Effect of Substrate Temperature on the Electrochemical and Supercapacitance Properties of Pulsed Laser-Deposited Titanium Oxynitride Thin Films

Electrocatalytically active titanium oxynitride (TiNO) thin films were fabricated on commercially available titanium metal plates using a pulsed laser deposition (PLD) method for energy storage applications. The elemental composition and nature of bonding were analyzed using x-ray photoelectron spectroscopy (XPS) to reveal the reacting species and active sites responsible for the enhanced electrochemical performance of the TiNO electrodes. Symmetric supercapacitor devices were fabricated using two TiNO working electrodes separated by an ion-transporting layer to analyze their real-time performance. The galvanostatic charge-discharge studies on the symmetric cell have indicated that TiNO films deposited on the polycrystalline titanium plates at lower temperatures are superior to TiNO films deposited at higher temperatures in terms of storage characteristics. For example, TiNO films deposited at 300°C exhibited the highest specific capacity of 69 mF/cm2 at 0.125 mA/cm2 with an energy density of 7.5 Wh/cm2. The performance of this supercapacitor (300°C TiNO) device is also found to be ∼ 22 % better compared to that of a 500°C TiNO supercapacitor with a capacitance retention ability of 90% after 1000 cycles. The difference in the electrochemical storage and capacitance properties is attributed to the reduced leaching away of oxygen from the TiNO films by the Ti plate at lower deposition temperatures, leading to higher oxygen content in the TiNO films and, consequently, a high redox activity at the electrode/electrolyte interface.