Nickel-based Electrodes Research Articles

Electronic Synergistic Effects on the Stability and Oxygen Evolution Reaction Efficiency of the Mesoporous LiMn2-xMxO4 (M = Mn, Fe, Co, Ni, and Cu) Electrodes.

Stable porous manganese oxide-based electrodes are essential for clean energy generation and storage because of their high natural abundance and health safety. This investigation focuses on mesoporous LiMn2-xMxO4 (where M is Fe, Co, Ni, and Cu and x is 0, 0.1, 0.3, 0.5, and 0.67) electrodes and thin/thick films. The mesoporous electrodes and films are fabricated by coating clear and homogeneous ethanol solutions of the salts (LiNO3, [Mn(OH2)4](NO3)2, and [M(OH2)x](NO3)2) and surfactants (P123 and CTAB) and calcining at elevated temperature (denoted as F-LiMn2-xMxO4, G-LiMn2-xMxO4, and meso-LiMn2-xMxO4, respectively). The electrochemical properties, stability, and oxygen evolution reaction (OER) performance of the F/G-LiMn2-xMxO4 electrodes are investigated in alkaline media using a three electrode setup. The F-LiMn1.33M0.67O4 electrodes (where M is Mn, Fe, Co, and Ni) exhibit low Tafel slopes of 60, 43, 44, and 32 mV/dec, respectively. While all the Mn-rich and F-LiMn2-xFexO4 electrodes degrade via Mn(VI) disproportionation reaction, the 33% Co electrode shows high stability during the OER. The nickel-based electrodes are stable with as little as 15% Ni and display excellent OER performance over 25% Ni, albeit undergoing a transformation that accumulates Ni(OH)2 species on the electrode surface. Copper in the F-LiMn2-xCuxO4 electrodes is homogeneous at low Cu percentages but forms a CuO phase above 15% Cu, undergoes degradation, and displays a weak OER performance. In short, Co and Ni stabilize the F-LiMn1.33Co0.67O4 and F-LiMn1.7Ni0.3O4 electrodes, which display excellent OER performance.

Effect of Catalyst and Electrode Structures on the Operating Current Densities of Liquid Alkaline Water Electrolyzers

Liquid Alkaline Water Electrolyzers (LAWEs) stand out as the technology best-suited for cost-effective hydrogen production. They do not require expensive platinum group metal catalysts and have proven durability afforded by nickel-based electrodes and porous separators. While nickel electrodes and porous separators provide chemical stability in highly alkaline conditions, they do suffer from lower catalytic activity for hydrogen and oxygen evolution reactions (HER and OER), and separators possess higher ohmic resistance due to the absence of ion-conducting groups. Consequently, most LAWEs operate at low current densities ranging from 0.2 to 0.6 A/cm2, resulting in a bulky footprint and comparatively lower energy efficiency due to a reduced hydrogen production rate. To address these challenges, considerable efforts have been directed towards developing thin separators and efficient transition metal-based electrocatalysts for HER and OER in alkaline media. However, the majority of studies related to catalysts are limited to half cells, with only a limited number of catalysts evaluated in relevant LAWE configurations.In this work, we introduce a next-generation Zero-gap LAWE testing capability, benchmarked for performance through H2NEW consortia. Employing this setup, we have evaluated hydrogen and oxygen evolution catalysts under LAWE-relevant conditions on different electrode substrates, each offering a unique electrode structure. Our preliminary findings indicate that Zero-gap LAWEs, when coupled with NiMo cathode and NiFe-type anode catalysts, can operate at current densities exceeding 0.75 A/cm2 at approximately 1.8 V without compromising their short-term durability. In contrast, the benchmark cell exhibited a meager current density of around 0.22 A/cm2. In this presentation, effects of electrode structure, catalyst type, and other relevant parameters related to Zero-gap LAWEs will be discussed in detail. Acknowledgement:This research is supported by the U.S. Department of Energy (DOE) Hydrogen and Fuel Cell Technologies Office through the Hydrogen from Next-generation Electrolyzers of Water (H2NEW) consortium.

Kinetics of Oxygen Catalyst Based on Pyrochlore Oxide Nano-Particles for Low Temperature Water Electrolysis

Alkaline water electrolysis is carried out at 60 to 80 oC using nickel-based electrode materials and highly concentrated KOH solutions, which make highly corrosive environment against the electrodes, the separator, the current collector, and the others of the cell. Reduction in operating temperature would be preferable to suppress corrosion, although it would also make the catalytic activity for OER and HER down, making the cell voltage up. Since oxygen evolution is known as a high overpotential reaction which is more than 400 mV with nickel-based oxides at 60 oC or more, and alternative materials with lower overpotential and higher stability for OER in AWE have been needed. This paper presents a novel oxygen catalyst nano-particles based on bismuth ruthenium oxide, in which ruthenium at the B site in the pyrochlore structure is partly replaced with manganese1).Mn-doped bismuth ruthenium oxide (MBRO) was prepared by precipitation of metal hydroxide precursor, which had been obtained by addition of NaOH solution into the metal salt solution containing Bi(III) and Ru(III) with Mn(II), followed by calcination at 600 oC. XRD, EDX, EXAFS, ICP-AES, and RBS were used for structural and compositional analyses of MBRO. The obtained oxide was added into distilled water and the solution was treated by ultrasonic vibration to make a suspension, which was then dropped on a titanium disk (4 mm diam.) and dried at RT for 24 h, resulting in oxide particles-coated titanium disk, in which no binders or ionomers were used in the process. The disk was mounted in a commercial rotating disk electrode and was used as the working electrode with a platinum counter electrode, an Hg/HgO reference electrode, and 0.1 mol/L KOH solution. Polarization curves were measured by LSV for OER, of which the results were analyzed to obtain the onset potential, Tafel slope, exchange current density. All measurements were performed at RT (25 oC).EDX and EXAFS studies of MBRO showed that Ru(IV) was replaced with Mn(IV) at the B-site of pyrochlore structure, and this doping made a single phase of pyrochlore structure oxide without sub-product up to 30 at% replacement . Linear sweep voltammetry revealed the overpotential of MBRO for OER was less than 200 mV and the Tafel slope analysis of the LSV curve gave 40 mV/dec or less. The onset potential and the Tafel slope were almost the same when Ru:Mn atomic ratio of MBRO was changed from 100:0 to 70:30 at%. Further analysis of the polarization curve indicated the exchange current density slightly decreased with increasing Mn ratio. These results suggest that Ru is the active site for OER but Mn is as well. The Tafel slope of OER catalysts reported in literatures is mostly 60 mV/dec or more, including more than 200 mV/dec of nickel-based oxides2,3). Therefore, MBRO is a hyper catalytic oxide for OER in alkaline media and can significantly reduce the overpotential of the anode in AWE even at ambient temperature.Ref.1) M. Morimitsu, Patent US.2022085387.A1.2) T. Shinagawa, A. T. Garcia-Esparza, K. Takanabe, Scientific Reports, Vol. 5, Article No.13801 (2015).3) S. Yagi, et al., Nature Communications, Vol. 6, Article No. 8249 (2015).

Corrosion behavior of austenitic stainless steel and nickel-based welded joints in underwater wet welding

Marine structures such as ports, bridges, pipelines, vessels, and platforms are an essential part of modern infrastructure, where the use of higher-strength steel provides savings in logistics and construction. However, the repair of higher-strength steels can be challenging, especially underwater. Wet shielded metal arc welding is the most widely used and least expensive method for underwater welding repairs, but is very susceptible to hydrogen-induced cracking. Thus, researchers and welding engineers aim to reduce the amount of hydrogen in the weld material. Recent success has been achieved through the use of austenitic welding consumables, such as austenitic stainless steel and nickel-based electrodes. The use of these consumables drastically reduces the amount of diffusible hydrogen in the weld metal. However, these austenitic materials usually have different corrosion potential as compared to the structural steel the weld beads are applied to. This creates the risk of severe galvanic corrosion. In the presented study, the corrosion behavior of welds created with austenitic stainless steel and nickel-based electrodes were studied. Samples were aged for 1.5 years in the Baltic Sea. Simultaneously, the effectiveness of corrosion protection systems such as coating and Impressed Current Cathodic Protection (ICCP) were evaluated. Localized corrosion occurred in the heat-affected zone when austenitic electrodes were used in the corrosive environment. The localized corrosion depth after 1.5 years in the Baltic Sea and in the salt spray layer was approximately 250 µm and 390 µm, respectively. The ICCP system and the use of a coating were effective in preventing localized corrosion. The low pitting corrosion density of 2.5 × 103 m−2 corresponds to grade A1 according to the standard and was found to be negligible as compared to the localized corrosion in the heat-affect zone.

Self-standing Ni–Cu–Ti/NCNTs electrocatalyst with porous structure for hydrogen evolution reaction

The development of water electrolysis hydrogen production technology is of great significance for accelerating the global carbon neutrality goals. Nickel-based electrode materials are considered the most promising catalysts for alkaline water electrolysis. However, the slow kinetics of the hydrogen evolution reaction remains a key challenge to be solved. To address this, a porous Ni–Cu–Ti/NCNTs cathode electrode was prepared using the powder metallurgy method. The microstructure characterizations and electrochemical measurements revealed that adjusting the content of NCNTs, while maintaining the Ni–Cu–Ti ratio of 5.5:3.5:1, can improve the catalytic activity of hydrogen evolution to a certain extent. Among the electrodes tested at room temperature, the one with 0.7% NCNT content exhibited the best performance in terms of hydrogen evolution. The analysis suggests that the porous structure of the electrode provides ample channels for object transmission. The addition of NCNTs further enhances the surface roughness of the electrode, exposing more active sites. Additionally, NCNTs promote electron transfer, synergize with Ni, Cu, and Ti, and improve the catalytic activity of hydrogen evolution.

3D-printed pyramid nickel-based electrode enabling directional bubble traffic and electrolyte flow for efficient hydrogen evolution

For efficient and stable large-scale water electrolysis, practical industrial electrodes should meet the following characteristics: high activity, structural stability, and fast bubble removal. Here we report a structured electrode (NiS–Co–NiP) prepared via 3D printing of nickel-based substrate and subsequent electrodeposition for the hydrogen evolution reaction (HER). With unique 3D nanosheets, the NiS–Co–NiP electrode exhibits large electrochemical surface area (ECSA), strong hydrophilicity, high mechanical strength and electrical conductivity, delivering outstanding HER activity. It requires low overpotentials of 134 mV and 169 mV to achieve the current densities of 100 mA cm−2 and 300 mA cm−2, respectively. Moreover, rational design of the NiS–Co–NiP electrode in pyramidal geometry facilitates directional bubble transport and electrolyte flow, resulting in superior stability of 350 h at a current density of 150 mA cm−2. This work demonstrates a new approach for manufacturing binder-free structured electrode of excellent HER performance at high current densities.

Hierarchical microporous Ni-based electrodes enable “Two Birds with One Stone” in highly efficient and robust anion exchange membrane water electrolysis (AEMWE)

Anion exchange membrane water electrolysis (AEMWE) is currently the most promising technology to produce green hydrogen. However, the lack of cost-effective and scalable methods for fabricating robust and highly active non-noble metal electrodes primarily inhibits its large-scale industrialization. This study unveils an effective strategy for tackling this challenge by creating a novel hierarchical conical-microporous nickel-based electrode, through a synergistic implementation of both rapid and scalable atmospheric plasma spraying (APS) and laser texturing (LT) processes. The resultant NA-LT-CA electrodes exhibits remarkable catalytic performances for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Notably, the AEMWE cell with NA-LT-CA electrodes yields a remarkable enhancement of cell efficiency, toward a reduction in cell voltage of 244 mV at 0.8 A cm−2, compared to the NA-CA electrode (without LT) cell. The notable achievements stem from the improved bubble dynamic contributed by the introduced hierarchical micropores into NA-LT-CA electrodes by the LT process. Moreover, the cell equipped with the NA-LT-CA electrodes demonstrates an outstanding durability, maintaining its performance for 1000 h without visible degradation under 0.8 A cm−2, which can be ascribed to the distinctive “pinning effect” produced by the transition layer during the LT process, adeptly preventing the catalytic layer peeling off even under industrial-scale current densities. Notably, introducing the LT process delivers a dual benefit, akin to achieving “Two Birds with One Stone.”. This work supports the effectiveness of combining APS and LT processes as a potent strategy for fabricating high-efficiency and enduring electrodes, thus advancing AEMWE for practical industrial applications.

An aqueous alkaline zinc-sulfur flow battery.

We demonstrate a rechargeable aqueous alkaline zinc-sulfur flow battery that comprises environmental materials zinc and sulfur as negative and positive active species. Meanwhile, a nickel-based electrode is also obtained by a two-step process to decrease the polarization of the sulfur redox reaction, thus greatly improving the voltage efficiency of the system from 32% to 78% at 10 mA cm-2.

Zn-doped NiMoO4 enhances the performance of electrode materials in aqueous rechargeable NiZn batteries.

In this work, zinc was introduced to prepare Ni1-xZnxMoO4 (0 ≤ x ≤ 1) nanoflake electrodes to increase the energy density and improve the cycling stability for a wider range of applications of aqueous rechargeable nickel-zinc (NiZn) batteries. This was achieved using a facile hydrothermal method followed by thermal annealing, which can be easily scaled up for mass production. Owing to the unique nanoflake structures, improved conductivity, and tunable electronic interaction, excellent electrochemical performance with high specific capacitance and reliable cycling stability can be achieved. When the Zn doping is 25%, the Ni0.75Zn0.25MoO4 nanoflake electrode displays a high specific capacitance of 345.84 mA h g-1 (2490 F g-1) at a current density of 1 A g-1 and improved cycling stability at a high current density of 10 A g-1. NiZn cells assembled with Ni0.75Zn0.25MoO4 nanoflake electrodes and zinc electrodes have a maximum specific capacity of 344.7 mA h g-1 and an energy density of 942.53 W h kg-1. This design strategy for nickel-based electrode materials enables high-performance energy storage and opens up more possibilities for other battery systems in the future.

Activity and Stability of High-Surface-Area Nickel-Based Catalysts for the Alkaline Hydrogen Evolution Reaction Under Industrially Relevant Conditions

Alkaline water electrolysis (AWE) is at a stage of high technological maturity, and modern pressurized designs have mitigated the weaknesses of now-outdated atmospheric electrolyzers. For instance, pressurized systems now deliver high hydrogen outputs and can efficiently adjust to rapid changes in power loads. These improvements were, in part, made possible through significant reductions to internal ohmic losses coming from improved gas separators, shorter distances between electrodes, and increased operating temperatures.From an industrial point of view, the critical parameter to optimize is the full stack voltage. The stack voltage is tightly bound to the individual cell voltage and can thus be lowered by employing more efficient electrocatalysts. However, reducing the cell voltage by raising the temperature of operation—thereby improving both reaction kinetics and the conductivity of the KOH electrolyte—can be of similar or even higher importance (e.g., ca. 4.5 mV/˚C, Figure 1) [1]. Therefore, stability under operation at elevated temperatures must be considered when evaluating novel hydrogen and oxygen evolution reaction catalysts for AWE. Else, a novel catalyst risks becoming the bottleneck in the pursuit of higher operating temperatures, limiting its applicability for large-scale electrolysis [2]. Many assessments of novel AWE catalysts are still carried out at room temperature in diluted electrolytes and at low current densities [3]. In the harsher conditions of an electrolyzer, catalysts experience higher dissolution rates and are subject to higher mechanical stress from, for instance, the aggressive bubble evolution. This gap hinders the transfer of catalyst developments from academia to industrial research laboratories and, ultimately, to practical applications.In this work, we attempted to narrow that gap by conducting electrochemical measurements under more application-oriented conditions (i.e., 80-120 °C and 8-11 M KOH). We evaluated the HER activity and the robustness of high-surface-area electrodes produced through controlled leaching of bimetallic nickel-based alloys. A parametric study of the overpotential and robustness as a function of electrochemically active surface area was enabled by varying the synthesis parameters of a Raney-type preparation. Direct coupling to renewable energy sources requires the electrolyzer to frequently and rapidly shut off and on. This intermittent operation induces additional stress on the electrodes as the catalysts transition through different redox states, which is often overlooked in AWE electrocatalyst research. To track redox, compositional, and morphological changes, we used ex situ X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy. At the same time, the dissolution and redeposition of ionic species were monitored using inductively coupled plasma mass spectrometry. By matching the characterization data with the evolution of the overpotential until complete deactivation, we gained an understanding of the degradation mechanisms in high-surface-area nickel-based electrodes. These results shed light on the challenges and prospects of this promising class of electrocatalysts for alkaline HER under industrial conditions.Acknowledgement:This work is partly funded by the Innovation Fund Denmark (IFD) under File No. 1044-00162B.

Reconstructed β-NiOOH enabling highly efficient and ultrastable oxygen evolution at large current density

As the active phase for most nickel-based electrodes in oxygen evolution (OER), nickel (oxy)hydroxides (NiOOH) suffer from insufficient electrochemical stability at large-current OER process due to the preferred redox into γ phase with limited charging reversibility. Herein, the reconstruction of β-NiOOH is enabled at large-current OER through constructing FeS2@NiS2 heterostructure to induce electronic-rich environment around Ni sites. By coupling with the FeS2 reconstructed FeOOH, the β-NiOOH@FeOOH is achieved as actual active phase for OER and features much superior electrochemical performance and stability over pristine NiS2 reconstructed γ-NiOOH, with the ultralow overpotential of 220 mV at 200 mA cm–2 and 150 h stably operating at large current. Revealed by DFT calculation, the strong electronic interaction at β-NiOOH@FeOOH interface not only enhances the electronic conductivity of NiOOH, but also tunes the d-band center of Ni-d orbitals and thus optimizing the binding strength of oxygen-containing intermediates for accelerated OER kinetics.

Tuning wettability of nickel-based electrode by micro-nano surface structure to boost OER catalysis

Electrolysis of water is a green and environmentally friendly hydrogen production method, but its low oxygen evolution reaction (OER) efficiency hinders its large-scale application. A major strategy to improve the catalytic performance of OER is constructing the micro-nano structure on the surface of the catalyst. However, the exact effects of micro-nano surface structure, such as roughness, morphology and hierarchical structure on the catalytic performance have not been systematically studied. Herein, Nickel-Cobalt-Cerium Oxide (Ni-Co-CeO2) catalytic electrodes with the different micro-nano surface structures are fabricated by magnetic field-induced scanning electrodeposition. The effects of the micro-nano surface structure on catalytic performance are investigated. The results show that the micro-nano surface structure of Ni-Co-CeO2 catalytic electrodes has a great influence on the wetting state, which may lead to the Wenzel-Cassie transition, resulting in severe degradation of catalytic performance. By optimizing the micro-nano surface structure, the Ni-Co-CeO2 catalytic electrode has the best catalytic performance with the overpotential of 309 mV for OER to achieve the current density of 10 mA/cm2 and the corresponding Tafel slopes of 39.52 mV/dec. The study also demonstrates that the magnetic field-induced scanning electrodeposition is an efficient and simple method for tuning the micro-nano surface structure of electrodes to boost the OER efficiency.

Electrochemical hydrogen production using captured CO2 in alkaline solution

In this work, a less toxic and corrosive captured CO2 in alkaline solution (KLC) supplied by the LowCarbon Co. was used as an electrolyte. A flow cell equipped with 25 cm2 nickel-based electrodes and a separator membrane was employed to produce H2 gas. A gas chromatography analysis of the exit gases showed that 99.75 % of H2 was produced at the cathode, while O2 was produced at the anode. However, CO2 gas was not detected in any of the exit gases. Performance evaluation of the cells revealed three processes through electrochemical impedance spectroscopy. A comparison of performance between cells operated using KLC and 10 wt% NaOH solutions as electrolytes revealed a significant overpotential in the KLC solution compared with NaOH, which is attributed mainly to the low electrical conductivity of the component ions as well as the nature of the anions.

Construction of specific nickel-based electrode using N,N-dimethylformamide/water as solvent and the application in metronidazole detection

Construction of specific nickel-based electrode using N,N-dimethylformamide/water as solvent and the application in metronidazole detection

A multi-layer-structured nickel-based electrode for high-performance binder-free asymmetric quasi-solid-state hybrid supercapacitors

A novel multi-layer-structured NiMn LDH/rGO/Ni(OH)2@Ni foam (LRN@NF) is synthesized by a method combining hydrothermal and dip-coating processes, acting as an excellent electrode material for supercapacitors. The specific multi-layer structure and synergism of all the components boosts the electrochemical performance. Microstructural characterization illustrates the successful formation of the multi-layer structure and also demonstrates the important role of the incorporated graphene layers for the growth of NiMn LDH. The NiMn LDH/rGO/Ni(OH)2@Ni foam shows a high specific capacity of 7.49C·cm−2 (specific capacitance of 14.40 F·cm−2) at 1 mA·cm−2. Furthermore, the asymmetric quasi-solid-state hybrid supercapacitor (LRN@NF//AC; AC represents activated carbon) exhibits a high specific energy density of 0.23 mWh·cm−2 at a specific power density of 0.91 mW·cm−2 with a voltage window of 1.6 V, and 0.12 mWh·cm−2 of energy density can be maintained even at 64.04 mW·cm−2. Therefore, the LRN@NF electrode is suggested to be a promising candidate for high-performance supercapacitors, and our research also demonstrates the feasibility and universality of the construction idea for excellent multi-layer-structured supercapacitor electrodes.

A Survey of Catalytic Materials for Ammonia Electrooxidation to Nitrite and Nitrate.

Studies of the ammonia oxidation reaction (AOR) for the synthesis of nitrite and nitrate (NO2/3 - ) have been limited to a small number of catalytic materials, majorly Pt based. As the demand for nitrate-based products such as fertilisers continues to grow, exploration of alternative catalysts is needed. Herein, 19 metals immobilised as particles on carbon fibre electrodes were tested for their catalytic activity for the ammonia electrooxidation to NO2/3 - under alkaline conditions (0.1 m KOH). Nickel-based electrodes showed the highest overall NO2/3 - yield with a rate of 5.0±1.0 nmol s-1 cm-2 , to which nitrate contributed 62±8 %. Cu was the only catalyst that enabled formation of nitrate, at a rate of 1.0±0.4 nmol s-1 cm-2 , with undetectable amounts of nitrite produced. Previously unexplored in this context, Fe and Ag also showed promise and provided new insights into the mechanisms of the process. Ag-based electrodes showed strong indications of activity towards NH3 oxidation in electrochemical measurements but produced relatively low NO2/3 - yields, suggesting the formation of alternate oxidation products. NO2/3 - production over Fe-based electrodes required the presence of dissolved O2 and was more efficient than with Ni on longer timescales. These results highlight the complexity of the AOR mechanism and provide a broad set of catalytic activity and nitrate versus nitrite yield data, which might guide future development of a practical process for the distributed sustainable production of nitrates and nitrites at low and medium scales.

Carbon cloth supported flower-like porous nickel-based electrodes boosting ion/charge transfer characteristics of flexible supercapacitors

Despite low cost and high theoretical specific capacitances, nickel-based compounds still suffer from poor conductivity, limited redox active sites and sluggish ion and charge transfer for their applications in flexible supercapacitors (FSCs). The rational structural control of nickel-based compound electrodes is vital but very challenging. Herein, a series of flower-like nickel-based compound electrodes are grown on carbon cloth (CC) by a general synthetic method, including Ni(OH)2/CC, NiS2/CC, NiO/CC and Ni2P/CC hybrid electrodes. The formation mechanism of such flower-like structure is investigated in-depth. Benefiting from the fibrous structure of flexible carbon cloth and flower-like porous structure of NiS2, the NiS2/CC hybrid electrodes are more accessible for the electrolyte ions, which facilitates their electrochemical kinetics and capacitive performances. The maximum specific capacitance of the NiS2/CC electrode is 1166.3 F/g at 0.4 A/g. Moreover, flexible asymmetric supercapacitors (FASCs) are assembled using NiS2/CC and activated carbon/CC (AC/CC) as positive and negative electrodes, respectively. Such FASCs exhibit an energy density of 34.1 Wh/kg at a power density of 561.3 W/kg, a long lifetime stability (96% retention after 8,000 cycles), and excellent mechanical stability. These superior electrochemical characteristics make the flower-like porous NiS2/CC hybrid a good candidate for next-generation flexible and high-performance electrode in FSCs.

Advances on Nickel-Based Electrode Materials for Secondary Battery Systems: A Review

Advances on Nickel-Based Electrode Materials for Secondary Battery Systems: A Review

High Performance Nickel Based Electrodes in State-of-the-Art Lithium-Ion Batteries: Morphological Perspectives

Li-ion batteries with “nickel” as the main material or the highest ratio material on the cathode or anode electrode have attracted considerable attention. Nickel has high strength and corrosion resistance. Nickel has also been utilized successfully as the cathode and anode materials. The specific capacity and energy and power density of the material increased with increasing nickel content. However, several problems have limited the use of nickel-based Li-ion batteries. Problems such as cation mixing, the properties of nickel, and highly Ni-rich compounds leading to side reactions, influence the electrochemical performance of Li-ion batteries. The morphology is another factor affecting the electrochemical performance. Further studies will be needed to synthesize materials with the desired morphology and determine how the morphology affects the electrochemical performance. In a morphological perspective, extensive morphological adjustments are a pathway to a long and stable life cycle. In this light, nickel-based electrodes are manufactured continuously and will always be considered for next-generation secondary energy storage. The morphology of nickel-based active materials is one of the main factors determining the high-performance of Li-ion batteries.

Phase-controlled growth of nickel hydroxide nanostructures on nickel foam for enhanced supercapacitor performance

The development of nickel-based electrode materials has always been a hot spot in the field of electrochemical energy. It is well known that nickel hydroxide nanostructures in situ grown on nickel foam has been well applied in supercapacitors, which can further be employed as a precursor to fabricate other nickel-based compounds and their composites as electrode materials. In this work, the controllable growth and phase transformation from initial β-Ni(OH)2 to nitrated α-Ni(OH)2 [i.e. Ni3(NO3)2(OH)4] in situ on nickel foam have been successfully achieved through a traditional mild hydrothermal route by tuning the concentration of reactants. The electrochemical studies show that the specific capacitance of α-type nickel hydroxide electrode is much higher than that of β-type. The former exhibits a large gravimetric capacitance of 2075 F g−1 at a current density of 0.5 A g−1. The asymmetric supercapacitor can provide a high specific energy of 31.5 Wh kg−1 at a specific power of 388 W kg−1 within a voltage window of 1.55 V. Therefore, this research develops a controllable preparation methodology for electrode materials of high-performance supercapacitors, which are also of great significance for the design of more new nickel-based electrode materials.