The mechanisms of formation of porous anodic alumina and anodic TiO₂ nanotubes (ATNTs) have attracted increasing attention due to the wide range of application of these materials. The field-assisted dissolution and field-assisted ejection theories are widely supported, despite the fact that many experimental results raise difficult questions. The oxygen bubble mould theory can explain experimental phenomena that contradict the field-assisted dissolution theory, but is controversial as there is a lack of evidence of oxygen evolution. In this work, cavities between the double walls of ATNTs obtained in electrolytes containing NH₄F and H₃PO₄ provide direct evidence of oxygen bubbles resulting in pore formation. Oxygen evolution proceeds at the interface between the anion-contaminated layer and the barrier oxide layer. Small oxygen bubbles that cannot rupture the anion-contaminated layer flow upward with the barrier oxide, resulting in cavities between the double walls of the nanotubes.

由于这些材料的广泛应用，多孔阳极氧化铝和阳极TiO ₂纳米管（ATNT）的形成机理引起了越来越多的关注。尽管许多实验结果提出了困难的问题，但是场辅助的溶出和场辅助的喷射理论得到了广泛的支持。氧气气泡模型理论可以解释与现场辅助溶解理论相矛盾的实验现象，但是由于缺乏氧气逸出的证据而引起争议。在这项工作中，在包含NH ₄ F和H ₃ PO _4的电解质中获得的ATNTs双层壁之间的空腔提供氧气泡导致孔形成的直接证据。氧逸出在阴离子污染层和势垒氧化物层之间的界面处进行。不会破坏阴离子污染层的小氧气气泡与势垒氧化物一起向上流动，从而在纳米管的双壁之间形成空腔。