Triple Regulations via Fe Redox Boosting Nitrate Reduction to Ammonia at Industrial Current Densities.

Abstract

Electrochemical nitrate reduction reaction (NO3-RR) has promising prospects for green synthesis of ammonia and environmental remediation. However, the performance of catalysts at high current density usually suffers from the high energy barrier for the nitrate (NO3-) to nitrite (NO2-) and the competitive hydrogen evolution. Herein, we proposed a two-step relay mechanism through spontaneous redox reaction followed electrochemical reaction by introducing low-valence Fe species into Ni2P nanosheets to significantly enhance the NO3-RR performance at industrial current density. The existence of low-valence Fe species bypasses the NO3- to NO2- step through the spontaneous redox with NO3- to produce NO2- and Fe2O3, regulates the electronic structure of Ni2P to reduce the barrier of NO2- to NH3, thirdly prohibits the hydrogen evolution by consuming the excess active hydrogen through reduction of Fe2O3 to recover low-valence Fe species. The triple regulations via Fe redox during the two-step relay reactions guarantee the Fe-Ni2P@NF high ammonia yield of 120.1 mg h-1 cm-2 with Faraday efficiency of more than 90% over a wide potential window and a long-term stability of more than 130 h at ~1000 mA cm-2. This work provides a new strategy to realize the design and synthesis of nitrate reduction electrocatalysts at high current densities.