Electrodeposited NiCoP on nickel foam as a self-supported cathode for highly selective electrochemical reduction of nitrate to ammonia

Abstract

Electrocatalytic reduction of NO3– is a promising approach to remove environmentally harmful NO3– from wastewaters while simultaneously generating ammonia, an important raw material for fertilizer production. Considering that multiple products may be generated, it is critical to prepare an efficient and highly selective electrocatalyst for NH3 formation. In this work, we reported on electrodeposition of cobalt–nickel bimetallic phosphide on three-dimensional nickel foam (NiCoP/NF), a binder-free electrode as an efficient catalyst for electroreduction of nitrate to NH3. Under 50 mM Na2SO4 and 50 mg N L-1 NaNO3, a low current density of 2 mA cm−2 and initial solution pH of 7, it not only ensured almost complete removal of nitrate (97.68%), but also presented excellent ammonia selectivity (95.44%). It is worth mentioning that nitrite, a more toxic intermediate, remained at a very low level (no higher than 0.085 mg N L-1) throughout the reaction and it's almost undetectable after the reaction. Additionally, this electrocatalyst exhibited excellent consecutive stability and low energy consumption. Two primary processes (i.e., Co-mediated direct reduction and H*-mediated indirect reduction) contributed to the nitrate electroreduction by the NiCoP/NF cathode. This study demonstrates the promising application of NiCoP/NF in electrocatalytic NO3– reduction for ammonia production and provides new insights for ration design of high-performance composite electrode materials.