The grievous carbon deposition in Ni-based anode limits its practical application in solid oxide fuel cells for methane conversion. In this work, nano-layer MgO decorated Ni-based anode is successfully prepared by in-situ reduction of Ni0.9-xCu0.1MgxO solid solution. Peak power density of 670 mW cm(-2) at 700 degrees C in humid methane is achieved using Ni0.875Cu0.1-0.025MgO/Sm0.2Ce0.8O2 anode thanks to the improved active surface and the special modulation effect of MgO nano-layer on anode reactions. Interestingly, synchrotron vacuum ultraviolet photoionization mass spectra and high temperature X-ray photoelectron spectra jointly suggest that the effect of MgO on carbon resistance differs with the operating temperatures, which accelerates the steam reforming of CH4 via improving dissociative adsorption of acidic gas H2O at similar to 500 degrees C, while depresses CH4 cracking to carbon and improves the formation of light olefin at similar to 700 degrees C. In addition, possible methane reaction paths over such anode are derived. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.