Metal-organic frameworks derived low-cost Cu-doped Co3O4 for efficient reduction of ultra-low nitrate concentrations to ammonia.

[Display omitted] • Metal-organic frameworks derived low-cost Cu-doped Cu-Co 3 O 4 /NF is simply prepared. • High ammonia yield rate and FE are obtained under ultra-low nitrate concentrations. • The introduction of Cu promotes the surface-to-interior charge transfer and intrinsic activity. • The results of In-situ FTIR and DFT reveal atomic hydrogen reduction pathway. • The synergistic effect of Cu and Co suppresses the HER and drops the free energy barriers of rate determining step. The electrochemical reduction of nitrate to ammonia represents a potential approach for the valorization of waste, offering the dual benefit of mitigating various environmental concerns and concurrently yielding the valuable product of ammonia. However, on the way to its further application, the lacking of low-cost and efficient electrocatalysts under low nitrate concentrations is still one pressing issue because of the intense hydrogen evolution reaction (HER) competition and many by-products. Herein, metal–organic frameworks (MOF) derived low-cost Cu-Co 3 O 4 /NF exhibits excellent electrocatalytic activity in the low nitrate concentrations (2 mmol/L), attaining the ammonia yield rate of 0.076 mmol h−1 cm−2 and 92.4 % Faradic efficiency at −0.53 V vs. RHE. The combined results of In-situ FTIR and theoretical calculation reveal the atomic hydrogen reduction pathway, decrease in free energy of intermediate reactions and inhibition of HER of Cu-Co 3 O 4 /NF. This work introduces one economical, efficient and simple strategy and further demonstrates the superior effect of MOF derivatives in fascinating low nitrate concentration reduction to ammonia. [ABSTRACT FROM AUTHOR]