Composite materials for electrochemical applications

Electrochemical behavior pertains to chemical processes brought about by the movement of charged species (ions and electrons) under the influence of an electric field. It occurs when there are ions that can move in a medium (liquid or solid) due to an electric field (i.e., a voltage gradient). The positive ions (cations) move toward the negative end of the voltage gradient, while the negative ions (anions) move toward the positive end of the voltage gradient (Figure 10.1). The medium containing the movable ions is called the electrolyte The electrical conductors in contact with the electrolyte for the purpose of applying the electric field are called electrodes. The electrode at the positive end of the voltage gradient is called the positive electrode or anode The electrode at the negative end of the voltage gradient is called the negative electrode or cathode. The electrodes must be sufficiently inert so that they do not react with the electrolyte. In order to apply the electric field, the electrodes are connected to a DC power supply (or a battery) such that the cathode is connected to the negative end of the power supply (so that the cathode becomes negative) and the anode is connected to the positive end of the battery (so that the anode becomes positive). In this way, electrons flow in the electrical leads (the outer circuit) from the anode to the cathode, while ions flow in the electrolyte. The electron flow in the outer circuit and the ion flow in the electrolyte constitute a loop of charge flow. Note that the anions flow from cathode to anode in the electrolyte, while the electrons flow from anode to cathode in the outer circuit and both anions and electrons are negatively charged.