Types of electrochemical cells

Electrochemical cells are divided into two types that may be thought of as opposite to one another in their processes:
Electrolytic cells in which electrical energy is used to drive a non-spontaneous redox reaction: Electrical energy causing a redox reaction.
Voltaic cells in which spontaneous redox reactions are used to generate electrical energy: A redox reaction causing electrical energy.
Oxidation is loss of electrons and reduction is gain of electrons.
In both types of cell oxidation occurs at the anode and reduction occurs at the cathode (that is how anode and cathode are defined in chemistry), but because the processes are the opposite of one another:
In a voltaic cell the anode is negative, and the cathode is positive.
In an electrolytic cell the anode is positive, and the cathode is negative.
Understanding the processes that are taking place is critical in getting to grips with this topic - watch the video: Electrochemical cells.