfaces between two phases
As two phases of different natures are made in contact, a charged region may be produced in each phases near the phase boundary due to
The potential within a phase, f, is called the inner potential (or Galvani potential) of the phase
2. The location of the excess charges in a conducting
3. The inner potential and outer potential of a phase
Chapter 6
The properties and structures of the electric double layer at
electrode/electrolyte interfaces
The electrode / electrolyte interfaces
It is essential to have an electrode/electrolyte interface for the electrochemical reactions to take place. Such an interface is established by direct contact of the electrode (electron conductors) with electrolyte (ion conductors).
a) Charge transfer between two phase, e.g., the dissolution
of metal: Ag Ag+ + e
b) Adsorption of charged species at interfaces c) Orientated arrangement of dipole

q E ds
This implies that the excess charge resides in the region near the surface of the conducting phase
The thermal processes will impede the compact accumulation of the excess charges strictly on the surface. Then a charged zone is established near the surface, which is called a space charge region , the thickness of which depends on the bulk concentration of the charge carriers.