N-doped Carbon Layer Research Articles

Strong Bonding of Lattice N Activates Metal Ni to Achieve Efficient Water Splitting.

Developing efficient and robust free-standing electrocatalysts for overall water splitting is a promising but challenging task. Herein, the N-incorporated Ni nanosheets non-fully encapsulated by N-doped carbon (NC) layer are fabricated (N─Ni©NC). The introduction of N not only regulates the size of nanosheets in N─Ni©NC but also promotes the electrochemical activity of metal Ni. Experimental and theoretical results reveal that strong bonding of the lattice N activates the inert metal Ni by promoting charge transfer between Ni and N. In addition, the upward shift of the d-band center induced by lattice N enhances the adsorption of intermediates, thereby making Ni as a new OER active site together with C. This strategy of generating Ni and C dual active sites by introducing lattice N greatly accelerates oxygen evolution reaction (OER) kinetics, resulting in excellent electrocatalytic performance of N─Ni©NC. At the current density of 10mA cm-2, the overpotentials of hydrogen evolution reaction (HER) and OER are 27 and 206mV, respectively, and the cell voltage for overall water splitting only needs 1.47V. This work offers a unique heteroatom activation approach for designing free-standing electrodes with high activity.

Fabrication of surface-carbonated boron nitride nanosheets and their application as water-based lubrication additives

As a typical two-dimensional layered material, hexagonal boron nitride nanosheets (BNNSs) have high mechanical strength, good conductivity, and excellent lubrication performance, which have great potential as solid nano lubricant additives in tribology. When BNNS is used as a water-based or oil-based lubricant additive, its inherent chemical inertness and poor dispersion stability make it difficult to achieve optimal anti-friction and anti-wear performance. In this paper, a simple and efficient preparation method for obtaining hexagonal boron nitride nanosheets (C-HPC-BNNSs) with surface carbonization modification and excellent dispersion stability in water-based lubricants was proposed. Using hydroxypropyl cellulose (HPC) as a modifier, a wet ball milling process combined with high-temperature carbonization treatment effectively reduced the thickness of BNNSs while uniformly modifying N-doped carbon layers on the surface of the nanosheets. Benefit from the smaller layer thickness of C-HPC-BNNSs, they exhibit excellent dispersion stability in the water-glycol solution and can maintain no significant agglomeration behavior for up to 30 days, which is the basis for the excellent lubrication performance of lubricant systems. In addition, the N-doped carbon layer modified on the surface is beneficial for enhancing the hydrophilicity of BNNSs and synergistically enhances the tribological properties of the material with BNNSs. The test results of the four-ball friction tester show that compared with the pure water-glycol solution and the water-glycol system with added C-HPC-BNNSs, the friction coefficient (COF) and wear volume of the system with added C-HPC-BNNSs could be as low as 0.095 and 1.99 × 10−4 mm3, respectively. This work has positive significance for the preparation, surface modification, and tribological application expansion of two-dimensional layered material BNNSs, which is conducive to further understanding the relationship between.

A Cu/Fe3O4@CN tandem catalyst for efficient ammonia electrosynthesis from nitrate reduction

Electrochemical nitrate reduction reaction (ENO3RR) is a green technology for value-added ammonia production meanwhile treating waste water at ambient conditions. However, it remains a great challenge to construct efficient catalysts due to the complex multiple proton and electron transfer process. Herein, we report a tandem catalyst Cu/Fe3O4@CN composed of N-doped carbon layer coated Cu/Fe3O4 heterostructure toward highly efficient electrocatalytic nitrate reduction to ammonia production in alkaline medium. The catalyst can achieve an ammonia Faradaic efficiency and ammonia yield rate as high as 96.57 % and 22104.15 μg h−1 mgcat−1 at the optimal potential of −0.9 V vs RHE in 0.1 M KOH. The outstanding ENO3RR performance outperforms the most of reported transitional metal-based ENO3RR electrocatalysts. More importantly, Cu/Fe3O4@CN also exhibits excellent stability even under large current density of 200 mA cm−2, and long-time durability for continuous electrolysis for 36 h. The experimental and theoretical calculations verify the tandem catalysis mechanism of NO3− → NO2− → NH3 through the synergism of the two components Cu and Fe3O4 in Cu/Fe3O4@CN. Specifically, Cu has strong NO3− adsorption capacity which can be reduced into NO2−, while Fe3O4 can boost water dissociation to generate abundant active *H, ensuring the smooth hydrogenation process while suppressing the occurrence of competitive hydrogen evolution reactions (HER). The heterostructure formation between Cu and Fe3O4 also significantly reduces the energy barrier of the rate-determining step (*NO → *NOH), which results in the high performance of Cu/Fe3O4@CN.

Prussian Blue-Derived Atomic Fe/Fe3C@N-Doped C Catalysts Supported by Carbon Cloth as Integrated Air Cathode for Flexible Zn-Air Batteries.

The development of an integrated air cathode with superior oxygen reduction reaction (ORR) performance is fundamental to flexible zinc-air batteries (ZABs) for wearable electronics. Herein, a self-assembled metal-organic framework (MOF)-derived strategy is proposed to prepare a atomic Fe/Fe3C@N-doped C catalysts supported by carbon cloth (CC) catalyst for use as an air cathode of flexible ZABs. The Prussian Blue precursor, which self-assembles on the surface of the carbon cloth due to electrostatic attraction, is critical in achieving the uniform dispersion of catalysts with high density loading on carbon cloth substrates. The hollow cubic structure, N-doped carbon layer coating, and the integrated electrode design can provide more accessible active sites and facilitate a rapid electron transfer and mass transport. Density functional theory (DFT) calculation reveals that the electronic interactions between the Fe-N4 and Fe3C dual active sites can optimize the adsorption-desorption behavior of oxygen intermediates formed during the ORR. Consequently, the Fe/Fe3C@N-doped C/CC exhibits an excellent half wave potential (E1/2 = 0.903V) and superior long-term cycling stability in alkaline environments. With excellent ORR performance, ZABs and flexible ZABs based on Fe/Fe3C@N-doped C/CC air cathode demonstrate excellent overall electrochemical performance in terms of open circuit voltage, maximum power density, flexibility, and cycling stability.

Fe3O4 encapsulated in hierarchically porous nitrogen-doped graphitic carbon layers for efficient oxygen reduction reaction: Enhanced intrinsic activity via directional interfacial charge transfer

Constructing efficient electrocatalysts for the oxygen reduction reaction (ORR) is crucial for the commercialization of metal-air batteries. Iron oxide-based catalysts exhibit promising potential for ORR. However, addressing the issue of inferior catalytic performance is essential, and a comprehensive understanding of the catalytic mechanism of iron oxide-based catalysts is also lacking. In this study, we present Fe3O4 nanoparticles encapsulated in N-doped graphitic carbon layers (NGC) hosted by hierarchically porous carbon (Fe3O4@NGC), achieved through a facile dual melt-salt template strategy. The encapsulation of Fe3O4 nanoparticles protects them from corrosion and exfoliation, endowing the catalysts with superior stability. Density functional theory (DFT) calculations discover that the electronic interaction between Fe3O4 nanoparticles and N-doped graphitic carbon layers induces directional interfacial electron transfer, which effectively modulates the surface electronic structure to improve the binding ability to O2, weaken the OO bond, and optimize the adsorption of intermediates, thus boosting the intrinsic activity. DFT unveils that the C atoms nearest to graphitic-N in NGC are active sites. Finally, the synergistic effects of Fe3O4 nanoparticles and NGC result in outstanding ORR performance and superior stability and methanol tolerance of Fe3O4@NGC, with a half-wave potential of 0.89 V, surpassing that of Pt/C by 50 mV. Fe3O4@NGC also shows better performance than Pt/C when used as the air-electrode catalyst in zinc-air battery.

Integrating Cu+/Cu0 sites on porous nitrogen-doped carbon nanofibers for stable and efficient CO2 electroreduction to multicarbon products

The Cu+/Cu0 sites of copper-based catalysts are crucial for enhancing the production of multicarbon (C2+) products from electrochemical CO2 reduction reaction (eCO2RR). However, the unstable Cu+ and insufficient Cu+/Cu0 active sites lead to their limited selectivity and stability for C2+ production. Herein, we embedded copper oxide (CuOx) particles into porous nitrogen-doped carbon nanofibers (CuOx@PCNF) by pyrolysis of the electrospun fiber film containing ZIF-8 and Cu2O particles. The porous nitrogen-doped carbon nanofibers protected and dispersed Cu+ species, and its microporous structure enhanced the interaction between CuOx and reactants during eCO2RR. The obtained CuOx@PCNF created more effective and stable Cu+/Cu0 active sites. It showed a high Faradaic efficiency of 62.5% for C2+ products in H-cell, which was 2 times higher than that of bare CuOx (∼31.1%). Furthermore, it achieved a maximum Faradaic efficiency of 80.7% for C2+ products in flow cell. In situ characterization and density functional theory (DFT) calculation confirmed that the N-doped carbon layer protected Cu+ from electrochemical reduction and lowered the energy barrier for the dimerization of *CO. Stable and exposed Cu+/Cu0 active sites enhanced the enrichment of *CO and promoted the C–C coupling reaction on the catalyst surface, which facilitated the formation of C2+ products.

Optimizing the size and electronic effects of core-shell heterostructures via well-constructed Ru clusters encapsulated in N-doped carbon layers

Optimizing the size and electronic effects of core-shell heterostructures via well-constructed Ru clusters encapsulated in N-doped carbon layers

Synthesis and performance evaluation of bio-derived and synthetic carbon as lithium-sulfur battery cathode

The next-generation of batteries need be both energy dense and environment friendly. Lithium sulfur batteries (LSBs) satisfy both criteria but their practical implementation is marred by the highly resistive nature of sulfur. Carbon-based cathodes play a vital role in mitigating the issue because their high conductivity allows for effective electron transfer during electrochemical cycling. Synthesis and electrochemical evaluation of carbon-based cathodes from two different sources for LSBs was carried out. Herein, two kinds of carbon, namely bio-derived carbon from coconut shells (CC500) and N-doped carbon (NC) from polyacrylonitrile fibers were synthesized and sulfur was incorporated via the melt diffusion route. The composites are characterized by PXRD and TGA, which determined 80 wt% mass loading of sulfur. The higher intensity of G-band over D-band in Raman spectroscopy indicates greater graphitic character for CC500 compared to NC. SEM images show large macro-pore like tunnels in CC500 while NC appears are irregular chunks. EDAX spectra showed 20 wt% N content in NC while CC500 is largely carbon with some minor surface oxygen. In galvanostatic charge–discharge cycling of coin cells, bare CC500/S shows better specific capacity compared to NC/S samples but the trend flips once a separator modified with 4 mg of graphene oxide (GO) is introduced (indicated as NC/S/GO4 and CC500/S/GO4). This points towards synergy between N-doped carbon and GO layer in retaining the soluble polysulfides in the catholyte region. NC/S/GO4 exhibited better capacity i.e., 1453, 1024, 866, 787, 697 mAh/g versus 1016, 779, 672, 551, 441 mAh/g offered by CC500/S/GO4 when discharged at 50, 100, 200, 300 and 500 mA/g, respectively.

Bifunctional heterostructured nitrogen-doped carbon-layer-loaded NiSe2-FeSe2 electrocatalyst for efficient water splitting

Developing high-performance, eco-friendly bifunctional electrocatalysts is crucial to popularizing water electrolysis for hydrogen production, but it still presents major challenges. Here, we develop a composite material with NiSe2-FeSe2 heterostructure loaded on N-doped carbon layers by utilizing the metal-organic framework as a sacrificial template (NiSe2-FeSe2/NC). According to microstructural studies, direct contact between NiSe2 and FeSe2 induces charge transfer and enhances conductivity, while sensible arraying of NiSe2-FeSe2/NC nanosheets fully exposes active sites and protects catalysts from violent reaction processes. The NiSe2-FeSe2/NC heterostructured catalysts show excellent bifunctional catalytic activity for hydrogen and oxygen evolution reactions, with overpotentials of 54 and 232 mV at 10 mA cm−2, respectively. Moreover, NiSe2-FeSe2/NC also retains superiority in a two-electrode system, needing lower voltage to drive the overall water splitting at 10 mA cm−2 (1.53 V) than Pt/C||RuO2 as well as long-term stability. This work introduces a novel concept for developing state-of-the-art non-noble metal catalysts for hydrogen production and new insights into interface engineering.

Enhanced hydrothermal stability by a semi-embedded structure: An efficient Ru catalyst for levulinic acid conversion in the aqueous phase

Catalyst stability is believed to be one of the greatest challenges faced for the supported metal catalysts in the catalytic conversion of biomass and its derivatives because many biomass transformations are conducted in the aqueous phase. In this work, we report a simple yet efficient coating-impregnation-pyrolysis (CIP) strategy to fabricate Al2O3 supported Ru catalyst (Ru-Al2O3@CN) with Ru NPs (nanoparticles) semi-embedded into N-doped carbon (CN) layer for the efficient hydrogenation of levulinic acid (LA) to γ-valerolactone in the aqueous phase. Benefit from the special structure of Ru-Al2O3@CN catalyst, it possesses both high catalytic activity and stability, giving a TOF of 28,099 h-1 for LA hydrogenation at 120 °C and 2 MPa H2, which is superior to the most of reported Ru-based catalysts. More importantly, compared with conventional impregnated Ru/Al2O3 catalyst, the Ru-Al2O3@CN catalyst exhibits a remarkably improved hydrothermal stability. Based on series of catalyst characterizations and control experiments, it was found that the presence of CN can weak the interaction between Ru and Al2O3, as well as protect the Al2O3 and Ru NPs from hydrolysis and aggregation, respectively. We anticipate that such a novel strategy may provide some valuable insights into the synthesis of oxides-supported metal catalyst with high hydrothermal stability.

Electron-Spin Regulation Driving Heterointerface Electron Distribution and Phase Transition toward Ultrafast and Durable Sodium Storage.

Phase engineering is an effective strategy for modulating the electronic structure and electron transfer mobility of cobalt selenide (CoSe2) with remarkable sodium storage. Nevertheless, it remains challenging to improve fast-charging and cycling performance. Herein, a heterointerface coupling induces phase transformation from cubic CoSe2 to orthorhombic CoSe2 accompanied by the formation of MoSe2 to construct a CoSe2/MoSe2 heterostructure decorated with N-doped carbon layer on a 3D graphene foam (CoSe2/MoSe2@NC/GF). The incorporated Mo cations in the bridged o-CoSe2/MoSe2 not only act an electron donor to regulate charge-spin configurations with more active electronic states but also trigger the upshift of d/p band centers and a decreased ∆d-p band center gap, which greatly enhances ion adsorption capability and lowers the ion diffusion barrier. As expected, the CoSe2/MoSe2@NC/GF anode demonstrates a high-rate capability of 447 mAh g-1 at 2 A g-1 and an excellent cyclability of 298 mAh g-1 at 1 A g-1 over 1000 cycles. The work deepens the understanding of the elaborate construction of heterostructured electrodes for high-performance SIBs.

Nanosheet-interwoven structures and ion-electron decoupling storage enable Fe1-xS fast ion transport in Li+/Na+/K+ batteries

Fe1-xS, known for its high theoretical capacity, abundant resources, and intrinsic safety, has become a focal point as a universal anode for Li+/Na+/K+ batteries. However, its fast-charging capability is unsatisfactory due to sluggish ion transport rate and low electrical conductivity. Furthermore, its Li+/Na+/K+ storage mechanisms are still unclear. Here, we fabricate a single-crystal Fe1-xS/N-doped carbon composite nanosheet interwoven structure, in which N-doped carbon layers onto surface of Fe1-xS nanosheets ameliorate the electrical conduction and the interwoven nanosheets form open pore channels that favor permeation of electrolytes to boost ion transport. In-situ magnetometry reveals that ion-electron decoupling storage and transport occur in two-phase composites of Fe/Li2S, Fe/Na2S, and Fe/K2S, in which Fe phase stores and transports electrons and sulfide phase stores and transports ions in a space-charge form, resulting in extra ion storage and fast ion transport. Consequently, the nanosheet interwoven structure delivers high capacities (1320.1/652.2/350.6 mAh g−1), outstanding fast-charging performances (679.6/295.4/106.4 mAh g−1 at 20 A g−1), and long cycling life over 5000 cycles as Li+/Na+/K+ battery anodes, respectively

Constructing stress-release layer on Si nanoparticles for high-performance lithium storage

Tailing structures of silicon anode to alleviate the mechanical stress has an important significance in the development of lithium-ion batteries (LIBs). Herein, the stress-released layer of N-doped cubic carbon on the surface of Si nanoparticles (Si@NCC) is explored to stabilize the electrode. Endowed with the unique superiority, the Si@NCC electrode delivers an impressive lithium storage performance with high specific capacity of 630 mAh/g at 0.1 A/g, excellent cycling stability (72.0 % capacity retention after 100 cycles at 0.1 A/g) and good rate capability (375 mAh/g at 2 A/g). It has been demonstrated that the N-doped cubic carbon shell with high conductivity can effectively limit the expansion and agglomeration of Si nanoparticles. Besides, the COMSOL simulations of the stress distributions in materials confirm that the N-doped cubic carbon layer could remarkably decrease the stress originated from the volume expansion of Si nanoparticles during the lithiation. Therefore, this work provides ideas for the mechanical effect of Si-based anodes for lithium storage and sheds lights on the designing advanced materials toward high-performance energy storage devices.

N-doped carbon confined ternary Pt2NiCo intermetallics for efficient oxygen reduction reaction

Developing high performance electrocatalysts for the cathodic oxygen reduction reaction (ORR) is essential for the widespread application of fuel cells. Herein, a promising Pt2NiCo atomic ordered ternary intermetallic compound with N-doped carbon layer coating (o-Pt2NiCo@NC) has been synthesized via a facile method and applied in acidic ORR. The confinement effect provided by the carbon layer not only inhibits the agglomeration and sintering of intermetallic nanoparticles during high temperature process but also provides adequate protection for the nanoparticles, mitigating the aggregation, detachment and poisoning of nanoparticles during the electrochemical process. As a result, the o-Pt2NiCo@NC demonstrates a mass activity (MA) and specific activity (SA) of 0.65 A/mgPt and 1.41 mA/cmPt2 in 0.1 mol/L HClO4, respectively. In addition, after 30,000 potential cycles from 0.6 V to 1.0 V, the MA of o-Pt2NiCo@NC shows much lower decrease than the disordered Pt2NiCo alloy and Pt/C. Even cycling at high potential cycles of 1.5 V for 10,000 cycles, the MA still retains ∼70%, demonstrating superior long-term durability. Furthermore, the o-Pt2NiCo@NC also exhibits strong tolerance to CO, SOx, and POx molecules in toxicity tolerance tests. The strategy in this work provides a novel insight for the development of ORR catalysts with high catalytic activity, durability and toxicity tolerance.

Direct recycling of spent lithium-ion battery cathodes inspired by the polymerization of dopamine

The direct recycling process shows excellent flexibility and potential for the regeneration of spent lithium-ion battery cathodes. However, conventional direct recycling methods involve high temperatures or potential secondary pollution. Herein, the green restoration of spent LiFePO4 (LFP) cathodes is achieved via a polymerization of dopamine (POD)-assisted process in water at room temperature. A unique mechanism is proposed based on DFT calculations: Some intermediates, rather than dopamine or polydopamine, restore the crystal structure of spent LFP. Furthermore, a short annealing treatment could not only increase the structural stability, but also avoid the potential secondary pollution caused by the reductants by converting the Polydopamine (PDA) layer to an N-doped carbon layer and improve the electrochemical performance of the regenerated LFP. A subsequent techno-economic analysis suggests that the present strategy promises great potential in practical application. Environmental implicationSpent lithium-ion batteries (LIBs) contain a large number of toxic and hazardous substances, which would affect ecological balance and human activities, so recycling and reuse of spent LIBs play a vital role in environmental protection. The POD-assisted recycling strategy can maximize the recycling value of the LiFePO4 cathode material, and avoid the secondary pollution caused by the reducing agent. Compared with the traditional pyrometallurgy and hydrometallurgy, the POD-assisted recycling strategy has less negative impact on the environment, higher economic value, and has a broad application prospect.

Constructing Si@CN@MXene from silicon waste as high-performance lithium-ion battery anodes

Silicon represents one of the most attractive materials for anodes in lithium-ion batteries (LIBs) due to highest theoretical specific capacity. Thus, there is a most urgent need to prepare Si-based nano materials in a very efficient way, and develop some reasonable approaches for their modification in order to resolve the short-falls of Si anode, which include both low conductivity and huge volume changes during intercalation of lithium ions. In this work, the kerf loss silicon (KL Si) from the photovoltaic industry has been used as an inexpensive Si source for the synthesis of the Si@CN@MXene (SCM) composite to be applied as an anode material. Meanwhile, the chitosan works as the charge bridge in sequence with the Si and MXene nanosheets under electrostatic force during composite preparation. The MXene nanosheet and N-doped carbon layer that build up during chitosan calcination can be attributed to forming a hierarchical high-speed conductive network over the surface of silicon, which contributed to alleviate the volume expansion of silicon. The SCM electrode discharge capacity was obtained at a stable value of 900.8 mAh g−1 at 0.5 A g−1, 861.9 mA g−1 at 1 A g−1 and 657.6 mA g−1 even at 2 A g−1 after 100 cycles. The SCM electrode also exhibited good rate performance from 0.2 to 5 A g−1. Therefore, this study recommends that the method is very promising for producing the silicon anode material for LIBs from KL Si.

Alleviated volume changes of germanium anode via facile chemical confinement strategy

Germanium (Ge) anode shows great promise in overcoming unsatisfied capacity and dendrite formation concerns facing conventional graphite anodes in next generation lithium ion batteries. However, volume changes during repeated alloying and de-alloying cycles seriously impair structural stability and cycle lifespan. In this work, a facile chemical confinement strategy has been firstly proposed to alleviate volume changes of Ge anode. Benefited from strong binding interaction between Ge and ZnS, discrete Ge nanoparticle can be successfully encapsulated within thin protective ZnS shell and N-doped carbon layer (Ge-ZnS@N-C) after two-step carbonization and sulfurization of polydopamine-coating Zn2GeO4 nanorod precursors. In contrast, bulk Ge aggregates and hollow N-doped carbon nanotubes can be formed without chemical confinement of ZnS. The as-prepared Ge-ZnS@N-C sample displays multifold structural merits, including nanosized Ge particles with highly electrochemical activity, sufficient pores and functional groups that facilitate ion diffusion. Besides, protective ZnS shell and N-doped carbon layer can suppress volume changes of Ge nanoparticles and guarantee high electrode reversibility, demonstrated by a series of in-situ and ex-situ experiments. The as-synthesized Ge-ZnS@N-C anodes exhibit stable long-cycle performance (1389.7 mAh/g after 450 cycles at a current density of 0.5 A/g) and excellent rate performance (548.5 and 397.8 mAh/g at 5.0 and 8.0 A/g, respectively).

Dual Strategy of Morphology Optimization and Interlayer Expansion in VS2 Cathode Toward High-Performance Mg-Li Hybrid Ion Batteries.

Combining the merits of the dendrite-free formation of a Mg anode and the fast kinetics of Li ions, the Mg-Li hybrid ion batteries (MLIBs) are considered an ideal energy storage system. However, the lack of advanced cathode materials limits their further practical application. Herein, we report a dual strategy of morphology optimization and interlayer expansion for the construction of hierarchical flower-like VS2 architecture coated by N-doped amorphous carbon layers. This tailored hierarchical flower-like structure coupled with homogeneous N-doped amorphous carbon layers cooperatively provide more active sites and buffer volume changes, thus realizing the enhancement of capacity and structural stability. Moreover, the enlarged interlayer spacing caused by the cointercalation of polyvinylpyrrolidone and ammonium ions can effectively promote the charge transfer rate and facilitate the rapid ion diffusion, as further demonstrated by electrochemical results and theoretical calculations. These features endow the hierarchical flower-like VS2 cathode with superior specific energy density (644.4 Wh kg-1, average voltage of 1.2 V vs Mg2+/Mg) and excellent rate capability (181.1 mAh g-1 at 2000 mA g-1). Systematic ex situ characterization measurements are employed to reveal the ion storage mechanism, which confirms that Li+ storage plays a leading role in the capacity contribution of MLIBs. Our strategy is in favor of providing useful insights to design and construct MLIBs with high energy density and excellent rate performance.

V2O3/VO2@NC@GO ultrathin nanosheets as a high-performance cathode for aqueous zinc-ion batteries

Recently, vanadium oxides have attracted much attention as advanced cathodes for aqueous zinc-ion batteries on account of their high theoretical specific capacity, multi-electron transfer and easy synthesis; however, structural instability and poor conductivity of the materials limit their practical application. Herein, N-doped carbon-coated V2O3/VO2 hybrid nanosheets were encapsulated into graphene oxide (V2O3/VO2@NC@GO) as an advanced cathode for aqueous zinc-ion batteries by the combined process of hydrothermal treatment, high-temperature annealing and freeze drying. The multi-valence of vanadium element activates diverse redox reactions and thus results in high specific capacity, while graphene oxide and N-doped carbon layer derived from polyvinyl pyrrolidone establish an efficient conductive network for electronic transfer and provide a rigid skeleton for enhancing the structural stability of the hybrid nanosheets. Benefiting from the above unique advantages of composition and micromorphology, the V2O3/VO2@NC@GO cathode exhibits excellent reaction dynamics and rapid electron transfer, generating high specific capacities of 493.0 mAh g−1 at 0.5 A g−1 and 411.9 mAh g−1 at 5 A g−1 and outstanding long-term cycling performance with a retention of 92.4 % after 1000 cycles at 5 A g−1. This work offers a viable approach for developing high-performance vanadium oxide-based cathodes for aqueous zinc-ion batteries by enriching the valence states of vanadium and encapsulating active materials into highly conductive carbon materials.

Cobalt-Copper-Embedded Nitrogen-Doped Carbon Nanostructures Derived from Zeolite Imidazolate Frameworks as Electrocatalysts for the Oxygen Reduction Reaction.

In recent years, researchers have focused on developing zeolite imidazolate frameworks (ZIFs) as an alternative to Pt electrocatalysts for various applications, including water splitting, lithium-air batteries, zinc-air batteries, and fuel cells. In this study, we synthesized CoCu-ZIF to be used as a precursor in the development of cathode catalysts for the oxygen reduction reaction (ORR) in fuel cells. Hydrazine played a crucial role in maintaining uniformity in the development and particle size of the ZIF-67 structures. Moreover, it facilitated the rapid formation of the ZIF-67 structures at higher temperatures. A unique pseudorhombic dodecahedral morphology was obtained at a Co/Cu molar ratio of 7:3. Among all the synthesized N-doped carbon nanostructures embedded with Co and Cu nanoparticles, CoCu@NC-750, pyrolyzed at 750 °C, showed superior ORR catalytic performance. This catalyst exhibited a notably higher half-wave potential of 0.816 V and demonstrated a clear 4-electron transfer mechanism. The overpotential of CoCu@NC-750 shifted by only 11 mV over 10,000 cyclic voltammetry cycles, whereas a 55 mV shift was observed for Pt/C. CoCu@NC-750 exhibited a ∼0.8% decrease in current density during a 12-h ORR, in contrast to the 8.3% decline shown by Pt/C. This superior catalytic activity and stability can be attributed to factors such as higher oxygen adsorption induced by the N-doped carbon layer due to the localized changes in electron density and the enhanced stability of the bimetallic core. Our findings suggest that CoCu@NC-750 is a promising alternative to Pt/C in fuel cell cathodes.