Rapid Quantification of Film Thickness and Metal Loading for Electrocatalytic Metal Oxide Films

Abstract

The thicknesses and metal loadings of amorphous nickel, iron, and iridium oxide films widely used for solar fuel electrocatalysis were determined by cross-sectional scanning electron microscopy (SEM) and X-ray fluorescence (XRF) spectroscopy measurements. The thicknesses for a series of films, which were systematically varied from 10 to 400 nm using photodeposition techniques, were accurately measured by cross-sectional SEM using a protocol that successfully resolves the relevant catalyst layers. XRF measurements recorded on each of the films provided a strong linear correlation (R2 > 0.97) with the thicknesses determined by cross-sectional SEM. The electrochemical surface areas (ECSAs) determined by double-layer capacitance measurements, a technique widely used in the electrocatalysis community, showed a linear relationship for iridium oxide film thicknesses but not with those consisting of nickel and iron. These results highlight the limitations of using ECSA to determine catalyst film thicknesses and m...