On the Interfacial Adhesion between TiO2 Nanotube Array Layer and Ti Substrate

Anodic titania nanotube arrays (TNTAs) with higher aspect ratio are observed to be liable to spontaneous curling or delamination from the underlying titanium (Ti) metal once dried because of the poor interfacial adhesion of the TNTA layer to the underlying Ti, especially when a thin Ti sheet is used. The interfacial adhesion strength was shown to decrease with increasing thickness of the TNTA layer. In this work, although the preparation of TNTAs in a frequently used fluoride-containing solution was completed, different anodization processes were further performed at lower current densities or at lower voltages for a short time in the same electrolyte to increase the adhesion. The mechanical test demonstrated that better adhesion properties have been achieved by applying these anodization posttreatment processes. It is believed that during the fabrication of TNTAs, a large residual stress at the interface of the nanotube layer and the underlying Ti is created. It is the residual stress that leads to the weak interfacial adhesion. The anodization posttreatment processes can reduce or eliminate the residual stress, thereby improving the interfacial adhesion. Further, these processes can also boost the performances of TNTAs for supercapacitors. When the anodization posttreatment processes are implemented at 1 mA cm(-2) or at 10 V for 5 min, considerable improvements in the interfacial adhesion are observed. Particularly, both posttreatment processes are also applicable to the very thin Ti sheet (similar to 18 mu m). The realization of robust and adherent TNTAs grown on very thin Ti sheets can not only significantly improve the volumetric capacitances of TNTAs but also make TNTAs an attractive material in flexible supercapacitor applications.