Carbon dots-boosted active hydrogen for efficient electrocatalytic reduction of nitrate to ammonia

Electrocatalytic nitrate reduction reaction (NO 3 RR) has gained great attention as a means of transforming environmental waste into fertilizers. However, the activity and efficiency of NO 3 RR is severely hindered by the inevitable self-coupling of active hydrogen (H* ads ) competing with nitrate (NO 3 - ) hydrogenation. Here, an efficient electrocatalyst is developed by combining multifunction carbon dots (CDs) with bornite (Cu 5 FeS 4 ) towards the comprehensive manipulation of the adsorption and conversion of H* ads . As a result, the optimized CDs/Cu 5 FeS 4 presents a remarkable NH 3 yield of 215.19 μmol h −1 cm −2 with a Faradaic efficiency of 86.52 %. Importantly, the introduction of CDs can greatly increase the NH 3 yield and FE compared with pure Cu 5 FeS 4 , even under a wide range of NO 3 - concentrations. Meanwhile, the catalyst can successfully transform simulated NO 3 - groundwater into NH 3 by using a flow cell. The cyclic voltammetry and electron paramagnetic resonance tests indicate that CDs effectively promote the production of H* ads and participate in NO 3 - hydrogenation. Kinetic isotope experiments reveal the role of CDs in accelerating water dissociation and proton transfer processes. In-situ Raman spectroscopy demonstrate that CDs effectively boosts the adsorption and conversion of NO 3 - to NO 2 - and NO 2 - to NH 3 . And DFT calculations reveal CDs significantly reduce the energy barrier of the key rate-determining step (*NO 3 to *NO 2 ), which thus promotes the hydrogenation reaction between H* ads and N-containing intermediates. This work provides an interesting insight for enhancing the catalytic activity of ammonia by utilizing CDs to promote the generation and conversion of H* ads . Multifunctional CDs modified Cu 5 FeS 4 directly reducing nitrate and nitrate groundwater to ammonia by comprehensively manipulating the adsorption and conversion of H* ads . • The optimized CDs/Cu 5 FeS 4 presents a remarkable ammonia yield rate. • CDs/Cu 5 FeS 4 can successfully transforms simulated nitrate groundwater into NH 3 . • CDs can promote the hydrogenation of N-containing intermediates through comprehensive manipulate of active hydrogen. • In-situ Raman spectroscopy and DFT calculations reveal the key role of CDs during the NO 3 RR process.