Strategies toward Selective Electrochemical Ammonia Synthesis

Abstract

The active and selective electroreduction of atmospheric nitrogen (N2) to ammonia (NH3) using energy from solar or wind sources at the point of use would enable a sustainable alternative to the Haber–Bosch process for fertilizer production. While the process is thermodynamically possible, experimental attempts thus far have required large overpotentials and have produced primarily hydrogen (H2). In this Perspective, we show how insights from electronic structure calculations of the energetics of the process, combined with mean-field microkinetic modeling, can be used to (1) understand the activity and selectivity challenges in electrochemical NH3 synthesis and (2) propose alternative strategies toward an economically viable process. In particular, we develop the theoretical understanding for two promising actionable avenues that are gaining interest in the experimental literature, (1) circumventing the scaling relations between adsorbed surface intermediates and (2) using nonaqueous electrolytes to suppress the competing hydrogen evolution reaction.

A Combined Theory‐Experiment Analysis of the Surface Species in Lithium‐Mediated NH3 Electrosynthesis

“…Recently, we proposed models that demonstrated how the large availability of protons in aqueous systems is the main reason why selectivity to NRR is so low . Following this model, we herein focus on non‐aqueous electrolytes, where the activity of protons can be controlled independently of catalyst surface by operating at a low proton concentration.…”

High‐Performance Nitrogen Fixation over Mo Atom Modified Defective α‐MnO2 (001)

“…We further calculated the kinetic barrier of adsorbed N 2 reduction to *N−*NH to assess the kinetic activity of Mo Mn +Vo@α‐MnO 2 (001) used as electrocatalyst of NRR. It is found that the formation of *N−*NH needs to overcome a low kinetic barrier of 0.8 eV comparable with that intrinsic barrier for the electrochemical steps (0.7 eV), meaning the fast kinetics for cathode reaction (Figure S8).…”

Plasma-driven catalysis: green ammonia synthesis with intermittent electricity

“…116,117 Current strategies include the use of three-dimensional materials and bio-inspired materials, as well as the use of non-aqueous electrolytes. 92,118,119…”