Environmental Engineering Reference
In-Depth Information
Cathode
+
Anode
-
Electrolyte
ionic
conductor
Figure 10.1 Cell construction
container. Electrons are transported through the electrolyte from cathode to anode
inside the cell, generating a potential across the cell as shown (cathode plate
becomes positive and anode plate becomes negative).
The origin of potential in an electrochemical cell can be viewed as the oxi-
dation of fuel, resulting in displacement of charge. Figure 10.2 illustrates this
process and some representative materials used for the anode and cathode. During
discharge, active material, the fuel, is oxidized at the anode where it takes up
electrons from the external circuit. Current flow in the external circuit releases
energy. Electrons exit via the cathode where a reduction process ensues and after
passing through an external circuit return at the oxidizing electrode, the anode.
During recharge, the process is reversed as is the nomenclature of anode and
cathode - electrons return via the anode, reconstituting the active materials at each
of the electrodes. It must be pointed out at this point that the reactions involved in
discharge and charge of battery systems may not be completely reversible, nor do
Oxidant
Electron
state 'high'
Lead
Zinc
Hydrogen
Lithium
Electron
state 'low'
Lead dioxide
Manganese
dioxide
Oxygen
Fuel
Anode
Cathode
Electron transport
electrical energy output
Figure 10.2 Development of voltage in a cell
