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

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.