Enhanced interfacial adhesion between TiO2 and underlying Ti substrate and its mechanism in boric acid contained electrolyte

TiO2 nanotube arrays prepared in a hydrofluoric electrolytes are prone to peeling off from the underlying titanium due to a weaker interfacial adhesion between the nanotube layers and Ti substrates. Herein, a new method is proposed to adjust the growth process of nanotubes by adding boric acid to the anodizing electrolytes to increase the adhesion. Results revealed that boric acid form complex with F- at high concentration and slowly releases F- as the reaction proceeds, thereby slowing down the growth rate of the nanotubes and inhibiting the fluoride-rich TiO2 layer that causes the poor adhesion. The improved binding force is attributed to the combined effect of the "fluoride ion enrichment" theory and the "residual stress" theory. Furthermore, the addition of boric acid increases the photoelectric catalytic performance of titanium dioxide nanotube arrays by about 7 times, and the capacitance area increased by 55.10%.