What is a key difference between an electrolytic cell and a voltaic cell? the anode is where the oxidation takes place. the cathode is where the reduction takes place. there are two half-reactions. there is an outside energy source. the electrons move from the anode to the cathode

the answer is "There is an outside energy source." in voltaic cells, there is not need of an external source of energy because they involve spontaneous reactions. 

in both types of cells, the electrons move from anode to cathode, the anode is where oxidation takes place and cathode for reduction (an ox, red cat). also both have two half reactions.