Efficient Electroreduction of Nitrate into Ammonia at Ultralow Concentrations Via an Enrichment Effect

Abstract

The electroreduction of nitrate (NO3−) pollutants to ammonia (NH3) offers an alternative approach for both wastewater treatment and NH3 synthesis. Numerous electrocatalysts have been reported for the electroreduction of NO3− to NH3, but most of them demonstrate poor performance at ultralow NO3− concentrations. In this study, a Cu‐based catalyst for electroreduction of NO3− at ultralow concentrations is developed by encapsulating Cu nanoparticles in a porous carbon framework (Cu@C). At −0.3 V vs reversible hydrogen electrode (RHE), Cu@C achieves Faradaic efficiency for NH3 of 72.0% with 1 × 10−3 m NO3−, which is 3.6 times higher than that of Cu nanoparticles. Notably, at −0.9 V vs RHE, the yield rate of NH3 for Cu@C is 469.5 µg h−1 cm−2, which is the highest value reported for electrocatalysts with 1 × 10−3 m NO3−. An investigation of the mechanism reveals that NO3− can be concentrated owing to the enrichment effect of the porous carbon framework in Cu@C, thereby facilitating the mass transfer of NO3− for efficient electroreduction into NH3 at ultralow concentrations.

Nanoreactor Based on Cyclodextrin for Direct Electrocatalyzed Ammonia Synthesis

“…In KOH electrolyte solution, the coordination of K + ions with hydroxyl groups in γ-CD induces the formation of extended 3D γ-CD-K + frameworks with six CDs as a building unit. − Such γ-CD-K + frameworks containing the uncoordinated hydroxyl groups and the complexed K + ions can act as cage nanoreactors to initiate NO 3 – RR. The uncoordinated edge hydroxyl groups within cage nanoreactors, as dominant catalytic sites, would effectively absorb and activate nitrate through hydrogen-bonding interactions to drive NO 3 – RR. , Besides, the electrostatic interaction through those complexed K + ions confined within cage nanoreactors and NO 3 – also contributes to the enhanced enrichment effect of nitrate ions and promotes the mass transfer, thus realizing the high-efficiency electroreduction of NO 3 – into NH 3 over the γ-CD-K + complex under ambient conditions.…”

“…The uncoordinated edge hydroxyl groups within cage nanoreactors, as dominant catalytic sites, would effectively absorb and activate nitrate through hydrogen-bonding interactions to drive NO 3 − RR. 51,52 Besides, the electrostatic interaction through those complexed K + ions confined within cage nanoreactors and NO 3 − also contributes to the enhanced enrichment effect of nitrate ions and promotes the mass transfer, thus realizing the highefficiency electroreduction of NO 3 − into NH 3 over the γ-CD-K + complex under ambient conditions.…”

Electrochemical ammonia synthesis by reduction of nitrate on Au doped Cu nanowires

“… 33,34 In addition, the bending mode of –NH 2 is also found at ∼1457 cm −1 . 34,35 Clearly, as the applied potential increased, the peak intensity of −NO x intermediates and –NH 2 gradually increased ( Fig. 4a ).…”

Cation modified Fe–N–C catalyst for the electrochemical reduction of nitrate in solutions of low ionic strength

“…25 Geng et al developed Cu nanoparticles encapsulated in porous carbon, which can convert NO 3 − to NH 3 in a solution containing 1 mM NO 3 − and 1 M KOH with a FE of 72% at −1.1 V vs. SHE. 26…”

“…25 FE of 72% at −1.1 V vs. SHE. 26 The NO 3 − RR in solutions of low ionic strength is hindered by the electrostatic repulsion between the negatively charged cathode and NO 3 − anions. Moreover, the reduction of anionic species is retarded by the so-called Frumkin effect, [27][28][29] which results from the potential difference between the outer Helmholtz plane (OHP) and the bulk electrolyte (orange curve in Fig.…”