Capacitor Plates?

[THATguy]

Do capacitor plates need to be made from the same type of metal?
Could one be Alumium and the other gold?

[mc172]

I don't actually know the answer, but in my mind, if your dielectric material is dry then I don't see why it would matter. However, if it's wet then you could end up with galvanic corrosion if the galvanic potential is above a certain threshold, which is usually considered to be over around 250 mV for mechanical structures. For electronic components I'd put it much lower - I would have thought that galvanic potential is completely undesirable and the higher the value, the lower the service life.

From memory, aluminium and gold are around 1000 mV apart in the galvanic series which is quite a considerable potential!

[nicalitz]

I don't believe so. As long as both materials are relatively conductive and have a somewhat similar surface roughness, the capacitor should behave roughly the same.

[nicalitz]

This assumption obviously wouldn't hold for, say, supercapacitors, where the electrode material needs to react with the electrolyte in a very specific way. Might still be possible to use different materials, but it would get significantly more complex.

[tpowell1830]

Do capacitor plates need to be made from the same type of metal?
Could one be Alumium and the other gold?

If you are talking air gap or other physical insulating material besides electrolytic , then no they do not have to be the same type of metal. However, just remember that there is considerable engineering into making a GOOD capacitor that is to be used for a specific application.

For experimental purposes, though, in order to understand capacitors, I think making your own home grown capacitors is a good learning experience.

I thought this was a neat home made electrolytic capacitor.

[Brumby]

As said above, when considering the theoretical definition of a capacitor, especially with a dielectric such as air, it does not matter in the least.

Where the materials DO matter comes into physical construction - and this is a topic of such immense proportions that I dare not venture into it.  Even then, the metallic composition of the plates has more to do with electro-chemical stability and other considerations than it does with capacitance.