Metal-nitrogen Bonds Research Articles

Superior Multielectron-Transferring Energy Storage by π-d Conjugated Frameworks.

Reversible multielectron-transfer materials are of considerable interest because of the potential impact to advance present electrochemical energy storage technology by boosting energy density. To date, a few oxide-based materials can reach an electron-transfer number per metal-cation (eM ) larger than 2 upon a (de)intercalation mechanism. However, these materials suffer from degradation due to irreversible rearrangements of the cation-oxygen bonds, and are based on precious metals, for example, Ir and Ru. Hence, a design of the non-oxide-based reversible multielectron-transfer materials with abundant elements can provide a promising alternative. Herein, it is demonstrated that the bis(diimino)copper framework can show eM = 3.5 with cation/anion co-redox mechanism together with a dual-ion mechanism. In this study, the role of the cation-anion interactions is unveiled by using an experiment/theory collaboration applied to a series of the model non-oxide abundant electrode systems based on different metal-nitrogen bonds. These models provide designer multielectron-transfer due to the tunable π-d conjugated electronic structures. It is found that the Cu-nitrogen bonds show a unique reversible rearrangement upon Li-intercalation, and this process responds to acquire a significant reversible multielectron-transfer. This work provides new insights into the affordable multielectron-transfer electrodes and uncovers an alternative strategy to advance the electrochemical energy storage reactions.

Factors Promoting Alkene Migratory Insertion into Metal-nitrogen Bond During Hydroamination in Recent Studies

: Migratory insertion is a fundamental organometallic transformation that enables the functionalization of an unsaturated bond. Recent reports on catalytic hydroamination provide evidence that supports an intermolecular migratory insertion pathway featuring alkene insertion into metalnitrogen (M-N) bonds. This article presents factors influencing the rate of migratory insertion in latetransition metal-catalyzed hydroamination, including steric and electronic effects from ligands, alkenes, and metal centers, along with stabilization from coordinated amine intermediates and ordered transition states.

SYNTHESIS, CHARACTERIZATION AND ANTIMICROBIAL ACTIVITIES OF Ni(II) AND Cu(II) COMPLEXES WITH SCHIFF BASE DERIVED FROM 2-ACETYL-5-METHYLFURAN GLYOXIME HYDRAZONE

A hydrazone Schiff base has been synthesized by the interaction of ethanolic solution of antiglyoxime hydrazine with 2-acetyl-5-methylfuran, to obtain the corresponding Schiff base L. The complexes of Ni(II) and Cu(II) of the Schiff base were synthesized and studied. The Schiff base and its metal(II) complexes characterized based on solubility, percentage yield, elemental analysis, melting/decomposition temperatures, infra- red spectral (FT-IR), conductivity measurement, magnetic susceptibility and water of crystallisation. The synthesized Schiff base and the complexes are coloured and stable at room temperature. Based on the results the prepared Schiff base and synthesized complexes are relatively soluble in most organic solvents but insoluble in distilled water. The melting point temperature of the ligand was 118oC while the decomposition temperature for metal complexes were 308 and 300oC respectively. The molar magnetic susceptibility of the complexes were 3.55 and 2.10 x 10-3 erg.G-2mol-1. The molar conductance values of 2.17 and 2.43ohm-1cm2mol-1 indicating non electrolytic nature of the complexes. The spectral data of the Schiff base showed band of 1584cm-1, revealing the formation of the azomethine. A bands of 791cm-1 indicate the metal nitrogen bond. The elemental analysis determination of the complexes and the Schiff base showed the metal ligand ratio of 1:2 (M:2L). The antibacterial and antifungal activities of the Schiff base and the metal(II) complexes were evaluated using disc diffusion method. The antibacterial assay was carried out on three pathogenic bacteria, Staphylococcus aureus, Staphylococcus epidermidis and Streptococcus pneumonia and two fungi viz: Candida utilis and Saccharomyces cerevisiae. All the Schiff base

Systematic investigation of anode catalysts for liquid ammonia electrolysis

Liquid ammonia is able to release hydrogen via electrolysis with a theoretical voltage of 0.077 V. However, the actual operation voltage is much higher (around 1–2 V) due to the large overpotential of the anodic reaction. We systematically investigated Pt, Ir, Ru, Ni, Co, Fe, Ta, and Ti as the anodic catalyst, and observed a volcano correlation when plotting the current density against the formation enthalpy of metal nitrides per nitrogen ΔfHMN (kJ/mol-N). ΔfHMN reflects the strength of metal-nitrogen bond, and Ru having a moderate ΔfHMN showed the highest catalytic activity. Then, the activity enhancement via microstructure control was examined. The sputtered Pt and Ni films having a columnar structure with a rough surface showed 7- and 13-times higher current density than the Pt and Ni plates, respectively. An anodic current density of 0.45 mA/cm2 was achieved for the sputtered Ni film at an anodic potential as low as 0.3 V vs H2/NH3.

Neutral Nitrogen Donor Ligand-based MOFs for Sensing Applications.

Neutral nitrogen donor (N-donor) ligand-based MOFs, with their enticing features inclusive of facile synthesis, labile metal-ligand bond, framework flexibility, atomic level tunability renders them appealing in molecular recognition-based studies. Intriguingly, the flexibility in such systems (owing to weaker metal-nitrogen bonds) promote maximization of host-analyte interactions, which is critical for the manifestation of a signaling response. Such host-analyte interactions can be tapped by discerning any change in the physical properties associated with the system, such as optical, fluorometric, chemiresistive, magnetic, dielectric constant, mass. This minireview presents a brief discussion on the various types of signal transduction pathways unveiled hitherto using neutral N-donor ligand-based MOFs and the fundamental insight into the signal's origin. Moreover, an elaborate compilation of the recent examples in this field has been presented. Also, the untapped prospects have been highlighted, which may serve as a beacon to drive future research.

Intrinsic Electron Localization of Metastable MoS2 Boosts Electrocatalytic Nitrogen Reduction to Ammonia.

The advancement of efficient electrocatalysts toward the nitrogen reduction reaction (NRR) is critical in sustainable ammonia synthesis under ambient pressure and temperature. Manipulating the electronic configuration of electrocatalysts is particularly vital to form metal-nitrogen (MN) bonds during the NRR through regulating the active electronic states of sites. Here, in sharp contrast to stable 2H MoS2 without metal chains, MoMo bonding in metastable polymorphs of MoS2 bulk (zigzag chain in the 1T' phase and diamond chain in the 1T″' phase) is discovered to significantly increase intrinsic electron localization around the metal chains. This can enhance the charge transfer from the adsorbed nitrogen molecule to the metal chains, allowing for boosted NRR kinetics. The electrochemical experiments show that the NH3 yield rate and the faradaic efficiency of the metastable 1T″' MoS2 rich with abundant Mo-Mo bonds are about 9 and 12 times above average than those of 2H MoS2 , correspondingly. Theoretical simulations reveal the high local electron density surrounding the MoMo chains and sites can promote π back-donation, which is beneficial for increasing nitrogen adsorption, strengthening the MN bonds, and reducing the cleavage barrier of the triple NN bond.

Alloys of Cobalt Grafted with CNT Supported on N-Doped Carbon Heterostructure As Bifunctional Electrocatalysts

Development of eco-friendly, stable, and affordable electrocatalysts is crucial for the sustainable energy production and storage units such as fuel cells, water electrolysis, and metal–air batteries. Metal organic frameworks (MOFs) are class of compounds in which metal ions are coordinated to an organic ligand. They have emerged as a great precursor for the synthesis of various electrocatalysts for Hydrogen Evolution Reaction (HER) and Oxygen Evolution Reaction (OER).Carbon motifs derived from zeolitic imidazole frameworks (ZIFs), a subfamily of MOFs, have exceptional mechanical and chemical stability due to the presence of metal-nitrogen bonds. Amongst various synthesized ZIFs, ZIF-67 has cobalt ions (Co2+) coordinated to imidazolate-type linkers. The ZIF-67 derived carbon precursors are generally mesoporous, possess high degree of graphitization and large surface area.Herein, we have tried to immobilize noble metals like Pd, Pt and Ru with short CNTs grafted on C matrix named as PdCo@NC, PtCo@NC and RuCo@NC, respectively. [1] We have synthesized a series of electrocatalysts by a novel H2-free method using simple one-step pyrolysis. The as-synthesized catalysts show excellent bifunctional catalytic activity towards HER as well as OER in alkaline medium. The catalysts show long cycle stability and compete with the state-of-the-art electrocatalysts like RuO2 and Pt/C. PtCo@NC and RuCo@NC shows the best HER and OER, respectively. Further, the excellent electrocatalytic activity is explained based on a synergistic effect between the noble metal and ZIF-67 derived N-doped carbon support.

S‐Block Multiple Bonds: Isolation of a Beryllium Imido Complex

A common feature of d- and p-block elements is that they participate in multiple bonding. In contrast, the synthesis of compounds containing homo- or hetero-nuclear multiple bonds involving s-block elements is extremely rare. Herein, we report the synthesis, molecular structure, and computational analysis of a beryllium imido (Be=N) complex (2), which was prepared via oxidation of a molecular Be0 precursor (1) with trimethylsilyl azide Me3 SiN3 (TMS-N3 ). Notably, compound 2 features the shortest known Be=N bond (1.464 Å) to date. This represents the first compound with an s-block metal-nitrogen multiple bond. All compounds were characterized experimentally with multi-nuclear NMR spectroscopy (1 H, 13 C, 9 Be) and single-crystal X-ray diffraction studies. The bonding situation was analyzed with density functional theory (DFT) calculations, which supports the existence of π-bonding between beryllium and nitrogen.

Flexible Transparent Barrier Applications of Oxide Thin Films Prepared by Photochemical Conversion at Low Temperature and Ambient Pressure

Photoconversion of metal-organic precursors to thin film metal oxides using ultraviolet (UV) radiation in oxidative atmosphere is an attractive technology because it can be applied at temperatures < 80 °C and at ambient pressure. Thus, it enables preparing this class of thin films in a cost-efficient manner on temperature sensitive substrates such as polymer films. In this article, various aspects of research and development in the field of photochemical thin-film fabrication, with particular focus to the application of the produced films as gas permeation barriers for the encapsulation of optoelectronic devices are reviewed. Thereby, it covers investigations on fundamental photochemically initiated reactions for precursor classes containing metal-oxygen and metal-nitrogen bonds, and emphazises the relevance of that understanding for applicative considerations like integration of the single-layer barrier films into relevant encapsulation films. Further perspectives are given concerning integration of additional functionalities like electrical conductivity to the flexible and transparent barrier films.

A Strategy for the Construction of Triply Interlocked Organometallic Cages by Rational Design of Poly-NHC Precursors.

Three-dimensional (3D) triply interlocked catenanes are a family of chemical topologies that consist of two identical, mechanically interlocked coordination cage components with intriguingly complex structures. Although only a few successful constructions of 3D interlocked catenanes have been achieved to date via metal-mediated assembly, these complex structures have thus far only been targeted by metal-nitrogen/oxygen coordination techniques. Here, taking advantage of rational ligand design, we report the efficient construction of a series of 3D triply interlocked [2]catenanes of the formula [Ag3L2]2, wherein the metal ions exclusively form bonds to N-heterocyclic carbene (NHC) units, and their subsequent transmetalation to the corresponding [Au3L2]2 gold analogues. The formation and transmetalation reactions proceed under mild conditions and are generally applicable. A series of characterization techniques were applied to confirm the formation and structure of the desired 3D triply interlocked architectures: multinuclear NMR spectroscopy, ESI-MS, and single-crystal X-ray diffraction analysis. The solid-state structure of [Ag3(1a)2]2(PF6)6 unambiguously confirms the existence of a 3D catenane that consists of two identical, mechanically interlocked trinuclear hexacarbene cage components. The interlocking of two 3D cages into a [2]catenane is driven by the efficient π···π stacking of triazine-triazine stacks with cooperative interactions between imidazo[1,5-a]pyridine subunits. Notably, the triply interlocked organometallic cages exhibit good stability toward various organic solvents, concentrations, and temperatures, and no disassembly occurred in the presence of coronene or pyrene. The future construction of mechanically interlocked architectures using metal-carbene bonds rather than metal-nitrogen bonds may provide assemblies with interesting properties for as-yet-unimagined applications in fields such as sensors and molecular electrical conductors.

Stabilization of unusual metal oxidation state +4 in the iron, cobalt, nickel, and copper complexes with trans-di[benzo]porphyrazine and two fluoride anions: a DFT quantum chemical analysis

Molecular structure calculations of heteroligand (6666)macrotetracyclic metal (MIV) chelates (M = Fe, Co, Ni, Cu) with trans-di[benzo]porphyrazine as the (N,N,N,N)-donor ligand and two F− anions were carried out at the OPBE/TZVP level of density functional theory. The key bond lengths, bond angles, and non-bond angles in the complexes were determined and corresponding standard enthalpies, entropies, and Gibbs energies of formation were calculated. All complexes have slightly distorted tetrahedral structures. The complex-forming agent MIV lies in the plane formed by the donor nitrogen atoms. The metal—nitrogen bonds are usually pair-wise equal. The six-membered metal chelate rings in the complexes are identical to one another from the standpoint of both the sum and set of the bond angles.

Metal-Diamidobenzoquinone Frameworks via Post-Synthetic Linker Exchange.

Metal-organic frameworks with amidic linkers often exhibit exceptional physical properties, but, owing to their strong metal-nitrogen bonds, are exceedingly challenging to isolate through direct synthesis. Here, we report a route to access metal-diamidobenzoquinone frameworks from their dihydroxobenzoquinone counterparts via postsynthetic linker exchange. The parent compounds (Me2NH2)2[M2L3] (M = Zn, Mn; H2L = 2,5-dichloro-3,6-dihydroxo-1,4-benzoquinone) undergo linker exchange upon exposure to a solution of monodeprotonated 2,5-diamino-3,6-dibromo-1,4-benzoquinone or 2,5-diamino-3,6-dichloro-1,4-benzoquinone, proceeding through single-crystal-to-single-crystal reactions. The presence of both types of linker in the resulting frameworks is confirmed by a combination of NMR, Raman, and energy-dispersive X-ray (EDX) spectroscopies. Moreover, the extent of linker exchange in the Zn frameworks is quantified using 13C NMR spectroscopy, and spatially resolved EDX spectroscopy reveals the two types of linker to be homogeneously distributed within a crystal. Finally, we propose a tentative mechanism of linker exchange based on pKa measurements, considerations of framework solubility, and powder X-ray diffraction analysis. This work provides the first method to exchange organic linkers with different donor atoms in metal-organic frameworks and in doing so demonstrates exchange between linkers with donor atoms differing in acidity by a remarkable 11 units of pKa. Together, these results offer a potentially general synthetic strategy toward new materials with exotic metal-linker coordination modes.

Effective electrochemical detection of dopamine with highly active molybdenum oxide nanoparticles decorated on 2, 6 diaminopyridine/reduced graphene oxide

Metal oxide nanoparticles are highly active structural components for developing catalysts on highly functionalized graphene sheets which provide superior electrocatalytic activity, high stability as well as cost-effectiveness in electrochemical sensing application.In this present study, 2, 6 diaminopyridine functionalized electrochemically reduced graphene oxide with molybdenum oxide ternary composites, (2, 6 DAP-ERGO/MoO3) for use as a potent electroactive catalyst for detection of dopamine (DA), has been developed for the first time using the hydrothermal method. The formation of metal-nitrogen (Me-N) bonds and the growth of the nanosized MoO3 sheets on 2, 6 DAP-ERGO exhibited an influential role in the electrocatalytic activity, resulting in a remarkable enhancement of both oxidation and reduction process of dopamine. The proposed 2, 6 DAP-ERGO/MoO3 nanocomposite had a broad electro active surface area which enhance the capacity for dopamine adsorption and ultimately cause a remarkable increment in the anodic peak current by about 30 times with respect to bare glassy carbon electrode(GCE), demonstrating the significant electrocatalytic activity towards dopamine with relatively better sensitivity (271.57 μAmM−1cm−2), and a broad linear range of detection (0.1–900 μM) and lower limit of detection (0.025 μM) having S/N = 3. Interference of coexisting electro active biomolecules was also investigated. The diffusion coefficient for dopamine determination was estimated to be 2.2 × 10−4 cm2s−1. Finally, the applicability of our proposed 2, 6 DAP-ERGO/MoO3 catalyst was analyzed using human urine sample.

Metal vacancies abundant Co0.6Fe0.4S2 on N-doped porous carbon nanosheets as anode for high performance lithium batteries

Transition metal sulfides have been considered as promising anodes for lithium batteries for its high theoretical specific capacity. However, the lower conductivity, larger volume change and slower electrochemical reaction dynamics still hinder its practical applications. Here, Co0.6Fe0.4S2 nanoparticles with metal vacancies anchored on the N-doped carbon nanosheets (NC@Co0.6Fe0.4S2) are designed and fabricated by a facile hydrothermal method. The NC@Co0.6Fe0.4S2 delivers high reversible capacity, stable cyclability and excellent rate capacity by retaining the capacities of 830mAh g−1 after 100 cycles at 200 mA g−1 and 696mAh g−1 after 500 cycles at 5000 mA g−1. The improved electrochemical performance is attributed to the metal vacancies, N-doped carbon nanosheets and strong metal-nitrogen bonds between the Co0.6Fe0.4S2 and N-doped carbon nanosheets, which greatly enhance charge transfer/transport and maintain structural integrity. The construction of metal vacancies along with N-doped carbon wrapping can be extended to prepare other transition metal sulfides for enhancing the electrochemical performance.

Enhanced photoelectrochemical hydrogenation of green-house gas CO2 to high-order solar fuel on coordinatively unsaturated metal-N sites containing carbonized Zn/Co ZIFs

Porous carbon-based catalysts facilitate CO2 photoelectrochemical reduction reaction (CO2PRR) through the high charge transfer ability and CO2 adsorption ability. However, the design of catalysts with high selectivity towards high-order solar fuels (such as ethanol and propanol) remains challenging. Herein, catalysts of carbonized Zn/Co Zeolitic Imidazolat Frameworks with various pyrolysis hours (xh-C-Zn/Co ZIFs) were synthesized and accessed for high selective CO2PRR for the first time. XRD and TEM analyses show that the C containing functional groups in pristine Zn/Co ZIF are carbonized and turned into amorphous porous carbon, while many Co and ZnO nanoparticles are formed during the pyrolysis process. Electrochemical characterizations of the catalysts prove that increasing pyrolysis time of Zn/Co ZIF from 1 h to 3 h, resulting in a decreased light current density from 3.3 mA/cm2 to 2.3 mA/cm2, which is much higher than that of Zn/Co ZIF (1.9 mA/cm2). Meanwhile, increasing pyrolysis time of Zn/Co ZIF from 1 h to 3 h results in decreased BET surface area and CO2 adsorption ability. XPS spectra suggest a decreased content of metal-nitrogen bonds in C–Zn/Co ZIF, which leads to the formation of coordinatively unsaturated metal-nitrogen sites. Density functional theory (DFT) calculations reveal that the coordinatively unsaturated CoN3V sites in C–Zn/Co ZIF had the highest catalytic activity towards high-order organics. The total carbon atom conversion rate reaches 5459 nmol/h·cm2 when 1h-C-Zn/Co ZIF is employed as catalyst in the CO2PRR system and the selectivity towards high-order solar fuel reaches 84%.

Rational design of metal organic framework derived hierarchical structural nitrogen doped porous carbon coated CoSe/nitrogen doped carbon nanotubes composites as a robust Pt-free electrocatalyst for dye-sensitized solar cells

A novel hierarchical structural hybrid of nitrogen-doped porous carbon (NPC) coated hollow CoSe nanoparticles anchored on nitrogen-doped carbon nanotubes (NCNTs) is enabled from the zeolitic imidazolate framework ZIF-67. In this composite, polypyrrole-derived NCNTs as a nitrogen-rich template effectively alleviates the irreversible aggregation of ZIF-67 derivatives. The hollow CoSe embedded NPC nanoparticles(CoSe@NPC) as high catalytic activity centres endow sufficiently available active sites for the reduction of triiodide, while NCNTs serve as both the bridge and the dispersant for the CoSe@NPC. Moreover, the outstanding catalytic metal-nitrogen bonds(Co-N-C) species take the role of high-speed transport pathway to facilitate transfer of electrons from the carbon skeleton to active sites. Benefiting from the above advantages, the hybrid of CoSe@NPC anchored on NCNTs shows fabulous electrocatalytic activity with an energy conversion efficiency of 7.58%, which is even higher than that of Pt counter electrode (7.27%). More remarkably, the composite also demonstrates a good long-term electrochemical stability in iodine-based electrolyte. The present work proves the rationality of the preparation of ZIFs-derived materials with special structures and their application in dye-sensitized solar cells system.

Coordination or Oxidative Addition? Activation of N–H with [Tp′Rh(PMe3)

A thermal reaction of amines, anilines, and amides with Tp'Rh(PMe3)(CH3)H (1, Tp' = tris(3,5-dimethyl-pyrazolyl)borate) is described in this report. No N-H bond cleavage was observed for reactions between ammonia or unsubstituted aliphatic amines with the reactive fragment [Tp'Rh(PMe3)]. Instead, amine coordination products (κ2-Tp')Rh(PMe3)(NHR1R2) (R1 = H, R2 = H, nPr, iPr, octyl; R1 = R2 = Et; R1, R2: pyrrolidine) were observed, and the crystal structure of (κ2-Tp')Rh(PMe3)(NH2 iPr) is reported. No coordination products were observed when 1 was reacted with 1,1,1,3,3,3-hexafluoropropan-2-amine, anilines, and amides. Instead, the oxidative addition products (κ3-Tp')Rh(PMe3)(NHR)H (R = CH(CF3)2, C6H5, 3,5-dimethylbenzyl, C6F5, C(O)CH3, C(O)CF3) were observed. Both RhI-N coordination products (κ2-Tp')Rh(PMe3)(NH2CH2CF3) and RhIII N-H addition products (κ3-Tp')Rh(PMe3)(NHCH2CF3)H were generated when 1 was reacted with 2,2,2-trifluoroethylamine. Coordination products dissociate ammonia and amines in benzene much faster than oxidative addition products eliminate anilines and amides. The relative metal-nitrogen bond energies were studied using established kinetic techniques. Analysis of the relationship between the relative M-N bond strengths and N-H bond strengths showed a linear correlation with a slope = RM-N/N-H of 0.91 (10), indicating that the Rh-N bond strength varies in direct proportion to the N-H bond strength.

On the Role of Ferromagnetic Interactions in Highly Active Mo‐Based Catalysts for Ammonia Synthesis

Reactions involving nitrogen fixation and transfer are of great industrial interest. In this regard, unveiling all the physical principles that determine their activity would be enormously beneficial for the rational design of novel catalysts with improved performance. Within this context, this work explores the activity of bulk molybdenum-based transition metal nitrides in ammonia synthesis. Our results highlight that the most active compositions show increasing ferromagnetism in the metal-nitrogen bonds, which constitute the active sites. We observe that the total spin accumulated in the bonds at the active sites is a physically meaningful descriptor to discriminate optimum catalysts. Higher activities are associated with ferromagnetic phases, and the underlying reason is an enhanced overlapping of the electronic wavefunctions; which also make the reaction steps spin-sensitive. These finding provides strong evidence of the general influence of electrons magnetic moment in catalysis, being part of the specific field of spintro-catalysis.

Unique photoelectrochemical behavior of TiO2 nanorods wrapped with novel titanium Oxy-Nitride (TiOxNy) nanoparticles

In this work, we developed novel titanium oxynitride (TiOxNy) nanoparticles with diameter of 25 ± 2 nm and crystalline size of ∼15 nm on hydrothermally grown one-dimensional (1D) TiO2 nanorod (TNR) arrays. Herein, the TiOxNy nanoparticles were synthesized by facile nitridation using TiO2 powder at 100% NH3 gas atmosphere. Titanium oxynitride composed of potentially energetic metal-nitrogen bonds (TiN), compared to the weaker TiO bond, becomes chemically stable in the alkaline environment, and is considered as a suitable material for photoelectrochemical (PEC) system. The PEC performance of TiOxNy decorated TNR (abbreviated as TiOxNy @TNR) films was evaluated in 0.1 M KOH solution under solar illumination condition, and achieved the potentially high photocurrent density (J) of 2.1 mA/cm2 at 1.23 V versus reversible hydrogen electrode (RHE) (abbreviated as VRHE) in the TiOxNy@TNR arrays, in comparison with the poor photoresponse (0.7 mA/cm2 at 1.23 VRHE) of the pristine TNR arrays. A nearly three-fold enhancement was attained in the TiOxNy decorated TNR arrays, attributed to the high visible light absorption and fast carrier separation, due to the hybridization with the visible active TiOxNy nanoparticles in the cascading band alignment between the TiOxNy and TNR materials. Furthermore, the introduction of TiOxNy layer on the TNR surface quite reduces the interfacial resistance in the solid-liquid interface region, and further, the TiOxNy layer contributes to the passivation of the surface states (e.g., defect, trap sites etc.) where the charge recombination reaction frequently happens, leading to the improvement of PEC performance.

Highly Efficient Oxygen Reduction Reaction Activity of Graphitic Tube Encapsulating Nitrided CoxFey Alloy

AbstractNonprecious metals are promising catalysts to avoid the sluggish oxygen reduction reaction (ORR) in next‐generation regenerative fuel cells or metal–air batteries. Therefore, development of nonprecious metal catalysts for ORR is highly desirable. Herein, precise tuning of the atomic ratio of Fe and Co encapsulated in melamine‐derived nitrogen‐rich graphitic tube (NGT) is reported. The Co1.08Fe3.34 hybrid with metalnitrogen bonds (1: Co1.08Fe3.34@NGT) shows remarkable ORR catalytic activities (80 mV higher in onset potential and 50 mV higher in half‐wave potential than those of state‐of‐the‐art commercial Pt/C catalysts), high current density, and stability. In acidic solution, 1 also shows compatible performance to commercial Pt/C in terms of ORR activity, current density, stability, and methanol tolerance. The high ORR activity is ascribed to the co‐existence of FeN, CoN, and sufficient metallic FeCo alloys which favor faster electron movement and better adsorption of oxygen molecules on the catalyst surface. In the alkaline anion exchange membrane fuel cell setup, this cell delivers the power density of 117 mW cm−2, demonstrating its potential use for energy conversion and storage applications.