Thiol Ligand-Modified Au for Highly Efficient Electroreduction of Nitrate to Ammonia

Electroreduction of nitrate (NO₃^–) to ammonia (NH₃) is an environmentally friendly route for NH₃ production, serving as an appealing alternative to the Haber–Bosch process. Recently, various noble metal-based electrocatalysts have been reported for electroreduction of NO₃^–. However, the application of pure metal electrocatalysts is still limited by unsatisfactory performance, owing to the weak adsorption of nitrogen-containing intermediates on the surface of pure metal electrocatalysts. In this work, we report thiol ligand-modified Au nanoparticles as the effective electrocatalysts toward electroreduction of NO₃^–. Specifically, three mercaptobenzoic acid (MBA) isomers, thiosalicylic acid (ortho-MBA), 3-mercaptobenzoic acid (meta-MBA), and 4-mercaptobenzoic acid (para-MBA), were employed to modify the surface of the Au nanocatalyst. During the NO₃^– electroreduction, para-MBA modified Au (denoted as para-Au/C) displayed the highest catalytic activity among these Au-based catalysts. At −1.0 V versus reversible hydrogen electrode (vs RHE), para-Au/C exhibited a partial current density for NH₃ of 472.2 mA cm^–2, which was 1.7 times that of the pristine Au catalyst. Meanwhile, the Faradaic efficiency (FE) for NH₃ reached 98.7% at −1.0 V vs RHE for para-Au/C. The modification of para-MBA significantly improved the intrinsic activity of the Au/C catalyst, thus accelerating the kinetics of NO₃^– reduction and giving rise to a high NH₃ yield rate of para-Au/C.