Ammonia (NH3) is an ideal carbon-free power source in the future sustainable hydrogen economy for growing energy demand. The electrochemical nitrate reduction reaction (NO3−RR) is a promising approach for nitrate removal and NH3 production at ambient conditions, but efficient electrocatalysts are lacking. Here, we present a metal–organic framework (MOF)–derived cobalt-doped Fe@Fe2O3 (Co-Fe@Fe2O3) NO3−RR catalyst for electrochemical energy production. This catalyst has a nitrate removal capacity of 100.8 mg N gcat−1 h−1 and an ammonium selectivity of 99.0 ± 0.1%, which was the highest among all reported research. In addition, NH3 was produced at a rate of 1,505.9 μg h−1 cm−2, and the maximum faradaic efficiency was 85.2 ± 0.6%. Experimental and computational results reveal that the high performance of Co-Fe@Fe2O3 results from cobalt doping, which tunes the Fe d-band center, enabling the adsorption energies for intermediates to be modulated and suppressing hydrogen production. Thus, this study provides a strategy in the design of electrocatalysts in electrochemical nitrate reduction.

Efficient n = O bond activation is crucial for the catalytic reduction of nitrogen compounds, which is highly affected by the construction of active centers. In this study, n = O bond activation was achieved by a single-atom catalyst (SAC) with phosphorus anchored on a Co active center to form intermediate N -species for further hydrogenation and reduction. Unique phosphorus-doped discontinuous active sites exhibit better n = O activation performance than conventional N -cooperated single-atom sites, with a high Faradic efficiency of 92.0% and a maximum ammonia yield rate of 433.3 μg NH4·h −1 ·cm −2 . This approach of constructing environmental sites through heteroatom modification significantly improves atom efficiency and will guide the design of future functional SACs with wide-ranging applications.

The electrochemical conversion of waste nitrate (NO 3 − ) to valuable ammonia (NH 3 ) is an economical and environmentally friendly technology for sustainable NH 3 production. It is beneficial for environmental nitrogen pollution management and is also an appealing alternative to the current Haber–Bosch process for NH 3 production. However, owing to the competing hydrogen evolution reaction, it is necessary to design highly efficient and stable electrocatalysts with high selectivity. Herein, we report a rational design of Fe nanoparticles wrapped in N-doped carbon (Fe@N 10 -C) as a high NH 3 selective and efficient electrocatalyst using a metal–organic framework precursor. We constructed a catalyst with new active sites by doping with nitrogen, which activated neighboring carbon atoms and enhanced metal-to-carbon electron transfer, resulting in high catalytic activity. These doped N sites play a key role in the NO 3 − electroreduction. As a result, the Fe@N 10 -C nanoparticles with optimal doping of N demonstrated remarkable performance, with a record-high NO 3 − removal capacity of 125.8 ± 0.5 mg N g cat −1 h −1 and nearly 100 % (99.7 ± 0.1%) selectivity. The catalyst also delivers an impressive NH 3 production rate of 2647.7 μg h −1 cm −2 and high faradaic efficiency of 91.8 ± 0.1%. This work provides a new route for N-doped carbon–iron catalysis application and paves the way for addressing energy and environmental issues.

Although most of the studies focus on the nanoscale zero‐valent iron (nZVI), it still ineffective when comes to in situ utilization due to its intrinsic drawbacks such as rapid aggregation, biotoxicity, high cost, complex preparation process, and so forth. With advantages of lower health risk, lower cost, and simpler fabricate method, microscale zero‐valent iron (mZVI) shows more attractiveness for groundwater remediation than nZVI if its main problem, passivation, can be alleviated. In order to overcome the passivation of mZVI, (mZVI+AC)/CA was produced by encapsulating mZVI and activated carbon (AC) in spherical calcium alginate (CA) matrix in this study. The method effectively solved the passivation of mZVI and showed great long‐effective removal of Cr(VI). The Cr(VI) removal efficiency of (mZVI+AC)/CA could maintain 1.6–2.69 times as much as that of pure mZVI for 0–1500 pore volumes. The maximum Cr(VI) removal capacity reached 100.47 mg/g, which exceeded most of mZVI‐based materials and even some nZVI‐based materials. In addition, mechanism of Cr(VI) removal was revealed by X‐ray diffraction and X‐ray photo‐electron spectroscopy. The results showed that chemisorption, physisorption, reduction, oxidation, and precipitation were involved in the process. Pseudo‐second order model and Freundlich isotherm model were best fitted in kinetics and isotherm experiments, respectively.

No abstract