Dendritic Cell-Inspired Designed Architectures toward Highly Efficient Electrocatalysts for Nitrate Reduction Reaction

Pd Clusters Loaded with Multivalent Cu Foam for Superior Electrochemical Nitrate Reduction and Selective N≡N Bond Formation

The electrochemical denitrification of nitrate (NO3 -) in actual wastewater to nitrogen (N2) is an effective approach to reversing the current imbalance of the nitrogen cycle and the eutrophication of water. However, electrostatic repulsion between NO3 - and the cathode results in the low efficiency of NO3 - reduction reaction (NO3RR). Here, density functional theory (DFT) calculations are used as a theoretical guide to design a Pd cluster-loaded multivalent Cu foam (Pd/Cu2O-CF) electrocatalyst, which achieves a splendid 97.8% NO3 - removal rate, 97.9% N2 selectivity, 695.5 mg N g-1 Pd h-1 reduction efficiency, and 60.0% Faradaic efficiency at -1.3 V versus SCE. The projected density of states (pDOS) indicates that NO3 - and Pd/Cu2O-CF are bonded via strong complexation between the O 2p (in NO3 -) and Cu 3d (in Cu2O) with the input of voltage, which reduces the electrostatic repulsion and enhances the enrichment of NO3 - on the cathode. In-situ characterizations demonstrate that Pd[H] can reduce Cu2O to Cu, and subsequently Cu reduces NO3 - to nitrite (NO2 -) accompanied by in situ reconfiguration of multivalent Cu foam. NO2 - is then transferred to the surface of Pd clusters by the cascade catalysis and accelerates the breaking of N─O bonds to form Pd─N, and eventually achieves the N≡N bond formation.

Tin (II) Chloride Salt Melts as Non-Innocent Solvents for the Synthesis of Low-Temperature Nanoporous Oxo-Carbons for Nitrate Electrochemical Hydrogenation

Carbonaceous electrocatalysts offer advantages over metal-based counterparts, being cost-effective, sustainable, and electrochemically stable. Their high surface area increases reaction kinetics, making them valuable for environmental applications involving contaminant removal. However, their rational synthesis is challenging due to the applied high temperatures and activation steps, leading to disordered materials with limited control over doping. Here, a new synthetic pathway using carbon oxide precursors and tin chloride as a p-block metal salt melt is presented. As a result, highly porous oxygen-rich carbon sheets (with a surface area of 1600 m2 g-1 ) are obtained at relatively low temperatures (400 °C). Mechanistic studies reveal that Sn(II) triggers reductive deoxygenation and concomitant condensation/cross-linking, facilitated by the Sn(II) → Sn(IV) transition. Due to their significant surface area and oxygen doping, these materials demonstrate exceptional electrocatalytic activity in the nitrate-to-ammonia conversion, with an ammonia yield rate of 221 mmol g-1 h-1 and a Faradic efficiency of 93%. These results surpass those of other carbon-based electrocatalysts. In situ Raman studies reveal that the reaction occurs through electrochemical hydrogenation, where active hydrogen is provided by water reduction. This work contributes to the development of carbonaceous electrocatalysts with enhanced performance for sustainable environmental applications.

Fabrication of High Surface Area Fe/Fe3 O4 with Enhanced Performance for Electrocatalytic Nitrogen Reduction Reaction

The development of high-efficient and large-scale non-precious electrocatalysts to improve sluggish reaction kinetics plays a key role in enhancing electrocatalytic nitrogen reduction reaction (NRR) for ammonia production under mild condition. Herein, Fe3 O4 and Fe supported by porous carbon (denoted as Fe/Fe3 O4 /PC-800) composite with a high specific surface area of 1004.1 m2  g-1 was prepared via a simple template method. On one hand, the high surface area of Fe/Fe3 O4 /PC-800 provides a large area to enhance N2 adsorption and promote more protons and electrons to accelerate the reaction, thereby greatly improving the dynamics. On the other hand, mesoporous Fe/Fe3 O4 /PC-800 provides high electrochemically active surface area for promoting the occurrence of catalytic kinetics. As a result, Fe/Fe3 O4 /PC-800 exhibited significantly enhanced NRR performance with an ammonia yield of 31.15 μg h-1  mg-1 cat. and faraday efficiency of 22.26 % at -0.1 V vs. reversible hydrogen electrode (RHE). This study is expected to provide a new strategy for the synthesis of catalysts with large specific area and pave the way for the foundational research in NRR.

Efficient Electroreduction of Nitrate to Ammonia with CuPd Nanoalloy Catalysts

The electroreduction of nitrate (NO3 - ) to valuable ammonia (NH3 ) is a green and appealing alternative to the Haber-Bosch process. Nevertheless, this process suffers from low performance for NH3 due to the sluggish multi-electron/proton-involved steps. In this work, a CuPd nanoalloy catalyst was developed toward NO3 - electroreduction at ambient conditions. By modulating the atomic ratio of Cu to Pd, the hydrogenation steps of NH3 synthesis during NO3 - electroreduction can be effectively controlled. At -0.7 V versus reversible hydrogen electrode (vs. RHE), the optimized CuPd electrocatalysts achieved a Faradaic efficiency for NH3 of 95.5 %, which was 1.3 and 1.8 times higher than that of Cu and Pd, respectively. Notably, at -0.9 V vs. RHE, the CuPd electrocatalysts showed a high yield rate of 36.2 mg h-1  cm-2 for NH3 with a corresponding partial current density of -430.6 mA cm-2 . Mechanism investigation revealed the enhanced performance originated from the synergistic catalytic cooperation between Cu and Pd sites. The H-atoms adsorbed on the Pd sites prefer to transfer to adjacent nitrogen intermediates adsorbed on the Cu sites, thereby promoting the hydrogenation of intermediates and the formation of NH3 .

Modulating the Active Hydrogen Adsorption on Fe─N Interface for Boosted Electrocatalytic Nitrate Reduction with Ultra-Long Stability

The electrocatalytic reduction of nitrate (NO3 - ) to nitrogen (N2 ) is an environmentally friendly approach for efficient N-cycle management (toward a nitrogen-neutral cycle). However, poor catalyst durability and the competitive hydrogen evolution reaction significantly impede its practical application. Interface-chemistry engineering, utilizing the close relationship between the catalyst surface/interface microenvironment and electron/proton transfer process, has facilitated the development of catalysts with high intrinsic activity and physicochemical durability. This study reports the synthesis of a nitrogen-doped carbon-coated rice-like iron nitride (RL-Fe2 N@NC) electrocatalyst with excellent electrocatalytic nitrate-reduction reaction activity (high N2 selectivity (≈96%) and NO3 - conversion (≈86%)). According to detailed mechanistic investigations by in situ tests and theoretical calculations, the strong hydrogenation ability of iron nitride and enhanced nitrate enrichment of the system synergistically contribute to the rapid hydrogenation of nitrogen-containing species, increasing the intrinsic activity of the catalyst and reducing the occurrence of the competing hydrogen-evolution side reaction. Moreover, RL-Fe2 N@NC shows excellent stability, retaining good NO3 - -to-N2 electrocatalysis activity for more than 40 cycles (one cycle per day). This paper could guide the interfacial design of Fe-based composite nanostructures for electrocatalytic nitrate reduction, facilitating a shift toward nitrogen neutrality.

A facile strategy to prepare FeNx decorated PtFe intermetallic with excellent acidic oxygen reduction reaction activity and stability

The construction of low-Pt-content intermetallic on carbon supports has been verified as a promising method to promote the activity of the oxygen reduction reaction (ORR). In this study, we have developed a simple and effective strategy to obtain a well-designed CNT-PtFe-PPy precursor. This precursor contains modulated Pt- and Fe-based content dispersed in polypyrrole (PPy) chain segments, which are in-situ generated on the templates of carbon nanotubes (CNTs). Subsequent pyrolysis of the CNT-PtFe-PPy precursor produces a CNT-PtFe@FeNC catalyst, which contains both Fe-N_x and PtFe intermetallic active sites. Due to the highly efficient dispersion of active species, the CNT-PtFe@FeNC electrocatalyst displays a 9.5 times higher specific activity (SA) and 8.5 times higher mass activity (MA) than those of a commercial Pt/C catalyst in a 0.1 M HClO₄ solution. Additionally, these results, combined with excellent durability (the SA and MA maintained 94 % and 91 % of initial activity after a 10-k cycle accelerated durability test), represent among the best performance achieved so far for Pt-based ORR electrocatalysts. Furthermore, density functional theory (DFT) calculations revealed that the presence of Fe-N₄ species reduces the adsorption energy between the PtFe intermetallic compound and OH*, accelerating the ORR process.

Controllable preparation of 2D carbon paper modified with flower-like WS2 for efficient microwave absorption

In the practical application of microwave absorbing materials, traditional powder materials need to be mixed with the matrix to fabricate composite coatings. However, the complex preparation process of composite coatings and the uneven dispersion of powders in the matrix limit their application. To solve these problems, two-dimensional (2D) F-WS₂/CP composite films were prepared by using carbon paper (CP) as a dispersion matrix and loading flower-like WS₂ on its surface through a simple hydrothermal method. The morphology and microwave absorption (MA) performance of the composite films are easily regulated by adjusting the amount of reaction precursors. The combination of WS₂ and CP facilitates impedance matching and improves the electromagnetic wave attenuation performance based on the synergistic effect of different loss mechanisms including multiple reflections and scattering, interfacial polarization, dipolar polarization, and conduction loss. At a low filler content (5 wt%), the maximum reflection loss (RL) of the composite film is up to -50 dB (99.999% energy absorption) at 12.5 GHz with 2.8 mm thickness. Moreover, at a relatively thin 1.8 mm thickness, its maximum RL remains -35 dB (>99.9% energy absorption). The as-prepared composite film shows excellent MA properties at a thinner thickness and lower filling content, providing inspiration for the preparation of light weight and efficient 2D thin-film microwave absorbers in the future.

In Situ Confinement of Ultrasmall Metal Nanoparticles in Short Mesochannels for Durable Electrocatalytic Nitrate Reduction with High Efficiency and Selectivity

Electrocatalytic reduction is a sustainable approach for NO₃ ^- removal and high-value N-containing compounds manufacturing, which, however, is strongly obstructed by sluggish kinetics, low selectivity, and poor stability. Herein, the in situ confinement of ultrasmall CuPd alloy nanoparticles in mesochannels of conductive core-shell structured carbon nanotubes@mesoporous carbon substrates (CNTs@mesoC@CuPd) via a simple molecule-mediated interfacial assembly method is reported. As a catalyst for electrocatalytic NO₃ ^- reduction, the CNTs@mesoC@CuPd shows a splendid conversion efficiency (100%), N₂  selectivity (98%), cycling stability (>30 days), and removal capacity as high as 30 000 mg N g^-1 CuPd, which are much superior to most of the prior reports. Notably, experimental (in situ testing and isotopic labeling) and theoretical results unveil that bimetallic and monometallic catalysts for electrocatalytic NO₃ ^- reduction exhibit exclusive selectivity for N₂  and NH₃ , respectively. This in situ confinement strategy is universal for the synthesis of stable and highly accessible metallic catalysts, which opens an appealing way to synthesize advanced catalysts with high activity, selectivity, and stability.

Harnessing Nickel Phthalocyanine-Based Electrochemical CNT Sponges for Ammonia Synthesis from Nitrate in Contaminated Water

Electrochemical reduction of nitrate to ammonia is of great interest in water treatment with regard to the conversion of contaminants to value-added products, which requires the development of advanced electrodes to achieve high selectivity, stability, and Faradaic efficiency (FE). Herein, nickel phthalocyanine was homogeneously doped into the fiber of a carbon nanotube (CNT) sponge, enabling the production of an electrode with high electrochemical double-layer capacitance (C_DL) and a large electrochemically active surface area (ECSA). The as-prepared NiPc-CNT sponge could achieve 97.6% nitrate removal, 88.4% ammonia selectivity, and 86.8% FE at a nitrate concentration of 50 mg-N L^-1 under an optimized potential of -1.2 V (vs Ag/AgCl). Meanwhile, the ammonia selectivity could be further improved at the high nitrate concentration. Density functional theory calculations showed that the exposure of Ni-N₄ active sites could effectively suppress the hydrogen evolution reaction and dinitrogen generation, enhancing the ammonia selectivity and Faradaic efficiency. Overall, this work sheds light on the conversion of nitrate to ammonia on the metal phthalocyanine-based electrode, offering a novel strategy for managing nitrate in wastewater.

One Bicopper Complex with Good Affinity to Nitrate for Highly Selective Electrocatalytic Nitrate Reduction to Ammonia

Ammonia (NH3) plays an irreplaceable role in human life as a promising energy carrier and indispensable chemical raw material. Nitrate electroreduction to ammonium (NRA) not only removes nitrate pollutants, but also can be used for efficient NH3 production under ambient conditions. However, achieving high efficiency and selectivity of electrocatalysts is still a great challenge. Herein, a complex Cu2(NO3)4(BMMB)·H2O with a bicopper core is assembled by Cu(NO3)2·3H2O and 1,4-bis{[2-(2’-pyridyl)benzimidazolyl]methyl}benzene (BMMB) for NRA under alkaline conditions. The optimal sample showed excellent nitrate reduction performance with the NO3− conversion rate of 70%, Faradaic efficiency of up to 90%, and NH3 selectivity of more than 95%. The high-catalytic activity is mainly due to the ingeniously designed copper cores with strong affinity for NO3−, which accelerates the transferring rate of adsorbed nitrate on the Cu surface and increases the efficiency of rate-determining step (NO3− → NO2−) in the whole catalytic process. Therefore, the transformation of surface-exposed nitrate can be rapidly catalyzed by the Cu active sites, facilitating the conversion efficiency of nitrate.

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

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.

Cu/CuOx In-Plane Heterostructured Nanosheet Arrays with Rich Oxygen Vacancies Enhance Nitrate Electroreduction to Ammonia

The artificial ammonia synthesis via electrochemical nitrate reduction has met increasing research interest, but it is still necessary to develop advanced catalysts with high nitrate-to-ammonia capability. Herein, we propose and demonstrate a one-step method to construct binder-free Cu foam-supported oxygen vacancy-rich Cu/CuO_x in-plane heterostructured nanosheet arrays (Cu/CuO_x/CF). In addition to exposing ample active sites, the two-dimensional nanosheet morphology greatly facilitates the mass/charge-transfer process during electrocatalysis. Besides, the in-plane heterojunctions and rich oxygen vacancies induced synergistic effect can modulate the electronic structure of active sites and thus tune the adsorption properties of the reactant intermediates and inhibit the formation of undesirable byproducts, which is conducive to the further improvement of nitrate reduction activity. As a result, these advantages endow the Cu/CuO_x/CF with superior performance for ammonia synthesis via nitrate electroreduction, achieving high ammonia selectivity (95.00%) and Faradaic efficiency (93.58%).

Atom-dispersed copper and nano-palladium in the boron-carbon-nitrogen matric cooperate to realize the efficient purification of nitrate wastewater and the electrochemical synthesis of ammonia

Electrochemical nitrate reduction reaction (NIRR) driven by sustainable energy is not only expected to realize the green production of ammonia under ambient conditions, but also a promising way to purify nitrate wastewater. The ammonia yield rate and Faradaic efficiency of NIRR catalyzed by Pd10Cu/BCN constructed with structural constraints and pre-embedded reducing agent strategies were as high as 102,153 μg h^-1 mg_cat.^-1 and 91.47%, respectively. Pd10Cu/BCN can remove nearly 100% of 50 mg L^-1 NO₃^- without NO₂^- residue within 10 h, and the realization of this effect does not require the participation of any chloride. Control experiments and DFT calculations explain the efficient operation mechanism of NIRR on Pd10Cu/BCN, where the Pd and CuN4 sites play the role of synergistic catalysis. Compared with the reported literature, Pd10Cu/BCN with good biocompatibility has become an outstanding representative of NIRR catalyst, which provides an alternative way for the green production of ammonia and the purification of nitrate wastewater.

Controlling the D-band for improved oxygen evolution performance in Ni modulated ultrafine Co nanoparticles embedded in Nitrogen-doped carbon microspheres

Despite the challenges on tuning the d-band structure of transition metals, the d-band is of great importance for promoting the interaction between catalytic and intermediates during the oxygen evolution reaction (OER) process. Herein, ultrafine Co nanoparticles embedded in the surface layer of nitrogen-doped carbon microspheres are prepared through an in-situ co-coordination strategy, and its d-band is modulated by introducing different Ni amounts. The introduction of Ni in the Co crystal lattice can tune the d-band center and unpaired electrons, which collectively result in an enhancement of OER activity and kinetics. By investigating the catalysts with Ni content from 0% to 75%, it is concluded that the catalyst with 25% Ni shows optimal OER activity, lower overpotential (285 mV at 10 mA cm^-2) and higher current densities (73.75 mA cm^-2 at 1.63 V). Moreover, the good stability is also demonstrated with the negligible decrease on current densities after 3000 CV cycles or 100 h of continuous test in alkaline media. This concept of modulating the d-band structure by introducing a transition metal with different contents in another transition metal crystal lattice could present an alternative pathway to the development of highly active catalytic materials for OER and beyond.

Electrocatalytic reduction of nitrate - a step towards a sustainable nitrogen cycle

Nitrate enrichment, which is mainly caused by the over-utilization of fertilisers and industrial sewage discharge, is a major global engineering challenge because of its negative influence on the environment and human health. To solve this serious problem, many technologies, such as the activated sludge method, reverse osmosis, ion exchange, adsorption, and electrodialysis, have been developed to reduce the nitrate levels in water bodies. However, the applications of these traditional techniques are limited by several drawbacks, such as a long sludge retention time, slow kinetics, and undesirable by-products. From an environmental perspective, the most promising nitrate reduction technology is enabled to convert nitrate into benign N₂, and features low cost, high efficiency, and environmental friendliness. Recently, electrocatalytic nitrate reduction has been proven by satisfactory research achievements to be one of the most promising methods among these technologies. This review provides a comprehensive account of nitrate reduction using electrocatalysis methods. The fundamentals of electrocatalytic nitrate reduction, including the reaction mechanisms, reactor design principles, product detection methods, and performance evaluation methods, have been systematically summarised. A detailed introduction to electrocatalytic nitrate reduction on transition metals, especially noble metals and alloys, Cu-based electrocatalysts, and Fe-based electrocatalysts is provided, as they are essential for the accurate reporting of experimental results. The current challenges and potential opportunities in this field, including the innovation of material design systems, value-added product yields, and challenges for products beyond N₂ and large-scale sewage treatment, are highlighted.

Atomic-dispersed copper simultaneously achieve high-efficiency removal and high-value-added conversion to ammonia of nitrate in sewage

Environmentally friendly electrochemical reduction pathways from NO₃^- to NH₃ or N₂ have provided feasible strategy into the green production of ammonia or the treatment of nitrate wastewater. Here, we anchored single-atom Cu with boron carbon nitride on carbon nanotube (BCN@Cu/CNT), and achieved the efficient operation of electrochemical nitrate reduction reaction (NIRR). BCN@Cu/CNT can efficiently catalyze the selective conversion of high-concentration nitrate into high-value-added ammonia, where the ammonia yield rate and Faradaic efficiency are as high as 172,226.5 μg h^-1 mg_cat.^-1 and 95.32% (at -0.6 V), respectively. BCN@Cu/CNT also shows the ability to efficiently remove low-concentration nitrates in sewage. Specifically, here only takes 5 h to nearly 100% (99.32%) eliminate NO₃^- (50 mg L^-1) in sewage without any residual NO₂^-. The excellent catalytic activity and physicochemical stability of BCN@Cu/CNT for NIRR suggest the promising industrial application prospects, including the green production of ammonia and the purification of nitrate wastewater.

How to Build a Microplastics-Free Environment: Strategies for Microplastics Degradation and Plastics Recycling

Microplastics are an emergent yet critical issue for the environment because of high degradation resistance and bioaccumulation. Unfortunately, the current technologies to remove, recycle, or degrade microplastics are insufficient for complete elimination. In addition, the fragmentation and degradation of mismanaged plastic wastes in environment have recently been identified as a significant source of microplastics. Thus, the developments of effective microplastics removal methods, as well as, plastics recycling strategies are crucial to build a microplastics-free environment. Herein, this review comprehensively summarizes the current technologies for eliminating microplastics from the environment and highlights two key aspects to achieve this goal: 1) Catalytic degradation of microplastics into environmentally friendly organics (carbon dioxide and water); 2) catalytic recycling and upcycling plastic wastes into monomers, fuels, and valorized chemicals. The mechanisms, catalysts, feasibility, and challenges of these methods are also discussed. Novel catalytic methods such as, photocatalysis, advanced oxidation process, and biotechnology are promising and eco-friendly candidates to transform microplastics and plastic wastes into environmentally benign and valuable products. In the future, more effort is encouraged to develop eco-friendly methods for the catalytic conversion of plastics into valuable products with high efficiency, high product selectivity, and low cost under mild conditions.

On-Demand Atomic Hydrogen Provision by Exposing Electron-Rich Cobalt Sites in an Open-Framework Structure toward Superior Electrocatalytic Nitrate Conversion to Dinitrogen

Electrocatalytic nitrate (NO₃^-) reduction to N₂ via atomic hydrogen (H*) is a promising approach for advanced water treatment. However, the reduction rate and N₂ selectivity are hindered by slow mass transfer and H* provision-utilization mismatch, respectively. Herein, we report an open-framework cathode bearing electron-rich Co sites with extraordinary H* provision performance, which was validated by electron spin resonance (ESR) and cyclic voltammetry (CV) tests. Benefiting from its abundant channels, NO₃^- has a greater opportunity to be efficiently transferred to the vicinity of the Co active sites. Owing to the enhanced mass transfer and on-demand H* provision, the nitrate removal efficiency and N₂ selectivity of the proposed cathode were 100 and 97.89%, respectively, superior to those of noble metal-based electrodes. In addition, in situ differential electrochemical mass spectrometry (DEMS) indicated that ultrafast *NO₂^- to *NO reduction and highly selective *NO to *N₂O or *N transformation played crucial roles during the NO₃^- reduction process. Moreover, the proposed electrochemical system can achieve remarkable N₂ selectivity without the additional Cl^- supply, thus avoiding the formation of chlorinated byproducts, which are usually observed in conventional electrochemical nitrate reduction processes. Environmentally, energy conservation and negligible byproduct release ensure its practicability for use in nitrate remediation.

Fabrication of an amorphous metal oxide/p-BiVO4 photocathode: understanding the role of entropy for reducing nitrate to ammonia

Entropy regulation makes an amorphous metal oxide/p-BiVO4 heterostructure a desirable catalyst for the NO3− reduction reaction in a photoelectrochemical system.

Flexible 2D Cu Metal: Organic Framework@MXene Film Electrode with Excellent Durability for Highly Selective Electrocatalytic NH3 Synthesis

Electrocatalytic nitrate reduction to ammonia (ENRA) is an effective strategy to resolve environmental and energy crisis, but there are still great challenges to achieve high activity and stability synergistically for practical application in a fluid environment. The flexible film electrode may solve the abovementioned problem of practical catalytic application owing to the advantages of low cost, light weight, eco-friendliness, simple and scalable fabrication, extensive structural stability, and electrocatalytic reliability. Herein, 2D hybridization copper 1,4-benzenedi-carboxylate (CuBDC) has been grown on electronegative MXene nanosheets (Ti₃C₂T_x) seamlessly to prepare a 2D flexible CuBDC@Ti₃C₂T_x electrode for ENRA. The flexible electrode simultaneously exhibits high Faradaic efficiency (86.5%) and excellent stability for NH₃ synthesis, which are comparable to previously reported nanomaterials toward ENRA. Especially, the flexible electrode maintains outstanding FE _NH3 toward ENRA after the bending, twisting, folding, and crumpling tests, indicating excellent electroconductibility, high stability, and durability. This work not only provides mild permeation-mediated strategy to fabricate a flexible electrode but also explores the practical applications of the electrode with effectively environmental adaptability in solving global environmental contamination and energy crisis by effective ENRA.

Organic/Inorganic Hybrid Fibers: Controllable Architectures for Electrochemical Energy Applications

Organic/inorganic hybrid fibers (OIHFs) are intriguing materials, possessing an intrinsic high specific surface area and flexibility coupled to unique anisotropic properties, diverse chemical compositions, and controllable hybrid architectures. During the last decade, advanced OIHFs with exceptional properties for electrochemical energy applications, including possessing interconnected networks, abundant active sites, and short ion diffusion length have emerged. Here, a comprehensive overview of the controllable architectures and electrochemical energy applications of OIHFs is presented. After a brief introduction, the controllable construction of OIHFs is described in detail through precise tailoring of the overall, interior, and interface structures. Additionally, several important electrochemical energy applications including rechargeable batteries (lithium-ion batteries, sodium-ion batteries, and lithium-sulfur batteries), supercapacitors (sandwich-shaped supercapacitors and fiber-shaped supercapacitors), and electrocatalysts (oxygen reduction reaction, oxygen evolution reaction, and hydrogen evolution reaction) are presented. The current state of the field and challenges are discussed, and a vision of the future directions to exploit OIHFs for electrochemical energy devices is provided.

Efficient Nitrate-to-Ammonia Electroreduction at Cobalt Phosphide Nanoshuttles

The nitrate electroreduction reaction (NO₃^--ERR) is an efficient and green approach for nitrate remediation, which requires a highly active and selective electrocatalyst. In this work, porous and amorphous cobalt phosphide nanoshuttles (CoP PANSs) are successfully synthesized by using Mg²⁺ ion-doped calcium carbonate nanoshuttles (Mg-CaCO₃ NSs) as the initial reaction precursor via precipitation transformation and a high-temperature phosphidation strategy. Various physical characterizations show that CoP PANSs have porous architecture, amorphous crystal structure, and big surface area. Electrochemical measurements reveal for the first time that CoP PANSs have outstanding electroactivity for NO₃^--ERR in a neutral electrolyte. At an applied potential of -0.5 V vs reversible hydrogen electrode, CoP PANSs can achieve a high Faraday efficiency (94.24 ± 2.8%) and high yield rate (19.28 ± 0.53 mg h^-1 mg_cat^-1) for ammonia production, which exceeds most reported values at various electrocatalysts for NO₃^--ERR. Thus, the present result indicates that cobalt phosphide nanomaterials have promising application for NO₃^--ERR.

Cooperativity of Cu and Pd active sites in CuPd aerogels enhances nitrate electroreduction to ammonia

By rationally choosing Pd as an active metal and Cu as a promoting metal, we developed Cu-rich CuPd bimetallic aerogels as a self-supported electrocatalyst for nitrate electroreduction. The spongy aerogel structure provides abundant catalytically active sites, while the synergistic benefit of the CuPd binary composition increases their reactivity, helping to achieve efficient nitrate-to-ammonia conversion.

Flexible electrocatalysts: interfacial-assembly of iron nanoparticles for nitrate reduction

We report a novel template-assisted epitaxial assembly strategy to assemble carbon-coated iron nanoparticles on a functionalized carbon cloth (CC/Fe@C). This delicate assembled architecture provides a useful guideline for designing flexible iron-based electrocatalysts.

Synergy between copper and iron sites inside carbon nanofibers for superior electrocatalytic denitrification

Developing low-cost electrocatalysts for the nitrate reduction reaction (NO₃RR) with superior performance is of great significance for wastewater treatment. Herein, we synthesized bimetal Cu/Fe nanoparticles encased in N-doped carbon nanofibers (Cu/Fe@NCNFs) through simple electrospinning followed by a pyrolysis reduction strategy. Metallic copper is beneficial for reducing nitrate to nitrite, and the existence of Fe is conducive to convert nitrate and nitrite into nitrogen. Additionally, the nitrogen-doped carbon nanofibers also facilitate the adsorption of nitrate, and the continuous and complete fiber structure enhances the stability of the catalyst and prevents the corrosion of the active sites. Therefore, the synergetic effect of bimetal Cu/Fe and N-doped carbon fiber plays a key role in promoting the efficiency of nitrate reduction. The obtained Cu/Fe@NCNF catalyst exhibits a satisfactory nitrate conversion efficiency of 76%, removal capacity of 5686 mg N g^-1 Cu/Fe and nitrogen selectivity of 94%.

Residual Chlorine Induced Cationic Active Species on a Porous Copper Electrocatalyst for Highly Stable Electrochemical CO2 Reduction to C2

Electrochemical carbon dioxide (CO₂ ) reduction reaction (CO₂ RR) is an attractive approach to deal with the emission of CO₂ and to produce valuable fuels and chemicals in a carbon-neutral way. Many efforts have been devoted to boost the activity and selectivity of high-value multicarbon products (C₂₊ ) on Cu-based electrocatalysts. However, Cu-based CO₂ RR electrocatalysts suffer from poor catalytic stability mainly due to the structural degradation and loss of active species under CO₂ RR condition. To date, most reported Cu-based electrocatalysts present stabilities over dozens of hours, which limits the advance of Cu-based electrocatalysts for CO₂ RR. Herein, a porous chlorine-doped Cu electrocatalyst exhibits high C₂₊ Faradaic efficiency (FE) of 53.8 % at -1.00 V versus reversible hydrogen electrode (V_RHE ). Importantly, the catalyst exhibited an outstanding catalytic stability in long-term electrocatalysis over 240 h. Experimental results show that the chlorine-induced stable cationic Cu⁰ /Cu⁺ species and the well-preserved structure with abundant active sites are critical to the high FE of C₂₊ in the long-term run of electrochemical CO₂ reduction.

Regulating the carbon distribution of anode materials in lithium-ion batteries

The exploration of electrode materials is considered to be a crucial process affecting the development of lithium-ion batteries. However, the large-scale commercial application of the great mass of anode materials has been hampered by the challenges with conductivity and volume change. These problems can be solved by the combination of a carbon-matrix with anode materials, which has proven to be an effective strategy. This review aims to outline recent advances in carbon-matrix composite anodes based on different dimensions (0D, 1D, 2D, 3D and atomic scale) and functions, with the emphasis on the regulation of carbon distribution of composite anodes. Besides, the matrix forms and carbon sources have also been summarized. This review will provide some light on the future carbon-matrix electrode design trends for LIBs.

Single-Atom Cu Catalysts for Enhanced Electrocatalytic Nitrate Reduction with Significant Alleviation of Nitrite Production

Metallic Cu is a well-known electrocatalyst for nitrate reduction reaction (NO₃ RR), but it suffers from relatively low activity, poor stability, and inducing nitrite accumulation during the long-term operation. Herein, it is found that Cu catalysts minimized at the single-atom level can overcome the limitations of bulk materials in NO₃ RR. A metal-nitrogen-carbon (M-N-C) electrocatalyst composed of carbon nanosheets embedding isolated copper atoms coordinated with N, Cu-N-C-800, is synthesized by pyrolysis of a Cu-based metal-organic framework at 800 °C. In comparison with Cu nanoparticles and Cu plate-800, kinetic measurements show that the Cu-N-C-800 electrocatalyst is more active and stable and distinctly suppresses the release of nitrite intermediate into the solution. The combined results of experimental data and density functional theory calculations indicate that Cu bound with N (particularly Cu-N₂ ) is the key to favorable adsorption of NO₃ ^- and NO₂ ^- . This strong binding is responsible for the enhanced rate of nitrate conversion to the end products of ammonia and nitrogen. These findings highlight the promise of single-atom Cu electrocatalysts for nitrate reduction with desirable performance.

Cobalt-Based Metal-Organic Frameworks and Their Derivatives for Hydrogen Evolution Reaction

Hydrogen has been considered as a promising alternative energy to replace fossil fuels. Electrochemical water splitting, as a green and renewable method for hydrogen production, has been drawing more and more attention. In order to improve hydrogen production efficiency and lower energy consumption, efficient catalysts are required to drive the hydrogen evolution reaction (HER). Cobalt (Co)-based metal-organic frameworks (MOFs) are porous materials with tunable structure, adjustable pores and large specific surface areas, which has attracted great attention in the field of electrocatalysis. In this review, we focus on the recent progress of Co-based metal-organic frameworks and their derivatives, including their compositions, morphologies, architectures and electrochemical performances. The challenges and development prospects related to Co-based metal-organic frameworks as HER electrocatalysts are also discussed, which might provide some insight in electrochemical water splitting for future development.

Boosting the electrocatalysis of nitrate to nitrogen with iron nanoparticles embedded in carbon microspheres

Human activities have increased the global nitrogen cycle imbalance, leading to serious water pollution. Inexpensive iron nanoparticles with large surface areas are in high demand in the field of environment restoration. Here, we report a hydrothermal method for the preparation of iron-carbon composites (Fe@C) with iron nanoparticles embedded in carbon microspheres. The resulting Fe@C catalyst shows a high nitrate conversion to nitrogen of 75.9% and a nitrogen selectivity of 98%. This study not only provides a simple strategy for the preparation of iron-carbon composites, but also boosts the practical application of Fe@C catalysts for water treatment.