Unusual Surfaces with Structural Gradients: Investigation of Potential Gradients on Bipolar Electrodes during Bipolar Anodization of Aluminum

The electrical potential gradients on aluminum bipolar electrodes (BPEs) subjected to bipolar anodization in an alternating current (AC) electric field were investigated by performing scanning electron microscopy, dyeing the anodized specimens, and measuring resistance in the alumina films after re-anodizing the samples. The aluminum sheets used as BPEs were suspended in an electrolyte solution and positioned horizontally in the center of the cell to visually assess the electrical potential gradients on the BPEs. The thickness and morphology of each alumina film varied, which reflected the unique potential distributions on the BPEs in the AC electric field. Electrical resistance was symmetric and increased linearly from the centers of the BPEs to their extremities. These variations were ascribed to the unique potential distributions and polarity reversal of the AC electric field. This synthetic approach will lead to the development of various functional materials using bipolar electrochemistry.