3d transition metal oxide-loaded Cu nanowires for enhanced electrochemical nitrate-to-ammonia conversion

Abstract

The electrocatalytic nitrate reduction reaction (eNO₃RR) provided a promising route to mitigate NO₃⁻ contamination while producing green ammonia (NH₃). Cu-based materials were employed as promising electrocatalysts to activate NO₃⁻ due to the strong interaction between the d-orbitals of Cu-based catalysts and the antibonding π* orbital of NO₃⁻. Nevertheless, Cu species exhibit limited adsorption affinity towards intermediates and face challenges in hydrogen activation, leading to the accumulation of byproducts and reducing the eNO₃RR efficiency. Herein, we employed an electrochemical deposition method to load transition metal oxides (TMOs, Fe, Co, and Ni) onto Cu nanowires (Cu NWs) and modulate the electron structure of the Cu species, thereby elevating the Cu d-band center and enhancing the adsorption of N-containing intermediates. The loaded TMOs act as active sites for water dissociation to boost hydrogen evolution activation and prevent H* from dissociating to form H₂, significantly improving the selectivity of the electrocatalyst. CoO_x/Cu exhibited outstanding eNO₃RR performance, achieving an NH₃ yield of 73.2 mg h⁻¹ cm⁻² and a high faradaic efficiency of 99.4% at −0.5 V vs. RHE. Furthermore, excellent electrochemical stability was also achieved with a voltage of approximately −0.43 V vs. RHE for more than 280 hours at a current density of 1 A cm⁻². The electrocatalytic efficiency and stability surpass those of most state-of-the-art Cu-based electrocatalysts. Additionally, in situ characterization revealed that incorporating CoO_x on Cu NWs enhanced the adsorption of N-containing intermediates on Cu species. This work highlights the synergistic interaction between TMOs and the Cu substrate, offering valuable insights for designing efficient electrocatalysts for electrocatalytic NO₃⁻ reduction.