Highly Efficient Electroenzymatic Cascade Reduction Reaction For The Conversion of Nitrite to Ammonia

Abstract The electrochemical nitrite reduction reaction provides an alternative approach to offer sustainable ammonia source routes for repairing imbalances in the global nitrogen cycle. In this work, electrocatalysis is combined with enzymatic catalysis to provide an efficient and clean process for recoverable ammonia production. NO₂⁻ is reduced to NH₃ by electroenzymatic cascade reduction reaction on a bioconjugate, in which 1‐butyl‐3‐methylimidazolium bromide (IL_BMB) modified chloroperoxidase (CPO) is fixed on polyethyleneimine (PEI) modified multi‐walled carbon nanotubes (MWCNT) to from bioconjugate (CPO‐IL_BMB/MWCNT‐PEI). ¹⁵N and ¹⁴N isotope labeling reveal that the NH₃ species is derived from NO₂⁻ reduction. Density functional theory calculations identify that the Fe^II species in heme center of CPO serve as the key active site for NO₂⁻ reduction. The amino groups derived from MWCNT‐PEI not only serve as a bridge to covalently immobilize CPO but also enrich the NO₂⁻ ion at electrode/solution interface through electrostatic interactions. The low energy barrier of NO₂⁻ reduction and low adsorption free energy of the intermediate result in high Faradaic efficiency (96.4%), NH₃ yield (112.7 mg h⁻¹ mg_CPO⁻¹), and high selectivity in pH 5.0 solution. The highly efficient electroenzymatic reaction ensurespromising applications in the conversion of NO₂⁻ to NH₃.