Nitrogen-doped Carbon Matrix Research Articles

Facile synthesis of the multidimensional oxygen redox electrocatalysts by anion-mediated self-template one-step in situ assembly

The exploration of a non-precious metal bifunctional electrocatalyst with novel structures for the efficient oxygen reduction reaction (ORR) and oxygen evolution reactions (OER) remains a great challenge. Multidimensional assembled nanostructures with nitrogen-doped carbon matrix inlaid with transition-metal (M-N-C) can be used as efficient electrocatalysts due to its large surface area and highly revealed active sites. Herein, we report an anion-mediated self-template one-step in situ transformation into multidimensional hierarchical nano-assembled M-N-C catalysts, which is assembled from 0D cobalt nanoparticles terminally inlaid in 1D carbon nanotubes growing on a honeycomb-like ultrathin 3D carbon network (denoted as Co@N-CNTs/CS). By further synthetic process characterization, the nitrate-mediated structural evolution during rising thermal stages is disclosed. Thanks to the fully exposed surfaces and highly accessible active sites in the unique multidimensional structure, our developed catalyst exhibits a large surface area and enhanced performance in bifunctional oxygen redox in alkaline media, which further endows potentials in rechargeable Zn-air batteries, surpassing the typical benchmark catalysts Pt/C + Ir/C. Our study affords a fresh path to facile fabrication of M-N-C electrocatalysts.

Restricted growth of molybdenum carbide nanoparticles in hierarchically porous nitrogen-doped carbon matrix for boosting electromagnetic wave absorption performance

With the development of electronic science and technology, electromagnetic pollution is becoming increasingly serious, which urgent people to develop wave-absorbing materials with the features of “thin, light, strong and wide”. In this paper, restricted growth of molybdenum carbide nanoparticles in hierarchically porous nitrogen-doped carbon matrix (Mo2C/NC) was designed and prepared via a salt-assisted template route and carbonization process, whose morphology and the wave-absorbing properties are regulated by changing the content of Mo2C/NC nanoparticles. The honeycomb porous Mo2C/NC composites with large specific surface area and smooth surface can optimize the impedance matching and allow the entrance, multiple reflections and scattering of incident electromagnetic waves (EMW), which effective enhance the electromagnetic wave consumption. Meanwhile, the honeycomb cross-linked carbon matrix facilitates the construction of the conductive network and enhances its conductive loss. Furthermore, numerous Mo2C/NC nanoparticles dispersed restricted growth in carbon matrix induces interfacial polarization. In addition, the heteroatom nitrogen doping acts as dipole centers to induce dipole polarization under electromagnetic field. The uniquely designed Mo2C/NC absorbers show satisfactory EMW absorption behaviors of a minimum reflection loss (RLmin) of −61.53 dB at 1.5 mm and an effective absorption bandwidth (EAB) of 9.6 GHz at 3.5 mm. This work enriches the variety of EMW absorbers and offers the route to promote the EMW absorption performance, especially large effective absorption bandwidth.

Accelerated inter/intra-layer electron transport by asymmetric metal site induced delocalization effect for photoelectrocatalytic water oxidation

Charge transfer at the primary catalyst, co-catalyst, and solution interface is fundamental for photoelectrocatalytic water oxidation. In this paper, we propose a strategy to create a co-catalyst comprised of zinc-cobalt diatomic sites on a nitrogen-doped carbon matrix (CoZn-NC) and load it on BiVO4, called CoZn-NC/BVO. Asymmetrically-doped nitrogen-carbon layer materials of Zn and Co (CoZn-NC) can enable the unrestricted mobility of lone pairs of electrons in metals upon exposure to light irradiation, which results in interlayer polarization and electron delocalization effects, leading to improved charge separation efficiency. Furthermore, due to the synergistic effect of bimetallic doping, not only does the intralayer polarized electric field formed on the surface of CoZn-NC improve the charge injection efficiency, but it also modulates the d-band center of the active site Co, thus reducing the Gibbs free energy of the reaction. The results show that the oxygen reduction reaction of CoZn-NC/BVO is excellent, with a photocurrent density of 5.84 mA cm−2 at 1.23 V vs. RHE, which is 4.35 and 2.1 times higher than that of BiVO4 and Co-NC/BVO, respectively. The charge separation and charge injection efficiencies were also significantly higher, at 84.89 % and 91.97 %, respectively. Overall, the proposed co-catalyst of CoZn-NC/BVO shows great potential in photoelectrocatalytic water oxidation and provides a valuable contribution to the field.

Cobalt oxide nanosheets anchored on loofah sponge-derived carbon as a high-performance bifunctional electrocatalyst for rechargeable zinc-air batteries

Rechargeable zinc-air batteries need bifunctional electrocatalysts to improve the kinetics of both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). Herein, we prepare a CoO@NC catalyst employing the 'carbonization-solvothermal-calcination' method, which involves affixing CoO nanosheets to the nitrogen-doped carbon matrix derived from the loofah sponge. The synergy of NC and CoO components creates abundant active sites, and their hierarchical porous structure enables the swift movement of relevant species, thus allowing the CoO@NC catalyst to display remarkable bifunctional performance with a potential difference of 0.73 V. Additionally, the CoO@NC-driven zinc-air battery exhibits a remarkable peak power density of 112.4 mW cm−2 and works reliably for more than 200 h, outperforming the commercial Pt/C-RuO2 catalysts. This research proposes a novel strategy for constructing noble-metal-free bifunctional electrocatalysts.

Heterostructured TiN/TiO2 on the hierarchical N-doped carbon for enhancing the polysulfide immobilization and sulfur reduction in lithium-sulfur battery

The commercialization of lithium-sulfur batteries (LSBs) is impeded by their low sulfur utilization and poor cycling stability. Herein, uniformly distributed TiN/TiO2 heterostructures on the hierarchical nitrogen-doped inter-connected multi-scale porous carbon matrix was developed as an effective polysulfide trapper and catalytic accelerator for sulfur reduction reaction. The performance of synthesized TiN/TiO2 heterostructures in LSBs are compared with those of TiN and TiO2. The synergetic effects of strong polysulfide adsorption of TiO2 and superior catalytical conversion ability of TiN draw rapid trap-diffusion-conversion process and enhance the reaction kinetics. This heterostructure-based LSBs exhibit a high specific capacity of 1458.5 mAhg−1 at 0.1 C and 684.9 mAhg−1 at 5 C. Over 1000 cycles, a high capacity of 576 mA h g−1 is retained with a low-capacity decay of 0.030 % per cycle at 2 C. Moreover, a high area capacity value of 6.65 mAh cm−2 is obtained at 0.5C with a high sulfur loading of 8.2 mg cm−2 and low electrolyte/sulfur ratio (E/S) of 4.7. This study provides a novel strategy to develop the transition metal nitride-oxide heterostructure on a three-dimensional porous carbon framework as efficient electrode materials for LSBs application.

Efficient activation of peroxymonosulfate by Fe single-atom: The key role of Fe-pyrrolic nitrogen coordination in generating singlet oxygen and high-valent Fe species

Nitrogen-doped carbon matrix single-atom catalysts (SACs) for the efficient removal of organic pollutants have attracted widespread attention. However, the ligand structure and the origin of the high activity between nitrogen species and single-atoms remain elusive. Herein, nitrogen-doped carbon matrix iron single-atom catalysts (Fe/NC-SACs) that exhibit high catalytic reactivity (98.2% SMX degradation in 5 min), broad pH resistance (pH 3.0–11.1), high stability, and sustainable water treatment capacity are reported. High-valent iron (Fe IV=O) and singlet oxygen (1O2) were the reactive oxygen species observed. The electrochemical results demonstrated the generation of catalyst-PMS complexes. The DFT calculations revealed that Fe-pyrrolic N4 was the best ligand for PMS, exhibiting the highest adsorption energy, bond length variation and electron transfer capacity. The central Fe single atom and the carbon electrons adjacent to the pyrrolic N were the reactive sites of the PMS. The main source of 1O2 was the oxidation of PMS. This work provides guidance for the discovery of high-performance catalysts and provides a single-atom catalyst that can be used for practical environmental purification.

Solvent-free Synthesis of Transition Metals Nanoparticles Decorated Foamy Flakes-like Nitrogen-doped Carbon as Bifunctional-catalyst for High-performance Rechargeable Zn-air Batteries

Transition metal-nitrogen-carbon (M/NC) demonstrates a promising effective electrocatalyst for enhancing oxygen evolution/reduction reactions (OER/ORR). However, synthesizing these catalysts is often complex, time-consuming, and involves hazardous solvents while producing a low yield. This work introduces a versatile, eco-friendly, and straightforward solvent-free method to produce M/NC (M = Co, Ni, and Fe) catalysts in ~3 h using a glucose, urea, and metal nitrate hydrate mixture. The high-yield M/NC catalysts exhibit a porous architecture and uniform distribution of metal nanoparticles within a foaming flakes-like nitrogen-doped carbon matrix. The metal nanoparticles are wrapped with protective nitrogen-doped carbon layers, producing stable active sites. Possessing these unique properties, the obtained M/NC catalysts show high-performance and stable bifunctional OER/ORR. As the best result, Co/NC presents an OER/ORR potential difference (ΔE) of 0.78 V and retains 96% and 89% of its OER and ORR performance after a 10 h stability test. In practical application, the Co/NC-based Zn-air battery depicts a high power density of 184 mW cm−2 and good rechargeability of up to 120 h, outperforming the battery with noble metal-based catalysts. This work sheds light on the versatile, eco-friendly, and scalable synthesis of M/NC catalysts while presenting a strategy to accelerate the generation of inexpensive and highly effective bifunctional OER/ORR catalysts.

NiS2/CoS2@NC@C nanocubes derived from prussian blue analogues as an advanced anode with extraordinary long-cycle performance for sodium ion batteries

Transition metal sulfides (TMSs) are regarded as one of the ideal anodes for sodium ion batteries (SIBs) owing to their high theoretical capacity and strong electrochemical activity; nonetheless, it still faces challenges such as large volume variation and low conductivity during chemical reactions for applications. Herein, the nanocubes of carbon-encapsulated NiS2/CoS2 embedded porous nitrogen-doped carbon matrixes (NiS2/CoS2@NC@C) are synthesized as a high-performance anode by in-situ carbonizing and subsequently sulphurating the resorcinol-formaldehyde (RF)-coated Ni-Co-based Prussian blue analogues (PBAs). The RF-derived carbon shell acts as a rigid skeleton to effectively relieve the bulk stress during charging and discharging for ensuring the structure integrity, while the porous nitrogen-doped carbon matrix improves the electronic conductivity, presents rich channels for ion/electron transfer and inhibits the agglomeration of active material during chemical reaction. In addition, the lattice distortion at the heterogeneous interface of the NiS2/CoS2 allows the redistribution of electrons, promoting the chemical reaction kinetics. Consequently, the NiS2/CoS2@NC@C nanocubes exhibit excellent electrochemical properties: a high discharge capacity of 489.9 mA h g−1 after 170 cycles at 1.0 A g−1 (920.6/807.9 mA h g−1 for the initial discharge/charge capacity with the initial coulomb efficiency of 87.7%) and a discharge capacity of 349.7 mA h g−1 with the CE close to 100.0% at 5.0 A g−1 even after 2000 cycles. This study proposes a viable approach for the effective construction of advanced anodes with unique micromorphology and chemical composition based on bimetallic PBAs for SIBs.

Graphitized Carbon-Coated Iron Fluoride Nanocavities for Enhanced Kinetics of Multielectron Cathode Conversion Reactions.

As for the conversion-type iron fluoride (FeF3) cathode material with multielectron reactions for lithium-ion batteries (LIBs), sluggish reaction kinetics and low electrical conductivity pose certain limitations for the long-lasting reversible conversion processes. Herein, the three-dimensional porous nitrogen-doped carbon matrix in situ anchoring FeF3 nanocavities coated by graphitized carbon (FeF3/GC) are rationally prepared. Through the Kirkendall effect, the low-temperature fluorination of NF3 enables the resultant hollow FeF3 nanoparticles to possess a large number of lithium storage cavities and outer graphitized carbon structure, further effectively buffering the expansion of volume. The FeF3/GC cathode delivers a superior discharge capacity of 504.2 mAh g-1 after 1200 cycles at 1000 mA g-1, with a capacity decay rate of only 0.01% per cycle. Even at a rate of 5000 mA g-1, the composite cathode still delivers a discharge capacity of 309.6 mAh g-1. Impressively, the existence of graphitized carbon and the short Li+ diffusion length ensure fast electron/ion transfer, which significantly enhances the conversion reaction kinetics. This study aims to provide a promising strategy for the efficiency enhancement of multielectron cathode conversion reactions for LIBs.

Silicon-carbon anode with high interfacial stability by a facile thermal reaction involving alkaline nitrogenous carbon source for lithium ion batteries

Silicon‑carbon composites are considered one of the most promising anodes for high-energy lithium-ion batteries. In this work, NC@Si nanospheres were prepared as silicon‑carbon anode materials for lithium-ion batteries by using an alkaline nitrogenous carbon source (polydopamine, PDA) to induce the anchoring of ultra-fine and high-purity SiO2 quantum dots onto a carbon matrix, followed by a magnesium thermal reduction treatment. The small volume expansion of silicon quantum dots (<10 nm) in NC@Si nanospheres and the thin Si3N4 outerwear formed on Si quantum dots due to the diffusion of N atoms and the local high temperature of magnesium heat synergistically ensure the structural integrity of NC@Si nanospheres and inhibit the excessive formation of SEI. The multi-point solid electrical contact between the silicon quantum dots and the nitrogen-doped carbon matrix provides sufficient conductive channels for fast Li+ diffusion and charge transfer. The as-prepared NC@Si anode exhibits a specific capacity of 497.2 mAh g−1 at 0.1 A g−1 with a capacity retention of 75.4% after 100 cycles, demonstrating a stable cycling performance. In the NC@Si||LFP full cell, the anode maintains a reversible capacity of 260.8 mAh g−1 after 80 cycles. The investigation of NC@Si composite anode proves that the silicon‑carbon anode by a facile thermal reaction involving alkaline nitrogenous carbon source can effectively improve the defects of silicon, offering the possibility of commercial application of silicon-based anode.

Indium/cobalt nanoparticles impregnated porous nitrogen-doped carbon matrix as a 3D sulfur host for lithium polysulfide adsorption-desorption and catalytic conversion in lithium-sulfur batteries

The development of high activity electrocatalysts is considered effective strategy to improve the cathode kinetics in lithium-sulfur batteries (LSBs), especially those operating at high current densities and containing lean electrolytes. Herein, a nanostructured bimetallic sulfur cathode electrocatalyst containing p-block element indium, In/Co-NC, is prepared for the first time. This In-based proof of concept catalyst slows the conversion of elemental sulfur into soluble polysulfides (LiPS) while accelerating their bi-directional liquid-solid conversion, thus reducing their accumulation in the electrolyte and ultimately inhibiting the shuttle effect. LSB cells assembled using the newly prepared electrocatalyst demonstrated high cycle capability of more than 600 cycles at 3 C, accompanied by a high rate capability. Moreover, the In/Co-NC cell containing a lean electrolyte (E/S = 9 μL mgsulfur−1) exhibited 250 stable cycles at 0.5C with only 0.011% capacity decay per cycle. The study provides new design direction for cathode electrocatalysts and guidance for optimization of adsorption and catalytic processes in LSBs.

Cu Single-Atom Catalysts for High-Selectivity Electrocatalytic Acetylene Semihydrogenation.

The site isolation strategy has been employed in thermal catalytic acetylene semihydrogenation to inhibit overhydrogenation and C-C coupling. However, there is a dearth of analogous investigations in electrocatalytic systems. In this work, density functional theory (DFT) simulations demonstrate that isolated Cu metal sites have higher energy barriers on overhydrogenation and C-C coupling. Following this result, we develop Cu single-atom catalysts highly dispersed on nitrogen-doped carbon matrix, which exhibit high ethylene selectivity (>80% Faradaic efficiency for ethylene, <1% Faradaic efficiency for C4, and no ethane) at high concentrations of acetylene. The superior performance observed in the electrocatalytic selective hydrogenation of acetylene can be attributed to the weak adsorption of ethylene intermediates and highly energy barriers on C-C coupling at isolated sites, as confirmed by both DFT calculations and experimental results. This study provides a comprehensive understanding of the isolated sites inhibiting the side reactions of electrocatalytic acetylene semihydrogenation.

Energy- and cost-efficient salt-assisted synthesis of nitrogen-doped porous carbon matrix decorated with nickel nanoparticles for superior electromagnetic wave absorption

Energy- and cost-efficient salt-assisted synthesis of nitrogen-doped porous carbon matrix decorated with nickel nanoparticles for superior electromagnetic wave absorption

CoZn-ZIF and melamine co-derived double carbon layer matrix supported highly dispersed and exposed Co nanoparticles for efficient degradation of sulfamethoxazole

Metal-organic framework (MOF)-derived carbon materials have drawn tremendous attention as activators of peroxymonosulfate (PMS) for the degradation of antibiotics. However, it is still challenging to construct MOF-derived materials with well-dispersed and highly-exposed metal active sites. Herein, the bimetallic Cobalt-Zinc-zeolite imidazolate framework and melamine co-derived double layer nitrogen-doped porous carbon matrix supported highly dispersed cobalt nanoparticles (Co NPs) (denoted as Co-NC-C) with the exposure of more Co NPs sites was developed by one-step pyrolysis method. The transmission electron microscopy results demonstrate that double layer carbon matrix as a dispersant can effectively inhibit the agglomeration of Co NPs, and Co-NC-C possessed more exposure of Co active sites compared with Co-NC without melamine. Co-NC-C efficiently activated PMS to remove over 96.67% of sulfamethoxazole (SMX) at a widespread range of pH within 120 min due to its the highly-exposed Co active sites and high graphitization degree. Additionally, the degradation mechanism dominated by the singlet oxygen was demonstrated. Finally, four products and two probable degradation pathways of SMX were confirmed. Half of the products were less toxic than SMX based on the ecological structure activity relationships analysis results. The study provides valuable insights for the development of MOF-derived catalysts with well-dispersed and highly-exposed metal active sites.

Covalent Organic Framework-Derived Nitrogen-Doped Carbon-Supported Cobalt Oxide Nanoparticles for Synergistic Boosting H2 Evolution from NaBH4

Developing nonprecious metal catalysts with fast charge transfer ability, abundant active sites, and easy recovery is of great significance toward sodium borohydride (NaBH4) hydrolysis for hydrogen (H2) production in alkaline solutions. Herein, magnetically separated nitrogen-doped carbon-supported cobalt oxide (CoxOy@NC) nanoparticles were prepared successfully by converting pyrazine-based covalent organic frameworks (COFs). Due to the porous structure and nitrogen-rich characteristics of the precursor, the prepared catalyst CoxOy@NC exhibited good conductivity and charge transfer ability. Cobalt oxide nanoparticles and nitrogen-doped carbon matrix are bonded by the Co–N bond, which makes full use of the conductivity of the substrate and the high activity of the cobalt oxide catalyst. Therefore, CoxOy@NC exhibits an excellent synergistic effect between CoxOy and NC. The H2 generation rate reaches a maximum of 2082.13 mL/min/g from NaBH4 in alkaline solutions. In addition, CoxOy@NC also exhibits good magnetic separation capability, which greatly simplifies the catalyst separation process. Density functional theory (DFT) calculation results indicate that Co2+ is the dominant active component in the heterogeneous catalyst CoxOy@NC. This work broadens new horizons for the development of COFs derivative catalysts for hydrogen production from sodium borohydride hydrolysis.

Bimetallic Cobalt-Nickel Selenide Nanocubes Embedded in a Nitrogen-Doped Carbon Matrix as an Excellent Li-Ion Battery Anode.

Lithium-ion batteries (LIBs) have been widely used for portable electronics and electric vehicles; however, the low capacity in the graphite anode limits the improvement of energy density. Transition-metal selenides are promising anode material candidates due to their high theoretical capacity and controllable structure. In this study, we successfully synthesize a bimetallic transition-metal selenide nanocube composite, which is well embedded in a nitrogen-doped carbon matrix (denoted as CoNiSe2/NC). This material shows a high capacity and excellent cycling for Li-ion storage. Specifically, the reversible capacity approaches ∼1245 mA h g-1 at 0.1 A g-1. When cycled at 1 A g-1, the capacity still remains at 642.9 mA h g-1 even after 1000 cycles. In-operando XRD tests have been carried out to investigate the lithium storage mechanism. We discover that the outstanding performance is due to the unique CoNiSe2/NC nanocomposite characteristics, such as the synergistic effect of bimetallic selenide on lithium storage, the small particle size, and the stable and conductive carbon structure. Therefore, this morphology structure not only reduces the volume change of metal selenides but also produces more lithium storage active sites and shortens lithium diffusion paths, which results in high capacity, good rate, and long cycling.

Metal-Organic Framework-Derived Mesoporous B-Doped CoO/Co@N-Doped Carbon Hybrid 3D Heterostructured Interfaces with Modulated Cobalt Oxidation States for Alkaline Water Splitting.

Heteroatom-doped transition metal-oxides of high oxygen evolution reaction (OER) activities interfaced with metals of low hydrogen adsorption energy barrier for efficient hydrogen evolution reaction (HER) when uniformly embedded in a conductive nitrogen-doped carbon (NC) matrix, can mitigate the low-conductivity and high-agglomeration of metal-nanoparticles in carbon matrix and enhances their bifunctional activities. Thus, a 3D mesoporous heterostructure of boron (B)-doped cobalt-oxide/cobalt-metal nanohybrids embedded in NC and grown on a Ni foam substrate (B-CoO/Co@NC/NF) is developed as a binder-free bifunctional electrocatalyst for alkaline water-splitting via a post-synthetic modification of the metal-organic framework and subsequent annealing in different Ar/H2 gas ratios. B-CoO/Co@NC/NF prepared using 10% H2 gas (B-CoO/Co@NC/NF [10% H2 ]) shows the lowest HER overpotential (196mV) and B-CoO/Co@NC/NF (Ar), developed in Ar, shows an OER overpotential of 307mV at 10mA cm-2 with excellent long-term durability for 100h. The best anode and cathode electrocatalyst-based electrolyzer (B-CoO/Co@NC/NF (Ar)(+)//B-CoO/Co@NC/NF (10% H2 )(-)) generates a current density of 10mA cm-2 with only 1.62V with long-term stability. Further, density functional theory investigations demonstrate the effect of B-doping on electronic structure and reaction mechanism of the electrocatalysts for optimal interaction with reaction intermediates for efficient alkaline water-splitting which corroborates the experimental results.

Solvent-free synthesis of Co/CoNx encapsulated by N-doped, sucrose-derived porous carbon as bifunctional air cathode catalyst for high-energy rechargeable zinc-air batteries

Rechargeable zinc-air batteries have a substantial theoretical energy density while potentially being manufactured at a minimized cost. Hence, developing low-cost bifunctional electrocatalysts is of crucial importance. Herein, the synthesis of an electrocatalyst containing zinc/cobalt species encapsulated in a nitrogen-doped carbon matrix modulated with a large number of carbon nanotubes (ZnCo@CN) was developed through a facile thermal method under solvent-free conditions. Using bio-based sucrose in the presence of inorganic catalysts (Zn/Co) resulted in a Zn/Co carbon foam-like structure. Subsequently, the high-temperature treatment with the addition of 2-methylimidazole resulted in a unique material (ZnCo@CN). The incorporation of highly active species dispersed in hierarchical porous carbon presented an excellent bifunctional electrocatalyst for ORR (half-wave potential of 0.85 V) and OER (overpotential of 327 mV). The assembled zinc-air battery with ZnCo@CN as a bifunctional air cathode exhibited an excellent power density of 206 mW cm-2 and an astonishing energy density of 983 Wh Kg-1.

Geometric and Electronic Engineering of Atomically Dispersed Copper-Cobalt Diatomic Sites for Synergistic Promotion of Bifunctional Oxygen Electrocatalysis in Zinc-Air Batteries.

The development of rechargeable zinc-air batteries is heavily dependent on bifunctional oxygen electrocatalysts to offer exceptional oxygen reduction/evolution reaction (ORR/OER) activities. However, the design of such electrocatalysts with high activity and durability is challenging. Herein, a strategy is proposed to create an electrocatalyst comprised of copper-cobalt diatomic sites on a highly porous nitrogen-doped carbon matrix (Cu-Co/NC) with abundantly accessible metal sites and optimal geometric and electronic structures. Experimental findings and theoretical calculations demonstrate that the synergistic effect of Cu-Co dual-metal sites with metal-N4 coordination induce asymmetric charge distributions with moderate adsorption/desorption behavior with oxygen intermediates. This electrocatalyst exhibits extraordinary bifunctional oxygen electrocatalytic activities in alkaline media, with a half-wave potential of 0.92 V for ORR and a low overpotential of 335mV at 10mAcm-2 for OER. In addition, it demonstrates exceptional ORR activity in acidic (0.85V) and neutral (0.74V) media. When applied to a zinc-air battery, it achieves extraordinary operational performance and outstanding durability (510h), ranking it as one of the most efficient bifunctional electrocatalysts reported to date. This work demonstrates the importance of geometric and electronic engineering of isolated dual-metal sites for boosting bifunctional electrocatalytic activity in electrochemical energy devices.

Dual-sources directed construction of N-doped carbon nanotube arrays as superior Self-supported bifunctional air electrodes for Rechargeable/Flexible Zinc-air batteries

Developing advanced hybrid nanocatalysts comprising non-precious metal alloys encased in nitrogen-doped carbon matrix are extremely promising to promote the oxygen electrochemistry, though the elaborate construction of highly-dispersed and stable metal–N–C active sites remains a tough challenge. Herein, we crafted self-supported CoFe nanoalloys catalyst confined in N-doped carbon nanotube arrays rooting on carbon cloth (CoFe@NCNTs) via a simple dual-sources directed synthetic route. Experimental results demonstrate that well-constructed CoFe@NCNTs catalyst owns attractive benefits including 3D interconnected conductive network, porous heterostructure and sufficient active sites, accelerating the mass transport and interfacial charge transfer to improve the redox kinetics for bifunctional oxygen catalysis. Theoretical calculation analyses further demonstrate the synergistic bimetallic effect in CoFe@NCNTs for effective adsorption of oxygen intermediates. Accordingly, CoFe@NCNTs achieves low overpotentials for OER and ORR. Also, aqueous rechargeable zinc-air batteries (ZABs) with the self-supported CoFe@NCNTs air cathode deliver high gravimetric energy density of 966.4 Wh kgZn-1 at 10 mA cm−2, a maximum power density of 158.4 mW cm−2 and superb cycling stability of over 400 h/1000 cycles. High performance all-solid-state flexible ZABs are also realized with high discharge capacities, impressive peak power density, superior rate capabilities and prominent mechanical flexibility toward various practical applications. This study could provide an alternative avenue to establish cost-effective non-precious metal nanoalloys-based multifunctional electrocatalysts.