Favorable Role of the Metal-Support Perimeter Region in Electrochemical NH Synthesis: A Density Functional Theory Study on Ru/BaCeO.

The catalytic electrochemical synthesis of NH on Ru/BaCeO was investigated using density functional theory. The competition between NH formation and the hydrogen evolution reaction (HER) is a key for a high NH formation rate. Our calculations show that H adsorbs more strongly than N at the Ru particle moiety, while the adsorption of N is stronger than the H adsorption at the Ru/BaCeO perimeter, a model for the triple-phase boundary that is proposed to be an active site by experimental studies. This indicates that, while the HER is more favorable at the Ru particle moiety, it should be suppressed at the Ru/BaCeO perimeter. We also calculated the Gibbs free energy changes along the NH formation and found that the NH formation, the NHNH formation, and the NH formation steps have a relatively large Gibbs energy change. Therefore, these are possible candidates for the potential-determining step. The calculated equilibrium potential ( = -0.70 V, vs RHE) is in reasonable agreement with experiments. We also evaluated the reaction energy (Δ) and the activation barrier ( ) of the NH formation at several sites. Δ and were high at the Ru particle moiety (Δ = 1.18 eV and = 1.38 eV) but became low (Δ = 0.32 eV and = 1.31 eV) at the Ru/BaCeO perimeter. These provide the atomic-scale mechanism how the proton conduction in BaCeO assists the electrochemical NH synthesis.