Formaldehyde electrocatalytic oxidation with an optimum activity at Cu-7.5 at.% Pd was found by screening along the entire compositional spread using the flow-type scanning droplet cell microscopy. Thin film combinatorial libraries were deposited by sputter co-deposition. The crystallographic properties, surface microstructure and contact potential difference were investigated along the compositional spread using X-ray diffraction (XRD), scanning electron microscopy (SEM), scanning kelvin probe (SKP) and on define points by X-ray photoelectron spectroscopy (XPS). The electrocatalytic oxidation was determined as a function of the Pd concentration along the thin film combinatorial libraries. The entire compositional spread (2.4-38.5 at% Pd) showed the suitability for being implemented in the formaldehyde detection, which was evidenced by cyclic voltammetric measurements. The maximum response was obtained at a Pd content of 7.5 at.% (E-sHE = -0.35 V) with a current density value of 1.81 mA cm(-2). In the same compositional region, the most prominent drop in the contact potential difference values measured by SKP was present. The results were explained based on a synergistic effect of Pd concentration, surface properties and different electron density. Also, a good stability and reproducibility of the values were achieved, indicating the suitability of this material as catalyst for formaldehyde oxidation, e.g. in a sensor. (C) 2016 Elsevier B.V. All rights reserved.