We demonstrate the great feasibility of MBenes as a new class of tandem catalysts for electrocatalytic nitrate reduction to ammonia (NO3RR). As a proof of concept, FeB2 is first employed as a model MBene catalyst for the NO3RR, showing a maximum NH3-Faradaic efficiency of 96.8% with a corresponding NH3 yield of 25.5 mg h-1 cm-2 at -0.6 V vs. RHE. Mechanistic studies reveal that the exceptional NO3RR activity of FeB2 arises from the tandem catalysis mechanism, that is, B sites activate NO3- to form intermediates, while Fe sites dissociate H2O and increase *H supply on B sites to promote the intermediate hydrogenation and enhance the NO3--to-NH3 conversion.

Tandem Electrocatalytic Nitrate Reduction to Ammonia on MBenes.

Electrochemical conversion of nitrate to ammonia offers an efficient approach to reducing nitrate pollutants and a potential technology for low-temperature and low-pressure ammonia synthesis. However, the process is limited by multiple competing reactions and NO3- adsorption on cathode surfaces. Here, we report a Fe/Cu diatomic catalyst on holey nitrogen-doped graphene which exhibits high catalytic activities and selectivity for ammonia production. The catalyst enables a maximum ammonia Faradaic efficiency of 92.51% (-0.3 V(RHE)) and a high NH3 yield rate of 1.08 mmol h-1 mg-1 (at - 0.5 V(RHE)). Computational and theoretical analysis reveals that a relatively strong interaction between NO3- and Fe/Cu promotes the adsorption and discharge of NO3- anions. Nitrogen-oxygen bonds are also shown to be weakened due to the existence of hetero-atomic dual sites which lowers the overall reaction barriers. The dual-site and hetero-atom strategy in this work provides a flexible design for further catalyst development and expands the electrocatalytic techniques for nitrate reduction and ammonia synthesis. 

/pdf/fe-cu-diatomic-catalysts-for-electrochemical-nitrate-17fjtud2.pdf

Fe/Cu diatomic catalysts for electrochemical nitrate reduction to ammonia

Designing genuine electrocatalysts that selectively reduce nitrate/nitrite (NOx−) is becoming ever more vital to produce ammonia (NH3) sustainably, safeguard the environment, and even rebalance the Earth’s nitrogen cycle. Since 2020, the aim of NH3 electrosynthesis from NOx− has been pursued, and with electrode design explosion, the field has been able to progressively distinguish effective strategies. Collective knowledge of state-of-the-art catalytic systems is indisputably essential for implementing this clean technology in industry. Hence, we present an overview of nicely constructed denitrifying electrocatalysts along with structural features that are more favorable for turning NOx− into NH3, focusing on performance, mechanisms, upgraded devices, etc. Key NH3-evolving efficiency optimization ideas with critical insights are identified and highlighted. We discuss high-quality works that exemplify gaps separating studies from large-scale deployment and proposed relevant bridging solutions. Outlook on challenges faced by NOx−-to-NH3 electrolysis systems are emphasized to inspire future works. Designing genuine electrocatalysts that selectively reduce nitrate/nitrite (NOx−) is becoming ever more vital to produce ammonia (NH3) sustainably, safeguard the environment, and even rebalance the Earth’s nitrogen cycle. Since 2020, the aim of NH3 electrosynthesis from NOx− has been pursued, and with electrode design explosion, the field has been able to progressively distinguish effective strategies. Collective knowledge of state-of-the-art catalytic systems is indisputably essential for implementing this clean technology in industry. Hence, we present an overview of nicely constructed denitrifying electrocatalysts along with structural features that are more favorable for turning NOx− into NH3, focusing on performance, mechanisms, upgraded devices, etc. Key NH3-evolving efficiency optimization ideas with critical insights are identified and highlighted. We discuss high-quality works that exemplify gaps separating studies from large-scale deployment and proposed relevant bridging solutions. Outlook on challenges faced by NOx−-to-NH3 electrolysis systems are emphasized to inspire future works. 

Advances in ammonia electrosynthesis from ambient nitrate/nitrite reduction

Electrochemical reduction of nitrate to ammonia (NO3RR) holds a great promise for attaining both NH3 electrosynthesis and wastewater purification. Herein, single‐atom Bi alloyed Pd metallene (Bi1Pd) is reported as a highly effective NO3RR catalyst, showing a near 100% NH3‐Faradaic efficiency with the corresponding NH3 yield of 33.8 mg h−1 cm−2 at −0.6 V versus RHE, surpassing those of almost all ever reported NO3RR catalysts. In‐depth theoretical and operando spectroscopic investigations unveil that single‐atom Bi electronically couples with its neighboring Pd atoms to synergistically activate NO3− and destabilize *NO on Bi1Pd, leading to the reduced energy barrier of the potential‐determining step (*NO→*NOH) and enhanced protonation energetics of NO3−‐to‐NH3 pathway.

Single‐Atom Bi Alloyed Pd Metallene for Nitrate Electroreduction to Ammonia

Natural nitrogen cycle has been severely disrupted by anthropogenic activities. The overuse of N-containing fertilizers induces the increase of nitrate level in surface and ground waters, and substantial emission of nitrogen oxides causes heavy air pollution. Nitrogen gas, as the main component of air, has been used for mass ammonia production for over a century, providing enough nutrition for agriculture to support world population increase. In the last decade, researchers have made great efforts to develop ammonia processes under ambient conditions to combat the intensive energy consumption and high carbon emission associated with the Haber-Bosch process. Among different techniques, electrochemical nitrate reduction reaction (NO3 RR) can achieve nitrate removal and ammonia generation simultaneously using renewable electricity as the power, and there is an exponential growth of studies in this research direction. Here we provide a timely and comprehensive review on the important progresses of electrochemical NO3 RR, covering the rational design of electrocatalysts, emerging C-N coupling reactions, and advanced energy conversion and storage systems. Moreover, future perspectives are proposed to accelerate the industrialized NH3 production and green synthesis of chemicals, leading to a sustainable nitrogen cycle via prosperous N-based electrochemistry. This article is protected by copyright. All rights reserved.

Electrochemical Nitrate Reduction: Ammonia Synthesis and the Beyond.

Nitrate electrocatalytic reduction (NO3RR) for ammonia production is a promising strategy to close the N‐cycle from nitration contamination, as well as an alternative to the Haber–Bosch process with less energy consumption and carbon dioxide release. However, current long‐term stability of NO3RR catalysts is usually tens of hours, far from the requirements for industrialization. Here, symmetry‐broken Cusingle‐atom catalysts are designed, and the catalytic activity is retained after operation for more than 2000 h, while an average ammonia production rate of 27.84 mg h−1 cm−2 at an industrial level current density of 366 mA cm−2 is achieved, obtaining a good balance between catalytic activity and long‐term stability. Coordination symmetry breaking is achieved by embedding one Cu atom in graphene nanosheets with two N and two O atoms in the cis‐configuration, effectively lowering the coordination symmetry, rendering the active site more polar, and accumulating more NO3− near the electrocatalyst surface. Additionally, the cis‐coordination splits the Cu 3d orbitals, which generates an orbital‐symmetry‐matched π‐complex of the key intermediate *ONH and reduces the energy barrier, compared with the σ‐complex generated with other catalysts. These results reveal the critical role of coordination symmetry in single‐atom catalysts, prompting the design of more coordination‐symmetry‐broken electrocatalysts toward possible industrialization.

Coordination Symmetry Breaking of Single‐Atom Catalysts for Robust and Efficient Nitrate Electroreduction to Ammonia

Nitrate has been commonly used in fertilizers, synthetic materials, and explosives; however, its irregular release leads to extensive contaminants in many sources of drinking water because of its high solubility and mobility. Unfortunately, efficient nitrate removal at low concentrations has been challenging for a long time. Inspired by nitrate reductase with iron as the active center in plants, we constructed a novel nanozyme catalyst, FeNPs@MXene, and proved that the confinement effect of Cl size facilitates the formation of FeOOH nanoshuttles. The FeNPs@MXene electrocatalyst can achieve selective catalytic reduction of nitrate to ammonia, including up to 97.8% conversion of nitrate and high selectivity toward ammonia (76.8%). By precisely analyzing in situ electrochemical online differential electrochemical mass spectrometry (DEMS) and 15N isotope labeling experiments, the electroreduction of nitrate to ammonia was clearly proven. Using density functional theory (DFT) calculations and conductive atomic force microscopy (C-AFM), the built-in electric field formed between FeOOH and MXene is proven to be beneficial to nitrate adsorption and can lower the reaction barrier of key intermediates. This design of iron-based nanozymes offers new illuminating insight into the NO3RR. 

A Bioinspired Iron-Centered Electrocatalyst for Selective Catalytic Reduction of Nitrate to Ammonia

Bimetallic Cu-Fe catalysts on MXene for synergistically electrocatalytic conversion of nitrate to ammonia.

Highly Dispersed In‐Situ Grown Bi
 2
 O
 3
 Nanosheets on Ti
 3
 C
 2
 T
 
 x
 
 MXene for Selective Electroreduction of Nitrate to Ammonia

Polyethylene has excellent electrical insulation, but its low thermal stability and breakdown strength limit its application in the field of high-voltage (HV) and ultrahigh voltage (UHV) power cables. In this work, we have developed a new organic peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy) hexane (Bi25), which can efficiently trigger the crosslinking of polyethylene (Bi25-XLPE). Bi25-XLPE does not produce gas byproducts and has a longer scorching time. All performance of Bi25-XLPE sheets fulfill the standard of the 500 kV power cable insulation due to the void-free nature, higher crosslinking density and crystallinity. In addition, one 500 kV power cable model was constructed by COMSOL, which confirmed the breakdown strength (up to 61.66 kV/mm) and stability of Bi25-XLPE. 

An efficient strategy triggered crosslinking of polyethylene and its application in
 degassing‐free
 ultrahigh voltage power cables

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Coordination Symmetry Breaking of Single‐Atom Catalysts for Robust and Efficient Nitrate Electroreduction to Ammonia

A Bioinspired Iron-Centered Electrocatalyst for Selective Catalytic Reduction of Nitrate to Ammonia

Bimetallic Cu-Fe catalysts on MXene for synergistically electrocatalytic conversion of nitrate to ammonia.

Highly Dispersed In‐Situ Grown Bi 2 O 3 Nanosheets on Ti 3 C 2 T x MXene for Selective Electroreduction of Nitrate to Ammonia

An efficient strategy triggered crosslinking of polyethylene and its application in degassing‐free ultrahigh voltage power cables