Regulation of the Electrochemical Tunnel Etching Behavior of Aluminum Foil for AECs using the Glycerol Additive

Glycerol, characterized by its multiple hydroxyl functional groups, exhibits strong interactions with aluminum foil surfaces. In this study, we systematically investigated the impact of glycerol additives on the tunnel etching behavior of aluminum foil. Through a comprehensive combination of theoretical calculations and experimental analyses, we elucidated the critical role of interfacial interactions between glycerol and the Al (001) plane in regulating the tunnel etching process. Unlike water molecule adsorption, the robust adsorption of glycerol molecules on the aluminum surface significantly stabilizes the nucleation of pitting sites. Furthermore, the uniform arrangement of glycerol molecules promotes the homogenization of chloride ion diffusion pathways, ultimately resulting in a reduction of merged-tunnels and an increase in their size. Notably, the etched aluminum foil obtained under these conditions demonstrates high specific capacitance even at elevated operating voltages. Electrochemical impedance spectroscopy (EIS) and polarization curve measurements revealed that the slight enhancement in corrosion resistance of the aluminum foil in the glycerol-containing electrolyte is instrumental in improving the overall tunnel etching behavior. This finding further highlights the substantial potential of glycerol additives in modulating the electrochemical corrosion behavior of metallic materials, paving the way for the development of advanced aluminum electrolytic capacitors with enhanced performance.