In the 1890s Charles Pollak found that an oxide layer on an aluminum anode was stable in a neutral or alkaline solution and was granted a patent in 1897 for a borax electrolyte aluminum capacitor.

These aluminum electrolytic capacitors are common residents on ... but actually foil–oxide–electrolyte. But there is more to [TubeTime]’s tour than this answer, which includes pictures ...

Film capacitors are critical in modern electronics, utilizing various dielectric materials like polyester, polypropylene, and polycarbonate to improve performance in applications such as power factor ...