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.