Computational insights into nitrogen reduction reaction catalyzed by transition metal doped graphene: Comparative investigations

The nitrogen reduction reaction (NRR) is not only applied for the electro-catalysis in water to produce ammonia (NH3), but also expected to be the discharge process in cathode of the proposed lithium nitrogen (Li-N-2) battery. In this work, we performed density functional theory (DFT) simulations on NRR electro-catalysis mediated by both proton (H+) and lithium ion (Li+), with transition metal doped graphene (MN4-Gr) as the catalytic substrate. Comparative calculations were carried out by taking the atom species, doping concentration, solvation effect and van der Waals (vdW) interaction into consideration. After computational screening of N-2 binding performance, CrN4-Gr, MnN4-Gr, FeN4-Gr and RuN4-Gr were selected as the suitable catalytic substrate. The free energy profiles indicate that MnN4-Gr is the best candidate for NRR electro-catalysis among the four MN4-Gr, with a limiting potential (U-L) of -0.68 V. Furthermore, we investigated the possible reaction pathway during the discharge process in cathode of Li-N-2 battery. The simulation results demonstrate that none of the MN4-Gr works as the applicable cathode catalysts. It is important to find out that the one exhibits low vertical bar U-L vertical bar value may be unsuitable cathode catalyst in Li-N-2 battery. Our work first compares the NRR mediated by H+ and Li+, which provides computational understanding on the newly proposed Li-N-2 battery.