Core-shell Arrays Research Articles

In-situ growth of hierarchical trifunctional Co4S3/Ni3S2@MoS2 core-shell nanosheet array on nickel foam for overall water splitting and supercapacitor

It is an enormous challenge to construct the cheap and effective multifunctional electrocatalysts for energy storage and conversion applications. Herein, a ZIF-67 derived Co4S3/Ni3S2@MoS2 core-shell nanosheet arrays were successfully developed on nickel foam via a simple two-step hydrothermal vulcanization method for electrocatalytic water splitting and supercapacitors. For overall water splitting, CNM 0.5 required the overpotentials of 96 and 269 mV at 10 mA cm−2 and 100 mA cm−2 for HER and OER in 1 M KOH. The dual-electrode electrolytic cell assembled from CNM 0.5 required only 1.447 V at 10 mA cm−2, and had nearly 100% Faraday efficiency and long-term stability (40 h). When used as the electrode for supercapacitors, CNM 0.5 had a large specific capacitance of 1238 F g−1 at 1 A g−1 current density and exceptional durability (85% retention after 2000 cycles). The ASC device assembled with CNM 0.5 provided the high-energy density of 41.2 W h kg−1 and long cycle-life (87% after 2000 cycles). The unique core-shell morphology with abundant active reactive edge sites would be beneficial for charge reduction and the volume shrinking/swelling during the rapid charge/discharge process. The well-ordered and vertically aligned nanosheet arrays possessed good conductivity and small interface resistance, which would facilitate the electron transfer and electrolyte penetration, ion insertion and de-intercalation.

CuCo2O4@NiFe2O4 core-shell structure array based on carbon paper is used as high-performance counter electrode of liquid thin film solar cells

In this paper, NiFe2O4 nanoparticles coated with CuCo2O4 linear core-shell structure crystals were grown in situ using carbon paper (CP) as support material by two-step hydrothermal method. The composite materials of CuCo2O4@NiFe2O4/CP are coated on a titanium mesh base to make the counter electrodes (CEs) of the dye-sensitized solar cells (DSSCs). The photovoltaic conversion efficiency (PCE) of the CuCo2O4@NiFe2O4/CP CEs is 10.00%, which is much higher than the representative Pt CEs (7.74%). Its excellent electrochemical performance can be put down to the core-shell structure with high porosity and specific surface area, which can provide abundant active sites for redox reactions in the electrolyte, and a large number of transition metal elements greatly enhance the catalytic ability of the electrode. In addition, the resistance between the electrode material and the substrate is greatly reduced by using titanium mesh as the substrate. This study provides a new idea and possibility for the development of high efficiency and platinum-free CEs materials and a new conductive substrate is developed to improve the photoelectric performance of the CEs.

Dehydrogenation Induced Formation of Chiral Core-Shell Arrays of Melamine on Ag(111)

The structural evolution of supramolecular phases of melamine on Ag(111) surface as a function of annealing temperature is investigated by employing low-temperature scanning tunneling microscopy/spectroscopy (LT-STM/STS). It is found that partial deprotonation of the melamine molecules leads to formation of distinct types of ordered supramolecular arrangements. Apart from two previously reported phases (α and β), a new phase comprising arrays of close-packed hexagonal core-shell-type clusters is identified for the first time. Based on high-resolution STM images as well as structural modeling, we show that the new phase presents a two-level hierarchical order and chirality is expressed at both levels. Using STS characterization, we further reveal that the chiral arrangement of the clusters confines surface electrons into a honeycomb pathway with handedness, which could give rise to novel interfacial electronic properties such as Dirac fermions as well as flat band.

Cobalt–manganese sulfide hybridized Fe-doped 1T-Vanadium disulfide 3D-Hierarchical core-shell nanorods for extreme low potential overall water-splitting

The cobalt manganese sulfide [CoMnS2] hybridized with Fe-doped (1T)-phase vanadium disulfide [VS2] 3D-hierarchical core-shell nanorods arrays electrocatalyst on nickel foam [NF] (CoMnS2@1T-Fe-VS2@NF) has been fabricated for overall water-splitting in the present study. The CoMnS2@1T-Fe-VS2@NF performs superior activities through the interface engineering between 1D cobalt manganese sulfide (CoMnS2) core and Fe-doped metallic (1T)-phase VS2 (1T-Fe-VS2) shell due to the modulation of surface electronic structure, hence, leading to enhancement of the intrinsic conductivity of the whole core-shell structure. The CoMnS2@1T-Fe-VS2@NF having plentiful heterointerfaces, requires a low overpotential of 89 mV to deliver 10 mA/cm2- for hydrogen evolution reaction (HER) and 260 mV to deliver 20 mA/cm2- for oxygen evolution reaction (OER). The CoMnS2@1T-Fe-VS2@NF (+, -) alkaline electrolyzer requires a low cell voltage of 1.51 V at 10 mA/cm2- for overall water splitting and demonstrates outstanding long-term stability during hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) over 30 h of continuous operation. The outstanding performance of CoMnS2@1T-Fe-VS2@NF can be ascribed to the synergistic catalysis of CoMnS2 core with the activated basal planes and edge sites of 1T-Fe-VS2 shell.

Self-powered ultraviolet photodetectors based on match like quasi one-dimensional n-TiO2/p-NiO core-shell heterojunction arrays with NiO layer sputtered at different power

Self-powered ultraviolet photodetectors (UV PDs) are urgently needed for portable, sustainable, maintenance free, and long-term applications. The geometry of device structure and interface energy band arrangement will affect the photoresponse performance of heterojunction PDs. In this work, a self-powered UV PDs based on match like quasi one-dimensional TiO2/NiO core-shell heterojunction arrays is fabricated by RF magnetron depositing NiO over TiO2 NRs. By controlling sputtering power, NiO(50 W)/TiO2, NiO(80 W)/TiO2 and NiO(120 W)/TiO2 devices were obtained. Under self-powered mode, the performance of PDs is carefully explored and the NiO (80 W)/TiO2 device displays a large photocurrent (1.2 ×10−6 A) and a high responsivity (74 mA/W) at 380 nm light irradiation. The results presented in this work suggest that a comprehensive consideration and a reasonable optimization of interface energy level structure and carrier transmission is the important for developing high-performance self-powered UV PDs.

Hydrogen-Induced Aggregation of Au@Pd Nanoparticles for Eye-Readable Plasmonic Hydrogen Sensors.

Plasmonic materials provide a promising platform for optical hydrogen detection, but their sensitivities remain limited. Herein, a new type of eye-readable H2 sensor based on Au@Pd core-shell nanoparticle arrays (NAs) is reported. After exposed to 2% H2, Au@Pd (16/2) NAs demonstrate a dramatic decrease in the optical extinction intensity, along with an obvious color change from turquoise to gray. Experimental results and theoretical calculations prove that the huge optical change resulted from the H2-induced aggregation of Au@Pd nanoparticles (NPs), which remarkably alters the plasmon coupling effect between NPs. Moreover, we optimize the sensing behavior from two aspects. The first is selecting appropriate substrates (either rigid glass substrate or flexible polyethylene terephthalate substrate) to offer moderate adhesion force to NAs, ensuring an efficient aggregation of Au@Pd NPs upon H2 exposure. The second is adjusting the Pd shell thickness to control the extent of NP aggregation and thus the detection range of the as-prepared sensors. This work highlights the advantage of designing eye-readable plasmonic H2 sensors from the aspect of tuning the interparticle plasmonic coupling in NP assemblies. Au@Pd NAs presented here have several advantages in terms of simple fabrication method, eye-readability in air background at room temperature, tunable detection range, and high cost-effectiveness.

Regulation of Macrophage Polarization Through Periodic Photo-Thermal Treatment to Facilitate Osteogenesis.

The richened reactive oxygen species (ROS) and their derived excessive inflammation at bone injured sites hinder osteogenesis of endosseous Ti-based implants. Herein, anti-oxidized polydopamine (PDA) is deposited on hydrothermal growth formed hydroxyapatite (HA) nanorods on Ti to form a core-shell structural nanorod-like array with HA as a core and PDA as an amorphous shell (PDA@HA), showing not only ROS scavenging ability but also near-infrared (NIR) light derived photo-thermal effects. PDA@HA suppresses inflammation based on its ROS scavenging ability to a certain extent, while periodic photo-thermal treatment (PTT) at a mild temperature (41 ± 1 °C) further accelerates the transition of the macrophages (MΦs) adhered to PDA@HA from the pro-inflammatory (M1) phenotype to the anti-inflammatory (M2) phenotype in vitro and in vivo. Transcriptomic analysis reveals that the activation of the PI3K-Akt1 signaling pathway is responsible for the periodic PTT induced acceleration of the M1-to-M2 transition of MΦs. Acting on mesenchymal stem cells (MSCs) with paracrine cytokines of M2 macrophages, PDA@HA with mild PTT greatly promote the osteogenetic functions of MSCs and thus osteogenesis. This work paves a way of employing mildly periodic PTT to induce a favorable immunomodulatory microenvironment for osteogenesis and provides insights into its underlying immunomodulation mechanism.

Highly-sensitive sensor based on toroidal dipole governed by bound state in the continuum in dielectric non-coaxial core-shell cylinder.

The electromagnetic fields distributed on the surface region of the nanostructure is very important to improve the performance of the sensor. Here, we proposed a highly sensitive sensor based on toroidal dipole (TD) governed by bound state in the continuum (BIC) in all-dielectric metasurface consisting of single non-coaxial core-shell cylinder nanostructure array. The excitation of TD resonance in a single nanostructure is still challenging. The designed nanostructure not only supports TD resonance in a single nanostructure but also has very high Q-factor. More importantly, its electric field distributes at the surface of outer cylinder-shell, which is very suitable for biosensing. To evaluate the sensing performance of our proposed structure, we investigated the sensitivity and the figure of merit (FOM) of nanostructure with different structural parameters. Maximum sensitivity and FOM can reach up to 342 nm/RIU and 1295 when the asymmetric parameter d =10 nm. These results are of great significance to the research of TD resonance and the development of ultrasensitive sensor.

Preface

Due to recent pandemic, 2022 2nd International Conference on Energy Engineering, New Energy Materials and Devices (NEMD 2022) was held virtually online during March 18-20, 2022. The decision to hold the virtual conference was made in compliance with many restrictions and regulations that were imposed by countries around the globe. Such restrictions were made to minimize the risk of people contracting or spreading the COVID-19 through physical contact. There were 110 individuals who attended this on-line conference, represented many countries including China, Kuwait, Algeria, Italy and Malaysia.The International Conference on Energy Engineering, New Energy Materials and Devices (NEMD), is an annual conference hold each year. NEMD provides a premier interdisciplinary platform for researchers, practitioners and educators to present and discuss not only the most recent innovations, trends, and concerns but also practical challenges encountered and solutions adopted in the fields of Energy Engineering, New Energy Materials and Devices. There will be participation of renowned Speakers, oral presentations, posters sessions and technical conferences related to the topics in the scientific program.During the conference, the conference model was divided into three sessions, including oral presentations, keynote speeches, and online Q&A discussion. In the first part, some scholars, whose submissions were selected as the excellent papers, were given about 5-10 minutes to perform their oral presentations one by one. Then in the second part, keynote speakers were each allocated 30-45 minutes to hold their speeches. In the second part, we invited two professors as our keynote speakers. A.Prof. Weiyong Yuan, Zhejiang University, China, performed a speech: Self-assembled hematite-based core-shell heteronanostructured arrays for photoelectrochemical water splitting. And then we had Prof. Fanian Shi, Shenyang University of Technology, China. He delivered a speech: Research progress of metal complexes and metal oxides as new-generation anode materials of lithium-ion batteries. Their insightful speeches had triggered heated discussion in the third session of the conference. Every participant praised this conference for disseminating useful and insightful knowledge.List of Committee member are available in this pdf.

Boosting Electrocatalytic Oxygen Evolution over Ce-Co9 S8 Core-Shell Nanoneedle Arrays by Electronic and Architectural Dual Engineering.

An dual electronic and architectural engineering strategy is a good way to rationally design earth-abundant and highly efficient electrocatalysts of the oxygen evolution reaction (OER) for sustainable hydrogen-based energy devices. Here, a Ce-doped Co9 S8 core-shell nanoneedle array (Ce-Co9 S8 @CC) supported on a carbon cloth has been designed and developed to accelerate the sluggish kinetics of the OER. Profiting from valance alternative Ce doping, a fine core-shell structure and vertically aligned nanoneedle arrayed architecture, Ce-Co9 S8 @CC integrates modulated electronic structure, highly exposed active sites, and multidimensional mass diffusion channels; together, these afford a favorable catalyzed OER. Ce-Co9 S8 @CC exhibits remarkable performance in the OER in an alkaline medium, where the overpotential requires only 242 mV to deliver a current density of 10 mA cm-2 for the OER; this is 70 mV superior to that of Ce-free Co9 S8 catalyst and other counterparts. Good stability and impressive selectivity (nearly 100 % Faradic efficiency) are also demonstrated. When integrated into a two-electrode OER//HER electrolyzer, the as-prepared Ce-Co9 S8 @CC displays a low operation potential of 1.54 V at 10 mA cm-2 and long-term stability, thus demonstrating great potential for economical water electrolysis.

Ni3S2 nanosheets decorated on NiCo2O4 flakes-arrays directional growth of Ni foam for enhanced electrochemical hydrogen generation

• NiCo 2 O 4 /Ni 3 S 2 /NF core–shell arrays on Ni foam were constructed by Ni 3 S 2 loaded on NiCo 2 O 4 arrays. • The hierarchical nanostructures of NiCo 2 O 4 /Ni 3 S 2 /NF contribute excellent activity and stability for HER. • NiCo 2 O 4 /Ni 3 S 2 /NF provides large active sites and faster charge transfer. Electrochemically production of hydrogen is an appealing approach to provide clean energy at an affordable price. Much research has been assigned to the development of functional catalysts that are efficient electrocatalysts for the hydrogen evolution reaction (HER). In this study, the nanocomposite catalyst composition of Ni 3 S 2 /NiCo 2 O 4 on nickel foam as a non-noble-metal has been prepared via a convenient chemical conversion route. The synthesized catalyst demonstrates excellent stability and durability in aqueous environments, which makes it a very active, stable, low-cost and promising catalytic system in the field of energy analysis, conversion and storage. Here, the prepared electrode to achieve a current density of 10 mA cm −2 requires an overpotential of 184 mV with a Tafel slope of 97 mV dec -1 in alkaline solution (1 M KOH) and an overpotential of 140 mV with a Tafel slope of 53.6 mV dec -1 in acidic condition (0.5 M H 2 SO 4 ). The catalytic system's activity can be maintained for at least 14 h in KOH 1 M and H 2 SO 4 0.5 M. Also, the present work investigates the electrochemical characterization of the samples in which the current density is normalized by geometric area, electrochemical active surface area (ECSA) and BET specific surface area.

Space-controllable TiO2@IrO2 core-shell nanotube array as a bio-interface electrode

This study develops a wet chemical approach to fabricate space-controllable TiO2@IrO2 core@shell nanotube arrays. The process begins with the space-controlling anodization of the TiO2 nanotube array, followed by a chemical bath deposition of IrO2. IrO2 uniformly covers the nanotubular TiO2 with a thickness range of 8– 15 nm. Charge storage capacity (CSC) and electrochemical impedance spectroscopy (EIS) are performed to evaluate the TiO2@IrO2 core-shell nanotube array as an electrode for neural activity application. Electron microscopy images confirm the formation of uniform IrO2 films on both inner and outer nanotube surfaces. An X-ray diffraction pattern shows a good crystallinity of the TiO2@IrO2 core-shell nanotube array. The TiO2@IrO2 core-shell nanotube array presents a large charge storage capacity of 42.84 mC/cm2 attributed to the high-aspect-ratio tubular nanostructure with a conformal IrO2 deposition. Additionally, the TiO2@IrO2 core-shell nanotube array exhibits stability, durability, and good biocompatibility.

Co9S8/NiCo2S4 core-shell array structure cathode hybridized with PPy/MnO2 core-shell structure anode for high-performance flexible quasi-solid-state alkaline aqueous batteries

The development of high-performance electrode materials for alkaline aqueous batteries (AAB) is important for the utilization of energy. Herein, we report a facile method for Co9S8 nanorods/NiCo2S4 nanosheets with core-shell structure growing directly on carbon cloth (CC). The unique structure allows for outstanding electrochemical performance when used as a cathode material, such as high specific capacity (314.7 mAh g−1), high cycling stability (88.5% after 5000 cycles) and excellent rate performance (90% at 10 A g−1). Further density functional theory (DFT) calculations reveal that the formation of a contact potential difference after NiCo2S4 coating on Co9S8 surface leads to raising the Fermi level by about 0.6 eV, which results in enhanced electronic activity and improved electrochemical properties. Subsequently, PPy/MnO2/CC anode with a core-shell structure is prepared by a simple two-step electro-deposition process and exhibits excellent capacity performance (234.4 mAh g−1). Impressively, the capacity of PPy can be increased by an order of magnitude by electro-deposition of MnO2, which solves the problem of low capacity of PPy as an anode material in alkaline electrolytes. The alkaline aqueous battery CS/NCS-6//PPy/MnO2-400 shows energy density of 74.71 Wh kg−1 at 800 W kg−1. Further assembled into a quasi-solid-state flexible battery, it can provide energy density of 0.1458 mWh cm−2 at 2.4 mW cm−2, and the devices can be used to drive a toy car for 0.32 m, run a small fan for 20 s and light up an LED for more than 3 min, which has potential applications in energy storage systems.

Hierarchical FeCoSe2@NiCo-layered double hydroxide nanosheet arrays with boosted performance for hybrid supercapacitors

For constructing high-performance hybrid supercapacitor devices, it is vital to exploit a battery-type cathode with enhanced kinetics and improved cyclic performance to match with a capacitive anode. Herein, highly porous FeCoSe2@NiCo-LDH core-shell nanosheet arrays were in situ decorated on face of carbon cloth via an electrodeposition approach and a selenylation treatment. The hierarchical heterostructure consisting of two types of vertically aligned interconnected two-dimensional nanosheets not only offers huge surface area and available diffusion pathways for quick electron/ion transport, but also generates plentiful heterointerfaces with modified electronic structure and enables synergetic effect between dual components. Consequently, the well-designed FeCoSe2@NiCo-LDH electrode displays a greatly boosted specific capacity of 220.9 mA h g−1 at 1 A g−1, 83.5% capacity retention at 20 A g−1, and wonderful cyclic stability, which are superior to those of single component. Furthermore, the hybrid supercapacitor device with a FeCoSe2@NiCo-LDH electrode and a hierarchical porous carbon electrode illustrates an extensive energy density of 65.9 Wh kg−1 at 1.248 kW kg−1 combined with long lifetime with 87.6% capacity retention over 10,000 cycles. These superb properties manifest that the integrated FeCoSe2@NiCo-LDH electrode owns a desirable application prospect in hybrid energy storage systems.

Embellishing hierarchical 3D core-shell nanosheet arrays of ZnFe2O4@NiMoO4 onto rGO-Ni foam as a binder-free electrode for asymmetric supercapacitors with excellent electrochemical performance

Tailoring hierarchical hybrid core-shell electrodes with impartial microstructural features and excellent electroactive constituents is crucial for the design of high-performance supercapacitors (SCs). Herein, for the first time, we fabricate uniformly aligned porous ZnFe2O4 (ZFO) nanosheet arrays onto reduced graphene oxide-garnished conductive Ni foam (rGO-NF) substrates and subsequently embellish the first layer of ZFO nanosheets with morphology-controlled secondary NiMoO4 nanosheets to achieve a hierarchical 3D core-shell structure of ZnFe2O4@NiMoO4 nanosheet arrays (NSAs) onto rGO-NF for SC applications. Improving the synergistic effect of the core-shell nanoarchitecture with a conductive rGO-NF substrate, the hierarchical 3D ZFO@NMO NSAs tend to have superb electronic conductivity, tailoribility, effective nanoporous channels, and appropriate roadways for rapid ion/electron transfer, which are required for rapid reversible redox reactions, thus reflecting the excellent electrochemical features, including the excellent specific capacitance, good rate performance, and prolonged cyclic performance of the three electrode assemblies for SCs. An asymmetric supercapacitor (ASC) device composed of ZFO@NMO NSAs@rGO-NF as the cathode and MOF-derived hollow porous carbon (MDHPC) as the anode exhibits a high energy density of 58.6 Wh kg-1 at a power density of 799 W kg-1 with prolonged cyclic durability (89.6 % after 7000 cycles), thus indicating its potential applicability towards advanced hybrid SCs.

Needle-like NiSχ@MnCoOχ core–shell nanoarrays with high charge storage performance for application in hybrid supercapacitors

Herein, this work demonstrates the design and synthesis of multicomponent hybrid material NiSχ@MnCoOχ/NF core–shell nanoarrays with high charge storage performance for supercapacitors. The needle-like MnCoOχ nanoarrays as the skeleton of the core layer are grown vertically on the Ni foam via a hydrothermal method, while the NiSχ nanosheets are engineered to anchor onto the surface to form the shell via an electrodeposition method. The unique core–shell architecture provides a large number of reactive sites for MnCoOχ and NiSχ, enhances the number of ion diffusion channels and fast electron transfer pathway. As advanced electrode, NiSχ@MnCoOχ/NF delivers a high specific capacity of 1358 C g−1 (4.84 C cm−2) at 0.5 A g−1, which is 2.05 times that of MnCoOχ/NF (661 C g−1 or 1.35 C cm−2). Furthermore, the hybrid supercapacitor device (NiSχ@MnCoOχ/NF//rGO/NF) exhibits a high specific capacitance of 181.71 F g−1 (2.26 F cm−2), a long cycle life, and a maximum specific energy of 64.61 Wh kg−1, suggesting a great potential for practical application. Therefore, an ingeniously designed core–shell array structure can effectively realize the charge storage potential of the Mn–Co oxides and Ni sulfides, and this work presents an alternative method for constructing hybrid architectures for advanced electrochemical energy storage materials.

Synthesis of hierarchical Ni3S2@NiMoO4 core-shell nanosheet arrays on Ni foam for high-performance asymmetric supercapacitors

Hierarchical Ni3S2@NiMoO4 core-shell nanosheet arrays were directly fabricated on Ni foam through a simple two-step hydrothermal reaction followed by an annealing treatment. The shell, ultra-thin NiMoO4 nanosheets grew on the surface of the core, interconnected Ni3S2 nanosheet arrays. The growth density of the NiMoO4 nanosheets was adjusted by controlling the hydrothermal reaction time. When the hydrothermal time was 1 h, the as-prepared Ni3S2@NiMoO4 with a core-shell structure could achieve a high specific capacity up to 1121.4 C g−1 at a current density of 5 mA cm−2. In addition, the Ni3S2@NiMoO4 demonstrated 91.6% capacity retention of its initial value for 5000 cycles at a current density of 30 mA cm−2. Additionally, an asymmetric supercapacitor (ASC) device was assembled based on the optimized Ni3S2@NiMoO4 electrode as the positive electrode and activated carbon (AC) as the negative electrode. The ASC exhibited a maximum energy density of 28.4 W h kg−1 at a power density of 90.8 W kg−1, and showed a remarkable cycling performance with 93.1% retention of the initial capacitance after 10,000 cycles at a current density of 30 mA cm−2.

Fabrication of hierarchical MoO3@NixCo2x(OH)6x core–shell arrays on carbon cloth as enhanced-performance electrodes for asymmetric supercapacitors

Advanced integrated electrode materials with designedcore–shell nanostructureplay a crucial role for the application in alternative energy storage system. Herein, hierarchical MoO3@NixCo2x(OH)6x core–shell arrays were equably grown on face of carbon cloth after a series of hydrothermal growth and electrochemical deposition processes. This core–shell arrays structure can not only provide large electroactive surface areas and high speed ion transport paths, but also keep the material structure stable during the process of redox reactions. Thus MoO3@NixCo2x(OH)6x displays excellent electrochemical performance (4.7 F cm−2 at 10 mA cm−2). Moreover, the asymmetric supercapacitor is assembled with MoO3@NixCo2x(OH)6x and carbon nanotubes, which delivers a maximal energy density of 0.50 mWh cm−2 at 4.25 mW cm−2, high specific capacitance and superior cycling stability (94.5% capacitance retention after 5000 cycles). We believe that MoO3@NixCo2x(OH)6x arrays could be a great prospective candidate energy storage materials.

Silicon nanowire-hydrogenated TiO2 core-shell arrays for stable electrochemical micro-capacitors

In this paper, we fabricated silicon nanowire-TiO2 core-shell arrays in a two-step process. First, silicon nanowire arrays (SiNW) were prepared in HF/AgNO3 aqueous solution using metal-assisted chemical etching of bulk silicon. Then, atomic layer deposition (ALD) technique was applied to coat a 20 nm thin shell TiO2 film. The TiO2/SiNW substrates were afterward annealed at 400°C in hydrogen atmosphere for 4 h and tested as electrode materials for electrochemical micro-capacitors. The electrochemical features of the constructed H−TiO2/SiNW electrode were assessed in an aqueous 1 M Na2SO4 electrolyte solution and revealed that the specific capacitance increased six times compared to non-annealed TiO2/SiNW and 20-fold compared to a reference SiNW electrode under the same operating conditions. Importantly, H−TiO2/SiNW also displayed a high stability over 30,000 cycles at 0.1 mA cm−2 with an overall decrease of 19% of the initial capacitance. The hydrogen treatment increased the density of hydroxyl group and enhanced the carrier density on TiO2 surface improving the capacitive properties of H−TiO2/SiNW.

Introducing oxygen vacancies for improving the electrochemical performance of Co9S8@NiCo-LDH nanotube arrays in flexible all-solid battery-capacitor hybrid supercapacitors

In this work, rich oxygen vacancies are obtained in Co9S8@NiCo-LDH core-shell nanotube arrays (NTAs), which boost its electrochemical energy storage performance. The flexible carbon cloth (CC) supported Co9S8@NiCo-LDH NTAs are synthesized by situ growth and electrodeposition method. After reacting with NaBH4, the rich oxygen vacancies are generated in NiCo-LDH nanosheets to obtain Co9S8@oxygen vacancies-NiCo-LDH NTAs (Co9S8@OV-NiCo-LDH NTAs). These oxygen vacancies increase the charge transfer rate in the multi-level redox processes and make the electrochemical performance improve sharply. At a current density of 0.5 A g−1, the mass specific capacity of Co9S8@OV-NiCo-LDH NTAs is up to 1335 C g−1, which is more than four times higher than that of the untreated Co9S8@NiCo-LDH NTAs. In addition, with the prepared Co9S8@OV-NiCo-LDH core-shell NTAs as a positive electrode, along with the negative electrode of activated carbon (AC), a high-performance flexible all-solid battery-capacitor hybrid supercapacitors (HSC) device is assembled. The maximum energy density is up to 101.1 Wh kg−1 when the power density is 800 W kg−1.