3D integrated non-noble metal oxides nano arrays for enhanced nitrate electroreduction to ammonia

Abstract

The electrochemical nitrate reduction reaction (eNO3RR) to ammonia (NH3) is a promising alternative method to the Haber-Bosch process that requires high temperature and pressure. In this contribution, the integrated Co3O4 nanowire arrays on Ni foam (Co3O4/NF) are reported to exhibit the outstanding performance with a high NH3 yield rate of 117.01 mg h−1cm−2, a superior NH3 Faradaic efficiency of 99.28 %, a high effective current density of 1475.71 mA cm−2, and a good operation durability during 40 consecutive recycling tests (40 h) in 1.0 M NaOH (0.1 M NaNO3). The high-valence metal cations as electron-deficient centers can act as Lewis-acid sites, favorably interacting with the Lewis base NO3−, and accordingly boosting the NO3− adsorption and activation. Moreover, the in-situ growth array configuration provides the substantial active sites and constructs a fast electron-transport channel, thus facilitating the conversion of NO3−-to-NH3. Density functional theory (DFT) calculations also reveal that the Co atoms as the active sites are preferred to adsorb NO3−, implying that the NO3− electroreduction dominates the cathodic reaction rather than hydrogen evolution reaction. This study provides a viable method to design integrated electrodes with enhanced eNO3RR activity and selectivity, which might have broad prospects in the application of renewable energy.