2D copper metal-organic framework as an electrocatalyst for the highly efficient electrochemical reduction of low concentration nitrate/nitrite-to-ammonia

Abstract

The accumulation of nitrate/nitrite (NO_x^–) in wastewater poses a threat on ecological safety. Electrocatalytic NO_x^– reduction to ammonia (NO_x^–RR) is feasible to realize green ammonia production. This work developed a 2D copper metal-organic framework of Cu-BDC (H₂BDC = 1,4-benzene dicarboxylic acid) as an efficient electrocatalyst for NO_x^–RR, exhibiting high-performance with the NH₃ yield of 71.20 μmol‧h⁻¹‧cm⁻² and a Faraday efficiency of 80.9 % at −0.746 V (vs. RHE) for NO₂⁻RR, and the NH₃ yield of 130.16 μmol‧h⁻¹‧cm⁻² and a Faraday efficiency of 67.42 % at −0.946 V (vs. RHE) for NO₃⁻RR. Isotope labelled ¹⁴NO₃⁻ and ¹⁵NO₃⁻ produced ¹⁴NH₄⁺ and ¹⁵NH₄⁺, supporting the formation of NH₃ comes from the NO₃⁻RR. In three NO_x^–RR cycles, all NH₃ yields and Faraday efficiencies show a slight change, demonstrating an excellent electrocatalytic stability in NO_x^–RR. Our work provides a new material platform for the elimination of nitrate and nitrite through electrocatalytic reduction.