Ni-Co Precursor Research Articles

GO based nanocomposite hydrogel enabled high performance wearable all-solid supercapacitor based on hierarchical structure electrodes derived from ZIF-67

The flexible and wearable supercapacitors have attracted wide interest because of their widespread application in smart electronic devices with rapid charging and discharging. As an important part of supercapacitor, the electrode materials with a hollow structure, especially those with hierarchical structures that provide an array of continuous hollow cages, are considered promising. Because of its porous shell which is rich in redox reaction sites for supercapacitors. In this work, we fabricated a ZIF-67 derived hollow Co3O4 growth on the surface of 1D NiCo2O4 to assemble into a beaded structure. In this case, NiCo precursor acted as a structure-directing agent to grow a ZIF-67, a promising electroactive material of electrochemical capacitors to provide capacitance after calcination. Combined with the grapheneoxide (GO) based high conductivity hydrogel as the solid electrolyte, the capacitance of the flexible supercapacitor exhibited a high specific capacitance of 90F g−1 at 0.5 A/g, and it was sturdy and durable. There was no significant loss of capacitance while suffering from bending and pressing. The outstanding electrochemical properties of the all-solid supercapacitor can be attributed to the unique nanostructure of the electrode that created more reactive active sites, increased the diffusion pathway for electrolyte ions, along with the high conductivity of the hydrogel electrolyte.

Synthesis of Urchin-like Ni@NP@NCP Composites with Three Solvothermal Systems for Highly Efficient Overall Seawater Splitting.

In this work, an urchin-like Ni@Ni2P@NiCoP (Ni@NP@NCP) composite was prepared on nickel foam by a simple hydrothermal treatment process. Using the prepared NiO nanosheets as templates, the NiCo precursor was prepared in the presence of three solvothermal systems of water/dimethylformamide (DMF)/dimethyl sulfoxide (DMSO) by the hydrothermal process. After mixing and calcining with sodium hypophosphite under a nitrogen atmosphere at a high temperature for phosphating, an urchin-like Ni@NP@NCP(F/SO/H) nanostructured catalyst was obtained with superior hydrogen evolution and oxygen evolution performance. To further explore their efficiency in seawater splitting. Ni@NP@NCP(F/SO/H) composites were used as the cathode and anode of an electrolytic cell, which delivered 1.822 V potential at 300 mA cm-2 in simulated seawater (1 M KOH and 0.5 M NaCl). This may provide an effective way of developing clean energy.

A novel method to preparing LiNi0.8Co0.15Al0.05O2 cathode materials using nano-sized Al(OH)3

The Ni-rich layered oxide LiNi0.8Co0.15Al0.05O2 (NCA) is primarily synthesized by mixing Ni-Co precursor with an Al source and LiOH followed by sintering the mixture at high temperatures. However, the particle size of the raw materials affects the electrochemical performance of the cathode material. This study used a homogeneous precipitation method to prepare nano-sized Al(OH)3. The Ni-Co precursor and Al(OH)3 were sonicated before calcination with LiOH at 800 °C for 20 h to obtain NCA. The first discharge of NCA had a specific capacity of 166.53 mAh/g at a current density of 0.2C. The capacity retention was 85.18 % after 120 cycles.

Electrochemical Nonenzymatic Glucose Detection Based on the Nanostructures of NiCo2O4 Nanosheets Wrapped CuO Nanowires

A kind of NiCo2O4-based hierarchically-nanostructured composites has been synthesized for electrooxidation of glucose. The Cu(OH)2 nanowires were initially growth in situ on the surface of Cu foam (CF) and wrapped with Ni-Co precursor (Ni-Co Pre) to prepare nanocomposites (Ni-Co Pre@Cu(OH)2 NWs/CF). Then, the obtained composites were annealed in air to form the NiCo2O4 nanosheets wrapped CuO nanowires nanostructures which were supported on the Cu foam (NiCo2O4@CuO NWs/CF). Because of the synergism of Ni, Co and Cu, as well as the enhanced surface area by hierarchical nanostructure, the as-prepared NiCo2O4@CuO NWs/CF sensor exhibits outstanding electrooxidation activity for glucose detection, including high sensitivity (7.98 μA/μM cm−2), wide linear range (1.0 × 10−3−2.0 mM), low detection limit (0.68 μM) and fast response/recovery times (1.3/2.0 s). Meanwhile, the as-fabricated sensor also possesses good reproducibility, flexibility, selectivity and long-term stability, which is a promising platform for glucose electrooxidation and determination in serum sample.

NiCoP selenization for enhanced oxygen evolution reaction in alkaline electrolyte

The electrocatalytic performance of bimetallic NiCo phosphide for oxygen evolution can be boosted via facile selenization by forming a crystal structure of metal phosphide and metal selenide. In the alkaline electrolyte, small overpotentials of 280 mV to drive 10 mA cm−2 were required, much smaller than that of NiCo phosphide and NiCo precursor. The improved performance was attributed to the increased electrochemical surface area that exposed more active sites. The high electrocatalytic efficiency of the active sites was also in line with the enhanced specific activity and turnover frequency values. In addition, high catalytic stability was also observed.

Construction of self-supporting, hierarchically structured caterpillar-like NiCo2S4 arrays as an efficient trifunctional electrocatalyst for water and urea electrolysis.

In this study, we have developed intriguing self-supporting caterpillar-like spinel NiCo2S4 arrays with a hierarchical structure of nanowires on a nanosheet skeleton, which can be used as a self-supporting trifunctional electrocatalyst for the oxygen evolution reaction (OER), hydrogen evolution reaction (HER) and urea oxidation reaction (UOR). The caterpillar-like NiCo precursor arrays are first in situ grown on carbon cloth (NiCo2O4/CC) by a facile hydrothermal reaction, which is followed by an anion exchange process (or sulfuration treatment) with Na2S to form self-supporting spinel NiCo2S4 arrays (NiCo2S4/CC) with a roughened nanostructure. Taking advantage of the bimetallic synergistic effect, the unique hierarchical nanostructure, and the self-supporting nature, the resultant NiCo2S4/CC electrode exhibits high activities toward the OER, HER and UOR, which are highly superior to the monometallic counterparts of NiS nanosheets and Co9S8 nanowires on a carbon cloth substrate. The comparison of the three electrodes also indicates that the hierarchically structured bimetallic electrode combines the morphological and structural characteristics of monometallic Ni-based nanosheets and Co-based nanowires. When assembling a two-electrode electrolytic cell with NiCo2S4/CC as both the anode and cathode, an applied cell voltage of only 1.66 V is required to deliver a current density of 10 mA cm-2 in water electrolysis. By using the same two-electrode setup, the applied voltage for urea electrolysis is further reduced to 1.45 V that produces hydrogen at the cathode with the same current density. This study paves the way for exploring the feasibility of future less energy-intensive and large-scale hydrogen production.

Surfactant-Assisted Growth of a Conversion-Type Binary Metal Oxide-Based Composite Electrode for Boosting the Reversible Lithium Storage.

High-performance anode materials play a crucial role in paving the development of next-generation lithium-ion batteries (LIBs). NiCo2O4, as a typical binary metal oxide, has been extensively demonstrated to possess higher capacity and electrochemical activity compared with a monometal oxide such as NiO or Co3O4. However, the advances in the application of LIBs are usually limited by the relatively low electrical conductivity and large volume change during repeated charging/discharging processes. Herein, a NiCo2O4@carbon nanotube (CNT) composite electrode with advanced architecture is developed through a facile surfactant-assisted synthetic strategy. The introduced polyvinyl pyrrolidone can greatly facilitate the heterogeneous nucleation and growth of the NiCo precursor on CNTs and thus benefit the uniform transformation to a well-confined NiCo2O4@CNT composite. The CNTs combined with NiCo2O4 tightly act as both a conductive network for enhancing the ion/electron transfer and a support for mitigating the volume expansion of NiCo2O4. As a result, the NiCo2O4@CNT electrode exhibits a high initial capacity of 830.3 mA h g–1 and a good cycling stability of 608.1 mA h g–1 after 300 cycles at 2000 mA g–1.

Millepore species-like ultra-long carbon fiber/cobalt nickel and its electrochemical activity

An ultra-long NiCo precursor having a morphology similar to Millepore species (Millipore sp.) was prepared to utilize a green homogeneous precipitation method. The Millepore species -like component is [MCO3]x · [M(OH)2]y · nH2O (M = Co, Ni; x, y, n = 1–5), which is a precursor of NiCo metal compounds, hydroxides, and oxides. There is no organic residue in the prepared product, making this synthetic procedure green. At the same time, the precursor grown in situ on carbon fiber produces ordered and controllable Millepore sp.-like materials as well as a stand-by electrode. The resistance of the adhesive bond to the glassy carbon electrode by the cobalt-nickel material is avoided. Following electrochemical activity tests, the Millepore sp.-like NiCo precursor showed significant redox activity on dopamine and uric acid. Differential pulse voltammetry can simultaneously detect two substances with excellent linear at the range of uric acid 0.04–0.2 mM and dopamine 6–20 μM.

Synthesis and electrochemical performance of core-shell NiCo2S4@nitrogen, sulfur dual-doped carbon composites via confined sulfidation strategy in a polydopamine nanoreactor

Abstract Nickel cobalt binary sulfides (NiCo2S4 ) have attracted huge attention as a promising anode material for lithium-ion batteries (LIBs). Herein, a polydopamine (PDA) shell with a controlled thickness was in-situ polymerized on a nanohorn-shaped Ni-Co precursor (Ni-Co-Pre), thus obtaining a core-shell Ni-Co-Pre@PDA, and then a high-temperature sulfidation was utilized to convert the Ni-Co-Pre@PDA into the NiCo 2S4 confined in nitrogen, sulfur co-doped hollow carbon nanohorns (NiCo2S4@NS-HCN) using cheap and environmental-friendly sulfur powder as sulfur sources. During the sulfidation, the Ni-Co-Pre core was converted into the NiCo2S4 , while the PDA shell as a nanoreactor was carbonized into the NS-HCN with simultaneous co-doping of nitrogen and sulfur. Benefitting from high-efficiency redox reactions of NiCo 2S4 and efficient structural protections of conductive carbon shells, the NiCo2S4 @NS-HCN electrodes showed significantly enhanced electrochemical properties including high reversible specific capacity of 1235 mA h g -1 at 0.1 A g-1 and excellent rate/cycling capability (69% capacity retention after 100 cycles). This study thus provides a simple and efficient confined sulfidation strategy for construction of binary transition-metal sulfides for LIB anode materials.

Synthesis of hierarchically porous NiCo2S4 core-shell hollow spheres via self-template route for high performance supercapacitors

The synthesis of hierarchical nickel cobalt sulfide with core-shelled hollow structures is greatly desired for electrochemical energy storage. Here we report a simple self-template route to synthesize hierarchical NiCo2S4 core-shell hollow spheres. Hierarchical Ni-Co precursor solid spheres are first prepared and utilized as the templates. After a sulfidation process, the solid precursor spheres can be transformed into hierarchical NiCo2S4 hollow spheres with a core-shelled hollow interior. The hierarchical NiCo2S4 core-shell hollow spheres possess a large specific surface area (98.8 m2 g−1) and mesoporous (about 12 nm in sizes) structure. In view of the large specific surface areas, porosities, and novel hollow structures, the hierarchically porous NiCo2S4 core-shell hollow spheres as electrode materials present a high specific capacitance of 1870.2 F g−1 at 2.0 A g−1 and an excellent long-duration cycling performance (about 9% loss after 3000 repeated charging-discharging cycles). Additionally, an asymmetric supercapacitor device using the NiCo2S4 as a positive electrode and activated carbon as a negative electrode is assembled, which delivers an energy density of 52.9 W h kg−1 at power density of 374.9 W kg−1. This work not only suggests the promising electrode materials of the hierarchically porous NiCo2S4 core-shell hollow spheres for application in electrochemical energy storage, but also provides an effective strategy on the metal sulfides design and preparation.

Phytic acid-assisted synthesis of ultrafine NiCo2S4 nanoparticles immobilized on reduced graphene oxide as high-performance electrode for hybrid supercapacitors

Incorporating graphene with transition metal sulfides nanoparticles (NPs) holds great potential as a high performance battery-type electrode for hybrid supercapacitors (HSCs). However, the poor interfacial contact between NPs and graphene sheets usually leads to compromised capacitance and stability of electrode materials. In order to tackle this problem, eco-friendly phytic acid (PA) is used as a bridging connection between graphene and NiCo2S4 NPs via the six phosphate groups of PA to afford NiCo2S4 NPs immobilized firmly on phytic acid modified reduced graphene oxide (PRGO) sheets. In addition, the morphology of NiCo precursor could be easily tuned by the addition of PA. Benefiting from the morphology and composition, the prepared NiCo2S4/PRGO hybrid battery-type electrode exhibits excellent electrochemical performance with high capacitance (1090 F g−1 at 2 A g−1), good rate performance (76.1% of the capacitance can be retained from 2 to 20 A g−1) and enhanced cycling stability. Moreover, a HSC device is fabricated using NiCo2S4/PRGO hybrid as positive electrode and active carbon (AC) as negative electrode, which exhibits a prominent energy density of 27.5 Wh kg−1 at a high power density of 446.5 W kg−1. The utilization of PA could offer a new avenue for the design of transition metal sulfides/PRGO hybrid for electrochemical or electrocatalytic applications.

Local Structure and in-Situ Average Structure Analysis of LiNi0.8Co0.2O2 Electrode during Charge-Discharge Process By Using Quantum Beam

INTRODUCTION LiCoO2-based materials have been mainly used as a cathode material of the Li ion rechargeable battery. However the Co has some problems, such as high cost and high environmental load. As a candidate of the alternative materials, LiNi0.8Co0.2O2, has drawn much attention because it shows high capacity comparatively, and has an advantage in respect to environmental problem due to low content of Co. The LiNi0.8Co0.2O2 was synthesized for the purpose of reducing cationic mixing and heat stability by substituting a part of Ni of LiNiO2 for Co and was studied. We reported the average structure by using the Rietveld method for neutron and X-ray diffraction patterns in the previous study1).Then we elucidated the local structure of LiNi0.8Co0.2O2 electrode in charge-discharge process by the PDF analysis using neutron and X-ray total scattering methods. The average structure analysis by the in-situ neutron diffraction patterns has been expected. However the measurement and the analytical technique are discussed2). In this research we examined the local structural charge of LiNi0.8Co0.2O2 electrode during charge-discharge process and the Rietveld method for in-situ neutron diffraction pattern of LiNi0.8Co0.2O2. Furthermore, we revealed the average structural change in charge-discharge process of the nonequilibrium state. EXPERIMENTAL LiNi0.8Co0.2O2 was synthesized by mixing Ni-Co precursor with lithium hydroxide hydrate. The precursor was prepared by co-precipitating the aqueous solution of the two metal nitrate salt (Ni, Co) in a stoichiometric ratio of 8:2, with lithium hydroxide. After suction filtration for a few hours, the precipitates were dried at 100°C overnight. The dried material was then mixed with a stoichiometric amount of LiOH-H2O. The mixture was annealed in air at 600 °C for 15 h, and then at 800 °C for 15 h. The product was identified by powder XRD. The composition of lithium and transition metals in the active material was determined by ICP. We analysed the local structure of LiNi0.8Co0.2O2 electrode in charge-discharge process by the PDF analysis using synchrotron X-ray total scattering (BL04B2, SPring-8) and neutron total scattering (BL21, J-PARC). To analyse the average structure of LiNi0.8Co0.2O2 electrode in charge-discharge process in the nonequilibrium state, we also performed the Rietveld method for in-situ neutron diffraction patterns (BL09, J-PARC) by using laminate cell. The cell film was used the PCTFE of the non-hydrogen film and the electrolyte substituted by deuterium. The charge and discharge test were measured at 0.1C. We examined the division time for the integrated in-situ diffraction data in the range of 10 to 40 minutes. Each divided date was analyzed by the Rietveld method using Z-Rietveld. RESULTS AND DISCUSSION We examined the local structure of LiNi0.8Co0.2O2 by PDF analysis using synchrotron X-ray total scattering and neutron total scattering. The Bond Valence Sum(BVS) of Ni and Co, the distortion parameters, λ, σ2 of the MO6(M=Ni, Co) octahedral were calculated from analysed results. It was revealed that the NiO6 octahedra was more distorted than the distortion of CoO6 octahedra. The reason why the distortion was large must cause the Jahn-Teller effect of Ni3+. Then we elucidated the local structure of LiNi0.8Co0.2O2 electrode in 2nd charge-discharge process by the PDF analysis using synchrotron X-ray total scattering method. The distortion parameter of the MO6octahedron came back original state after discharge. It was cearly revealed that there was locally reversible structural changein charge-discharge process. We also examined the method of the analysis for in-situ neutron diffraction data. We compared charge and discharge test using the laminating cell with the electrolyte substituted deuterium or nonsubstituted. In this study we understood there were no change in the electrochemical peroperty by using the electrolyte substituted deuterium. The comparison between the ex-situ and in-situ diffraction data was examined by Rietveld analyses. Furthermore, we examined Rietveld analysis method for neutron diffraction pattern in in-situ measurements. We got the neutron diffraction pattern by dividing the integrated neutron diffraction data in in-situ diffraction data. For example we observed the shift of a peak derived from (101) plane equivalent to the cathode in discharge process. The change of the Li composition and the quantity of cationic mixing in 3a site and 3b site in discharge process was revealed. In addition, no cationic mixing was observed in only discharge process. The technique of the analysis for in-situ neutron diffraction was needed to be further developed. It was performed by help of NEDO (RISING) and shows thanks to the members. References 1) Y. Idemoto, Y. Tsukada, N. Kitamura, A. Hoshikawa and T. Ishigaki, Chem. Lett., 40,168-170 (2011). 2) M. Roberts, et al., J. Power Sources, 226, 249-255 (2013) Figure 1

1D Ni-Co oxide and sulfide nanoarray/carbon aerogel hybrid nanostructures for asymmetric supercapacitors with high energy density and excellent cycling stability.

The fabrication of supercapacitor electrodes with high energy density and excellent cycling stability is still a great challenge. A carbon aerogel, possessing a hierarchical porous structure, high specific surface area and electrical conductivity, is an ideal backbone to support transition metal oxides and bring hope to prepare electrodes with high energy density and excellent cycling stability. Therefore, NiCo2S4 nanotube array/carbon aerogel and NiCo2O4 nanoneedle array/carbon aerogel hybrid supercapacitor electrode materials were synthesized by assembling Ni-Co precursor needle arrays on the surface of the channel walls of hierarchical porous carbon aerogels derived from chitosan in this study. The 1D nanostructures grow on the channel surface of the carbon aerogel vertically and tightly, contributing to the enhanced electrochemical performance with ultrahigh energy density. The energy density of NiCo2S4 nanotube array/carbon aerogel and NiCo2O4 nanoneedle array/carbon aerogel hybrid asymmetric supercapacitors can reach up to 55.3 Wh kg-1 and 47.5 Wh kg-1 at a power density of 400 W kg-1, respectively. These asymmetric devices also displayed excellent cycling stability with a capacitance retention of about 96.6% and 92% over 5000 cycles.