Fabrication of Ni-Ti-O nanotube arrays by anodization of NiTi alloy and their potential applications

Nickel-titanium-oxide (Ni-Ti-O) nanotube arrays (NTAs) prepared on nearly equiatomic NiTi alloy shall have broad application potential such as for energy storage and biomedicine, but their precise structure control is a great challenge because of the high content of alloying element of Ni, a non-valve metal that cannot form a compact electronic insulating passive layer when anodized. In the present work, we systemically investigated the influence of various anodization parameters on the formation and structure of Ni-Ti-O NTAs and their potential applications. Our results show that well controlled NTAs can be fabricated during relatively wide ranges of the anodization voltage (5-90 V), electrolyte temperature (10-50°C) and electrolyte NH₄F content (0.025-0.8 wt%) but within a narrow window of the electrolyte H₂O content (0.0-1.0 vol%). Through modulating these parameters, the Ni-Ti-O NTAs with different diameter (15-70 nm) and length (45-1320 nm) can be produced in a controlled manner. Regarding potential applications, the Ni-Ti-O NTAs may be used as electrodes for electrochemical energy storage and non-enzymic glucose detection, and may constitute nanoscaled biofunctional coating to improve the biological performance of NiTi based biomedical implants.