In this study, we have examined the preparation of thin films of Ni oxyhydroxide, which are used for batteries, supercapacitors, and electrochromic devices, by reactive sputtering. Transmittance and resistivity were found to decrease with the incorporation of H 2 O into the sputtering gas. This indicates that the valence state of Ni atoms in the film changes from Ni 2þ to Ni 3þ . Peaks due to Ni-OH and hydrogen bonded OH were observed by Fourier transform IR (FTIR) spectroscopy of the films sputtered in O 2 þ H 2 O mixed gas. From the obtained results, it is confirmed that Ni oxyhydroxide films are formed by reactive sputtering in O 2 þ H 2 O mixed gas. An electrochromic coloration efficiency of 29 cm 2 /C was obtained in 1 M KOH aqueous electrolyte solution for the Ni oxyhydroxide films.

Ni oxyhydroxide (NiOOH) thin films were prepared by reactive sputtering in an atmosphere of H2O gas, and the effects of sputtering gas pressure on their electrochromic properties in KOH aqueous electrolyte were studied. The largest optical density change was obtained for the thin films deposited under high sputtering gas pressures of approximately 6.7 Pa because of their low film density and chemical composition close to NiOOH. Stable transmittance change during coloring and bleaching cycles was obtained for the film from the first cycle up to 100 cycles.

Ni oxyhydroxide (NiOOH) thin films were prepared by reactive sputtering in an atmosphere of H2O gas, and effects of sputtering gas pressure on their electrochromic properties were studied. The largest optical density change was obtained for the thin films deposited under high sputtering pressures of around 50 mTorr because of their low film density and chemical composition close to NiOOH.

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