Active hydrogen tuning by copper–cobalt bimetal catalysts for boosting ammonia electrosynthesis from simulated wastewater†

Abstract

The electrochemical nitrate reduction reaction (NO₃RR) represents a promising approach to balance the nitrogen cycle, converting environmental pollutant NO₃⁻ to valuable ammonia (NH₃). However, the whole reaction involves complex proton-coupled electron transfer processes, requiring the development of efficient catalysts. Owing to unique d-orbitals, Cu-based catalysts exhibit excellent performance. Here, we design a Cu₅–Co₅ bimetal nanocomposite that achieves a high FE_NH3 of 94.1%, a yield rate of 14.8 mg h⁻¹ cm⁻² and great stability over twenty hours. The yield rate can be enhanced in a flow cell and reach 30.9 mg h⁻¹ cm⁻². We test the performance of the Cu₅–Co₅ catalyst for simulated wastewater treatment, exhibiting a yield rate of 6.7 mg h⁻¹ cm⁻² at −100 mA cm⁻². Furthermore, in situ ATR-SEIRAS and Raman spectra reveal the reaction pathway on the Cu₅–Co₅ catalyst. The Cu can adsorb NO₃⁻ and convert to *NO₂⁻, while Co(OH)₂ derived from metallic Co can promote water spillover and facilitate the subsequent *NO₂⁻-to-NH₃ conversion.