A capacitor is a passive electronic device that stores electric charge. Polarized aluminum electrolytic capacitors have an anode electrode (+) made of pure aluminum foil, electrolyte that acts as the cathode, and a thin insulating layer of aluminum oxide that acts as the dielectric. Electrolytic capacitors have higher capacitance-voltage (CV) product per unit volume than ceramic capacitors or film capacitors. Applications include audio, automotive, bypass, decoupling, and motor starting capacitors.