what are some factors that affect the voltage of electrolysis?

the voltage is usually set by the user. for instance if i used a 9V battery, the voltage would be 9V

Might find a few ideas here...

Indeed, the user sets the voltage.

 

But there is a minimum needed, which depends on the type of reaction (so on the two half reactions). The concentration of the reactants too. The pH might be an issue, but this can be considered part of the previous point (concentrations).

If you are stuck looking at some bit of science with nothing to do it's often worth wondering "What happens if I change the temperature or pressure?".

Of course, if you have better things to do than wonder that then please feel free.