Electrochemical ammonia synthesis via nitrate reduction on Fe single atom catalyst

TLDR

Electrochemical nitrate reduction to ammonia offers a green alternative to Haber‑Bosch, but competing pathways and lack of efficient catalysts hinder selective conversion. DFT calculations show that atomically dispersed Fe sites mediate nitrate reduction via specific intermediates and identify the potential‑limiting steps. The Fe single‑atom catalyst achieves ~75 % Faradaic efficiency and a yield of ~20 000 µg h⁻¹ mg_cat⁻¹ (0.46 mmol h⁻¹ cm⁻²), suppressing N–N coupling and thereby delivering high ammonia selectivity.

Abstract

Abstract Electrochemically converting nitrate, a widespread water pollutant, back to valuable ammonia is a green and delocalized route for ammonia synthesis, and can be an appealing and supplementary alternative to the Haber-Bosch process. However, as there are other nitrate reduction pathways present, selectively guiding the reaction pathway towards ammonia is currently challenged by the lack of efficient catalysts. Here we report a selective and active nitrate reduction to ammonia on Fe single atom catalyst, with a maximal ammonia Faradaic efficiency of ~ 75% and a yield rate of up to ~ 20,000 μg h −1 mg cat. −1 (0.46 mmol h −1 cm −2 ). Our Fe single atom catalyst can effectively prevent the N-N coupling step required for N 2 due to the lack of neighboring metal sites, promoting ammonia product selectivity. Density functional theory calculations reveal the reaction mechanisms and the potential limiting steps for nitrate reduction on atomically dispersed Fe sites.