Bipolar Electrochemical Anodization Route for the Fabrication of Porous Anodic Alumina with Nanopore Gradients.

Abstract

Porous anodic alumina (PAA) films with homogeneous nanopores are achieved by traditional anodization. Here, we present a unique anodization technique based on bipolar electrochemistry to fabricate PAA films with nanopore gradients. In an oxalic acid solution dissolved in ethylene glycol, a stable bipolar anodization process is realized. The PAA film prepared at 280 V exhibits a continuous change in interpore distance from ∼171 to ∼83 nm over a range of only 5 mm on the aluminum sheet. Higher driving voltages lead to larger interpore distances and steeper nanopore gradients. Further, no direct electrical connection is required for this bipolar anodization.