In an electrolytic cell, electrical energy is used to drive a chemical reaction that would not occur spontaneously. In the Downs cell, for example, electrical energy is used to electrolyze molten cryolite, which produces aluminum metal and oxygen gas. In the Nelson cell, electrical energy is used to electrolyze molten calcium chloride, which produces calcium metal and chlorine gas.
In a voltaic cell, a spontaneous chemical reaction is used to generate electrical energy. In the Daniel cell, for example, the spontaneous reaction of zinc metal and copper sulfate solution produces electrical energy.
The main difference between an electrolytic cell and a voltaic cell is the direction of the flow of electrons. In an electrolytic cell, electrons flow from the positive electrode (anode) to the negative electrode (cathode). In a voltaic cell, electrons flow from the negative electrode (anode) to the positive electrode (cathode).
