Preparation of titanium nitride/oxynitride nanotube array via ammonia-free PECVD method for enhancing supercapacitor performance

In this work, TiN/TiON nanotubes are developed by 3 step anodization of titanium sheet and facile plasma nitriding process of TiO2 nanoarrays in a PECVD reactor as a supercapacitor electrode. The plasma chamber temperature was changed to find the best nitrogen doping condition to increase electrical conductivity and areal capacitance. Also, the plasma temperatures were 450, 550, and 650 °C. X-ray diffraction (XRD) indicates the TiN peaks at 2θ= 37°, 43.2°, 62.2°, 47.6°, and 78.6° when the substrate temperature arrives at 650 °C. Raman spectroscopy was used to evaluate the phase and structure of nitrided samples when the electron microscopy analysis showed the unchanged morphology of TiO2 nanotubes before and after nitriding. XPS spectra of the plasma nitrided sample at 650 °C show the presence of oxynitride and nitride on the surface of nanotubes. So, the highest nitrogen incorporation in the TiO2 structure occurs at 650 °C. Also, electrochemical investigations showed an areal capacitance of 35.14 mFcm−2 for plasma nitrided electrode at 650 °C that represents 9 times more capacity than annealed TiO2 electrode (3.82 mF cm−2). Moreover, the novel plasma nitrided electrode has also indicated superior rate capability (80%) and cycle stability with low degradation of about 15% after 6000 cycles.