Ruthenium-Doped Copper Nanowires for Nitrite/Nitrate to Ammonia Conversion and Their Integration in Zinc–Nitrite Batteries

Abstract

The electrochemical reduction of nitrite (NO₂⁻) and nitrate (NO₃⁻) not only enables sustainable, circular routes to produce ammonia (NH₃), but also eliminates pollutants in groundwater. In this article, we report a facile synthesis of Ru-doped Cu nanowires on Cu foam electrodes with low Ru (0.48 wt.%) loading. The composite electrode shows high-performance in the NO₂⁻/NO₃⁻ to NH₃ electroreduction, giving NH₃ Faradaic efficiency of up to 100% and NH₃ yield rates up to 33.2 mg h⁻¹ cm⁻² at −0.2 V versus RHE in NO₂⁻ reduction. For the nitrate-to-ammonia reduction, the electrode also shows high activity with Faradaic efficiency of 88.4% (at −0.6 V versus RHE) and a yield rate of 62.5 mg h⁻¹ cm⁻² (at −1.0 V versus RHE). We show that the electrode can easily be integrated into a Zn–nitrite battery, giving a power density of 9.1 mW cm⁻², a NH₃ yield rate of 1.88 mg h⁻¹ cm⁻² and a nitrite-to-ammonia Faradaic efficiency of 88.9% at a current density of 20 mA cm⁻². The system combines three productive outputs, that is removal of NO_x⁻ pollutants, synthesis of valuable NH₃ and generation of “green” electricity.