Exploration of mixed metal oxide films as urea oxidation electrocatalysts.

Sputter coating of mixed metal oxides is realized with composition gradients for effective materials exploration. Specifically, we use NiO as a basis for urea oxidation electrocatalysis and generate a sample series in which a second metal is added in various concentrations, namely Cu, Co, or Mo. The parameters are set so that the film thickness is maintained approximately constant on the order of 30 nm for ease of comparison. The films are characterized in terms of elemental composition (X-ray microanalysis, EDXS), phase composition (grazing incidence X-ray diffraction, GI-XRD), and thickness (X-ray reflectometry, XRR, complemented with spectroscopic ellipsometry, SE) and tested for electrocatalytic proficiency with cyclic voltammetry and electrochemical impedance spectroscopy (EIS). The sample exhibiting the most obvious preference for urea oxidation at low applied potential contains approximately 50% molybdenum (molar amount with respect to the total metal).