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 NOx− pollutants, synthesis of valuable NH3 and generation of “green” electricity.