Electrochemical promotion of Ni9Pd nanoparticles (NPs) with low Pd content (Ni:Pd = 9:1 atomic ratio) supported on yttria-stabilized zirconia (YSZ) solid-electrolyte was evaluated for the first time for complete methane oxidation. Electron Energy Loss Spectroscopy (EELS) showed a Pd core with a Ni first shell surrounded by 3-4 nm layer of Pd outer shell. This core double-shell structure of Ni9Pd NPs enhanced the catalytic activity and stability compared to mono-metallic Pd and Ni NPs under open-circuit. The reversible electrochemical promotion of Ni9Pd was obtained upon positive polarization between 425 and 500 degrees C. At 425 degrees C, the reaction rate increase reached 240% corresponding to apparent Faradaic efficiency of 25. On Ni9Pd NPs the reaction exhibited electrophobic behavior, i.e., the rate increased with anodic polarization, under all experimental conditions of this study. The results demonstrate the advantage of using Ni9Pd bi-metallic nanoparticles with core double-shell structure for methane complete oxidation due to the synergetic effect between Pd and Ni and very low amount of expensive Pd phase. EPOC with this type of highly dispersed and low noble metal content catalysts may find a way in the real world catalytic converters for gas exhaust treatment. (C) 2019 Elsevier Inc. All rights reserved.