Electrochemical Screening of Tungsten Trioxide-Nickel Oxide Thin Film Combinatorial Library at Low Nickel Concentrations.

Author(s) Lee, J.S.; Mardare, C.Cela; Mardare, A.Ionut; Hassel, A.Walter
Journal ACS Comb Sci
Date Published 2020 Jan 10

The electrochemical behavior of a tungsten trioxide-nickel oxide (WO-NiO) thin film library was investigated using scanning droplet cell microscopy (SDCM) in 0.1 mol dm sodium perchlorate (NaClO) solution. The WO-Ni film library was deposited by thermal coevaporation on an indium tin oxide (ITO)-coated glass substrate in an atomic Ni concentration range from 2.8 to 15.6 at. %. After an oxidation/crystallization heat treatment, the Ni was oxidized and the crystal structure of WO-NiO was transformed from monoclinic WO (3.5 at. % Ni) to cubic WO (up to 7.1 at. % Ni) and again to monoclinic WO when the Ni amount increased (>11.8 at. %). Proton (H) intercalation (cathodic reaction) and deintercalation (anodic reaction) into the WO-NiO mixed phases was induced. Electrochemical impedance spectroscopy (EIS) and Mott-Schottky (M-S) analysis revealed that the WO-NiO film has n-type bilayer capacitive property, with the outer capacitive layer having a higher defect density than the inner capacitive layer. With a Ni concentration of 7.1 at. %, the WO-NiO film was the most defective in the library. Introduction of the Ni cation into the WO network was associated with changes of the semiconducting properties of the film.

DOI 10.1021/acscombsci.8b00117
ISSN 2156-8944
Citation ACS Comb Sci. 2020.

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