Growth and electrochemical characterization of single phase Mo_xN films for the fabrication of hybrid double layer capacitors

摘要

The electrochemical stability and capacitance in H_2SO_4. KOH, and propylene carbonate of single phase polycrystalline gamma -Mo_2N and delta -MnN thin film electrodes deposited at 350 and 700 deg C, respectively, at a rate of 0.5 mu m/min on Ti substrates have been determined. The films were prepared by chemical vapor deposition at 100 torr using Mo(CO)_6 and NH_3 flowing at 1.5 standard liters per minute (silm). Cyclic voltammetry referenced to a standard Ag/AgCl electrode indicated that both phases possessed a more positive voltage stability limit in H_2SO_4 than KOH. Films of gamma -Mo_2N had voltage stability ranges of-0.3 to 0.6 V and 1.3 to 0.3 V in 4.4 M H_2SO_4 and 7.6 M KOH, respectively. Films of delta -MoN possessed voltage stability ranges of-0.3 to 0.7 V and -1.3 to-0.3 V in the same respective electrolytes. Both phase had a voltage stability of approximately one volt in the propylene carbonate elecrolyte. These results were used to design and fabricate a hyrid capacitor composed of a Ta/Ta_2O_5 anode and a delta -MoN cathode contained in an electrolyte of 4.4M H_2SO_4. The hybrid device and an operating voltage range between 0 and 50 V, a temperature range of -55 to +90 deg C, a capacitance of approx 5.0 mF and an energy density of approx approx 1.32 J/cm~3. This device is now in pre-production at Evans Capacitor Corporation.