Fabrication of ordered porous anodic alumina with ultra-large interpore distances using ultrahigh voltages

Fabrication of ordered porous anodic alumina (PAA) with ultra-large interpore distances (Dint) is still a great challenge because of the occurrence of the breakdown or burning during anodization under ultrahigh voltages. Herein, the anodizing of aluminum at ultrahigh voltages (600–800 V) is realized in a series of mixed electrolytes consisting of solutions of citric acid in ethylene glycol and aqueous phosphoric acid solutions. Ordered PAA and patterned Al substrate with ultra-large Dint (1400–2036 nm) have been fabricated by two-step anodization on unpolished substrates successfully.