1. Electronic Structural Origin of the Catalytic Activity Trend of Transition Metals for Electrochemical Nitrogen Reduction
- Author
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Yeo, Byung Chul, Kong, Jimin, Kim, Donghun, Goddard, William A., Park, Hyun S., and Han, Sang Soo
- Abstract
As an alternative to the conventional Haber–Bosch process for NH3synthesis that operates under harsh conditions, an electrochemical process has recently been pursued. Here, using a joint experiment–density functional calculation approach, we determine the activity trend of four transition metals (TMs) (Fe, Ru, Rh, and Pd) for N2reduction to NH3: Fe > Ru > Pd > Rh, where the protonation step of *N2to form *N2H (* indicates surface sites) is a potential determining step (PDS). The activity trend of the electrocatalysts is determined by the ability of the adsorbate (*N2) over the catalyst surfaces to easily obtain electrons at the PDS with an assumption of a scaling relationship between the activation energy barrier and the free energy difference. In electronic structures, the ability can be estimated by the energy difference between the lowest unoccupied molecular orbital (LUMO) of the adsorbed N2on the TM surfaces and the fermi energy (EF). For early TMs (e.g., Sc and Ti) where the PDS is *NH protonation reaction to form *NH2, the activity of the TMs can be similarly explained with an electronic structural feature that is the energy difference between the LUMO of the *NH and the EF. Based on the origin, we additionally consider 10 TMs (Ni, Cr, Mn, Co, Cu, Mo, Ag, W, Pt, and Au) and then determine the activity trend of the total 16 diverse TMs for NH3synthesis. We expect that this work could pave the way to novel alloy catalysts with a high activity for electrochemical NH3synthesis.
- Published
- 2019
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