The development of electrocatalysts capable of efficient reduction of nitrate (NO3-) to ammonia (NH3) is drawing increasing interest for the sake of low carbon emission and environmental protection. Herein, we present a CuCo bimetallic catalyst able to imitate the bifunctional nature of copper-type nitrite reductase, which could easily remove NO2- via the collaboration of two active centers. Indeed, Co acts as an electron/proton donating center, while Cu facilitates NOx- adsorption/association. The bio-inspired CuCo nanosheet electrocatalyst delivers a 100 ± 1% Faradaic efficiency at an ampere-level current density of 1035 mA cm-2 at -0.2 V vs. Reversible Hydrogen Electrode. The NH3 production rate reaches a high activity of 4.8 mmol cm-2 h-1 (960 mmol gcat-1 h-1). A mechanistic study, using electrochemical in situ Fourier transform infrared spectroscopy and shell-isolated nanoparticle enhanced Raman spectroscopy, reveals a strong synergy between Cu and Co, with Co sites promoting the hydrogenation of NO3- to NH3 via adsorbed *H species. The well-modulated coverage of adsorbed *H and *NO3 led simultaneously to high NH3 selectivity and yield. 

/pdf/ampere-level-current-density-ammonia-electrochemical-359k7gih.pdf

Ampere-level current density ammonia electrochemical synthesis using CuCo nanosheets simulating nitrite reductase bifunctional nature

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

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.

Abstract Electrochemical nitrate reduction to ammonia offers an attractive solution to environmental sustainability and clean energy production but suffers from the sluggish *NO hydrogenation with the spin–state transitions. Herein, we report that the manipulation of oxygen vacancies can contrive spin−polarized Fe 1 −Ti pairs on monolithic titanium electrode that exhibits an attractive NH 3 yield rate of 272,000 μg h −1 mg Fe −1 and a high NH 3 Faradic efficiency of 95.2% at −0.4 V vs. RHE, far superior to the counterpart with spin−depressed Fe 1 −Ti pairs (51000 μg h –1 mg Fe –1 ) and the mostly reported electrocatalysts. The unpaired spin electrons of Fe and Ti atoms can effectively interact with the key intermediates, facilitating the *NO hydrogenation. Coupling a flow−through electrolyzer with a membrane-based NH 3 recovery unit, the simultaneous nitrate reduction and NH 3 recovery was realized. This work offers a pioneering strategy for manipulating spin polarization of electrocatalysts within pair sites for nitrate wastewater treatment. 

Spin polarized Fe1−Ti pairs for highly efficient electroreduction nitrate to ammonia

Renewable energy driven electroreduction nitrate to ammonia and in-situ ammonia recovery via a flow-through coupled device.

Electrochemically upcycling wastewater nitrogen such as nitrate (NO3-) and nitrite (NO2-) into an ammonia fertilizer is a promising yet challenging research topic in resource recovery and wastewater treatment. This study presents an electrified membrane made of a CuO@Cu foam and a polytetrafluoroethylene (PTFE) membrane for reducing NO3- to ammonia (NH3) and upcycling NH3 into (NH4)2SO4, a liquid fertilizer for ready-use. A paired electrolysis process without external acid/base consumption was achieved under a partial current density of 63.8 ± 4.4 mA·cm-2 on the cathodic membrane, which removed 99.9% NO3- in the feed (150 mM NO3-) after a 5 h operation with an NH3 recovery rate of 99.5%. A recovery rate and energy consumption of 3100 ± 91 g-(NH4)2SO4·m-2·d-1 and 21.8 ± 3.8 kWh·kg-1-(NH4)2SO4, respectively, almost outcompete the industrial ammonia production cost in the Haber-Bosch process. Density functional theory (DFT) calculations unraveled that the in situ electrochemical conversion of Cu2+ into Cu1+ provides highly dynamic active species for NO3- reduction to NH3. This electrified membrane process was demonstrated to achieve synergistic nitrate decontamination and nutrient recovery with durable catalytic activity and stability.

Electrocatalytic Upcycling of Nitrate Wastewater into an Ammonia Fertilizer via an Electrified Membrane.

Structural and compositional design of multifunctional materials is critical for electrocatalysis, but their rational modulation and effective synthesis remain a challenge. Herein, a controllable one-pot synthesis for construction of trifunctional sites and preparation of porous structures is adopted for synthesizing dispersed MoCoP sites on N, P codoped carbonized substance. This tunable synthetic strategy also endorses the exploration of the electrochemical activities of Mo (Co)-based unitary, Mo/Co-based dual and MoCo-based binary metallic sites. Eventually benefiting from the structural regulation, MoCoP-NPC shows excellent oxygen reduction abilities with a half-wave potential of 0.880 V, and outstanding oxygen evolution and hydrogen evolution performance with an overpotential of 316 mV and 91 mV, respectively. MoCoP-NPC-based Zn-air battery achieves excellent cycle stability for 300 h and a high open-circuit voltage of 1.50 V. When assembled in a water-splitting device, MoCoP-NPC reaches 10 mA cm-2 at 1.65 V. Theoretical calculations demonstrate that the Co atom in the single-phase MoCoP has a low energy barrier for oxygen evolution reaction (OER) owing to the migration of Co 3d orbital toward the Fermi level. This work shows a simplified method for controllable preparation of prominent trifunctional catalysts.

Structural Design Induced Electronic Optimization in Single-Phase MoCoP Nanocrystal for Boosting Oxygen Reduction, Oxygen Evolution, and Hydrogen Evolution.

As a widely used, low-cost, and environmentally friendly carbohydrate polymer, poly(vinyl alcohol) (PVA) is employed to prepare dual cross-linked anion exchange membranes (AEMs) for vanadium flow batteries (VFBs). Tertiary amine group functionalized PVA (i.e., poly(vinyl acetal) (PVAc)) is first synthesized via the acetalization reaction between 4-dimethylaminobenzaldehyde (DMABA) and PVA. Then (5-bromopentyl)-trimethylammonium bromide (BPTMA) is used as the quaternary ammonium reagent, while α,α′-dibromo-p-xylene (DBPX) is adopted as the first cross-linker. Meanwhile, glutaraldehyde (GA) is used as the second cross-linker to further improve the dimensional stability of AEMs. The formed dual cross-linked PVAc-BPTMA-DBPX-GA membranes display enhanced sulfonic acid (SA) uptake and low area resistance (AR), and maintain low VO2+ permeability and suitable mechanical strength simultaneously. For example, the PVAc-0.5BPTMA-0.5DBPX-GA membrane shows a low AR of 0.27 Ω cm2 and an ultralow vanadium ion permeability of 8.09 × 10–8 cm2 min–1. Therefore, the above membrane exhibits a significant ion selectivity of 5.95 × 105 S min cm–3, which is nearly 2 orders of magnitude higher than that of Nafion 115 (i.e., 6.66 × 103 S min cm–3). The VFB based on PVAc-0.5BPTMA-0.5DBPX-GA displays a higher energy efficiency of 85.2% at 100 mA cm–2 than the cell with Nafion 115 (71.1%). Meanwhile, the battery also maintains a stable performance in a long-term operation of 150 cycles. 

Dual Cross-Linked Poly(vinyl alcohol)-Based Anion Exchange Membranes with High Ion Selectivity for Vanadium Flow Batteries

Energy storage systems have aroused public interest because of the blooming development of intermittent renewable energy sources. Vanadium redox flow batteries (VRFBs) are the typical candidates owing to their flexible operation and good cycle durability. However, due to the usage of perfluorinated separator membranes, VRFBs suffer from both high cost and serious vanadium ions cross penetration. Herein, we fabricate a series of low-budget and high-performance blend membranes from polyvinylpyrrolidone (PVP) and cardo-poly(etherketone) (PEKC) for VFRB. A PEKC network gives the membrane excellent mechanical rigidity, while PVP endows the blend membranes with superior sulfonic acid uptake owing to the present N-heterocycle and carbonyl group in PVP, resulting in low area resistance. Meanwhile, blend membranes also display low vanadium ion permeability resulting from the electrostatic repulsion effect of protonated PVP polymer chains towards vanadium ions. Consequently, the 50%PVP-PEKC membrane has a high ionic selectivity of 1.03 × 106 S min cm−3, while that of Nafion 115 is nearly 17 times lower (6.03 × 104 S min cm−3). The VRFB equipped with 50%PVP-PEKC membrane has high coulombic efficiencies (99.3–99.7%), voltage efficiencies (84.6–67.0%) and energy efficiencies (83.9–66.8%) at current densities of 80–180 mA cm−2, and possesses excellent cycle constancy, indicating that low-cost x%PVP-PEKC blend membranes have a great application potentiality for VRFBs.

/pdf/high-performance-and-low-cost-membranes-based-on-poly-31fbnz6u.pdf

High-Performance and Low-Cost Membranes Based on Poly(vinylpyrrolidone) and Cardo-Poly(etherketone) Blends for Vanadium Redox Flow Battery Applications

In this work, a chemical modification method was used to prepare silicone grease with high thermal conductivity. We report two preparation methods for thermal conductive fillers, which are hydroxylated boron nitride-grafted carboxylic silicone oil (h-BN-OH@CS) and amino boron nitride-grafted carboxylic silicone oil (h-BN-NH2@CS). When h-BN-OH@CS and h-BN-NH2@CS were filled with 30 wt% in the base grease, the thermal conductivity was 1.324 W m−1 K−1 and 0.982 W m−1 K−1, which is 6.04 and 4.48 times that of the base grease (0.219 W m−1 K−1), respectively. The interfacial thermal resistance is reduced from 11.699 °C W−1 to 1.889 °C W−1 and 2.514 °C W−1, respectively. Inorganic filler h-BN and organic filler carboxylic silicone oil were chemically grafted to improve the compatibility between h-BN and the base grease. The covalent bond between functionalized h-BN and carboxylic silicone oil is stronger than the van der Waals force, which can reduce the viscosity of the silicone grease.

/pdf/enhanced-thermally-conductive-silicone-grease-by-modified-1f5amxut.pdf

Enhanced Thermally Conductive Silicone Grease by Modified Boron Nitride

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