CoFe-double hydroxide honeycomb covered CuCo2O4 nanosheets as core-shell nanostructure catalyst for efficient electrocatalytic nitrate conversion to ammonia

Abstract

A unique sandwich structure electrocatalyst was prepared for electrocatalytic nitrate reduction (ECNO3R) into ammonia. CuCo2O4 spinel oxide nanosheets were grown on a carbon cloth (CC), and CoFe layered double hydroxide (CoFe-LDH) honeycomb was subsequently electroplated on each CuCo2O4 nanosheet. Compared with CoFe-LDH directly grown on CC, this sandwich structure has much larger electrochemically active surface area with more catalytic sites, and also provide better contact between the catalytic sites and the nitrate substrates. This therefore enhanced the effective conversion of a wide concentration range of nitrate into ammonia. Meanwhile, the nitrate removal rate, ammonia selectivity and Faraday efficiency (FE) are all larger than 90% at the nitrate concentration lower than 500 mg L -1 . After 14 times of repeated stability tests, the FE retained 86% -91% of the initial value, and the ammonia yield did not decline significantly. The isotope tracing and blank comparison experiments verified that the ECNO3R was not contaminated by any external nitrogen sources. Both density functional theory and X-ray photoelectron spectroscopy confirmed the synergistic catalytic effect between CuCo2O4 and CoFe-LDH. Moreover, active hydrogen (* H) was not involved in the ECNO3R. This work provided an effective and green way to transform nitrate pollutants into valuable ammonia.