Reaction mechanism and kinetics for N reduction to ammonia on the Fe-Ru based dual-atom catalyst

Environmental and energy considerations demand that the Haber-Bosch process for reducing N 2 to NH 3 be replaced with electrochemical ammonia synthesis where the H atoms come from water instead of from H 2 . But a practical realization of electrochemical N 2 reduction reaction (NRR) requires the development of new generation electrocatalysts with low overpotential and high Faraday efficiency (FE). A major problem here is that the hydrogen evolution reaction (HER) competes with NRR. Herein, we consider new generation dual-site catalysts involving two different metals incorporated into a novel two-dimensional C 3 N-C 2 N heterostructure that provides a high concentration of well-defined but isolated active sites that bind two distinct metal atoms in a framework that facilitates electron transfer. We report here the mechanism and predicted kinetics as a function of applied potential for both NRR and HER for the (Fe-Ru)/C 3 N-C 2 N dual atom catalyst. These calculations employ the grand canonical potential kinetics (GCP-K) methodology to predict reaction free energies and reaction barriers as a function of applied potential. The rates are then used in a microkinetic model to predict the turn-over-frequencies (TOF) as a function of applied potential. At U = 0 V, the FE for NRR is 93%, but the current is only 2.0 mA cm −2 . The onset potential (at 10 mA cm −2 ) for ammonia on Fe-Ru/C 3 N-C 2 N is −0.22 V RHE . This leads to a calculated TOF of 434 h −1 per Fe-Ru site. We expect that the mechanisms for NRR and HER developed here will help lead to new generations of NRR with high TOF and FE. To understand the reaction mechanism and kinetics of N 2 reduction reaction and competing hydrogen evolution reaction on the dual-atom catalyst as a function of applied potential by applying the Grand canonical potential kinetics.