charles pollak (born karol pollak), a producer of accumulators, found out that the oxide layer on an aluminum anode remained stable in a neutral or alkaline electrolyte, even when the power was switched off. in 1896 he filed a patent for an "electric liquid capacitor with aluminum electrodes" (de: "elektrischer flüssigkeitskondensator mit aluminiumelektroden") based on his idea of using the oxide layer in a polarized capacitor in combination with a neutral or slightly alkaline electrolyte.