Enhancing electroreduction of NO3− to NH3 over Co3O4 nanowires via N-doping†

Abstract

Electroreduction of nitrate (NO₃⁻) has emerged as a promising strategy for producing ammonia (NH₃) at room temperature in recent years. However, the formation of the less electron-consuming H₂ byproduct seriously limits the conversion efficiency of NO₃⁻ to NH₃. In this study, we identify that N-doped Co₃O₄ can effectively convert NO₃⁻ to NH₃ with a high performance (NH₃ yield rate: 7.18 ± 0.59 mg h⁻¹ cm⁻², faradaic efficiency: 96.7 ± 0.88%), which is significantly higher than that of pure Co₃O₄ (NH₃ yield rate: 4.95 ± 0.54 mg h⁻¹ cm⁻²) and most reported Co-based catalysts (Table S1, ESI). Density functional theory (DFT) calculations coupled with X-ray absorption near-edge structure (XANES) experiments reveal that N-doping in Co₃O₄ releases more positive charge on the Co atom site due to charge compensation. This oxidized Co atom site enhances the adsorption of NO₃⁻ while weakening the adsorption of H⁺ through Coulombic interactions, thus improving NO₃RR activity. Overall, our study provides an efficient electrocatalyst to avoid the formation of the H₂ byproduct to facilitate the conversion of NO₃⁻ to NH₃, and opens new avenues towards achieving green ammonia production by controlling Coulombic interactions.