Effect of electrodepositing Ag on DC etching aluminum foils for electrolytic capacitor

Ag nuclei were electrodeposited on the surface of aluminum foil to induce tunnel etching. The effects of Ag nuclei on the surface and cross-section etching morphologies and electrochemical behavior of Al foil was investigated with SEM, polarization curve (PC) and electrochemical impedance spectroscopy (EIS). It is proved that the tunnels etched in this way are distributed more uniformly and the density of tunnels and pits are enhanced, leading to increase in specific capacitance of etched Al foil. These effects can be attributed to the mechanism that the Ag nuclei can serve as the favorable sites for tunnel initiation on aluminum foil surface owing to the formation of Ag–Al micro-batteries, in which Ag is cathode and Al is anode. This mechanism is supported by the SEM, PC and EIS.