I tried to in detail, explain what creates the high voltage in a Van de Graff generator. But I got problem doing that.
Van de Graaff generator:
First some background of a Van de Graaff generator, there is a comb that is "combing" a rolling belt to create and transfer charge away to create a voltage in a ball shaped metal encasing.
More info about the whole process can be found here: https://en.wikipedia.org/wiki/Van_de_Graaff_generator
Though, I never understood what creates the super high voltage (1 million volt) of a Van de Graaff generator? And an argument that contradicts the high voltage creations of a Van de Graaff generator is that the energy required to remove an electron of an atom(ionization energy) is just a few eV(around 5eV - 30eV). Assuming the voltage of this system is the same as the voltage required to remove an electron. Then, a Van de Graaff generator can only generate the same voltage as the voltage needed to remove one electron from the atom, (i.e. a few volts)?
I'm a bit reluctant on accepting that the voltage is proprtional to the amount of charge of the Van de Graaff generator, because voltage is always relative (Energy/Charge). It's like saying a battery can generate few million volts because it can carry a lot of charge.