Effect of cobalt electroless deposition on nickel hydroxide electrodes

The effects of cobalt additive on the positive electrode surface of nickel alkaline batteries are investigated. Electrode surface modifications by electroless cobalt deposits were made at different immersion times. The performance of nickel hydroxide electrodes was studied by optical techniques, such as scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX) and electrochemical methods as cyclic voltammetry, charge–discharge curves and electrochemical impedance spectroscopy (EIS). According to these results, electroless cobalt deposits obtained with 5 min of immersion time in the electroless-bath exhibit a better electrode performance.     

Study on the in situ sulfidation and electrochemical performance of spherical nickel hydroxide

In this paper, atmospheric reflux in water is used to directly form a nickel sulfide layer in-situ with excellent conductivity sulfide on the surface of spherical nickel hydroxide particles, significantly improving the conductivity of nickel hydroxide particles. The experimental results show that the spherical Ni(OH)₂@NiS material synthesized by the in situ sulfurization method. As the cathode active material of nickel-iron batteries exhibits excellent electrochemical performance, especially high-rate discharge and cycle performance, which are better than nickel hydroxide electrodes with cobalt oxide. The atmospheric reflux method in water has a simple process and equipment and has no pollution to the environment. Spherical Ni(OH)₂@NiS materials synthesized by in situ vulcanization can completely replace nickel hydroxide material with cobalt, and they have great commercial application value and market competitiveness as cathode active materials for alkaline nickel-based batteries.     

Nickel hydroxide/activated carbon composite electrodes for electrochemical capacitors

In this paper, a nickel hydroxide/activated carbon (AC) composite electrode for use in an electrochemical capacitor was prepared by a simple chemical precipitation method. The structure and morphology of nickel hydroxide/AC were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that nano-sized nickel hydroxide was loading on the surface of activated carbon. Electrochemical performance of the composite electrodes with different loading amount was studied by cyclic voltammetry and galvanostatic charge/discharge measurements. It was demonstrated that the introduction of a small amount of nickel hydroxide to activated carbon could promote the specific capacitance of a composite electrode. The composite electrodes have good electrochemical performance and high charge–discharge properties. Moreover, when the loading amount of nickel hydroxide was 6 wt.%, the composite electrode showed a high specific capacitance of 314.5 F g⁻¹, which is 23.3% higher than pure activated carbon (255.1 F g⁻¹). Also, the composite electrochemical capacitor exhibits a stable cyclic life in the potential range of 0–1.0 V.     

Nanocomposites of α-hydroxides of nickel and cobalt by delamination and co-stacking: Enhanced stability of α-motifs in alkaline medium and electrochemical behaviour

Dodecylsulfate-intercalated α-hydroxides of nickel and cobalt delaminate to give colloidal dispersions in 1-butanol. When these colloidal dispersions are mixed in different proportions and evaporated, composites are obtained and these consist of a random stacking of layers from the two hydroxides. The surfactant anion of these composites can be exchanged with nitrate ions and the resultant nitrate-intercalated composites are very stable in alkaline medium and show a high reversible charge capacity.     

Evidence for electronic and ionic limitations at the origin of the second voltage plateau in nickel electrodes,as deduced from impedance spectroscopy measurements

The second plateau occurring during the reduction of the nickel oxyhydroxide electrode (NOE) was studied by impedance spectroscopy on a cell with a pasted electrode prepared from commercial undoped β-Ni(OH)₂. Measurements were performed at diverse states of reduction and a large variation of impedance upon the transition from the first to the second plateau was observed. This variation mainly takes place at low frequencies and is hence related to ionic diffusion. We observed that the impedance becomes more capacitive on the second plateau meaning that the proton diffusion is limited. These results would be consistent with the gradual formation of an insulating layer of nickel hydroxide at the interface between the NOE and the electrolyte upon reduction. Once this layer becomes compact the ionic diffusion would be hindered and forced to occur through this layer, which could explain the voltage drop observed.     

Evaluation of the effects of oxygen evolution on the capacity and cycle life of nickel hydroxide electrode materials

The effect of charge–discharge cycling on the capacity of surface-adhered nickel hydroxide (Ni(OH)₂) micro-particles is investigated in aqueous KOH by cyclic voltammetry, and compared with that for pasted nickel hydroxide electrodes. Cyclic voltammetry on adhered Ni(OH)₂ micro-particles enables rapid screening of four types of commercially available, battery-grade, nickel hydroxide samples and allows the separation of the oxidation process from the oxygen evolution reaction. With large pasted electrodes, due to their high uncompensated resistance (R_u), these processes are poorly resolved. Pasted β-nickel hydroxide electrodes with a specific capacity of between 190 and 210 mAh g⁻¹ are charged and discharged at constant currents greater than 15 C (18 mA cm⁻²). With no voltage limit in the charging profile, excess oxygen evolution occurs and capacity fading is observed within the first 50 cycles. Loss of capacity is attributed to the degradation of the electrode due to excess oxygen evolution at switching potentials greater than 0.55 V versus Hg/HgO (1 M KOH). X-ray diffraction (XRD) measurements confirm the formation of γ-NiOOH in these electrodes. Limiting the cell voltage to 1.5 V, and thereby minimizing oxygen evolution, results in no observed capacity loss within 100 cycles, and only β-Ni(OH)₂ can be detected by XRD phase analysis.     

Facile in-situ electrochemical fabrication of highly efficient nickel hydroxide-iron hydroxide/graphene hybrid for oxygen evolution reaction

Oxygen evolution reaction (OER) is an essential process in energy conversion and storage, especially in water electrolysis, while developing active and low-cost catalysts is the key to maximizing O₂ production. Here a facile three-electrode electrolysis system is firstly applied to synthesize nickel hydroxide-iron hydroxide/graphene hybrid. To fully utilize the electrical energy and simplify the catalyst synthesis, we made graphite exfoliated into graphene at the cathode and nickel-iron hydroxide synthesized at the anode simultaneously. The best electrocatalytic performance of Ni–Fe/G for OER shows an overpotential of 280 mV (without iR compensation) at 10 mA cm^?2, superior to commercial RuO₂ (341 mV). Results show that the introduction of Fe in Ni–Fe/G not only converts part of α-Ni(OH)₂ into more active β-Ni(OH)₂, but promotes the electric conductivity and electrochemically active surface area (ECSA) of the obtained Ni–Fe/G, therefore Ni–Fe/G shows the superior OER performance. The OER activity of Ni–Fe/G can be further adjusted by experiment conditions including electrolysis time and electrolyte concentration. This work provides a novel and facile method for highly efficient OER via engineering the non-noble metal hydroxide/graphene hybrid.     

Enhanced electrochemical performance of nickel hydroxide electrode with monolayer hollow spheres composed of nanoflakes

Nickel hydroxide electrodes with hollow spheres were fabricated using a PS (polystyrene) sphere template and electrochemical deposition. The nickel hydroxide grew perpendicular to the electrode substrate during anodic deposition and around the PS spheres during cathodic deposition. After the removal of the PS template, hollow spheres or open hollow spheres were formed via cathodic deposition. The nickel hydroxide electrode with hollow spheres and nanoflakes showed greatly enhanced electrochemical performance in alkaline solution compared with the bare nickel hydroxide electrode. The opening of the hollow spheres facilitated easy electrolyte transport to the reaction sites and led to a further increase in the specific capacitance of the nickel hydroxide electrode. The specific capacitance of the electrode with the open hollow spheres reached 800 F g⁻¹, which was much higher than that of the bare electrode (224 F g⁻¹) and the hollow-sphere electrode (342 F g⁻¹) at a discharge current density of 10 A g⁻¹.     

Nickel hydroxide deposited indium tin oxide electrodes as electrocatalysts for direct oxidation of carbohydrates in alkaline medium

In this work, the direct electrochemical oxidation of carbohydrates using nickel hydroxide modified indium tin oxide (ITO) electrodes in alkaline medium is demonstrated; suggesting the feasibility of using carbohydrates as a novel fuel in alkaline fuel cells applications. The chosen monosaccharides are namely glucose and fructose; disaccharides such as sucrose and lactose; and sugar acid like ascorbic acid for this study. ITO electrodes are chemically modified using a hexagonal lyotropic liquid crystalline phase template electrodeposition of nickel. Structural morphology, growth, orientation and electrochemical behaviour of Ni deposits are characterized using SEM, XRD, XPS and cyclic voltammetry (CV), respectively. Further electrochemical potential cycling process in alkaline medium is employed to convert these Ni deposits into corresponding nickel hydroxide modified electrodes. These electrodes are used as novel platform to perform the electrocatalytic oxidation of various carbohydrates in alkaline medium. It was found that bare and Ni coated ITO electrodes are inactive towards carbohydrates oxidation. The heterogeneous rate constant values are determined and calculated to be two orders of magnitude higher in the case of template method when compared to non-template technique. The observed effect is attributed to the synergistic effect of higher surface area of these deposits and catalytic ability of Ni(II)/Ni(III) redox couple.     

Comparative structural and electrochemical study of high density spherical and non-spherical Ni(OH)2 as cathode materials for Ni-metal hydride batteries

In this paper we compare the behavior of non-spherical and spherical β-Ni(OH)₂ as cathode materials for Ni-MH batteries in an attempt to explore the effect of microstructure and surface properties of β-Ni(OH)₂ on their electrochemical performances. Non-spherical β-Ni(OH)₂ powders with a high-density are synthesized using a simple polyacrylamide (PAM) assisted two-step drying method. X-ray diffraction (XRD), infrared spectroscopy (IR), scanning electron microscopy (SEM), thermogravimetric/differential thermal analysis (TG-DTA), Brunauer-Emmett-Teller (BET) testing, laser particle size analysis, and tap-density testing are used to characterize the physical properties of the synthesized products. Electrochemical characterization, including cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and a charge/discharge test, is also performed. The results show that the non-spherical β-Ni(OH)₂ materials exhibit an irregular tabular shape and a dense solid structure, which contains many overlapped sheet nano crystalline grains, and have a high density of structural disorder and a large specific surface area. Compared with the spherical β-Ni(OH)₂, the non-spherical β-Ni(OH)₂ materials have an enhanced discharge capacity, higher discharge potential plateau and superior cycle stability. This performance improvement can be attributable to a higher proton diffusion coefficient (4.26 × 10⁻⁹ cm² s⁻¹), better reaction reversibility, and lower electrochemical impedance of the synthesized material.     

In situ electrodeposition of nickel cobalt selenides on FTO as an efficient counter electrode for dye-sensitized solar cells

Construction of transition metal selenides with high electrocatalytic performance is of significant importance, but it is still a challenge to develop the corresponding counter electrodes (CEs) by an electrodeposition technique. In the present work, nickel cobalt selenide (Ni_xCo_ySe) films are prepared in situ on fluorine-doped tin oxide (FTO) glasses through a potential reversal electrodeposition technique. The morphology and electronic structure of Ni_xCo_ySe films can be tuned by controlling the Ni/Co molar ratio in electroplating solution. Specially, Ni_xCo_ySe-6 film (the Ni/Co molar ratio of 1:1) with the optimized interaction between the Ni and Co elements displays numerous particles composed of sheets attached with nanocrystals, resulting in the more electrocatalytic active sites. Benefiting from the unique morphology and optimized synergistic effect, Ni_xCo_ySe-6 CE exhibits superior electrocatalytic activity for the triiodide reduction. Then, the dye-sensitized solar cell (DSC) fabricated by Ni_xCo_ySe-6 CE has demonstrated a power conversion efficiency (PCE) over 7.40%, which is higher than that of platinum (Pt)-based device (6.32%). Furthermore, Ni_xCo_ySe-6 array CE is also prepared by using polystyrene array as template. The PCE of the DSC with Ni_xCo_ySe-6 array CE reaches its maximum value of 7.64% and 20.9% larger than that of Pt-based device.     

High-rate discharge properties of nickel hydroxide/carbon composite as positive electrode for Ni/MH batteries

A chemical co-precipitation method was attempted to synthesize nickel hydroxide/carbon composite material for high-power Ni/MH batteries. The XRD analysis showed that there were a large amount of defects among the crystal lattice of the Ni(OH)₂/C composite, and the SEM investigation revealed that the as-synthesized spherical particles were composed of hundreds of nanometer crystals with a unique three-dimensional petal shape. Compared with pure Ni(OH)₂, the Ni(OH)₂/C composite showed improved electrochemical properties such as superior cycling stability, higher discharge capacity and higher mean voltage of discharge under high-rate discharge conditions, the discharge capacity and the mean discharge voltage of the Ni(OH)₂/C composite were about 281 mAh g⁻¹ and 0.303 V (vs. Hg/HgO) at 1 C-rate, 273 mAh g⁻¹ and 0.296 V at 5 C-rate, 250 mAh g⁻¹ and 0.292 V at 10 C-rate, respectively. The cyclic voltammetry (CV) tests showed that the Ni(OH)₂/C composite exhibited good electrochemical reversibility and the formation of γ-NiOOH during the charge–discharge processes was prevented. The existence of carbon in the Ni(OH)₂/C composite contributed great effect on the improvement of high-rate discharge performance.     

The influences of some additives on electrochemical behaviour of nickel electrodes

Nickel hydroxide is used as an active material in positive electrodes of rechargeable alkaline batteries. Since the nickel hydroxide electrode exhibits a poor performance which results not only from the competitive reactions of the oxidation of the active material but also from the evolution of oxygen. Its reduced charge acceptance is suspected to be related to a relatively long distance between nickel hydroxide particles and the nearest portion of the substrate. The practical capacity of the positive nickel electrode depends on the efficiency of the conductive network connecting the Ni(OH)₂ particle with the current collector.     

Hierarchically hollow interconnected rings of nickel substituted cobalt carbonate hydroxide hydrate as promising oxygen evolution electrocatalyst

The present work highlights fabrication of nanostructured nickel-substituted cobalt carbonate hydroxide hydrates (NCCHH) through one-step reflux method. It is noted that optimized 30 mol% nickel-substituted cobalt carbonate hydroxide hydrate (NCCHH-30) nanostructures show quite high specific surface area (～229.55 m² g^?1) owing to the formation of hierarchically hollow interconnected ring-type morphology facilitating the electrode-electrolyte interfacial interaction. As a result, NCCHH-30 showed significant amplification in electrocatalytic oxygen evolution reaction (OER) activity with ultralow overpotential (～141 mV @ 10 mA cm^?2), Tafel slope (～49 mV dec^?1), and excellent durability (12 h and 2000 cycles) in 1.0 M KOH. Notably, to the best of our knowledge, interconnected NCCHH-30 hierarchical hollow rings exhibited the best overpotential (η₁₀₀ ～198 mV) value reported for cobalt-based electrocatalysts in alkaline OER. In addition, this material exhibited exceptionally high oxygen evolution performance in comparison to the state-of-the-art commercial RuO₂ electrocatalyst in 1.0 M KOH. Such interconnected hierarchically hollow nickel (30 mol%)-substituted cobalt carbonate hydroxide hydrate nanostructured rings could act as an ultraefficient, cost-effective, and stable electrocatalyst for OER in alkaline medium.     

Asymmetric capacitor based on superior porous Ni-Zn-Co oxide/hydroxide and carbon electrodes

Hierarchical porous multi-phase Ni-Zn-Co oxide/hydroxide is synthesized by using metal-organic framework-5 (MOF-5) as the template. Hierarchical porous carbon is obtained by the facile direct decomposition of the MOF-5 framework with phenolic resin. The structures and textures are characterized by X-ray diffraction, high-resolution transmission electron microscopy, scanning electron microscopy, and nitrogen sorption at 77 K. An asymmetric capacitor incorporating the Ni-Zn-Co oxide/hydroxide as the positive electrode and the porous carbon as the negative electrode is fabricated. A maximum energy density of 41.65 Wh kg⁻¹ is obtained, which outperforms many other available asymmetric capacitors. The asymmetric capacitor also shows a good high-rate performance, possessing an energy density of 16.62 Wh kg⁻¹ at the power density of about 2900 W kg⁻¹.     

Reliability of multilayer ceramic capacitors with nickel electrodes

The reliability of multilayer ceramic capacitors (MLCCs) with Ni internal electrodes has been studied trom the viewpoint of partial oxygen pressure (P_O2) during firing. It is shown that the load-life time of the insulation resistance (1R) was prolonged by firing under low Po₂ annealing after firing, and the addition of dopants. It is also shown that the generation of oxygen vacancies led to the degradation of IR. Annealing treatment for the oxidation of the dielectric body accelerates the dielectric aging of MLCCs. It is found that the appropriate control of the P_O2 during firing can improve the reliability of MLCCs with Ni electrodes to a level as high as that of MLCCs with precious metal electrodes. Thus, we have developed an MLCC with Ni electrodes that features high reliability and a large capacitance of 10 μF for the Y5V characteristic and 4.7 μF for the X7R characteristic, both in the case of the C3216 (3.2 mm × 1.6 mm × 1.4 mm) form.     

NiCo layered double hydroxide/hydroxide nanosheet heterostructures for highly efficient electro-oxidation of urea

Urea oxidation is an important reaction for direct urea fuel cells as well as hydrogen production and/or water remediation via electrolysis using urea-rich wastewater. The key to efficient urea oxidation is to explore a well-designed high-performing catalyst. Herein, NiCo layered double hydroxide/hydroxide (NiCo LDH/NiCo(OH)₂) microspheres composed of ultrasmall nanosheets have been grown on Ni foam by a solution method at room temperature. The NiCo LDH/NiCo(OH)₂ heterostructures have been confirmed by TEM and XRD analysis. The high activity with a small onset potential of 0.29 V vs. Hg/HgO is mainly attributed to the rich NiCo LDH-NiCo(OH)₂ interfaces and the bimetallic nature of the catalysts. The NiCo LDH/NiCo(OH)₂ heterostructures can be promising catalysts for urea oxidation and offer new insights into the design of high-performance nickel-based catalysts.     

Nickel-cobalt layered double hydroxide ultrathin nanosheets coated on reduced graphene oxide nonosheets/nickel foam for high performance asymmetric supercapacitors

Here in, for the first time, we report a new and simple procedure for preparing reduced graphene oxide/nickel-cobalt double layered hydroxide composite on the nickel foam (Ni-Co LDH/rGO/NF) via a fast and simple two-step electrochemical method including potentiostatic routes in the presence of CTAB as a cationic surfactant. Graphene oxide coated nickel foam prepared by simple immersion method. After that, the prepared electrode reduced electrochemically to obtain rGO/NF electrode. Finally, the rGO/NF electrode was used as cathode for electrodeposition of Ni-Co LDH in the presence of CTAB as cationic surfactant. The prepared electrodes were characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), x-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), Energy-dispersive X-ray spectroscopy (EDS), Brunauer, Emmett and Teller (BET) and electrochemical techniques such as voltammetry (CV), galvanostatic charge-discharge curves (GCD) and electrochemical impedance spectroscopy (EIS). The resulting electrode which prepared in the presence of CTAB afforded extremely high specific capacitance of 2133.3 F g^?1 at a current density of 4 A g^?1. FE-SEM, TEM and EDS mapping results showed that Ni-Co LDH nanosheets uniformly covered the surface of rGO/NF in the presence of CTAB, and is closely packed and thinner in thickness compared with the sample prepared in similar way without using surfactant. Such new thin and dense morphology facilitates electrolyte ions diffusion through the prepared electrode. A good cycling stability was obtained for the electrode in alkaline media. EIS measurements showed low values of internal resistance (R_s) and charge transfer resistance (R_ct), indicating that the prepared nanocomposite is a promising candidate for supercapacitor applications. The asymmetric supercapacitor (ASC) based on the Ni-Co LDH/CTAB/rGO/NF as a positive electrode and rGO/NF as a negative electrode was assembled and it exhibited a C_s of 71.4 F g^?1 at a current density of 2 A/g and correspondingly energy density of as high as 68 Wh kg^?1.     

Effects of different Ni(OH)2 precursors on the structure and electrochemical properties of NiOOH

Nickel oxyhydroxide (NiOOH), an active material for alkaline Zn-NiOOH batteries, was synthesized by electrolysis oxidation of different Ni(OH)₂ precursors, which were prepared by three methods: polyacrylamide (PAM) assisted two-step drying (PTSD), conventional co-precipitation (CCP), and “controlled crystallization” (CC). The NiOOH samples were characterized and tested using X-ray diffraction (XRD), infrared spectroscopy (IR), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) testing, laser particle size analysis, tap-density testing, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and a discharge test. The results demonstrate that the physical and electrochemical properties of NiOOH are strongly dependent on the properties of the Ni(OH)₂ precursor, such as its morphology, microstructure, tap density, and specific surface area. The results of the electrochemical studies also show that the sample prepared by the PTSD method is superior to the others in electrochemical performance. The as-prepared, high-density, non-spherical NiOOH is a promising active material for the positive electrode in Zn-NiOOH batteries.     

Cobalt-molybdenum carbide@graphitic carbon nanocomposites: Metallic cobalt promotes the electrochemical hydrogen evolution reaction

In this work, a series of metallic cobalt-molybdenum carbide@graphitic carbon (CoMo(x:y)-T@GC) nanocomposites for the electrochemical hydrogen evolution reaction (HER) were synthesized by a sol-gel method. In the as-prepared nanocomposites, β-Mo₂C and metallic Co coexisted and were encapsulated by graphitic carbon. The presence of metallic Co effectively enhanced the crystallinity of β-Mo₂C, charge transfer efficiency and electrochemical active surface area (ECSA), thus resulting in the improved HER catalytic activities of the CoMo(x:y)-T@GC nanocomposites. The optimized electrocatalyst CoMo(0.5:0.5)-800@GC required the lowest overpotential of ～165 mV to deliver a current density of 10 mA cm^?2 in 0.1 M KOH, which was at the forefront compared with recently reported Mo₂C-based electrocatalysts.