Anodic growth of ultra-long Ni-Ti-O nanopores

Although long nanotubes with a large specific surface area are desirable in many applications, it is difficult to produce long Ni-Ti-O nanotubes on nearly equiatomic NiTi alloy in fluoride (F)-containing ethylene glycol (EG) by anodization. In this work, a new electrolyte composed of EG, H₂O, and HCl is designed and adopted to fabricate long nanopores rather than nanotubes on the NiTi alloy. By applying an anodization voltage of 10 V to the EG solutions containing 5.0–11.0 vol% H₂O and 0.125–0.75 M HCl, Ni-Ti-O nanopores with a diameter of about 70 nm are produced. The nanopore length increases almost linearly with anodization time and by optimizing the experimental conditions, nanopores with a length of 160 μm can be prepared.