Bit late, but no.. not zener diodes. They're actually used to create a reference voltage for power supplies - not what you wanna do.
As Reido & Dazco said use rectifier diodes (also called power diodes). I use 1N4007's - should cost you about $0.20 each from radio shack.
FYI a diode is sort of an electronic "valve"... it'll let electricity flow one way through it but not the other. They'll have a band or stripe around one end that marks the "cathode" or negative side of the diode. The other side's called the "anode" to which you connect the positive voltage. More trivia: an LED is also a diode, its name stands for Light Emitting Diode (which is why they don't work if you connect them backwards).
