Cascade Electrocatalytic Reduction of Nitrate to Ammonia Using Bimetallic Covalent Organic Frameworks with Tandem Active Sites

Abstract

Electrochemical nitrate reduction reaction (NO₃RR) is a promising approach to simultaneously realize pollutant removal and ammonia generation. However, this process involves the transfer of eight electrons and nine protons along with multiple by-products, resulting in a significant challenge for achieving high ammonia yield and selectivity. Herein, we introduced bimetallic covalent organic frameworks catalysts with Cu and Co active sites to achieve a two-step tandem reaction, avoiding excessive nitrite accumulation and enabling efficient NO₃RR. For the initial two-electron process, the Cu sites in the bimetallic catalyst exhibit a strong binding affinity with nitrate, promoting their conversion to nitrite. The Co sites enhance the supply and adsorption of active hydrogen and stabilize the subsequent six-electron process, thereby improving the overall catalytic efficiency. Compared to monometallic Cu and Co catalysts, the CuCo bimetallic catalyst demonstrates superior ammonia yield and Faradaic efficiency (NH₃ yield rate = 20.8 mg·h^-1·cm^-2, FE = 92.16% in 0.3 M nitrate). Such coordinated two-step process advances the efficiency and applicability of NO₃RR through optimizing a cascade catalytic reaction, thereby establishing an innovative path for the engineering of NO₃RR electrocatalysts.