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

Electrocatalytic nitrate reduction reaction (NO3RR) has gained great attention as a means of transforming environmental waste into fertilizers. However, the activity and efficiency of NO3RR is severely hindered by the inevitable self-coupling of active hydrogen (H*ads) competing with nitrate (NO3- ) hydrogenation. Here, an efficient electrocatalyst is developed by combining multifunction carbon dots (CDs) with bornite (Cu5FeS4) towards the comprehensive manipulation of the adsorption and conversion of H*ads. As a result, the optimized CDs/ Cu5FeS4 presents a remarkable NH3 yield of 215.19 mu mol h- 1 cm-2 with a Faradaic efficiency of 86.52 %. Importantly, the introduction of CDs can greatly increase the NH3 yield and FE compared with pure Cu5FeS4, even under a wide range of NO3 - concentrations. Meanwhile, the catalyst can successfully transform simulated NO3 - groundwater into NH3 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 NO3 - hydrogenation. Kinetic isotope experiments reveal the role of CDs in accelerating water dissociation and proton transfer processes. Insitu Raman spectroscopy demonstrate that CDs effectively boosts the adsorption and conversion of NO3 - to NO2and NO2 - to NH3. And DFT calculations reveal CDs significantly reduce the energy barrier of the key ratedetermining step (*NO3 to *NO2), 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.