A comparative theoretical study of the mechanism of ammonia decomposition on various Co/Ni catalysts using density functional theory

Abstract

Bimetallic Co/Ni catalysts have emerged as promising candidates for efficient H₂ production via ammonia decomposition. However, due to the diverse range of surface configurations and atomic ratios observed in various Co/Ni catalysts, it is necessary to systematically understand their heightened activity. In this study, a comparative theoretical investigation employing density functional theory was presented to explore the mechanisms of ammonia decomposition on the Co-Ni(1 1 1), Ni-Co(1 1 1), Co₂Ni(1 1 1), and CoNi₂(1 1 1) surfaces. Our findings highlighted the outstanding catalytic activity presented by Co/Ni catalysts can be attributed to the simplified NN recombination process, with Ni-Co(1 1 1) displaying the lowest energy barrier. We verified that the exceptional performance of Co/Ni surfaces is due to the exclusive synergistic and alloying effects that arise from combining Co and Ni metals. Electronic structure analysis had proved the combined effect of electron transfer from Cobalt to Nickel, resulting in moderate N binding energy, aid in the desorption and transfer of Nitrogen atoms. In addition, we showed that the appropriate Co/Ni catalyst ratio and catalyst surface configuration can improve the catalytic activity of hydrogen production, which provided another strategy for catalyst design.