Efficient electrochemical reduction of nitrate to ammonia over metal-organic framework single-atom catalysts

The design and preparation of efficient catalysts for ammonia production under mild conditions is a desirable but highly challenging target. Here, we report a series of single-atom catalysts [M-SACs, M = Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Mo(II)] derived from UiO-66 containing structural defects and their application to electrochemical reduction of nitrate (NO3 -) to ammonia (NH3). Cu-SAC and Fe-SAC exhibit remarkable yield rates for NH3 production of 30.0 and 29.0 mg h-1 cm-2, respectively, with a high Faradaic efficiency (FENH3) of over 96% at -1.0 V versus the reversible hydrogen electrode. Importantly, their catalytic performance can be retained in various simulated wastewaters. Complementary experiments confirmed the nature of single-atom sites within these catalysts and the binding domains of NO3 - in UiO-66-Cu. In situ spectroscopic techniques, coupled with density functional theory calculations confirm the strong binding of NO3 - and the formation of reaction intermediates, thus facilitating the catalytic conversion to NH3. Producing ammonia is challenging and requires efficient and selective catalysts to drive the reaction. Here, a series of single-atom catalysts derived from UiO-66 containing structural defects show efficient electrochemical reduction of nitrate to ammonia.