Self-supported cobalt–molybdenum oxide nanosheet clusters as efficient electrocatalysts for hydrogen evolution reaction

In this paper, we report the three-dimensional self-supported CoMoO₄ nanosheet clusters on the nickel foam (denoted as CoMoO₄/NF) by a facile hydrothermal-calcination method for efficient hydrogen generation. As a result, the freestanding CoMoO₄ electrode exhibits an efficient electrochemical activity towards hydrogen evolution reaction, showing overpotentials as low as 68 and 178 mV at current densities of 10 and 100 mA cm⁻² in the alkaline condition (1 M KOH), respectively, a Tafel slope value of 82 mV per decade. Moreover, the electrode exhibits remarkable electrochemical durability for 1000 cycles. Significantly, the water splitting electrolyzer assembled with CoMoO₄/NF || NiFe LDH/NF (the nickel iron layered double hydroxide supported on the nickel foam) system achieved 20 mA cm⁻² at 1.63 V, showing the CoMoO₄/NF is promising for practical water splitting applications.     

Electrochemical characterization of porous nickel–cobalt oxide electrodes

The electrochemical characterization of mixed oxides containing cobalt and nickel prepared by cathodic electrodeposition is presented. Their catalytic properties are discussed according to the results obtained employing stationary polarization curves, voltammetry, electrochemical impedance spectroscopy, and scanning electron microscopy. Impedance results were analyzed considering a porous electrode and approximated in terms of a finite transmission line model of conical pores linked in parallel. For sake of comparison, results obtained with Co–Ni cobaltites prepared by thermal decomposition are also presented.     

Nanosized Zn–Sn metal composite oxide: a new anode material for Li ion battery

Abstract

The morphological evolution of nanosized Zn–Sn composite oxides, synthesised by the decomposition of ZnSn(OH)₆ precursor at temperature ranged from 300 to 800°C was investigated by using XRD and high resolution TEM. The precursor was also studied by thermal analysis. The electrochemical performance of Zn–Sn composite oxides as anode materials for Li ion batteries was measured in the form of Li/Zn–Sn composite oxides cells. The results reveal that the samples calcined at low temperatures (300 and 500°C) were amorphous Zn₂SnO₄ and SnO₂, and the samples calcined at high temperatures (720 and 800°C) were crystal Zn₂SnO₄ and SnO₂. All the samples have a high reversible specific capacity of over 800 mAh g^?1, and the first charge specific capacity is up to 903 mAh g^?1 for the sample calcined at 500°C. The charge capacity and cyclability were sensitive to the structure and composition of the electrode active materials; the samples calcined at phase transition temperature rage exhibited relatively worse electrochemical properties.     

Metal-organic frameworks supported Ni–Co–S nanosheet arrays for advanced hybrid supercapacitors

Constructing self-supporting porous electrode material with abundant electrochemical active sites can effectively improve the energy storage capacity of supercapacitors. Herein, a novel electrode material (NCS@Co-ZIF/NF) is developed by depositing zeolitic imidazolate frameworks (Co-ZIF) on nickel foams (NF), which is adopted as a precursor (Co-ZIF/NF) to electrodeposit nickel-cobalt sulfides (NCS). The nanosheet arrays with cross-porous structures provide NCS@Co-ZIF/NF with excellent electrochemical characteristics, including a high specific capacity of 144.4 mAh g^?1 at the current density of 1 mA cm^?2, 60.5% capacity retention at 50 mA cm^?2, and superb long-term cycle stability. Furthermore, NCS@Co-ZIF/NF//AC hybrid supercapacitor is fabricated by using NCS@Co-ZIF/NF as positive electrodes and activated carbon (AC) as negative electrodes, which exhibits a high energy density of 33.9 Wh kg^?1 at a power density of 145 W kg^?1.     

Aligned Co3O4–CoOOH heterostructure nanosheet arrays grown on carbon paper with oxygen vacancies for enhanced and robust oxygen evolution

Developing efficient and stable non-noble metal oxygen evolution reaction (OER) electrocatalysts for sustainable overall water-splitting is extremely desirable but still a great challenge. Herein, we developed a facile strategy to fabricate Co₃O₄–CoOOH heterostructure nanosheet arrays with oxygen vacancies grown on carbon paper (Co₃O₄–CoOOH/CP). Benefiting from the unique 3D architecture, large surface area, synergistic effects between Co₃O₄, CoOOH and oxygen vacancies, the obtained self-supporting Co₃O₄–CoOOH/CP presents excellent electrocatalytic OER activity (low overpotentials of 245 and 390 mV at 10 and 100 mA cm⁻²) and robust long-term stability in alkaline condition. The present strategy provides the opportunities for the future rational design and discovery of high-performance non-noble metal based electrocatalysts for advanced water oxidation and beyond.     

Preparation and characterization of a new nanosized silicon–nickel–graphite composite as anode material for lithium ion batteries

A new type of nanosized silicon–nickel–graphite (Si–Ni–G) composite was prepared by high energy mechanical milling (HEMM) and pyrolysis using SiO as the precursor of Si for the first time. X-ray diffraction (XRD), high-resolution transmission electron microscope (HRTEM) and scanning electron microscopy (SEM) were used to determine the phases obtained and to observe the microstructure and distribution of the composite. The composite powders consisted of Si, Ni, SiO₂, NiO and a series of Si–Ni alloys. The formation of the inactive SiO₂ and Si–Ni alloy phases could accommodate the large volume changes of the active particles during cycling. In addition, cyclic voltammetry (CV) and galvanostatic discharge/charge tests were carried out to characterize the electrochemical properties of the composite. The composite electrodes exhibited an initial discharge and charge capacity of 1450.3 and 956.4 mAh g⁻¹, respectively, maintaining a reversible capacity of above 900 mAh g⁻¹ for nearly 60 cycles.     

Study of cobalt-doped lithium–nickel oxides as cathodes for MCFC

Cobalt substituted lithium–nickel oxides were synthesized by a solid-state reaction procedure using lithium nitrate, nickel hydroxide and cobalt oxalate precursor and were characterized as cathodes for molten carbonate fuel cell (MCFC). LiNi_0.8Co_0.2O₂ cathodes were prepared using non-aqueous tape casting technique followed by sintering in air. The X-ray diffraction (XRD) analysis of sintered LiNi_1−xCo_xO₂ indicated that lithium evaporation occurs during heating. The lithium loss decreases with an increase of the cobalt content in the mixed oxides. The stability studies showed that dissolution of nickel into the molten carbonate melt is smaller in the case of LiNi_1−xCo_xO₂ cathodes compared to the dissolution values reported in the literature for state-of-the-art NiO. Pore volume analysis of the sintered electrode indicated a mean pore size of 3 μm and a porosity of 40%. A current density of 160 mA/cm² was observed when LiNi_0.8Co_0.2O₂ cathodes were polarized at 140 mV. The electrochemical impedance spectroscopy (EIS) studies done on LiNi_0.8Co_0.2O₂ cathodes under different gas conditions indicated that the rate of the cathodic discharge reaction depends on the O₂ and CO₂ partial pressures.     

Synthesis and characterization of spinel LiMn2−xNixO4 for lithium/polymer battery applications

Spinel LiMn₂O₄ and LiMn_1.95Ni_0.05O₄ powders with sub-micron, narrow-size-distribution, and phase-pure particles are synthesized by a sol–gel method. The effects of heat treatment on the physicochemical properties of the spinel LiMn₂O₄ powder are examined with X-ray diffractometry, the Brunauer–Emmett–Teller method and scanning electron microscopy. For lithium/polymer battery applications, the LiMn₂O₄ and LiMn_1.95Ni_0.05O₄ electrodes are characterized electrochemically by charge–discharge experiments and a.c.-impedance spectroscopy. Although the Ni-doped electrode has a smaller initial capacity of 126 mA h g⁻¹, it exhibits better cycling performance than the conventional electrode which delivers a higher initial capacity of 145 mA h g⁻¹. The improvement in cycling performance of the former electrode is attributed to stabilization of the spinel structure by the presence of nickel ion. The cycling performance of a Li/polymer electrolyte/LiMn_1.95Ni_0.05O₄ cell at various temperatures is discussed in terms of interfacial resistance and lithium-ion diffusion determined by a.c.-impedance spectroscopy.     

One step hydrothermal synthesis of novel Cu2S-MoO3 nanocomposite for lithium ion battery and photocatalytic applications

Novel Cu₂S-MoO₃ nanocomposite (NC) has been synthesized successfully by single step hydrothermal method. The crystal structure, morphology and optical properties of Cu₂S-MoO₃ NC were individualised by XRD, FTIR, SEM, TEM, UV–Visible spectroscopy. As synthesized Cu₂S-MoO₃ NC was used as anode material for lithium ion battery (LIB) and manifested first discharge capacity 1516 mAhg^?1 at C/4 current rate. Cu₂S-MoO₃ NC is also implemented for photocatalytic hydrogen generation. In addition to above applications, it is materialized for degradation of organic dye (methylene blue) and chromium reduction [Cr(VI) to Cr(III)] with peerless activity.     

Potentiostatically deposited bimetallic cobalt–nickel selenide nanostructures on nickel foam for highly efficient overall water splitting

The fabrication of efficient electrocatalysts for water splitting is vital for production of clean fuels. Herein, cobalt–nickel selenide (CoNi₂Se₄) nanostructures were fabricated on a Ni foam substrate using a facile potentiostatic method at different deposition solution pH levels. Nanoparticle-, fluffy-, and flake-like CoNi₂Se₄ nanostructures were deposited by changing the aqueous solution pH to 2.0, 2.5, and 3.0, respectively. The desired flake-like CoNi₂Se₄ electrode fabricated at pH 3.0 presented the best electrocatalytic performance of all CoNi₂Se₄ nanostructures in this study and required overpotentials as low as 244 and 184 mV to deliver a current density of 10 mA cm^?2 for the OER and HER in 1.0 M KOH, respectively. Furthermore, the electrodes presented long-term stability over 20 h at current densities of 10 and ?10 mA cm^?2. Besides, this bifunctional flake-like CoNi₂Se₄ electrocatalyst delivered outstanding overall water splitting performance and required an external potential of 1.63 V to deliver a current density of 10 mA cm^?2.     

A new nickel–ceria composite for direct-methane solid oxide fuel cells

Various Ni–La_xCe_1−xO_y composites were synthesized and their catalytic activity, catalytic stability and carbon deposition properties for steam reforming of methane were investigated. Among the catalysts, Ni–La_0.1Ce_0.9O_y showed the highest catalytic performance and also the best coking resistance. The Ni–La_xCe_1−xO_y catalysts with a higher Ni content were further sintered at 1400 °C and investigated as anodes of solid oxide fuel cells for operating on methane fuel. The Ni–La_0.1Ce_0.9O_y anode presented the best catalytic activity and coking resistance in the various Ni–La_xCe_1−xO_y catalysts with different ceria contents. In addition, the Ni–La_0.1Ce_0.9O_y also showed improved coking resistance over a Ni–SDC cermet anode due to its improved surface acidity. A fuel cell with a Ni–La_0.1Ce_0.9O_y anode and a catalyst yielded a peak power density of 850 mW cm⁻² at 650 °C while operating on a CH₄–H₂O gas mixture, which was only slightly lower than that obtained while operating on hydrogen fuel. No obvious carbon deposition or nickel aggregation was observed on the Ni–La_0.1Ce_0.9O_y anode after the operation on methane. Such remarkable performances suggest that nickel and La-doped CeO₂ composites are attractive anodes for direct hydrocarbon SOFCs and might also be used as catalysts for the steam reforming of hydrocarbons.     

Efficient and stable Ni–Co–Fe–P nanosheet arrays on Ni foam for alkaline and neutral hydrogen evolution

The development of highly efficient and superior durability electrocatalysts is vital to expedite hydrogen evolution reaction (HER). Herein, a mixed amorphous and nano-crystalline Ni–Co–Fe–P alloy on Ni foam after 75 s dealloying in 3 M HCl (Ni–Co–Fe–P/NF-3-75) is synthesized by the preparation strategy of two-step method consisting of electroless deposition and dealloying process. Ni–Co–Fe–P/NF-3-75 shows an excellent HER performance and high durability in both alkaline and neutral conditions by optimizing the composition of the catalysts, acid concentration, and the time of dealloying. Benefitting from the high conductivity of Ni foam carrier, coordination between polymetallic phases, and the large exposure of defects, the as-prepared Ni–Co–Fe–P/NF-3-75 requires only a low overpotential of 56 mV and 104 mV to reach the current density of 10 mA cm⁻² in 1.0 M KOH and 1.0 M phosphate buffer (PBS), respectively. Remarkably, the Ni–Co–Fe–P/NF-3-75 electrode exhibits superior cycling stability and long-term robust durability without obvious overpotential decline. The successful preparation of the Ni–Co–Fe–P/NF-3-75 catalyst indicates that this method provides an efficient way to synthesize polymetallic phosphides for hydrogen evolution reaction.     

Electrochemical properties and lithium ion solvation behavior of sulfone–ester mixed electrolytes for high-voltage rechargeable lithium cells

Sulfone–ester mixed solvent electrolytes were examined for 5 V-class high-voltage rechargeable lithium cells. As the base-electrolyte, sulfolane (SL)–ethyl acetate (EA) (1:1 mixing volume ratio) containing 1 M LiBF₄ solute was investigated. Electrolyte conductivity, electrochemical stability, Li⁺ ion solvation behavior and cycleability of lithium electrode were evaluated. ¹³C NMR measurement results suggest that Li⁺ ions are solvated with both SL and EA. Charge–discharge cycling efficiency of lithium anode in SL–EA electrolytes was poor, being due to its poor tolerance for reduction. To improve lithium charge–discharge cycling efficiency in SL–EA electrolytes, following three trials were carried out: (i) improvement of the cathodic stability of electrolyte solutions by change in polarization through modification of solvent structure; isopropyl methyl sulfone and methyl isobutyrate were investigated as alternative SL and EA, respectively, (ii) suppression of the reaction between lithium and electrolyte solutions by addition of low reactivity surfactants of cycloalkanes (decalin and adamantane) or triethylene glycol derivatives (triglyme, 1,8-bis(tert-butyldimethylsilyloxy)-3,6-dioxaoctane and triethylene glycol di(methanesulfonate)) into SL–EA electrolytes, and (iii) change in surface film by addition of surface film formation agent of vinylene carbonate (VC) into SL–EA electrolytes. These trials made lithium cycling behavior better. Lithium cycling efficiency tended to increase with a decrease in overpotential. VC addition was most effective for improvement of lithium cycling efficiency among these additives. Stable surface film is formed on lithium anode by adding VC and the resistance between anode/electrolyte interfaces showed a constant value with an increase in cycle number. When the electrolyte solutions without VC, the interfacial resistance increased with an increase in cycle number. VC addition to SL–EA was effective not only for Li/LiCoO₂ cell with charge cut-off voltage of 4.5 V but also for Li/LiNi_0.5Mn_1.5O₄ cells even with high charge cut-off voltage of 5 V in Li/LiNi_0.5Mn_1.5O₄ cells.     

Efficient MOF- derived V–Ni3S2 nanosheet arrays for electrocatalytic overall water splitting in alkali

The synergistic achievement of low-cost earth-abundant electrocatalysts and high efficiency to meet renewable energy need is highly desirable yet challenging. Here, we developed a simple Ni foam self -templating route for V-doped Ni₃S₂ nanosheet arrays through in situ formation of metal-organic frameworks (MOFs) combined with subsequent conversion. The as-prepared MOF-V-Ni₃S₂/NF catalyst delivers outstanding electrocatalytic performance in the alkaline solution, which requires low overpotentials of 118.1 mV @10 mA cm^?2 and 268 mV @10 mA cm^?2 for hydrogen evolution reaction and oxygen evolution reaction, respectively. The V-doping and MOF-derived 3D hieratical nanostructure play a vital role in the catalytic process, which provides efficient active sites and large surface areas. Furthermore, an alkaline electrolyzer was assembled with two pieces of MOF-V-Ni₃S₂/NF, which achieves efficient water splitting at 1.58 V @10 mA cm^?2. This strategy opens up new channels to synthesize MOF-based bifunctional electrocatalysts toward overall water spitting.     

Preparation of Sn–Co alloy electrode for lithium ion batteries by pulse electrodeposition

Sn–Co alloy films for Li-ion batteries were prepared by pulse electrodeposition on the copper foils as current collectors. Nanocrystalline Sn–Co alloy electrodes produced by using a solution containing cobalt chloride and tin chloride at constant electrodeposition conditions (pulse on-time t_on at 5 ms and pulse off-time t_off at 5 ms) with varying peak current densities, Jp have been investigated. The structures of the electroplated Sn–Co alloy thin films were studied to reveal film morphology current density relationships and the effect of the current density parameters on the electrochemical properties. X-Ray Diffractometer (XRD), Scanning Electron Microscopy (SEM), Brunauer–Emmett–Teller (BET) surface area analyzer and Energy-Dispersive X-ray Spectroscopy (EDS) facilities were used for determination the relationships between structure and experimental parameters. Cyclic voltammetry (CV) tests were carried out to reveal reversible reactions between cobalt–tin and lithium. Galvanostatic charge/discharge (GC) measurements were performed in the cells formed by using anode composite materials produced by pulse electro co-deposition. The discharge capacities of these cells were cyclically tested by a battery tester at a constant current in the different voltage ranges between 0.02 V–1.5 V. The results have shown that Sn–Co alloy yielded promising reversible discharge capacities with a satisfactory cycle life for an alternative anode material to apply for the Li-ion batteries.     

High-energy,high-power Pulses Plus™ battery for long-term applications

Pulses Plus™ batteries were developed at Tadiran and introduced into the market few years ago. These batteries combine a primary high-energy bobbin type Li/SOCl₂ cell with a hybrid layer capacitor (HLC). The HLC is a battery-like capacitor consisting of lithium intercalation compounds as electrodes with pseudo capacitance of 785 F for standard AA size.The Pulses Plus™ battery can deliver very high energy at very high-power pulses (above 15 A at RT). Under low temperature conditions, its power capabilities are also very good, as 2 A, 1 s pulses above 2.5 V at −40 °C can be obtained. The stability of performance after elevated temperature storage and its low self-discharge rate make this a battery to operate under high pulse power over 20 years.     

High performance nickel–metal hydride battery in bipolar stack design

The consumption of fuel in cars can be reduced by using hybrid concepts. Even for fuel cell vehicles, a high power battery may cut costs and allow the recovery of energy during retarding. Alkaline batteries, such as nickel–metal hydride batteries, have displayed long cycle life combined with high power ability. In order to improve the power/energy ratio of Ni/MH to even higher values, the cells may be arranged in a bipolar stack design.     

Bipotential deposition of nickel–cobalt hexacyanoferrate nanostructure on graphene coated stainless steel for supercapacitors

Graphene oxide (GO) was deposited on inexpensive and mechanically stable stainless steel (SS) electrode by electrophoretic deposition (EPD) technique. GO was reduced electrochemically in NaNO₃ to obtain electrochemically reduced graphene oxide (ERGO). Next, Hybrid nickel–cobalt hexacyanofarrate (NiCoHCF) nanoparticles were deposited from solution containing Ni⁺² and Co⁺² with ratio of 1:1 on ERGO/SS by bipotential method. Morphological investigation of prepared sample by scanning electron microscopy showed the presence of nanoparticles with diameters in the range of 15–50 nm. Crystal structure of nanocomposite was investigated by X-ray diffraction technique. Electrochemical behavior of prepared film indicates that hybrid nanocomposite has higher specific capacitance (411 F g⁻¹) than ERGO (185.2 F g⁻¹) in KNO₃ solution at current density of 0.2 A g⁻¹. In other words, pseudocapacitor that is formed based on the faradaic behavior of NiCoHCF can improve the capacitive performance of ERGO.