Constructing a CoO–CuOx heterostructure for efficient electrochemical reduction of nitrate to ammonia

Abstract

The electrochemical nitrate reduction reaction (NtrRR) represents a sustainable approach to realize the green synthesis of ammonia, yet developing efficient electrocatalysts to improve the sluggish reaction kinetics and the undesirable selectivity towards NH₃, while simultaneously suppressing the hydrogen evolution reaction (HER), is critical. Herein, we report a CoO–CuO_x heterostructure catalyst that is prepared by in situ growing Cu(OH)₂ nanoarrays on Cu foam (CF), followed by hydrothermal treatment in the presence of a Co salt. Multiple characterizations revealed that a well-defined heterostructure with a distinct interface is formed between the CoO and CuO_x phases. In the NtrRR test, the CoO–CuO_x/CF catalyst displayed a high NH₃ selectivity of 94.29%, an NH₃ faradaic efficiency (FE_NH3) of 92.15%, and a high NH₃ yield rate of 0.510 mmol h⁻¹ cm⁻². Also, the heterostructure catalyst had remarkable catalytic stability, evidenced by the negligible FE_NH3 decay after four consecutive cycling tests. This excellent catalytic performance is attributed to the fact that the interfaces in the CuO_x and CoO heterostructure can facilitate the electron transfer, hence improving the reaction kinetics. This study offers a generic strategy for preparing efficient and durable electrocatalysts toward the NtrRR and other multiple electron/proton-involved electrocatalytic reactions.