CoFe alloy nanoparticles embedded in Carbon nanofibers for efficient synthesis of ammonia from nitrate reduction

Abstract

Alloy can optimize the rate determining step of nitrate reduction through synergistic effect, significantly reducing the reaction overpotential, so series of CoxFey alloy nanoparticles embedded in carbon nanofibers (CNFs) are fabricated to reduce nitrate to ammonia. Co9Fe1@CNFs attains a large ammonia yield rate of 31.1 mg h⁻¹ mg⁻¹cat. and a high Faradaic efficiency (FE) of 83.5%% at -0.6 V vs. RHE. In situ electrochemical tests and density functional theory (DFT) calculations reveal that the reaction follows a deoxygenation-hydrogenation pathway, where the alloyed sites lower the rate-determining step (RDS) barrier to only 0.40 eV. Ammonia (NH3) acts as a fundamental chemical feedstock and a promising carbon-free energy carrier, garnering significant attention in agriculture, food production, pharmaceuticals and power generation. [1][2][3] Currently, industrial NH3 synthesis relies predominantly on the conventional Haber-Bosch process, which suffers from excessive energy consumption and substantial greenhouse gas emissions. 4 Consequently, developing sustainable and energy-efficient alternatives for ammonia synthesis is critically urgent.In recent years, by virtue of the high liquid solubility of nitrate (NO3 -) and low dissociation energy of N=O bond (204 kJ mol -1 ), electrochemical nitrate reduction to ammonia (NO3RR) emerges as a prominent alternative approach for ammonia production. [5][6][7] Nevertheless, this reduction process involves an intricate eightelectron and nine-proton transfer mechanism, where competition between intermediates and hydrogenolysis reactions (HER) severely limits its efficiency and selectivity. 8, 9 Thus, efficient and durable catalysts with high selectivity for NH3 generation are desirably required.Recently, some supported metal catalysts have attracted significant attention due to their high activity in NO3RR. 10-14 Among