Figure 3.

FESEM images of a the surface of typical PAA fabricated in 0.3 M oxalic acid under 5°C and 40 V for 10 h, b the cross-section of typical PAA fabricated in 5 wt% phosphoric acid under −1.5°C and 160 V for 6 h and pore widened in 5 wt% H₃PO₄ at 30°C for 1 h, c oblique view of PAA fabricated 0.3 M oxalic acid under 25°C and 40 V for 3 min and post-treated in 60°C deionized water for 1 h, d the cross-section of PAA fabricated in a mixture of 0.3 M oxalic acid, 0.1 M Al₂SO₄ and 1 wt% ethylene glycol at 60°C for 1 h, e the surface image of Fig. 3(d)