The ethanol photoelectro-oxidation reaction was investigated under visible irradiation on TaON-based catalysts modified with Pd and IrO2. Prepared catalysts were characterized by energy dispersive X-ray analysis, X-ray diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy. Electrochemical investigations were conducted in 0.2 mol L-1 NaOH solution, by voltammetric multi-cycling experiments for dark and illuminated electrodes. Product and intermediate distribution analyses were carried out by differential electrochemical mass spectrometry and high-resolution liquid chromatography aiming at establishing the photoelectrocatalytic reaction pathways. The presence of small amounts of palladium (ca 2 atom% Pd in TaON) is essential to obtain enhanced ethanol photoelectro-oxidation under visible light in alkaline medium. Photocatalytic reaction promotes formation of molecular hydrogen, carbon dioxide, acetate ions, and acetaldehyde (the last one subsequently converted into crotonaldehyde and acetaldol), while the main product formed by the ethanol photoelectro-oxidation is only acetate ion. (C) The Author(s) 2018. Published by ECS.