Search

Developing non-noble metal-based electrocatalyst with high catalytic activity is essential for advancing hydrogen energy technologies. This study introduces a hydrothermal method for synthesizing order Ni(OH)2 nanosheets, with H3O40PW12 (denoted as PW12) loaded onto reduced graphene oxide (rGO) coated on nickel foam (referred to as PW12-Ni(OH)2/rGO). This method contrasts with the electrodeposition of Ni(OH)2, where PW12 is added to the synthetic system to direct the assembly and morphology of the Ni(OH)2 through a hydrothermal reaction. In this work, the nickel foam acts dual roles as both the substrate and the source of nickel for the formation of Ni(OH)2. The PW12-Ni(OH)2/rGO nanosheets, when successfully prepared and loaded onto the nickel foam (NF), exhibited superior electrocatalytic activity for the hydrogen evolution reaction (HER) in an alkaline electrolyte, achieving a current density of 10 mA·cm−2 at an overpotential of 69 mV. Furthermore, we endeavored to expand the application of this material towards the oxygen evolution reaction (OER) by preparing PW12-(Fe/Co)Ni(OH)2/rGO through the addition of metal cations. This nanocomposite displayed outstanding electrocatalytic activity in alkaline electrolytes, with a current density of 10 mA·cm−2 at an overpotential of 211 mV, and demonstrated excellent stability over a 50 h period in a 1 M KOH solution. The results presented in this paper offer an effective strategy for the preparation of polyoxometalate-based inorganic materials with diverse functionalities, applicable to both HER and OER. [ABSTRACT FROM AUTHOR]

Exploring a novel strategy for large‐scale production of battery‐type Ni(OH)2‐based composites, with excellent capacitive performance, is still greatly challenging. Herein, we developed a facile and cost‐effective strategy to in situ grow a layer of Ni(OH)2/Ti3C2Tx composite on the nickel foam (NF) collector, where Ti3C2Tx is not only a conductive component, but also a catalyst that accelerates the oxidation of NF to Ni(OH)2. Detailed analysis reveals that the crystallinity, morphology, and electronic structure of the integrated electrode can be tuned via the electrochemical activation, which is beneficial for improving electrical conductivity and redox activity. As expected, the integrated electrode shows a specific capacity of 1.09 C cm−2 at 1 mA cm−2 after three custom activation cycles and maintains 92.4% of the initial capacity after 1500 cycles. Moreover, a hybrid supercapacitor composed of Ni(OH)2/Ti3C2Tx/NF cathode and activated carbon anode provides an energy density of 0.1 mWh cm−2 at a power density of 0.97 mW cm−2, and excellent cycling stability with about 110% capacity retention rate after 5000 cycles. This work would afford an economical and convenient method to steer commercial Ni foam into advanced Ni(OH)2‐based composite materials as binder‐free electrodes for hybrid supercapacitors. [ABSTRACT FROM AUTHOR]

[Display omitted] • Large area, 2D β-Ni(OH) 2 , < 3 nm thin nanosheets synthesized at water–air interface. • Device shows 820 mAh.cm−3 capacity with 70% retention after 30,000 cycles. • Device achieved ultrahigh energy density of 0.33 Wh.cm−3 at 275.86 W.cm −3. • β- Ni(OH) 2 shows enhanced OER activity η 10 :308 mV with Tafel value of 42 mV dec-1. • After charge storage & OER, XPS analysis confirms structural stability of the film. Bifunctional electrode materials are highly desirable for meeting increasing global energy demands and mitigating environmental impact. However, improving the atom-efficiency, scalability, and cost-effectiveness of storage systems, as well as optimizing conversion processes to enhance overall energy utilization and sustainability, remains a significant challenge for their application. Herein, we devised an optimized, facile, economic, and scalable synthesis of large area (cm2), ultrathin (∼2.9 ± 0.3 nm) electroactive nanosheet of β-Ni(OH) 2, which acted as bifunctional electrode material for charge storage and oxygen evolution reaction (OER). The β-Ni(OH) 2 nanosheet electrode shows the volumetric capacity of 2.82 Ah.cm−3(0.82 µAh.cm−2) at the current density of 0.2 mA.cm −2. The device shows a high capacity of 820 mAh.cm−3 with an ultrahigh volumetric energy density of 0.33 Wh.cm−3 at 275.86 W.cm −3 along with promising stability (30,000 cycles). Furthermore, the OER activity of ultrathin β-Ni(OH) 2 exhibits an overpotential (η 10) of 308 mV and a Tafel value of 42 mV dec-1 suggesting fast reaction kinetics. The mechanistic studies are enlightened through density functional theory (DFT), which reveals that additional electronic states near the Fermi level enhance activity for both capacitance and OER. [ABSTRACT FROM AUTHOR]

Developing a high-performance anode and cathode for a supercapacitor that simultaneously has a high specific capacitance and a high energy density is a difficult task. Pyrolysis of Ni-MOF is used in this study to build Ni–C nanoparticles with a porosity that can be tuned and a high surface area. A straightforward acid treatment can be used to produce an N-doped porous carbon anode and Ni(OH)2-coated Ni–C (Ni(OH)2-Ni-C) cathode, both of which are based on Ni–C. The capacitance of the N-doped porous carbon anode is three times that of the Ni–C nanoparticle. This is because the N-doped porous carbon anode inherited the porous structure of the Ni–C nanoparticle, and it also included more carbon. The Ni(OH)2-Ni-C cathode also demonstrates suitable capacitance and rate performance. This is because of the synergistic effect of the ultrathin nano-active layer and the Ni nanoparticles for high-rate discharge ability, which is supplied by the cathode's distinctive core–shell structure. The manufactured asymmetric supercapacitor, which uses the cathode and anode described in the previous sentence, demonstrates outstanding capacitive performance and significant reversibility. The capacitor has an energy density of 49.7 Wh kg−1 when the current is 2 A g−1. The porous structure, adequate conductivity, and the one-of-a-kind Ni(OH)2 ultrathin nano-active layer contribute to the material's great performance. The straightforward yet effective design procedure will be useful for the application of MOF in the field of energy storage, which includes fields like batteries and supercapacitors. [ABSTRACT FROM AUTHOR]

[Display omitted] Developing high performance and durable electrocatalysts is crucial for the practical application of large-scale water splitting under high current density. Here, we constructed a Mott–Schottky heterojunction bifunctional electrocatalyst coating of Ni 3 S 4 with Ni(OH) 2 thin film supported on Ni foam substrate (Ni 3 S 4 @Ni(OH) 2) for anion exchange membrane water electrolyzers (AEMWEs). Remarkably, the η 500 is as low as 274.6 mV toward the hydrogen evolution reaction and 423.8 mV toward the oxygen evolution reaction. AEMWEs deliver a stable performance that achieves current densities of 500 and 1000 mA cm−2 at a cell voltage of 1.84 and 1.95 V, respectively. In particular, the Ni 3 S 4 @Ni(OH) 2 exhibits durable stability for 100 h at 500 mA cm−2 without significant degradation and uses 0.75 kW·h of electricity less than commercial Ni foam electrode to produce each standard cubic meter of hydrogen gas at 500 mA cm−2. The excellent performance is ascribed to the triple roles of Ni(OH) 2 , which prevent the inner Ni 3 S 4 from decomposing during the reaction process, promoting the dissociation of water and formation of adsorbed hydrogen intermediate and accelerating electron transfer ability due to the Mott–Schottky heterojunction between Ni(OH) 2 and Ni 3 S 4. This work sheds light on the development of advanced bifunctional electrocatalysts based on non-precious transition metals for AEMWEs. [ABSTRACT FROM AUTHOR]

The realization of membrane-less and decoupled water splitting holds immense significance in facilitating cost-efficient and substantial H 2 supply. In this study, a two-step hydrothermal reaction was employed to synthesize a Co x Ni 1-x (OH) 2 @MnO 2 freestanding electrode, utilizing nickel foam (NF) as the substrate, MnO 2 as the seed layer, and Co x Ni 1-x (OH) 2 nanofiber as the surface layer. This fabrication approach resulted in a buffer electrode with an expanded potential window and enhanced charge storage capacity. Notably, the optimized Co x Ni 1-x (OH) 2 @MnO 2 @NF electrode functioned as an effective charge mediator, successfully decoupling the synchronous oxygen and hydrogen evolution reactions (OER and HER). Consequently, the need for separators was eliminated, introducing a novel two-step water electrolysis hydrogen production technology. Remarkably, the initial HER process at the cathode exhibited robust performance, sustaining a current of 100 mA for an impressive duration of 1500 s. Simultaneously, the Co x Ni 1-x (OH) 2 @MnO 2 mediator underwent oxidation, attaining its corresponding oxidation state and yielding a commendable applied potential of 1.564 V. Subsequently, the OER step entailed the revival of the buffer electrode, enabling the facilitated production of anodic O 2 at an operating potential of 0.392 V. Beyond that, the integration of an oxidizing buffer medium and a zinc foil enabled the development of a battery configuration, effectively replacing the second step of OER. This pioneering integration facilitated the concurrent realization of persistent H 2 generation and battery discharging, presenting an innovative approach to hydrogen production that circumvents reliance on an external power supply. Thus, this decoupled HER-OER apparatus offers a propitious strategy for effectively converting renewable resources into hydrogen. A membrane-less water splitting approach was developed for achieving decoupled hydrogen and oxygen evolution using Co x Ni 1-x (OH) 2 @MnO 2 as a buffer electrode. [Display omitted] • Co x Ni 1-x (OH) 2 @MnO 2 @nickel foam as highly-efficient capacitive electrode. • Co-doping enhances the conductivity of Ni(OH) 2 and facilitates charge transport. • MnO 2 increases the storage capacity of the buffer medium. [ABSTRACT FROM AUTHOR]

Sand-rose shaped β-Ni(OH)2 submicron particles were successfully synthesized by a simple wet-chemistry process. The influence of the as-prepared material on the thermal decomposition of ammonium perchlorate (AP) was explored by thermogravimetry and differential scanning calorimetry analyses. The in-situ formation of active NiO species in the AP/β-Ni(OH)2 system is beneficial for electron transfer in the decomposition steps of AP, leading to the acceleration of its thermal decomposition. In particular, the addition of 5 wt. % β-Ni(OH)2 to AP lowers the decomposition temperature of the latter by 68.5°C and, moreover, the apparent heat of decomposition is increased almost twofold compared to that of pure AP. [ABSTRACT FROM AUTHOR]

An ultra-sensitive immunosensor was designed for the accurate determination of Carcinoembryonic Antigen (CEA). To enhance the performance of immunosensor, an MWCNT/Ni(OH)2 nanocomposite was utilized as the electrochemical interface and modifier of the electrode surface. The simple preparation procedures for MWCNT/Ni(OH)2 composite were provided. Its characteristics and properties were investigated by HRTEM, FESEM, XRD, and FTIR techniques. Leveraging the unique electrochemical characteristics shown by the MWCNT/Ni(OH)2 nanocomposite and its correlation with CEA, high accuracy in CEA detection was achieved. Experimental findings provide evidence that the proposed immunosensor has the ability to detect CEA in laboratory samples. This research contributes towards achieving precise and rapid CEA detection in cancer diagnosis and prognosis. Across a wide concentration range of CEA, the designed immunosensor demonstrated a linear response from 0.0001 ng/mL to 2 ng/mL, and its limit of detection (LOD) was just 0.076 pg/mL. To evaluate the practical applicability of the electrochemical immunosensor, blood serum samples were examined, revealing the immunosensor's remarkable specificity and longevity. Its high accuracy and stability make it a valuable tool in clinical settings and biomedical research, paving the way for improved cancer management and patient outcomes.

Hierarchically porous materials are promising electrode materials for supercapacitors due to their high surface area and large amounts of interconnected active sites. As a three-dimensional (3D) porous material, aerogels can further increase the exposure of active sites and improve the ion transport by constructing hierarchically porous structures. Herein, a kind of 3D hierarchically porous Ni-(OH)2 aerogel (HP-NiA) constructed by a template-directed Ni-(OH)2 nanosheet can be obtained via combining the sol–gel method and template-etching method, in which the controllable pore size was achieved via using the mesoporous silica-KIT-6 and silicon template KH570 as sacrificial templates. The microporous cavities are interconnected with mesopores and macropores, which enable full contact of active sites with electrolytes and facilitate quick transport of ions. Benefiting from the hierarchically porous structure and the high active specific surface area (1577.5 cm2), the amorphous HP-NiAs exhibit ultrahigh specific capacitance (5578 F/g at 1 A/g), excellent rate performance (3698 F/g at 20 A/g), and superior cycling stability (72.5% capacitance retention after 10,000 cycles), which are superior to the state-of-the-art supercapacitor electrode materials. This work highlights the importance of the rational design on the hierarchical structure and provides a feasible strategy to construct hierarchical porous materials for energy-storage applications. [ABSTRACT FROM AUTHOR]

The CQDs + Ni(OH) 2 /BiVO 4 photoanode was fabricated by introducing CQDs with fluorescence and optical properties. The CQDs + Ni(OH) 2 /BiVO 4 photoanode exhibited a low water oxidation onset potential (∼0.2 V vs. RHE) and a photocurrent density of 3.05 mA cm−2 at a voltage of 1.23 V vs. RHE, which is about 2.5 times than that of the unmodified BiVO 4 electrode, and the charge injection efficiency is 65%. Surface dynamics test showed that CQDs + Ni(OH) 2 /BiVO 4 photoanode had higher charge transfer rate and lower charge recombination rate than BiVO 4 electrode. As a cheap and stable catalyst for water oxidation, Ni(OH) 2 combined with CQDs can effectively improve the migration of photogenerated electrons and holes, thereby improving the photoelectrochemical (PEC) water oxidation activity of the photoanode. [Display omitted] • Compared with other electrodes, CQDs + Ni(OH) 2 /BiVO 4 showed the largest photocurrent. • The joint effect of CQDs and Ni(OH) 2 enhances the charge injection efficiency. • CQDs and Ni(OH) 2 jointly reduce the surface charge recombination. • Ni(OH) 2 combined CQDs improve the migration of photogenerated electrons and holes. • The stability of CQDs + Ni(OH) 2 /BiVO 4 is far superior to that of other electrodes. [ABSTRACT FROM AUTHOR]

This study reports a novel Ni(OH)2/Co3O4 heterostructured nanomaterial synthesized through a simple two-step hydrothermal method combined with subsequent heat treatment. The Ni(OH)2/Co3O4 heterostructured nanomaterial showed excellent performance in the detection of xylene gas. XRD, SEM, and EDS characterized the crystal structure, microstructure, and composition elements of Co3O4 and Ni(OH)2/Co3O4, and the gas sensing properties of the Co3O4 sensor and Ni(OH)2/Co3O4 sensor were systematically tested. The test results indicate the Ni(OH)2/Co3O4 sensor has an optimal operating temperature of 175 °C, which is 10 °C lower than that of the Co3O4 sensor; has a response of 14.1 to 100 ppm xylene, which is 7-fold higher than that of the Co3O4 sensor; reduces the detection limit of xylene from 2 ppm to 100 ppb; and has at least a 4-fold higher response to xylene than other gases. The Ni(OH)2/Co3O4 nanocomposite exerts the excellent catalytic performance of two-dimensional nanomaterial Ni(OH)2, solves the deficiency in the electrical conductivity of Ni(OH)2 materials, and realizes the outstanding sensing performance of xylene, while the construction of the p–n heterojunction between Ni(OH)2 and Co3O4 also improves the sensing performance of the material. This study provides a strategy for designing high-performance xylene gas sensors using two-dimensional Ni(OH)2 materials. [ABSTRACT FROM AUTHOR]

Direct seawater electrolysis provides a grand blueprint for green hydrogen (H2) technology, while the high energy consumption has severely hindered its industrialization. Herein, a promising active site implantation strategy is reported for Ni(OH)2 nanowire network electrode on nickel foam substrate by Ru doping (denoted as RuNi(OH)2 NW2/NF), which can act as a dual‐function catalyst for hydrazine oxidation and hydrogen evolution, achieving an ultralow working potential of 114.6 mV to reach 1000 mA cm−2 and a small overpotential of 30 mV at 10 mA cm−2, respectively. Importantly, using the two‐electrode hydrazine oxidation assisted seawater electrolysis, it can drive a large current density of 500 mA cm−2 at 0.736 V with over 200 h stability. To demonstrate the practicability, a home‐made flow electrolyzer is constructed, which can realize the industry‐level rate of 1 A cm−2 with a record‐low voltage of 1.051 V. Theoretical calculations reveal that the Ru doping activates Ni(OH)2 by upgrading d‐band centers, which raises anti‐bonding energy states and thus strengthens the interaction between adsorbates and catalysts. This study not only provides a novel rationale for catalyst design, but also proposes a feasible strategy for direct alkaline seawater splitting toward sustainable, yet energy‐saving H2 production. [ABSTRACT FROM AUTHOR]

Ni(OH)2, as a multifunctional material, has found its applications in a great number of research areas. In particular, it is an efficient catalyst for urea oxidation reaction (UOR), which is an important alternative to oxygen evolution reaction in electrocatalytic water splitting. This work investigates the effect of materials morphology on the electrocatalytic UOR performance of β–Ni(OH)2, as well as the importance of characterising the catalysts’ surface by electrochemical active surface area. Three different morphologies (nanoflowers, nanocubes, and nanosheets) were prepared via a simple hydrothermal approach. The morphology and structure of the as-prepared samples were carefully examined by scanning electron microscopy, transmission electron microscopy, and powder X-ray diffraction. The UOR performance of β–Ni(OH)2 was evaluated by means of cyclic voltammetry, linear sweep voltammetry, Tafel analysis, and electrochemical surface area. Nanosheet Ni(OH)2 electrocatalyst exhibits higher current density responses (28.3 mA cm−2 ECSA at 1.6 V vs. RHE) and a lower slope in the Tafel plot (72.6 mV dec-1). Consequently, due to the exposure of more active sites to the reactants, the Ni(OH)2 electrode with nanosheet morphology displayed higher electrocatalytic performance during UOR compared to the nanoflower and nanocube samples.

Photoreduction of CO2 is a sustainable way of producing carbon‐neutral fuels. However, the development of robust catalyst for the selective reduction of CO2 to value‐added chemicals remains a challenge. Using a photochemical approach, encapsulation of nitrogen‐doped carbon and Ni(OH)2 is to form a hybrid (Ni(OH)2/NC) for photocatalytic CO2 reduction. The as‐synthesized Ni(OH)2/NC catalyst exhibits enhanced selectivity and activity for CO production under visible light. A CO evolution rate of 14.93 μmol h−1 with 84 % selectivity is achieved, outperforming the bare Ni(OH)2 (8.51 μmol h−1 evolution rate and 45 % selectivity for CO). The structures and physicochemical properties of the Ni(OH)2/NC were carefully analyzed by various characterization techniques and density functional theory (DFT) calculations. Results suggest that the NC modification can modulate the electronic structures of Ni(OH)2, and thus consolidate the adsorption and activation of CO2. Furthermore, the interface charge transfer between photosensitizer and Ni(OH)2 can also be promoted after NC modification. As a result, the Ni(OH)2/NC catalyst exhibits superior activity for CO2‐to‐CO photoreduction. Moreover, NC‐encapsulated NiO (NiO/NC) was successfully prepared under the same conditions. This NiO/NC catalyst also exhibits enhanced selectivity and activity for CO2 reduction with visible light, suggesting the effectiveness of carbon‐modification for managing CO2 reduction. This work provides a new avenue to modulate the selectivity and activity of CO2 reduction over transition metal hydroxides or oxide catalysts. [ABSTRACT FROM AUTHOR]

In this work, we report the synthesis of (Mg/Al)-doped Ni(OH)2 by a microwave-assisted co-precipitation route and its subsequent electrophoretic deposition (EPD) on ITO-coated glasses under an applied voltage of 12 V for 15 min. The X-ray diffraction (XRD) patterns of the powder samples with different Al3+ content show the presence of β-Ni(OH)2 and a layered double hydroxide (LDH) structure with characteristic peaks for the (006) and (009) diffraction planes. The analysis carried out by scanning electron microscopy (SEM) confirmed the lamellar morphology of the samples. Methanol, ethanol, and isopropanol were evaluated as dispersing media for the EPD of the doped nickel hydroxide. Based on zeta potential measurements, isopropanol was selected as the dispersion medium for EPD. XRD analysis of the as-prepared coatings indicates that the EPD of the LDH structure is preferred over the β-Ni(OH)2 phase. Moreover, the LDH increased the surface coverage due to the incorporation of Al3+ ions into the Ni(OH)2 structure. These results generate interesting expectations for the preparation of doped-metal oxide films from hydroxide precursors using EPD. [ABSTRACT FROM AUTHOR]

Dye-sensitized photocatalysis has been extensively studied for photocatalytic solar energy conversion due to the advantage in capturing long-wavelength photons with a high absorption coefficient. The rational integration of photosensitizer with semiconductor and cocatalyst to collaboratively operate in one system is highly desired. Here, we fabricate a Ni(OH)2-loaded titanate nanosheet (Ni(OH)2/H2Ti6O13) composite for high-performance dye-sensitized photocatalytic CO2 reduction. The ultrathin H2Ti6O13 nanosheets with negative surface charge provide an excellent support to anchor the dye photosensitizer, while the loaded Ni(OH)2 serves as an adsorbent of CO2 and electron sink of photoelectrons. As such, the photoelectrons derived from the [Ru(bpy)3]Cl2 sensitizer can be targeted transfer to the Ni(OH)2 active sites via the H2Ti6O13 nanosheets linker. A high CO production rate of 1801 μmol g-1 h-1 is obtained over the optimal Ni(OH)2/H2Ti6O13, while the pure H2Ti6O13 shows significantly lower CO2 reduction performance. The work is anticipated to trigger more research attention on the rational design and synthesis of earth-abundant transition metal-based cocatalysts decorated on ultrathin 2D platforms for artificially photocatalytic CO2 reduction.

In general, NiSn alloys are known as plating films with elegant lustre and excellent corrosion resistance. Electroplating methods have already reached a practical application level because high Sn-containing films can be obtained. On the other hand, electroless plating methods have not yet reached the level of practical application because the Sn content in the deposited film is not only low but also the corrosion resistance is not sufficient. The authors have studied in detail the composition of electroless plating baths to obtain NiSnP films with Sn content above 50 wt%. In particular, the plating bath using nickel hydroxide instead of nickel sulphate as the Ni source increased bath stability and obtained high Sn content. The effects of Ni source in the bath on the deposition films were studied. The bath using nickel hydroxide as the Ni source was almost unaffected by the bath ratio. Furthermore, the amount of dissolved oxygen (DO) in the plating bath also varied depending on the Ni source, affecting the composition of the deposited film and the bath stability. It was confirmed that electroless plating baths using nickel hydroxide have excellent bath stability and can be applied to a relatively wide range of plating operation conditions to obtain high Sn-containing films. In addition, the corrosion resistance was improved by increasing the Sn content in the film. It was also confirmed that the NiSnP with high Sn content does not dissolve in nitric acid. [ABSTRACT FROM AUTHOR]

Supercapacitors are considered as important energy conversion and storage devices, and one‐dimensional carbon nanofibers derived from electrospinning have been widely applied for supercapacitor electrode materials. The integration of carbon and metal hydroxide materials has become particularly important in order to pursue their higher electrochemical properties. In this paper, a one‐dimensional core‐shell electrode with Ni(OH)2 as shell and carbon nanofibers as core (Ni/CNFs@Ni(OH)2) was fabricated by electrospinning, high‐temperature carbonization and hydrothermal synthesis. This electrode exhibited high energy storage performance (785 F g−1 (1 A g−1)), good coulombic efficiency and cycling stability. Furthermore, the asymmetric supercapacitor (ASC) assembled with activated carbons as negative electrode and Ni/CNFs@Ni(OH)2 as positive electrode demonstrated a good energy storage performance (62.5 F g−1 (1.6 V)). Meanwhile, this ASC displayed a significant energy density of 22.2 Wh kg−1 at 800 W kg−1 and an outstanding rate capability, indicating that Ni/CNFs@Ni(OH)2 had a high potential application value in supercapacitors. [ABSTRACT FROM AUTHOR]

We herein report a facile two‐pot method to prepare a series of the two‐dimensional Ni(OH)2 nanocrystals with varied surface structures via the in‐situ surface transformation derived from Nickel metal‐organic framework (Ni‐MOF) in KOH solution at room temperature. The Ni(OH)2 obtained at the KOH concentration of 0.25 M displayed superior performance among the samples in terms of activities and stability. Further investigation proves that the enhanced urea oxidation reaction (UOR) activities can be ascribed to the cooperation of the larger electrochemical surface area, a faster electronic transfer speed, and a lower transfer resistance on the surface. These findings provide a new route for the rational design and synthesis of advanced electrocatalysts with relatively lower energy consumption that aims to be large‐scale synthesized and utilized in clean energy conversion and applications. [ABSTRACT FROM AUTHOR]

This study reports a novel Ni(OH)2/Co3O4 heterostructured nanomaterial synthesized through a simple two-step hydrothermal method combined with subsequent heat treatment. The Ni(OH)2/Co3O4 heterostructured nanomaterial showed excellent performance in the detection of xylene gas. XRD, SEM, and EDS characterized the crystal structure, microstructure, and composition elements of Co3O4 and Ni(OH)2/Co3O4, and the gas sensing properties of the Co3O4 sensor and Ni(OH)2/Co3O4 sensor were systematically tested. The test results indicate the Ni(OH)2/Co3O4 sensor has an optimal operating temperature of 175 °C, which is 10 °C lower than that of the Co3O4 sensor; has a response of 14.1 to 100 ppm xylene, which is 7-fold higher than that of the Co3O4 sensor; reduces the detection limit of xylene from 2 ppm to 100 ppb; and has at least a 4-fold higher response to xylene than other gases. The Ni(OH)2/Co3O4 nanocomposite exerts the excellent catalytic performance of two-dimensional nanomaterial Ni(OH)2, solves the deficiency in the electrical conductivity of Ni(OH)2 materials, and realizes the outstanding sensing performance of xylene, while the construction of the p–n heterojunction between Ni(OH)2 and Co3O4 also improves the sensing performance of the material. This study provides a strategy for designing high-performance xylene gas sensors using two-dimensional Ni(OH)2 materials.

Regulable loading of Ni(OH)2 crystals by using three dimensionally ordered mesoporous carbon (3DOMC) as a support is achieved through a confined growth strategy accompanied by steam-assisted crystallization. Dual forms of high-crystalline nanosheet-like Ni(OH)2 severally distribute within mesopores or over the outer surface of 3DOMC particles depending on the loading amount (3% − 15%) of Ni(OH)2. Benefitted from the highly hybrid combination and efficient electrolyte diffusion, the obtained Ni(OH)2/carbon nanocomposites exhibit an excellent electrochemical performance, and the optimal sample of 6%_Ni(OH)2/3DOMC with confined extra-small Ni(OH)2 nanosheets as dominant shows the highest specific capacitance of 552.5F.g−1 at 1.0A·g−1, which is 330% higher than the contrast sample by using actived carbon as the support. Furthermore, the assembled hybrid supercapacitor by using 6%_Ni(OH)2/3DOMC and 3DOMC as positive and negative electrodes displays an energy density of 11.7 Wh.kg−1 at 288.1 W.kg−1 and a superior charge/discharge stability. It is expected that the flexible component, well-defined structure, and superior electrochemical performance could promote a great application potential of Ni(OH)2/3DOMC nanocomposites as supercapacitor electrodes and in other energy storage devices.

The hierarchical CuCo2O4-Ni(OH)2 core-shell nanowire arrays on Ni foam were fabricated using facile and cost-effective two-step hydrothermal synthesis. The growth of CuCo2O4 nanowires was developed on Ni foam as the apposite basis of the conductive scaffold, and the ultrathin Ni(OH)2 nanowires were subsequently immobilized to form CuCo2O4-Ni(OH)2 core-shell nanowire arrays (NWAs). The prepared materials were further characterized in structural, morphological, and electrochemical properties. The obtained CuCo2O4-Ni(OH)2 pseudocapacitor electrode, incorporated by unique core-shell heterostructures nanowire arrays, exhibited great specific capacitance of 1201.67 F g-1 at 1 mA g-1, which is much higher than pristine CuCo2O4 nanowire of 638.89 F g-1 at 1 mA g-1. Simultaneously, it also has a high power density of 5.56 kW kg-1 at an energy density of 73.33 Wh kg-1 and good long-term cycling performance (~84 capacitance retention after 1000 cycles). The improved morphological and structural properties have substantiated the CuCo2O4-Ni(OH)2 core-shell nanowire arrays properties owing to higher surface active area and richer redox activity for boosting the electrochemical properties.

Hydrogen evolution reaction (HER) carried out from electrocatalysis of water splitting is playing a major role in the production of green and clean hydrogen. In this paper, we report on the synthesis of graphitic carbon nitride on nickel hydroxide (g-C 3 N 4 /Ni(OH) 2) nanocomposites by a simple ultrasonication method. The characterizations include the XRD, Raman, FESEM and electrochemical studies to analyze the performance of the as developed material over hydrogen evolution reaction. The morphological analysis shows that the aggregated interconnected g-C 3 N 4 /Ni(OH) 2 (GCN/NH) nanocomposites with an average particle size of ∼20 nm. These GCN/NH nanocomposites exhibit the lowest overpotential of 341 mV at 10 mA/cm2 which is smaller than that of the pristine Ni(OH) 2 nanosheets at 367 mV. Further, the Tafel slope for GCN/NH nanocomposites reveals a lower value of 131 mV/dec. As a result, g-C 3 N 4 decorated sheet-like β-Ni(OH) 2 exhibits the potential hydrogen evolution in alkaline KOH solution. Excitingly, the as developed hybrid β-Ni(OH) 2 nanocomposites show superior electrocatalytic behaviour during the hydrogen evolution reaction and also improve the catalytic stability than pure nanosheets. From these observations, one can say that this g-C 3 N 4 /Ni(OH) 2 nanocomposite electrocatalyst can play a splendid role in future energy technology. • One step synthesis of β-Ni(OH) 2 and g-C 3 N 4 /Ni(OH) 2 via sonochemical method. • Prepared electrodes were characterized for the electrocatalytic HER studies. • The electrochemically active surface area of nanocomposite is higher than that of the pristine. • The overpotential of the g-C 3 N 4 /Ni(OH) 2 nanocomposite is lower than that of the pristine Ni(OH) 2. [ABSTRACT FROM AUTHOR]

The application of transition metal oxides/hydroxides in energy storage has long been studied by researchers. In this paper, the core-shell CNFs@Ni(OH)2/NiO composite electrodes were prepared by calcining carbon nanofibers (CNFs) coated with Ni(OH)2 under an N2 atmosphere, in which NiO was generated by the thermal decomposition of Ni(OH)2. After low-temperature carbonization at 200 °C, 250 °C and 300 °C for 1 h, Ni(OH)2 or/and NiO existed on the surface of CNFs to form the core-shell composite CNFs@Ni(OH)2/NiO-X (X = 200, 250, 300), in which CNFs@Ni(OH)2/NiO-250 had the optimal electrochemical properties due to the coexistence of Ni(OH)2 and NiO. Its specific capacitance could reach 695 F g−1 at 1 A g−1, and it still had 74% capacitance retention and 88% coulomb efficiency after 2000 cycles at 5 A g−1. Additionally, the asymmetric supercapacitor (ASC) assembled from CNFs@Ni(OH)2/NiO-250 had excellent energy storage performance with a maximum power density of 4000 W kg−1 and a maximum functional capacity density of 16.56 Wh kg−1. [ABSTRACT FROM AUTHOR]

A composite electrode material (CF-MCNT/Ni@Ni(OH)2) with hierarchical structure composed of cotton fabric (CF), multi-walled carbon nanotubes (MCNT) and core-shell structured nickel@nickel hydroxide (Ni@Ni(OH)2) was prepared by ultrasound-assisted impregnation-drying, chemical deposition and anodic oxidation. The structure and properties were characterized by means of scanning electron microscopy, X-ray diffraction analysis and electrochemical tests. The results show that the area specific capacitance of the electrode can reach 6 300 mF/cm² (4 927 mF/cm² at 3 mA/cm²) at a current density of 0.5 mA/cm² in 2 mol/L KOH solution, which is higher than that of CF-Ni@Ni(OH)2, and the charge/discharge cycle performance has also been improved. The introduction of MCNT facilitates the formation of rough conductive layers on the surface of CF, which provides a reference for optimizing the electrode structure to prepare devices with high performance energy storage. [ABSTRACT FROM AUTHOR]

Transition−metal−based materials show great promise for energy conversion and storage due to their excellent chemical properties, low cost, and excellent natural properties. In this paper, through simple strategies such as classical electrospinning, air calcination, and the one−step hydrothermal method, a large area of Ni(OH)2 nanosheets were grown on NiMoO4 nanofibers, forming NiMoO4@Ni(OH)2 nanofibers. The one−dimensional nanostructure was distributed with loose nanosheets, and this beneficial morphology made charge−transfer and diffusion more rapid, so the newly developed material showed good capacitance and conductivity. Under the most suitable experimental conditions, the optimal electrode exhibited the highest specific capacitance (1293 F/g at 1 A/g) and considerable rate capability (56.8% at 10 A/g) under typical test conditions. Most interestingly, the corresponding asymmetrical capacitors exhibited excellent electrochemical cycle stability, maintaining 77% of the original capacitance. NiMoO4@Ni(OH)2 nanofibers were verified to be simple to prepare and to have good performances as energy−storage devices within this experiment. [ABSTRACT FROM AUTHOR]

In this paper, a facile and rapid aqueous-based electrochemical technique was used for the phase conversion of Ni into Ni(OH)2 thin film. The Ni(OH)2 thin film was directly converted and coated onto the network surface of Ni foam (NF) via the self-hydroxylation process under alkaline conditions using a simple cyclic voltammetry (CV) strategy. The as-formed and coated Ni(OH)2 thin film on the NF was used as the catalyst layer for the direct growth of carbon nanotubes (CNTs). The self-converted Ni(OH)2 thin film is a good catalytic layer for the growth of CNTs due to the fact that the OH− of the Ni(OH)2 can be reduced to H2O to promote the growth of CNTs during the CVD process, and therefore enabling the dense and uniform CNTs growth on the NF substrate. This binder-free CNTs/NF electrode displayed outstanding behavior as an electric double-layer capacitor (EDLC) due to the large surface area of the CNTs, showing excellent specific capacitance values of 737.4 mF cm−2 in the three-electrode configuration and 319.1 mF cm−2 in the two-electrode configuration, at the current density of 1 mA cm−2 in a 6 M KOH electrolyte. The CNTs/NF electrode also displayed good cycling stability, with a capacitance retention of 96.41% after 10,000 cycles, and this the excellent cycling performance can be attributed to the stable structure of the direct growth of CNTs with a strong attachment to the NF current collector, ensuring a good mechanical and electrical connection between the NF collector and the CNTs. [ABSTRACT FROM AUTHOR]

FeNi-based hybrid materials are among the most representative catalysts for alkaline oxygen evolution reaction (OER), but the modulation of their surface atoms to achieve the optimal catalytic properties is still a big challenge. Here, we report the surface modification of Ni(OH)2/nickel foam (NF)-based electrocatalyst with a trace amount of ferrocene formic acid (FFA) (FFA-Ni(OH)2/NF) for highly efficient OER. Owing to the strong electron interaction and synergistic effects of Fe-Ni heteroatoms, FFA-Ni(OH)2/NF exhibits an overpotential of 311 mV at a current density of 100 mA cm−2. Impressively, the overpotential of FFA-Ni(OH)2/NF at 100 mA cm−2 is 108 mV less than that of bulk phase doped Ni/FFA(OH)2/NF, demonstrating the surprising effect of heteroatomic surface modification. In addition, by introducing a small amount of surface modifier into the electrolyte, the weak surface reconstruction process in the electrochemical process can be fully utilized to achieve obvious modification effects. Therefore, this work fully proves the feasibility of improving catalytic activities of FeNi-based catalysts by modifying surface heterogeneous atom pairs. [ABSTRACT FROM AUTHOR]

The temporal and spatial segregation of the hydrogen and oxygen evolution reactions (HER and OER) are essential for advancing membrane-free electrolysis technology in H 2 production through water splitting. This investigation employed a two-step fabrication approach to craft a three-dimensional self-supporting buffered electrode. This method involved utilizing a Ni(OH) 2 @NiCo 2 O 4 core-shell nanoneedle array as the active material and nickel foam (NF) as the substrate. Remarkably, the H 2 production at the cathode displayed remarkable efficiency, maintaining an uninterrupted operation duration of 1500 s at a current of 100 mA. Simultaneously, the Ni(OH) 2 @NiCo 2 O 4 mediator on the anodic electrode underwent oxidation during this process, leading to the generation of its respective oxidized state, accompanied by a noteworthy operating voltage of 1.50 V. Afterwards, the second step of the OER involved the recovery of the buffered electrode and the generation of O 2 at an operational voltage of 0.46 V, with the O 2 -production duration being equivalent to that of the first step in the HER process. Interestingly, the revival process of the buffered electrode in the second step can also be coupled with zinc sheets, thereby constructing a battery. During the discharge process of the battery, the regeneration of the buffered electrode was achieved, and this discharge process could also provide a power supply for the first step of H 2 -evolution. Therefore, this decoupled water electrolysis system presents a promising avenue for facilitating the effective transformation of renewable sources into hydrogen. [Display omitted] • Ni(OH) 2 @NiCo 2 O 4 core-shell nanoneedle as a highly-efficient capacitive electrode. • Ni(OH) 2 @NiCo 2 O 4 heterojunction reduces electron transfer resistance. • Decoupled water electrolysis enabled sequential O 2 and H 2 generations. [ABSTRACT FROM AUTHOR]

A facile ammonia-mediated strategy is developed for the kinetically controlled synthesis of Co 3 O 4 nanoparticles on Ni(OH) 2 nanosheet arrays, in which the sample prepared with 2 M NH 3(aq) exhibits superior catalytic performance toward oxygen evolution reaction. [Display omitted] • Ammonia mediated hydrothermal decomposition of Co(NH 3) 6 3+ produces Co 3 O 4 NPs. • Ammonia decides the dissociation of Co(NH 3) 6 3+ to control the growth of Co 3 O 4 NPs. • Moderate dispersion of Co 3 O 4 NPs on Ni(OH) 2 increases active site number for OER. • Electron transfer from Ni(OH) 2 to the Co 3 O 4 phase boosts OER activity of Co 3 O 4 NPs. Co 3 O 4 is a promising electrocatalyst for oxygen evolution reaction (OER), yet its controllable synthesis has been challenging. Herein, a versatile approach is developed to fabricate Co 3 O 4 nanoparticles (NPs) on diverse supports through the hydrothermal treatment of Co(NH 3) 6 3+ with an ammonia mediator. The ammonia is critical as it determines the dissociation kinetics of Co(NH 3) 6 3+, which in turn affects the nucleation and growth processes for kinetically controlling the size and dispersion of Co 3 O 4 NPs. The Co 3 O 4 NPs grown on 3D architectured Ni(OH) 2 nanosheet arrays (Co 3 O 4 @Ni(OH) 2) are applied as the catalysts for OER. Promoting by electron migration from Ni(OH) 2 to Co 3 O 4 to improve the intrinsic activity and the structural merits, the optimal Co 3 O 4 @Ni(OH) 2 exhibits excellent OER performance, showing a competitive η 100 of 399 mV and a small Tafel slope of 60 mV dec−1. This research presents a simple and efficient ammonia-mediated strategy to controllably synthesize Co 3 O 4 on various supports for OER and beyond. [ABSTRACT FROM AUTHOR]

Synergistic heteroatomic doping, morphology engineering and reconstruction strategy of phosphate doped Ni(OH) 2 /FeOOH microtubes to boost OER activity. [Display omitted] • Hierarchical hollow PO x -Ni(OH) 2 /FeOOH with high activity and durability was prepared by reconstruction strategy. • Hierarchical hollow structure is the key for the complete reconstruction of the catalyst during OER process. • The generation of hydroxides/oxyhydroxides is responsible for excellent OER performance. Developing electrocatalysts with remarkable activity and durability is significant for efficient oxygen evolution reaction (OER). Herein, we designed phosphate doped Ni(OH) 2 /FeOOH hierarchical microtubes (denoted as PO x -Ni(OH) 2 /FeOOH HMTs), obtained by phosphate doped NiFe Prussian blue analogue hierarchical microtubes (denoted as P-NF-PBA HMTs) completely reconstructing in OER process. PO x -Ni(OH) 2 /FeOOH HMTs possess an extremely low overpotential of 237 mV at 30 mA cm−2 in alkaline electrolyte with the Tafel slope of 35 mV dec−1, and the catalysts can maintain excellent durability for 100 h at 30 mA cm−2. The remarkable electrochemical catalytic activity comes from the advantages of the hierarchical hollow structure, the modulation of electronic structure caused by phosphate doping, and the synergistic effect of Ni(OH) 2 and FeOOH species produced by catalyst complete reconstruction in the OER process. This work may provide an effective strategy to develop highly efficient and durable electrocatalysts towards OER. [ABSTRACT FROM AUTHOR]

Electrochemical water splitting has excellent application prospects in clean energy technology. However, due to the large overpotential required for the OER reaction during the water-splitting reaction, the modification of electrocatalysts is a vital strategy to address the slow kinetics of the OER reaction. In this paper, a simple and rapid two-step hydrothermal sulfidation method was used to prepare S-modified Ni(OH)2 nanosheets electrocatalysts at 120 °C. At the same time, the well-designed nanostructured catalyst on the nickel foam substrate exposes a large number of active sites, and the simultaneously generated oxygen vacancies are beneficial to the penetration of the electrolyte and release of O2, thus significantly improving the OER performance. In 1.0 M KOH electrolyte, Ni9S8/Ni(OH)2/NF exhibits excellent catalytic activity for OER. The catalyst requires only 430 mV overpotential at a current density of 100 mA cm-2. In addition, Ni9S8/Ni(OH)2/NF also has excellent long-term stability. This work reports the formation of Ni9S8/Ni(OH)2/NF heterojunctions by sulfiding Ni(OH)2 on porous nickel foam. Surprisingly, these Ni9S8/Ni(OH)2/NF heterojunctions exhibit excellent oxygen evolution reaction performance and long-term stability. This is superior to most reported electrocatalysts for oxygen evolution reactions. [ABSTRACT FROM AUTHOR]

We synthesized an electrochemical structurally stable composite electrode, containing Ni‐doped Co(CO3)0.5OH ⋅ 0.11H2O nanoneedles and nanoflake‐/nanofrustum‐like Ni(OH)2 with highly hydrophilic group, leading to enhanced rare performance. The electrode exhibits an outstanding ultra‐long cycle life of more than 140,000 cycles. Specially, the assembled aqueous hybrid supercapacitor presents more than 80 % capacity retention even after 170,000 cycles and high energy density of 44.5 Wh kg−1. This work highlights a feasible strategy to design and develop high‐efficiency electrodes via engineering on composition and nanostructure. [ABSTRACT FROM AUTHOR]

The V doping not only regulates the phase type and degree of crystallization, but also modulates the electronic environment, generates more oxygen vacancies and more catalytic active Ni3+ species, ultimately boosting UOR performance. [Display omitted] Direct urea fuel cell (DUFC) and overall urea splitting system have attracted considerable attention as promising choice for energy conversion. Whereas, the anodic half reaction of electrocatalytic urea oxidation reaction (UOR) in these systems awfully limited their practical application due to the complex 6-electron transfer process. Herein, vanadium doped nickel (V-Ni(OH) 2) with highly efficient electrocatalytic activity toward UOR was developed by a simple coprecipitation method. The introducing of V not only promotes the phase transforming from inactive β-Ni(OH) 2 to highly active α-Ni(OH) 2 , but also simultaneously modulates the electron environment of Ni, facilitating high valence species Ni3+ generation in low overpotential, enhancing the electrocatalytic activity potent of each Ni3+ site and speeding up the electrocatalytic reaction. The optimal V-Ni(OH) 2 catalyst exhibits a summit current density of 241 mA cm−2 at 1.6 V vs. RHE, a Tafel slope of 32.15 mV dec-1, outperforming β-Ni(OH) 2 and most catalysts that tested on glassy carbon electrode. Furthermore, the assembled direct urea hydrogen peroxide fuel cell (DUPFC) offers a maximum power density of 13.4 mW cm−2 at 20 °C. This work provides an example of combing phase-regulation and electron modulation method for effective UOR electrocatalysts design. [ABSTRACT FROM AUTHOR]

Drop–dry deposition (DDD) is a method of depositing thin films by heating and drying the deposition solution dropped on a substrate. We prepared Ni(OH)2 precursor thin films by DDD and annealed them in air to prepare NiO thin films. The appropriate deposition conditions were found by changing the number of drop–dry cycles and the concentrations of chemicals in the solution, and the Ni(OH)2 precursor film with a thickness of 0.3 μm and optical transmittance of more than 95% was successfully deposited. Raman and X-ray diffraction measurements were performed, and it was found that the NiO film was successfully fabricated after annealing at 400 °C. The p-type conductivity of the annealed film was confirmed by photoelectrochemical measurements. In addition, we prepared n-type ZnO by electrochemical deposition on NiO thin films. The current–voltage measurement results show that the ZnO/NiO heterojunction had rectification properties. [ABSTRACT FROM AUTHOR]

Dual co-catalysts have an essential effect on improving the photoelectrochemical (PEC) performance of semiconductor materials. In this study, Ni–Ni(OH) 2 or/and Nikel phosphate (NiPi) nanocrystals co-catalysts were deposited on the surface of as-prepared TiO 2 nanotube arrays (TNTAs) by a simple electrodeposition route for PEC hydrogen production. The TNTAs loading with Ni and NiPi bifunctional co-catalysts exhibited remarkably enhanced PEC performance, with about an 8.3-fold increase in the photocurrent; and an 11.7-fold improvement in H 2 evolution rate in comparison to bare TNTAs. The constructed ternary TNTAs/Ni–Ni(OH) 2 /NiPi comprised the advantage of Ni–Ni(OH) 2 and NiPi nanoparticles to enhance visible-light absorption and promote oxygen evolution reaction (OER) kinetics. The internal electric field is generated between supported p-type Ni(OH) 2 and n-type TiO 2 under light irradiation, which will drive holes to flow to Ni(OH) 2 and oxidize it as the OER active layer. Also, the photo-generated holes remaining in the TiO 2 valence band can migrate to NiPi co-catalysts to cause OER. Therefore, the photogenerated electron-hole pairs can be successfully separated under the synergetic influence of Ni–Ni(OH) 2 and NiPi co-catalyst, leading to a superior PEC water splitting ability. • Dual Ni-based co-catalysts were electrodeposited on TiO 2 nanotube arrays (TNTAs). • Ternary TNTAs/Ni–Ni(OH) 2 /NiPi exhibited higher photocurrent than bare TNTAs. • Both Ni–Ni(OH) 2 and NiPi enhance light absorption and promote the OER of TNTAs. • Ni–Ni(OH) 2 and NiPi have a synergetic effect to improve carrier's separation ability. [ABSTRACT FROM AUTHOR]

Ni-(OH)2 has low production cost and high theoretical specific capacity, while on account of the poor electronic conductivity, it shows inferior electrochemical performance including cycling stability and rate capability. This work focuses on a composite material that is in situ grown Ni-(OH)2 nanosheets on reduced graphene oxide (rGO), and employing the fewer-defect rGO to build a three-dimensional conductive network provides outstanding conductivity. The specific capacitances (Cm) of the Ni-(OH)2/rGO (NHG) electrode are 2776 F·g–1 at 2 A·g–1 and even 1570 F·g–1 at 50 A·g–1, demonstrating remarkable rate capability. It indicates that the combination of the nano grown Ni-(OH)2 and rGO conductive substrate shortens the ion diffusion path and increases the electron transfer rate; hence, the composite rate capability has been significantly improved. The composite materials and active carbon were combined to be an asymmetric supercapacitor, which had a high energy density of 39.24 Wh·kg–1 at 1962 W·kg–1. After 10,000 cycles at 5 A·g–1, the capacity retains 91.4%. [ABSTRACT FROM AUTHOR]

A bifunctional electrocatalyst was fabricated by in-situ vertical growth of Ni(OH) 2 nanosheets on nickel foam (NF), with subsequent accretion of nickel vacancy NiFe-LDHs (NivacFe-LDHs) by two step hydrothermal method. It was exhibited to be a high-efficiency overall water splitting performance with good stability. The low over-potentials of 292, 330, and 376 mV were acquired when the current density was selected as 50, 100, and 200 mA/cm2 for oxygen evolution reaction (OER) with a relatively low Tafel slope. It also achieved low over-potentials of 116 and 247 mV when the current densities were 10 and 200 mA/cm2 for hydrogen evolution reaction (HER), and Tafel slope was estimated to be 95.87 mV/dec. For the overall water splitting, NF–Ni(OH) 2 -NivacFe-LDHs needed only a low overpotential (291 mV) to achieve 25 mA/cm2 in 1 mol/L potassium hydroxide. The long-term testing of this electrode for 24 h chronopotentiometric test at 25 mA/cm2 demonstrated very eminent stability. [Display omitted] • Ni(OH) 2 nanosheets were grown on skeleton of nickel foam. • Nickel Vacancy NiFe-LDHs was accumulated on the surface of Ni(OH) 2. • Require 1.521 V @ 25 mA/cm2 for over water splitting. • The electrode of NF–Ni(OH) 2 - NivacFe-LDHs reveal excellent stability. [ABSTRACT FROM AUTHOR]

Pt group metals display lower HER activity in alkaline solution than in acidic solution, because they are inefficient in the water dissociation step (Volmer step). Compared with Pt, the activity difference of Rh in alkaline and acidic media is much smaller. Meanwhile, Ni(OH) 2 is proved to be an effective catalyst for water dissociation. Therefore, Rh–Ni(OH) 2 /C nanocomposites with different Rh:Ni(OH) 2 ratios were synthesized by a co-deposition/partial reduction method, and their microstructures as well as electrocatalytic properties were studied. The results show that Rh and Ni(OH) 2 display synergistic effect in Rh–Ni(OH) 2 /C nanocomposites. The Rh–Ni(OH) 2 /C nanocomposite with a molar ratio of Rh to Ni(OH) 2 of 1:1 exhibits the highest activity. It shows an overpotential of 36 mV at 10 mA cm−2 and a Tafel slope of 32 mV dec−1 for HER in alkaline media, which is superior to commercial Pt/C. In addition, the Rh–Ni(OH) 2 /C (1:1) nanocomposite shows excellent durability in alkaline media as well. • A set of Rh–Ni(OH) 2 /C nanocomposite catalysts were synthesized by a co-deposition/partial reduction method. • The degree of dispersion of Rh and Ni(OH) 2 nanoparticles on carbon spheres was influenced by Ni(OH) 2 content. • Rh and Ni(OH) 2 display synergistic effect in Rh–Ni(OH) 2 /C nanocomposites in alkaline solution. • The Rh–Ni(OH) 2 /C nanocomposite with a molar ratio of Rh to Ni(OH) 2 of 1:1 exhibits superior HER catalytic activity. • The combined use of Ni(OH) 2 and Rh provides a way of designing low-cost and high efficient HER electrocatalysts. [ABSTRACT FROM AUTHOR]

The hierarchical CuCo2O4-Ni(OH)2 core-shell nanowire arrays on Ni foam were fabricated using facile and cost-effective two-step hydrothermal synthesis. The growth of CuCo2O4 nanowires was developed on Ni foam as the apposite basis of the conductive scaffold, and the ultrathin Ni(OH)2 nanowires were subsequently immobilized to form CuCo2O4-Ni(OH)2 core-shell nanowire arrays (NWAs). The prepared materials were further characterized in structural, morphological, and electrochemical properties. The obtained CuCo2O4-Ni(OH)2 pseudocapacitor electrode, incorporated by unique core-shell heterostructures nanowire arrays, exhibited great specific capacitance of 1201.67 F g-1 at 1 mA g-1, which is much higher than pristine CuCo2O4 nanowire of 638.89 F g-1 at 1 mA g-1. Simultaneously, it also has a high power density of 5.56 kW kg-1 at an energy density of 73.33 Wh kg-1 and good long-term cycling performance (~84 capacitance retention after 1000 cycles). The improved morphological and structural properties have substantiated the CuCo2O4- Ni(OH)2 core-shell nanowire arrays properties owing to higher surface active area and richer redox activity for boosting the electrochemical properties. [ABSTRACT FROM AUTHOR]

A Ni(OH)2 surface was fluorinated at 25 °C using F2 gas for 1 h under absolute pressure of 6.67 kPa. Some fluorides and oxyfluorides were detected only on the Ni(OH)2 particle surface, although most Ni(OH)2 remained inside of the particles. Fluorine-introduced NiO (NiO(F)) was obtained by heating the surface-fluorinated Ni(OH)2. After sintering at 750 °C for 6 h, the NiO(F) crystal size and surface area were, respectively, 0.6 times smaller and 4.7 times larger than those of NiO obtained from untreated Ni(OH)2. LiNiO2 samples were prepared via reaction between NiO(F) and Li2CO3 at 700 °C for 20 h and 30 h, respectively (LiNiO2 (20 h, F) and LiNiO2 (30 h, F)). The density of LiNiO2 (30 h, F) was 4.697, which was larger than the 4.556 of LiNiO2 prepared from NiO and Li2CO3 under the same conditions. The discharge capacity of LiNiO2 (30 h, F) was 202 mAh g−1, whereas the LiNiO2 prepared under the same condition from NiO and Li2CO3 was 172 mAh g−1. The discharge capacity of LiNiO2 as a cathode of LIB might be improved by introducing fluorine to its preparation process between NiO and Li2CO3.

Nano-petal nickel hydroxide was prepared on multilayered modified montmorillonite (M-MMT) using one-step hydrothermal method for the first time. This nano-petal multilayered nanostructure dominated the ion diffusion path to be shorted and the higher charge transport ability, which caused the higher specific capacitance. The results showed that in the three-electrode system, the specific capacitance of the nanocomposite with 4% M-MMT reached 1068 F/g at 1 A/g and the capacity retention rate was 70.2% after 1,000 cycles at 10 A/g, which was much higher than that of pure Ni(OH)2 (824 F/g at 1 A/g), indicating that the Ni(OH)2/M-MMT nanocomposite would be a new type of environmentally friendly energy storage supercapacitor.

• Synthesis of Ni(OH) 2 /graphene nanoplatelets composite under reflux condition. • Ni dispersion on graphene nanoplatelet has been confirmed with TEM analysis. • Ni dispersed over composite facilitates stability and exposure of active sites. • Tafel slope analysis suggests preferential oxidation of urea over OER. In this work, Ni(OH) 2 decorated over graphene nanoplatelets (GNP) synthesised by simple reflux reaction using hydrazine as complexing agent and sodium borohydride as reducing agent. Nickel-graphene platelet (NGP) composites are labelled as NGP-I,II and III for varying Ni-to-GNP ratios. Ni(OH) 2 anchoring on GNP has been confirmed with TEM and EDS analysis. The in situ growth of Ni(OH) 2 on graphene increases the stability and active sites of electrocatalysts for water splitting and direct oxidation of urea. The OER and urea oxidation on NGP-III composite were studied in 1 M KOH electrolyte, exhibiting lower potential of 1.53 V and 1.34 V vs. RHE and Tafel slope of 47 mV dec–1 and 56 mV dec–1, respectively. The negative shift in the oxidation potential of urea suggest that the urea oxidation is preferred over OER. [ABSTRACT FROM AUTHOR]

• Cycle life of the Ni(OH) 2 has been improved by incorporating WC. • WC has been used as a pillaring agent to improve the cycle life, the very first time with Ni(OH) 2. • High specific energy was achieved at ⁓ 67 Wh kg−1 using Ni(OH) 2. • Ni(OH) 2 has been prepared on a large scale using a simple solution co-precipitation process. • Practical viability of the as-prepared composite material is demonstrated by lighting LEDs using hydrogel electrolyte-based pouch cells. This study focuses on synthesizing tungsten carbide incorporated β-Ni(OH) 2 composite as a positive electrode in asymmetric supercapacitor applications. The composite was prepared for different concentrations of WC (5,10, and 15 wt.%). The bare β-Ni(OH) 2 and β-Ni(OH) 2 /WC composites were tested in the three-electrode system using a KOH electrolyte. The characteristics performances were optimized based on the electrochemical performance of the three electrode configurations. The typical lab-scale asymmetric supercapacitor device delivered a maximum specific energy of 66.78 Wh kg−1 at ⁓0.3 A g−1 in a 2 M KOH electrolyte medium. Further, the pouch-type supercapacitor was fabricated using a PVA-KOH hydrogel electrolyte. The pouch cell delivers a specific energy of 18.69 Wh kg−1 at a specific power of 3.282 kW kg−1 at 1 A g−1. The supercapacitor also shows a capacitance retention of 76 % even after 17,000 cycles at 1.25 A g−1. Thus, it is evident that an optimum composition of the β -Ni(OH) 2 / WC(5 wt.%) composite will be an effective positive electrode in an asymmetric supercapacitor for obtaining high specific energy. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] Artificial photoreduction of CO 2 to chemical fuel is an intriguing and reliable strategy to tackle the issues of energy crisis and climate change simultaneously. In the present study, we rationally constructed a Ni(OH) 2 -modified covalent triazine-based framework (CTF-1) composites to serve as cocatalyst ensemble for superior photoreduction of CO 2. In particular, the optimal Ni(OH) 2 -CTF-1 composites (loading ratio at 0.5 wt%) exhibited superior photocatalytic activity, which surpassed the bare CTF-1 by 33 times when irradiated by visible light. The mechanism for the enhancement was systematically investigated based on various instrumental analyses. The origin of the superior activity was attributable to the enhanced CO 2 capture, more robust visible-light response, and improved charge carrier separation/transfer. This study offers an innovative pathway for the fabrication of noble-metal-free cocatalysts on CTF semiconductors and deepens the understanding of photocatalytic CO 2 reduction. [ABSTRACT FROM AUTHOR]

Carbon nanotubes grafted on carbon papers (CP-CNTs) are used as substrates for electrodeposition of Ni-(OH)2 catalysts for the alkaline oxygen evolution reaction (OER). The OER performance measured at 0.7 V (vs Hg/HgO) in 1.0 M KOH results in a fivefold increase in the turnover frequency for Ni-CP-CNT compared to Ni-CP (0.118 vs 0.022 s–1). Moreover, Ni-CP-CNT maintains a high conductivity of 0.431 S cm–2, while that of Ni-CP is low at 0.117 S cm–2. Cyclic voltammetry (CV) and X-ray photoelectron spectroscopy (XPS) analyses confirm the phase reversibility of Ni-(OH)2/NiOOH in Ni-CP-CNT but show irreversible and unstable behavior of Ni-CP. These results demonstrate that the use of CNT-grafted carbon substrates for Ni-(OH)2 helps us to overcome the drawbacks of low conductivity and poor stability and enhances catalytic performance in the alkaline OER. [ABSTRACT FROM AUTHOR]

Nickel hydroxide (Ni(OH)2) is a promising electrocatalyst for the 5‐hydroxymethylfurfural oxidation reaction (HMFOR) and the dehydronated intermediates Ni(OH)O species are proved to be active sites for HMFOR. In this study, Ni(OH)2 is modified by platinum to adjust the electronic structure and the current density of HMFOR improves 8.2 times at the Pt/Ni(OH)2 electrode compared with that on Ni(OH)2 electrode. Operando methods reveal that the introduction of Pt optimized the redox property of Ni(OH)2 and accelerate the formation of Ni(OH)O during the catalytic process. Theoretical studies demonstrate that the enhanced Ni(OH)O formation kinetics originates from the reduced dehydrogenation energy of Ni(OH)2. The product analysis and transition state simulation prove that the Pt also reduces adsorption energy of HMF with optimized adsorption behavior as Pt can act as the adsorption site of HMF. Overall, this work here provides a strategy to design an efficient and universal nickel‐based catalyst for HMF electro‐oxidation, which can also be extended to other Ni‐based catalysts such as Ni(HCO3)2 and NiO. [ABSTRACT FROM AUTHOR]