To facilitate the understanding of the Ni-Fe bimetallic system, unsupported nickel, iron and a series of Ni-Fe catalysts were synthesized, characterized and tested for the CO2 methanation relevant for power to gas technology. Characterizations revealed the formation of various types of Ni-Fe alloys in the reduced catalysts. The activity results revealed that Ni-Fe catalysts with weight ratio of Ni:Fe > 1 showed a significantly improved rate (similar to 2-5 times) of CO2 conversion and CH4 formation compared to Ni and Fe due to the formation of suitable nickel-rich Ni-Fe alloy. A change in surface morphology of these alloy catalysts was also detected. The Ni-rich Ni-Fe alloy formed in 90Ni10Fe and 75Ni25Fe differed from each other. The former was the most active due to the absence of unalloyed Fe, in contrast to the presence of unalloyed Fe in the later. Such observations would be helpful to design better performing Ni-Fe catalysts. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.