Sustainable ammonia production from nitrate reduction assisted by methanol oxidation using Co@CF bifunctional electrocatalysts

Abstract

Global nitrate pollution poses a significant challenge to ecological water systems. The electrocatalytic treatment of nitrate wastewater, coupled with high-value ammonia production, offers a promising solution. Herein, we have developed a copper-based cobalt catalyst, Co@CF, using in situ electrodeposition, achieving a faradaic efficiency of 92.49% for catalytic ammonia production and an ammonia yield of 5.99 mg h⁻¹ cm⁻². As a bifunctional catalyst, Co@CF also demonstrates excellent performance in catalyzing methanol oxidation to produce formic acid. Coupling the methanol oxidation reaction (MOR) with the nitrate reduction reaction (NO₃RR) significantly enhances the faradaic efficiency and yield of ammonia production to 95.16% and 7.51 mg h⁻¹ cm⁻², respectively, while achieving an anodic formic acid production efficiency of 91.74% and a yield of 18.53 mg h⁻¹ cm⁻². Moreover, the coupling system maintains excellent catalytic performance for ammonia synthesis over 60 h. In situ Raman spectroscopy reveals that Co²⁺ and Co³⁺ in Co@CF consume OH⁻ from hydrolysis, allowing H⁺ to participate in the hydrogenation of intermediate species during NO₃⁻ reduction, thereby enhancing ammonia selectivity. This study presents an effective strategy for the clean and efficient conversion of nitrate to ammonia, offering a promising approach for sustainable ammonia synthesis.