Hierarchical 3D Cobalt-Doped Fe3 O4 Nanospheres@NG Hybrid as an Advanced Anode Material for High-Performance Asymmetric Supercapacitors

Inhabiting Inactive Transition by Coupling Function of Oxygen Vacancies and Fe─C Bonds achieving Long Cycle Life of an Iron-Based Anode

Fe-based battery-type anode materials with many faradaic reaction sites have higher capacities than carbon-based double-layer-type materials and can be used to develop aqueous supercapacitors with high energy density. However, as an insurmountable bottleneck, the severe capacity fading and poor cyclability derived from the inactive transition hinder their commercial application in asymmetric supercapacitors (ASCs). In this work, driven by the "oxygen pumping" mechanism, oxygen-vacancy-rich Fe@Fe3 O4 (v) @Fe3 C@C nanoparticles that consist of a unique "fruit with stone"-like structure are developed, and they exhibit enhanced specific capacity and fast charge/discharge capability. Experimental and theoretical results demonstrate that the capacity attenuation in conventional iron-based anodes is greatly alleviated in the the Fe@Fe3 O4 (v) @Fe3 C@C anode because the irreversible phase transition to the inactive γ-Fe2 O3 phase can be inhibited by a robust barrier formed by the coupling of oxygen vacancies and Fe─C bonds, which promotes cycle stability (93.5% capacity retention after 24 000 cycles). An ASC fabricated using this Fe-based anode is also observed to have extraordinary durability, achieving capacity retention of 96.4% after 38 000 cycles, and a high energy density of 127.6 W h kg-1 at a power density of 981 W kg-1 .

A crosslinked network polypyrrole coated cobalt doped Fe2O3@carbon cloth flexible anode material for quasi-solid asymmetric supercapacitors

Iron(III) oxide (Fe2O3) exhibits a substantial theoretical specific capacitance and a broad operational voltage window, making it a prospective anode material. The crystal structure of Fe2O3 was altered through cobalt doping, and its electronic conductivity was improved by supporting it with carbon cloth (Co-Fe2O3@CC). Subsequently, a crosslinked network of polypyrrole (PPy) was synthesized onto Co-Fe2O3@CC via an ice-water bath, resulting in the formation of PPy/Co-Fe2O3@CC. This PPy nano-crosslinked network not only established three-dimensional electron transport pathways on the Fe2O3 surface but also amplified the composite material's specific surface area to 45.229 m2 g-1, thereby promoting its electrochemical performance. At a current density of 2 mA cm-2, PPy/Co-Fe2O3@CC displayed an area specific capacitance of 704 mF cm-2, a value 2.2 times higher than that of Co-Fe2O3@CC. The assembled PPy/Co-Fe2O3@CC//Ni-MnO2@CC asymmetric supercapacitor demonstrated an energy density of 1.41 mW h cm-3 at a power density of 54 mW cm-3, making the synthesized electrode material a promising candidate for flexible supercapacitors.

Enhancing the Mn-Removal Efficiency of Acid-Mine Bacterial Consortium: Performance Optimization and Mechanism Study

In this study, an acclimated manganese-oxidizing bacteria (MnOB) consortium, QBS-1, was enriched in an acid mine area; then, it was used to eliminate Mn(Ⅱ) in different types of wastewater. QBS-1 presented excellent Mn removal performance between pH 4.0 and 8.0, and the best Mn-removal efficiency was up to 99.86% after response surface methodology optimization. Unlike other MnOB consortia, the core bacteria of QBS-1 were Stenotrophomonas and Achromobacter, which might play vital roles in Mn removal. Besides that, adsorption, co-precipitation and electrostatic binding by biological manganese oxides could further promote Mn elimination. Finally, the performance of the Mn biofilter demonstrated that QBS-1 was an excellent inoculant, which indicates good potential for removing Mn contamination steadily and efficiently.

Synergistic modulation of inverse spinel Fe3O4 by doping with chromium and nitrogen for efficient electrocatalytic water splitting

Earth-abundant Fe-based oxides have drawn less attention in electrocatalytic water splitting owing to the inferior intrinsic activity and poor conductivity. Therefore, developing an effective method to increase the catalytic performance of Fe-based oxides is of great importance for the practical application. Herein, a novel Cr/N co-doped Fe₃O₄ electrocatalyst (denoted as Cr-Fe₃O₄-N/NF) is designed and prepared by a simple immersion treatment followed by a calcination method for efficient water splitting. The resultant Cr-Fe₃O₄-N/NF shows significant catalytic activity for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) with overpotentials of 218 and 95 mV at 10 mA cm^-2. Furthermore, the water splitting system using Cr-Fe₃O₄-N/NF could afford a current density of 10 mA cm^-2 at 1.53 V, which is superior to two-electrode system composed of Pt/C and RuO₂. The high activities are attributed to the synergistic effect between Cr and N element doping. Specifically, the introduction of electron-deficient Cr is conductive to accelerate the dissociation process of water, adsorption process of intermediates, adjust the electronic structure. Simultaneously, N doping can increase the adsorption of H intermediates, provide more active sites for hydrogen absorption, and improve the electrical conductivity. This study provides a new strategy for Cr and N co-doped metal oxides electrocatalysts for high-performance water splitting.

Cure Kinetics of Samarium-Doped Fe3O4/Epoxy Nanocomposites

To answer the question “How does lanthanide doping in iron oxide affect cure kinetics of epoxy-based nanocomposites?”, we synthesized samarium (Sm)-doped Fe3O4 nanoparticles electrochemically and characterized it using Fourier-transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy dispersive X-Ray analysis (EDX), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy analyses (XPS). The magnetic particles were uniformly dispersed in epoxy resin to increase the curability of the epoxy/amine system. The effect of the lanthanide dopant on the curing reaction of epoxy with amine was explored by analyzing differential scanning calorimetry (DSC) experimental data based on a model-free methodology. It was found that Sm3+ in the structure of Fe3O4 crystal participates in cross-linking epoxy by catalyzing the reaction between epoxide rings and amine groups of curing agents. In addition, the etherification reaction of active OH groups on the surface of nanoparticles reacts with epoxy rings, which prolong the reaction time at the late stage of reaction where diffusion is the dominant mechanism.

Preparation of Hollow Core-Shell Fe3O4/Nitrogen-Doped Carbon Nanocomposites for Lithium-Ion Batteries

Iron oxides are potential electrode materials for lithium-ion batteries because of their high theoretical capacities, low cost, rich resources, and their non-polluting properties. However, iron oxides demonstrate large volume expansion during the lithium intercalation process, resulting in the electrode material being crushed, which always results in poor cycle performance. In this paper, to solve the above problem, iron oxide/carbon nanocomposites with a hollow core-shell structure were designed. Firstly, an Fe2O3@polydopamine nanocomposite was prepared using an Fe2O3 nanocube and dopamine hydrochloride as precursors. Secondly, an Fe3O4@N-doped C composite was obtained by means of further carbonization treatment. Finally, Fe3O4@void@N-Doped C-x composites with core-shell structures with different void sizes were obtained by means of Fe3O4 etching. The effect of the etching time on the void size was studied. The electrochemical properties of the composites when used as lithium-ion battery materials were studied in more detail. The results showed that the sample that was obtained via etching for 5 h using 2 mol L-1 HCl solution at 30 °C demonstrated better electrochemical performance. The discharge capacity of the Fe3O4@void@N-Doped C-5 was able to reach up to 1222 mA g h-1 under 200 mA g-1 after 100 cycles.

Fabrication of Robust, Highly Conductive, and Elastic Hybrid Carbon Foam Platform for High-Performance Compressible Asymmetry Supercapacitors

Highly conductive and elastic three-dimensional (3D) porous carbon materials are ideal platforms to fabricate electrodes for high-performance compressible supercapacitors. Herein, a robust, highly conductive, and elastic carbon foam (CF) hybrid material is reported, which is fabricated by integrating cellulose nanofiber/multiwalled carbon nanotube (CNF/MWCNT) aerogel sheets with a melamine sponge (MS), followed by carbonization. The carbonized CNF/MWCNT aerogel sheets contribute to the high conductivity and specific surface area of the CF, and the 3D network-like skeleton derived from the carbonization of the MS enhances the elasticity and stability of the CF. More importantly, the CF possesses good scalability, allowing the introduction of electroactive materials such as polypyrrole (PPy) and Fe₃O₄ to fabricate high-performance compressible PPy-CF and Fe₃O₄-CF electrodes. Moreover, an assembled PPy-CF//Fe₃O₄-CF device shows reversible charging-discharging at a voltage of 1.6 V and demonstrates a high specific capacitance (172.5 F/g) and an outstanding energy density (59.9 W h/kg). The device exhibits capacitance retention rates reaching 98.3% and stable energy storage characteristics even under different degrees of compressive deformation. This study offers a scalable strategy for fabricating high-performance compressible supercapacitors, thereby providing a new means of satisfying the energy storage needs of portable electronic devices that are prone to deformation.

Synergistic effects of Fe and Mn dual-doping in Co3S4 ultrathin nanosheets for high-performance hybrid supercapacitors

Dopant engineering in nanostructured materials is an effective strategy to enhance electrochemical performances via regulating the electronic structures and achieving more active sites. In this work, a robust electrode based on Fe and Mn co-doped Co₃S₄ (FM-Co₃S₄) ultrathin nanosheet arrays (NSAs) on the Ni foam substrate is prepared through a facile hydrothermal method followed by a subsequent sulfurization reaction. It has been found that the incorporation of Fe ions is beneficial to higher specific capacity of the final electrode and Mn ions contribute to the excellent rate capability in the reversible redox processes. Density functional theory (DFT) calculations further verify that the Mn doping in the Co₃S₄ obviously shorten the energy gap of Co₃S₄, which favors the electrochemical performances. Due to the synergetic effects of different transition metal ions, the as-prepared FM-Co₃S₄ ultrathin NSAs exhibit a high specific capacity of 390 mAh g^-1 at 5 A g^-1, as well as superior rate capability and excellent cycling stability. Moreover, the corresponding quasi-solid-state hybrid supercapacitors constructed with the FM-Co₃S₄ ultrathin NSAs and active carbon exhibit a high energy density of 55 Wh kg^-1 at the power density of 752 W kg^-1. These findings demonstrate a new platform for developing high-performance electrodes for energy storage applications.

ZnO/SiO2 core/shell nanowires for capturing CpG rich single-stranded DNAs

Atomic layer deposition (ALD) is capable of providing an ultrathin layer on high-aspect ratio structures with good conformality and tunable film properties. In this research, we modified the surface of ZnO nanowires through ALD for the fabrication of a ZnO/SiO2 (core/shell) nanowire microfluidic device which we utilized for the capture of CpG-rich single-stranded DNAs (ssDNA). Structural changes of the nanowires while varying the number of ALD cycles were evaluated by statistical analysis and their relationship with the capture efficiency was investigated. We hypothesized that finding the optimum number of ALD cycles would be crucial to ensure adequate coating for successful tuning to the desired surface properties, besides promoting a sufficient trapping region with optimal spacing size for capturing the ssDNAs as the biomolecules traverse through the dispersed nanowires. Using the optimal condition, we achieved high capture efficiency of ssDNAs (86.7%) which showed good potential to be further extended for the analysis of CpG sites in cancer-related genes. This finding is beneficial to the future design of core/shell nanowires for capturing ssDNAs in biomedical applications.

Preparation of Fe3O4@polypyrrole composite materials for asymmetric supercapacitor applications

The assembled Fe3O4@PPy//MoO3 asymmetric coin supercapacitor exhibits a high energy density and excellent cycling stability.

ZnS-Ni7S6 Nanosheet Arrays Wrapped with Nanopetals of Ni(OH)2 as a Novel Core-Shell Electrode Material for Asymmetric Supercapacitors with High Energy Density and Cycling Stability Performance

Supercapacitors possess minimum energy density, lower rate capability, and inferior long-term cycling stability performance, and these issues have restricted their practical applications. In these circumstances, supercapacitors based on a new class of hybrid nanomaterial are strongly desirable. Herein, for the first time, a complex nanoarchitecture comprised of a ZnS-Ni₇S₆/Ni(OH)₂ core/shell is constructed via a multistep hydrothermal process. The ZnS-Ni₇S₆/Ni(OH)₂ core/shell nanoarchitecture illustrates a commendable areal capacitance of 13.55 F cm^-2 at a lower current density value of 5 mA cm^-2, respectively. The ZnS-Ni₇S₆/Ni(OH)₂ core/shell hybrid nanomaterial maintains a high cycling stability performance of 95.12% after a maximum 10 000 number of cycles. Moreover, the asymmetric supercapacitor device made up of ZnS-Ni₇S₆/Ni(OH)₂ and nitrogen-sulfur-codoped graphene nanosheets (NSGNs) delivers an ultrahigh energy density value of 68.85 W h kg^-1 at a power density of 700.16 W kg^-1. The cycling stability of the ZnS-Ni₇S₆/Ni(OH)₂//NSGN asymmetric supercapacitor was performed and was 91.79% after 10 000 GCD cycles. The ZnS-Ni₇S₆/Ni(OH)₂ core/shell hybrid electrode material has helped in promoting an asymmetric supercapacitor device with an elevated performance and can be considered as a potential electrode material to develop energy storage devices in the future.

Rational Construction of 2D Fe3 O4 @Carbon Core-Shell Nanosheets as Advanced Anode Materials for High-Performance Lithium-Ion Half/Full Cells

Transition metal oxides have vastly limited practical application as electrode materials for lithium-ion batteries (LIBs) due to their rapid capacity decay. Here, a versatile strategy to mitigate the volume expansion and low conductivity of Fe₃ O₄ by coating a thin carbon layer on the surface of Fe₃ O₄ nanosheets (NSs) was employed. Owing to the 2D core-shell structure, the Fe₃ O₄ @C NSs exhibit significantly improved rate performance and cycle capability compared with bare Fe₃ O₄ NSs. After 200 cycles, the discharge capacity at 0.5 A g^-1 was 963 mA h g^-1 (93 % retained). Moreover, the reaction mechanism of lithium storage was studied in detail by ex situ XRD and HRTEM. When coupled with a commercial LiFePO₄ cathode, the resulting full cell retains a capacity of 133 mA h g^-1 after 100 cycles at 0.1 A g^-1 , which demonstrates its superior energy storage performance. This work provides guidance for constructing 2D metal oxide/carbon composites with high performance and low cost for the field of energy storage.

Cross-Linked Surface Engineering to Improve Iron Porphyrin Catalytic Activity

Quasi-two-dimensional (QTD) structural heterogeneous catalysts have attracted a broad interest in multidisciplinary research due to their unique structure, preeminent surface properties and outstanding catalytic performance. Herein, a HZIF@TCPP-Fe/Fe heterogeneous catalyst based on cross-linked surface engineering is constructed by supporting QTD TCPP-Fe/Fe ultra-thin metallized film (≈2 nm) on hollow skeleton of zeolite imidazolate frameworks. The designed QTD structure exhibits high efficiency for the catalytic oxidative dehydrogenation of aromatic hydrazides reactions which is the key technology in various industrial processes. Taking advantage of QTD structure with excellent accessibility, the metallized film with irregular defects not only enhances electron transfer during the reaction but also exposes more surface-active sites. Furthermore, the prepared HZIF@TCPP-Fe/Fe heterogeneous catalyst can be recycled and reused, which is of great significance in the field of green chemistry.

A polypyrrole-adorned, self-supported, pseudocapacitive zinc vanadium oxide nanoflower and nitrogen-doped reduced graphene oxide-based asymmetric supercapacitor device for power density applications

Herein, a distinctive approach has been implemented for exploiting a typical battery material zinc vanadium oxide (ZV) as a supercapacitor electrode material.

Hydrangea-like α-Ni1/3Co2/3(OH)2 Reinforced by Ethyl Carbamate "Rivet" for All-Solid-State Supercapacitors with Outstanding Comprehensive Performance

Improving the self-conductivity and structural stability of electrode materials is a key strategy to improve the energy density, rate performance, and cycle life of supercapacitors. Controlled intercalation of ethyl carbamate (CH₃CH₂OCONH₂) as the rivet between Ni-Co hydroxide layers can be used to obtain sufficient ion transport channels and robust structural stability of hydrangea-like α-Ni_1/3Co_2/3(OH)₂ (NC). Combining the improved electronic conductivity offered by the coexistence of Ni²⁺ and Co²⁺ optimizing itself electronic conductivity and the addition of carbon nanotubes (CNTs) as the electron transport bridge between the active material and the current collector and the large specific surface area (296 m² g^-1) reducing the concentration polarization, the capacitance retention ratio of NC-CNT from 0.2 to 20 A g^-1 is up to 93.4% and its specific capacitance is as high as 1228.7 F g^-1 at 20 A g^-1. The large total hole volume (0.40 cm³ g^-1) and wide crystal plane spacing (0.71 nm) provide an adequate space to withstand structure deformation during charge/discharge processes and enhance the structural stability of the NC material. The capacitance fading ratio of NC-CNT is only 4.5% at 10 A g^-1 for 10 000 cycles. The aqueous supercapacitor (NC-CNT//AC) and all-solid-state supercapacitor (PVA-NC-CNT//PVA-AC) exhibit high energy density (35.2 W h kg^-1 at 100.0 W kg^-1 and 35.4 W h kg^-1 at 100.7 W kg^-1), ultrahigh rate performance (the specific capacitances at 20 A g^-1 are 92.8 and 87.2% compared to that at 0.5 A g^-1), and long cycling life span (the specific capacitances after 100 000 cycles at 10 A g^-1 are 91.5 and 90.8% compared with that of their initial specific capacitances), respectively. Therefore, hydrangea-like NC could be a promising material for advanced next-generation supercapacitors.

Flocculant-Assisted Synthesis of Graphene-Like Carbon Nanosheets for Oxygen Reduction Reaction and Supercapacitor

The rational treatment of hazardous textile sludge is critical and challenging for the environment and a sustainable future. Here, a water-soluble chitosan derivative was synthesized and used as an effective flocculant in removal of reactive dye from aqueous solution. Employing these chitosan-containing textile sludges as precursors, graphene-like carbon nanosheets were synthesized through simple one-step carbonization with the use of Fe (III) salt as graphitization catalyst. It was found that the resultant graphene-like carbon nanosheets material at thickness near 3.2 nm (NSC-Fe-2) showed a high graphitization degree, high specific surface area, and excellent bifunctional electrochemical performance. As-prepared NSC-Fe-2 catalyst exhibited excellent oxygen reduction reaction (ORR) activity (onset potential 1.05 V) and a much better methanol tolerance than that of commercial Pt/C (onset potential 0.98 V) in an alkaline medium. Additionally, as electrode materials for supercapacitors, NSC-Fe-2 also displayed an outstanding specific capacitance of 195 F g-1 at 1 A g-1 and superior cycling stability (loss of 3.4% after 2500 cycles). The good electrochemical properties of the as-prepared NSC-Fe materials could be attributed to the ultrathin graphene-like nanosheets structure and synergistic effects from codoping of iron and nitrogen. This work develops a simple but effective strategy for direct conversion of textile sewage sludge to value-added graphene-like carbon, which is considered as a promising alternative to fulfill the requirements of environment and energy.

Asymmetric supercapacitors with high energy densities

The low energy densities of supercapacitors (SCs) are generally limited by the used anodes. To develop SCs with high energy densities, Fe3+ modified V2O5@GQDs (m-V2O5@GQDs) and ZIF-67-derived nanoporous carbon loaded with Mn3O4 (C/N-Mn3O4) were synthesized. After their detailed characterization using electron microscopy, X-ray methods and electrochemical techniques, they were further utilized as the anode and the cathode, respectively, to construct asymmetric supercapacitors (ASCs). The as-synthesized m-V2O5@GQDs improve the poor conductivity of V2O5, contributing greatly to a specific capacitance of 761 F g-1 at a current density of 2 A g-1. With application of a cell voltage of 2 V, an energy density of up to 99.4 W h kg-1 is achieved at a power density of 1000 W kg-1. Such ASCs also exhibit outstanding cycling performance (95% of initial capacitance even after 10 000 charging/discharging cycles). This study thus provides a new way to design and construct ASCs with high energy densities.

Toward fiber-, paper-, and foam-based flexible solid-state supercapacitors: electrode materials and device designs

Flexible solid-state supercapacitors possess promising safety performance and intrinsic fast charging-discharging properties, enabling them to accomplish the requirements of lightweight and multifunctional wearable electronics that have recently become fairly popular. Because electrode materials are the core component of flexible solid-state supercapacitors, we exhaustively review the recent investigations involving electrode materials that have used carbons, metal oxides, and conductive polymers. The principles and methods of optimizing and fabricating electrodes for use in flexible supercapacitors are discussed through a comprehensive analysis of the literature. In addition, we focused on three types of flexible solid-state supercapacitors (fiber-, paper-, and porous foam-based structures) to satisfy the requirements of flexible electronic devices. Further, we summarize the practical applications of flexible solid-state supercapacitors, including energy conversion/collection devices and energy storage/detection devices. Finally, we provide the developmental direction for flexible solid-state supercapacitors in the future.

Hybrid hollow spheres of carbon@CoxNi1-xMoO4 as advanced electrodes for high-performance asymmetric supercapacitors

Combining pseudocapacitive materials with conductive substrates is an effective approach to enhance the overall performance of electrodes for supercapacitors. Herein, NiMoO4 nanosheets were grown on the surface of porous carbon nanospheres (PCNS) that were derived from cyclodextrin, resulting in PCNS@NiMoO4 hollow nanospheres. Co was further doped into NiMoO4 which gave rise to a composite PCNS@CoxNi1-xMoO4. The capacitive performance of these materials was systematically examined. Compared with pure NiMoO4 and PCNS@NiMoO4, PCNS@Co0.21Ni0.79MoO4 showed the highest specific capacitance of 954 F g-1 at 1 A g-1 and an extraordinary rate performance of 92.8% retention at 40 A g-1, which are significantly higher than those of PCNS@NiMoO4 and pure NiMoO4. This enhancement was due to the fact that PCNS provides high electrical conductivity, the hollow structure enables excellent contact and facile penetration of the electrolyte into the active material, and Co doping further improves the electrical conductivity and provides extra redox reaction sites. By using PCNS@Co0.21Ni0.79MoO4 as the positive electrode and activated carbon (AC) as the negative electrode, an asymmetric supercapacitor was fabricated. Such a device delivered an energy density of 36.7 W h kg-1 at a power density of 346.4 W kg-1, and an outstanding cycling stability with 90.2% retention of its initial capacitance after 5000 cycles of charge and discharge.

Metal-Organic Framework Derived Spindle-like Carbon Incorporated α-Fe2O3 Grown on Carbon Nanotube Fiber as Anodes for High-Performance Wearable Asymmetric Supercapacitors

Iron oxide (Fe₂O₃) has drawn much attention because of its high theoretical capacitance, wide operating potential window, low cost, natural abundance, and environmental friendliness. However, the inferior conductivity and insufficient ionic diffusion rate of a simple Fe₂O₃ electrode leading to the low specific capacitance and poor rate performance of supercapacitors have impeded its applications. In this work, we report a facile and cost-effective method to directly grow MIL-88-Fe metal-organic framework (MOF) derived spindle-like α-Fe₂O₃@C on oxidized carbon nanotube fiber (S-α-Fe₂O₃@C/OCNTF). The S-α-Fe₂O₃@C/OCNTF electrode is demonstrated with a high areal capacitance of 1232.4 mF/cm² at a current density of 2 mA/cm² and considerable rate capability with capacitance retention of 63% at a current density of 20 mA/cm² and is well matched with the cathode of the Na-doped MnO₂ nanosheets on CNTF (Na-MnO₂ NSs/CNTF). The electrochemical test results show that the S-α-Fe₂O₃@C/OCNTF//Na-MnO₂ NSs/CNTF asymmetric supercapacitors possess a high specific capacitance of 201.3 mF/cm² and an exceptional energy density of 135.3 μWh/cm². Thus, MIL-88-Fe MOF derived S-α-Fe₂O₃@C will be a promising anode for applications in next-generation wearable asymmetric supercapacitors.

Encapsulation of Ni/Fe3O4 heterostructures inside onion-like N-doped carbon nanorods enables synergistic electrocatalysis for water oxidation

The rational modulation of composition and structure is critical for the development of robust and efficient oxygen evolution reaction (OER) catalysts for water splitting. In this study, an onion-like N-doped carbon nanorods hybrid (denoted as ONC) with encapsulated Ni/Fe₃O₄ heterostructures has been fabricated by the pyrolysis of an NiFe-based coordination polymer under a N₂ atmosphere. The nanorod-like morphology is transferred from the polymer to the hybrids and generates ONC nanolayers encapsulated with core-shell Ni/Fe₃O₄ nanostructures. The synergistic effects between the ONC layers and the encapsulated Ni/Fe₃O₄ heterostructures result in high electronic conductivity due to the nitrogen-doped carbon with an appropriate level of defects and enlarged electrochemical surface area due to the well-defined mesoporous morphology. Compared with Ni@ONC, Fe₃O₄@ONC, NiFe₂O₄ and commercial RuO₂ electrocatalysts, the as-prepared Ni/Fe₃O₄@ONC exhibits extraordinary electrocatalytic activity for water oxidation with an overpotential of merely 296 mV at 10 mA cm^-2 and a small Tafel slope of 61 mV dec^-1. This Ni/Fe₃O₄@ONC OER catalyst highlights the great potential of integrating hetero-composite nanocatalysts with hetero-atom doped nanocarbon supports for the development of high-performance electrocatalysts for renewable energy applications.

Rational construction of core–shell Ni3S2@Ni(OH)2 nanostructures as battery-like electrodes for supercapacitors

Core–shell Ni₃S₂@Ni(OH)₂ nanostructures on Ni foam were fabricated via hydrothermal and chemical bath processes and showed good electrochemical performances.