Amorphous Nickel Hydroxide Research Articles

Surficial Reconstruction of Pt-Ni/NiS and Its Effect on Electrocatalytic Hydrogen Evolution in Alkaline Medium.

Cyclic voltammetry pretreatment of Pt-based electrocatalysts has been proven to be a normal activation process on achieving the optimal alkaline hydrogen evolution performance. Until now, the congruent relationship between the microstructural evolution and performance improvement during this process has rarely been reported. Herein, when the in situ transmission electron microscopy and in situ Raman analyses are employed, a self-reconstruction process from crystalline NiS into amorphous nickel hydroxide hydrate [Ni(OH)2-x·H2O, where x ≈ 0.3] on the surface of platinum-nickel nanowires has first been captured, which is the critical water dissociation active site to offer a sufficient proton supply. Furthermore, such a surficial reconstruction triggers an increase in the current density from -2.3 to -38.8 mA/cm2 (at -70 mV), which is nearly 17 times. These observations point to the fact that it is essential to consider the fundamental mechanisms of hydrogen evolution on the active sites when the process is scaled up.

Amorphous Nickel Hydroxide Shell on Ni8P3 Nanorods for Boosted Highly Stable Overall Water Splitting at High Current.

Developing highly active, highly stable, and cheap electrocatalysts for water splitting is of great significance for hydrogen production. Herein, we report an amorphous Ni(OH)2-clothed transition Ni8P3 catalyst, in which the amorphous Ni(OH)2 shell provides catalytic active sites and serves as a proton conductive encapsulation layer to ensure efficient proton supply to the active Ni8P3 sites. As expected, the Ni8P3@Ni(OH)2 catalyst exhibits significant water decomposition performance at low and high current densities of 10, 100, and 1000 mA cm-2 at 1.45, 1.71, and 2.21 V, respectively, which is comparable to those of commercial electrocatalysts. In particular, the prepared Ni8P3@Ni(OH)2 electrodes possess exceptional long-term durability (200 h) at high current (over 1 A). The significantly improved water-splitting activity and durability in alkaline medium are expected to make them attractive catalyst materials to produce renewable chemical fuels.

Self-Terminated Surface Reconstruction of Lanthanum Nickelates Promotes Alkaline Oxygen Evolution

Oxygen evolution reaction (OER) itself is expected to have a strong impact on the state of the surface of the electrocatalyst, yet the actual structure of the surface under operating conditions is rarely considered while formulating structure-activity correlations in electrocatalysis. In this study, changes in the surface structure of Ruddlesden-Popper-type lanthanum nickelate, La2NiO4+δ, and the perovskite LaNiO3 are probed and contrasted using a series of complementary surface sensitive techniques, including XPS, HRTEM and O K-edge XAS. We found noticeable surface changes to occur on La2NiO4+δ after exposure its exposure to the alkaline electrolyte that is accompanied by the emergence of a strong Nin+/n+1 redox feature and the coincides with a 45-fold enhancement of the OER activity (at η = 370 mV) in 0.1 M KOH, as compared to the pristine La2NiO4+δ phase. We observe that the in situ formation of an amorphous nickel (oxy)hydroxide layer on the surface increases the electrochemically-active surface area of La2NiO4+δ and imparts a high stability of the catalyst under OER conditions (the formation of the amorphous layer self-terminates at ca. 3 nm). In addition, the transition from octahedral Ni sites (O h ) to square-planar Ni sites (D 4h ) in the reconstructed surface was observed using O K-edge X-ray absorption spectroscopy. Further, we found no evidence for any surface transformations in the perovskite-based catalyst LaNiO3 that also did not demonstrate any improvement in its activity over cycling. This work highlights the importance of a detailed surface analysis of the catalysts under operation to build robust structure-activity correlations for the metal oxides under electrochemical reaction conditions. Figure 1

Synergistic enhancement of photocatalytic hydrogen evolution by ultrathin oxygen-doped graphitic carbon nitride nanosheets loaded amorphous mesoporous nickel hydroxide

Graphitic carbon nitride (g-C3N4, CN) is widely utilized in the field of photocatalytic hydrogen production owing to its exceptional visible light absorption, addressing the challenge of energy scarcity. However, its development has been hindered by the issue of low charge separation efficiency. In this study, an ultrathin (∼1.65 nm) oxygen-doped graphitic carbon nitride nanosheets loaded amorphous mesoporous nickel hydroxide (a-Ni(OH)2/OCN) photocatalyst was developed through a straightforward calcination and stirring approach. Under visible light irradiation, a-Ni(OH)2/OCN exhibited a remarkably high photocatalytic hydrogen evolution rate of 4764.9 μmol·h−1 g−1, which is 4.7 times greater than that of the original CN. The synergistic effect between O-doping and heterojunction was proved by experimental data analysis combined with DFT calculations. Totally, the introduction of oxygen into CN led to a reduction in its band gap, while a-Ni(OH)2/OCN heterojunction achieved a broaden light absorption range and an effective charge separation due to a type-Ⅱ internal electric fields.

Amorphous nickel hydroxide shell tailors local chemical environment on platinum surface for alkaline hydrogen evolution reaction.

In analogy to natural enzymes, an elaborated design of catalytic systems with a specifically tailored local chemical environment could substantially improve reaction kinetics, effectively combat catalyst poisoning effect and boost catalyst lifetime under unfavourable reaction conditions. Here we report a unique design of 'Ni(OH)2-clothed Pt-tetrapods' with an amorphous Ni(OH)2 shell as a water dissociation catalyst and a proton conductive encapsulation layer to isolate the Pt core from bulk alkaline electrolyte while ensuring efficient proton supply to the active Pt sites. This design creates a favourable local chemical environment to result in acidic-like hydrogen evolution reaction kinetics with a lowest Tafel slope of 27 mV per decade and a record-high specific activity and mass activity in alkaline electrolyte. The proton conductive Ni(OH)2 shell can also effectively reject impurity ions and retard the Oswald ripening, endowing a high tolerance to solution impurities and exceptional long-term durability that is difficult to achieve in the naked Pt catalysts. The markedly improved hydrogen evolution reaction activity and durability in an alkaline medium promise an attractive catalyst material for alkaline water electrolysers and renewable chemical fuel generation.

Multistep Dissolution of Lamellar Crystals Generates Superthin Amorphous Ni(OH)2 Catalyst for UOR.

Urea oxidation reaction (UOR) is an ideal replacement of the conventional anodic oxygen evolution reaction (OER) for efficient hydrogen production due to the favorable thermodynamics. However, the UOR activity is severely limited by the high oxidation potential of Ni-based catalysts to form Ni3+ , which is considered as the active site for UOR. Herein, by using in-situ cryoTEM, cryo-electron tomography, and in-situ Raman, combined with theoretical calculations, we report a multistep dissolution process of nickel molybdate hydrate, whereby NiMoO4 ·xH2 O nanosheets exfoliate from the bulk NiMoO4 ·H2 O nanorods due to the dissolution of Mo species and crystalline water, and further dissolution results in superthin and amorphous nickel (II) hydroxide (ANH) flocculus catalyst. Owing to the superthin and amorphous structure, the ANH catalyst can be oxidized to NiOOH at a much lower potential than conventional Ni(OH)2 and finally exhibits more than an order of magnitude higher current density (640mA cm-2 ), 30 times higher mass activity, 27 times higher TOF than those of Ni(OH)2 catalyst. The multistep dissolution mechanism provides an effective methodology for the preparation of highly active amorphous catalysts. This article is protected by copyright. All rights reserved.

Coupling Amorphous Ni Hydroxide Nanoparticles with Single-Atom Rh on Cu Nanowire Arrays for Highly Efficient Alkaline Seawater Electrolysis.

Exploring efficient catalysts for alkaline seawater electrolysis is highly desired yet challenging. Herein, coupling single-atom rhodium with amorphous nickel hydroxide nanoparticles on copper nanowire arrays is designed as a new active catalyst for the highly efficient alkaline seawater electrolysis. We found that an amorphous Ni(OH)2 nanoparticle is an effective catalyst to accelerate the water dissociation step. In contrast, the single-atom rhodium is an active site for adsorbed hydrogen recombination to generate H2. The NiRh-Cu NA/CF catalyst shows superior electrocatalytic activity toward HER, surpassing a benchmark Pt@C. In detail, the NiRh-Cu NA/CF catalyst exhibits HER overpotentials as low as 12 and 21 mV with a current density of 10 mA cm-2 in fresh water and seawater, respectively. At high current density, the NiRh-Cu NA/CF catalyst also exhibits an outstanding performance, where 300 mA cm-2 can be obtained at an overpotential of 155 mV and shows a slight fluctuation in the current density over 30 h.

Operando leaching of pre-incorporated Al and mechanism in transition-metal hybrids on carbon substrates for enhanced charge storage

Operando leaching of pre-incorporated Al and mechanism in transition-metal hybrids on carbon substrates for enhanced charge storage

Study on the Treatment of Nickel-Contaminated Soil Using Calcium Oxide

Nickel-contaminated soil was treated by adding different amounts of calcium oxide in this study. The leaching concentration, pH, and bioavailability of the soil samples were investigated on the 3rd, 6th, 9th, 12th, and 15th days. The chemical speciation changes of the contaminated soil treated with calcium oxide were analyzed, and the soil phases were analyzed by X-ray diffraction (XRD). Results showed that the application of calcium oxide increased the pH of the soil, resulting in passivation of nickel ions in soil by forming a poorly soluble precipitate. It was identified that addition of 5% of calcium oxide showed the best result, with the leaching concentration on the third day reaching 0.35 mg/L, which is 99.21% lower than the untreated soil’s leaching concentration of 44.24 mg/L. On the 15th day, the bioavailability of nickel decreased from the untreated soil’s 93.82 to 36.73%. It was also observed that the pH of the soil increased at the beginning and decreased afterwards. The pH value was 7.94 on the 15th day. In addition, the water-soluble fraction of Ni decreased from 7.39 without treatment to 0.19%; the reducible fraction of Ni decreased from 35.14 to 25.79%, and the oxidizable fraction of Ni increased from 10.37 to 29.10%, respectively, on the 15th day after the treatment with calcium oxide. XRD analysis of soil samples showed the amorphous nickel hydroxide may be formed in the precipitation process.

Aqueous substitution synthesis of platinum modified amorphous nickel hydroxide on nickel foam composite electrode for efficient and stable hydrogen evolution

Exploring highly active and stable electrocatalysts toward hydrogen evolution reaction (HER) is vital for the production of green energy and storage of intermittently renewable electrical energy. In this study, we fabricate Pt-modified Ni(OH)2 on 3D nickel foam (Pt content: 1.5 wt %) via a one-step galvanic replacement reaction in aqueous solution to achieve a top performance of HER under alkaline conditions. It exhibits a negligible onset potential, a Tafel slope of 17 mV dec−1, and overpotentials of 38, 114, and 203 mV to deliver 10, 50, and 100 mA cm−2 current densities, respectively, which outperforms the commercial Pt/C and Pt sheet. Moreover, this catalyst shows enhanced durability towards HER, sustaining electrolysis at −20 mA cm−2 for 4, 500 min in 1 M KOH with little degradation. Its good performances come from the synergism of flake-like Pt and amorphous Ni(OH)2. This work provides not only a facile and easy scale-up approach to fabricate Pt−modified electrocatalysts with improved HER performance but also a new strategy to design self-supported high-performance hybrid materials of noble-metal and amorphous transitional metal hydroxides for sustainable energy conversion and storage.

Nitrogen treatment generates tunable nanohybridization of Ni5P4 nanosheets with nickel hydr(oxy)oxides for efficient hydrogen production in alkaline, seawater and acidic media

Hybrid engineering of electrocatalysts is still very challenging for electrochemical water splitting. Ni5P4 is a promising electrocatalyst for hydrogen evolution reaction (HER) but the formation of phosphide-hydrogen on Ni5P4 (P-Hads) bonds usually weakens the HER activity. Herein, we report a simple nitrogen treatment strategy to controllably hybridize Ni5P4 porous nanosheets with amorphous nickel hydr(oxy)oxide [Ni2+δOδ(OH)2−δ] layer and utilize as efficient electrocatalyst for hydrogen evolution reaction (HER) in neutral (real seawater), alkaline and acidic media. The in situ derived Ni5P4@Ni2+δOδ(OH)2−δ hybrid nanosheets can be obtained by annealing the nickel hydroxide-precursor nanosheets coupled with decomposition of NaH2PO2·H2O in nitrogen atmosphere. Benefiting from the thin amorphous Ni2+δOδ(OH)2−δ coated layer, the optimized Ni5P4@Ni2+δOδ(OH)2−δ with 3 nm amorphous layer achieve a current density of 10 mA cm−2 at low overpotential of 87, 144 and 66 mV in alkaline, seawater and acidic media, respectively. Theoretical and experimental analyses show that the hybridization of Ni5P4 and Ni2+δOδ(OH)2−δ could not only serve as protection to further enhance the electrocatalytic properties and high surface area of the hybrid electrocatalyst but also create good electronic interaction and synergistic properties for suppressing P-Hads bonds, which is beneficial for promoting water adsorption and optimizing the free energy of hydrogen adsorption for triggering the catalytic pathway at all pH range. This work offers new insights for facile designing of non-precious transition metal compound hybrids for HER with enhancing electrocatalytic performance and opens a promising pathway for hydrogen production at all-pH range.

Oxygen evolution NiOOH catalyst assisted V2O5@BiVO4 inverse opal hetero-structure for solar water oxidation

Using vanadium oxide (V2O5) inverse opal (IO) as a three-dimensional (3D) electron transporting tunnel, bismuth vanadate (BiVO4) as a light harvester, and Amorphous Nickel Hydroxide (NiOOH) as an oxygen evolution co-catalyst, a V2O5@BiVO4@NiOOH IO architecture was fabricated as an efficient photoanode on a conductive fluorine doped tin oxide (FTO) substrate for photoelectrochemical (PEC) water oxidation. V2O5 is the visible light absorbing photoanodes for water oxidation; however, the efficiency of this compound remains low (∼0.08 mA/cm2 at 1.23 V vs. reversible hydrogen electrode (VRHE)) and the unfavorable surface trap states limits the activity of V2O5 photoelectrodes in a PEC system. We found that the photoactive thin conductive BiVO4 (∼12 nm) in the V2O5 IO greatly enhanced the charge separation efficiency to achieve better PEC water oxidation through modification of the surface states. The subsequent addition of NiOOH as an effective Oxygen evolution catalyst subsequently reduces the large overpotential and generates the photocurrent density of 1.14 mA/cm2 at 1.23 VRHE. Electrochemical impedance spectroscopy (EIS) evidenced that NiOOH deposition can substantially lower the charge transfer resistance (Rct) at the semiconductor interface. Specifically, the consecutive and ordered morphology renders direct conduction pathways for the extraction of photogenerated electron/hole pairs and the convenient structure to penetrate the photogenerated carriers toward the semiconductor surface over the electrolyte. It is expected that the uninterrupted pathways will improve the electron transportation and thus the charge collection properties.

Operando Spectroscopic Identification of Active Sites in NiFe Prussian Blue Analogues as Electrocatalysts: Activation of Oxygen Atoms for Oxygen Evolution Reaction.

Developing highly efficient oxygen evolution reaction (OER) catalysts and understanding their activity are pivotal for electrochemical conversion technologies. Here, we report NiFe Prussian blue analogue (PBA) as a promising electrocatalyst for OER in alkaline conditions. This material has an impressively low overpotential of 258 mV that reaches a current density of 10 mA cm-2. Post-mortem characterization showed that the as-prepared catalyst is entirely transformed into amorphous nickel hydroxide after the electrochemical treatment, and Ni(OH)2 acts as the active species. Operando X-ray spectroscopic studies further found that this in situ generated Ni(OH)2 displays an unique feature that allows deprotonation under applied potential creating NiOOH2- x that contains Ni4+ ions. The deprotonation reaction is reversible and potential-dependent, i.e., the amount of Ni4+ increases with increasing applied potential. Theoretical calculations were used to show that the role of Ni4+ is to trigger oxidized oxygen ions as electrophilic centers with the subsequent activation of anion redox reactions for OER.

Anion insertion enhanced electrodeposition of robust metal hydroxide/oxide electrodes for oxygen evolution

Electrochemical deposition is a facile strategy to prepare functional materials but suffers from limitation in thin films and uncontrollable interface engineering. Here we report a universal electrosynthesis of metal hydroxides/oxides on varied substrates via reduction of oxyacid anions. On graphitic substrates, we find that the insertion of nitrate ion in graphene layers significantly enhances the electrodeposit–support interface, resulting in high mass loading and super hydrophilic/aerophobic properties. For the electrocatalytic oxygen evolution reaction, the nanocrystalline cerium dioxide and amorphous nickel hydroxide co-electrodeposited on graphite exhibits low overpotential (177 mV@10 mA cm−2) and sustains long-term durability (over 300 h) at a large current density of 1000 mA cm−2. In situ Raman and operando X-ray diffraction unravel that the integration of cerium promotes the formation of electrocatalytically active gamma-phase nickel oxyhydroxide with exposed (003) facets. Therefore, combining anion intercalation with cathodic electrodeposition allows building robust electrodes with high electrochemical performance.

A Stable and Electrocatalytic Iron Electrode for Oxygen Evolution in Alkaline Water Electrolysis

Iron electrodes disintegrate in alkali at the anodic potentials needed for oxygen evolution. Hence, relatively expensive nickel-based electrodes and substrates have been the workhorse of materials for industrial water electrolysis. We report here a novel surface-modification method that transforms iron into an electrocatalytically-active and robust oxygen evolution electrode for alkaline water electrolysis. This surface modification consists of an electrochemical oxidation step followed by a thermal decomposition step. The electrochemical oxidation of the iron substrate in alkali transformed the surface to high surface area iron(II) hydroxide with a coral-like morphology that converted to magnetite upon heat treatment. On this high-surface area substrate an electrocatalytic layer of amorphous nickel hydroxide was produced by the thermal decomposition step. Such a surface-modified iron electrode exhibited an extremely low overpotential of 195 mV at 10 mA/cm2 and a low Tafel slope of 43 mV/decade. The electrochemical oxidation step during preparation results in doubling of the electrochemically active area. Even after 1500 h of oxygen evolution at 10 mA/cm2, there was no noticeable change in the electrode potential, morphology, or surface composition of these iron electrodes. This durability was attributed to the conductive oxide layer of magnetite that protects iron surface at the anodic potentials of oxygen evolution. The remarkable electrocatalytic activity was attributed to the amorphous layer of nickel hydroxide. Development of such a robust and electrochemically-active iron electrode presents a unique opportunity for the advancement of alkaline water electrolysis.

Copper (0) Doping Makes Cobalt-Nickel Hydroxide a High-Efficiency Catalyst for Hydrogen Evolution Reaction

The improvement catalytic performance of nickel-cobalt-based catalysts for hydrogen evolution reaction (HER) is still challenging. In this work, the three dimensional metallic copper doped amorphous cobalt nickel hydroxide (Cu(0)-CoNi-OH) composite was deposited on nickel foam (NF) via a facile cyclic voltammetry method, and the doping effect of metal Cu on cobalt nickel hydroxide composite in Cu(0)-CoNi-OH for HER was studied systematically. It is found that the optimal as-prepared Cu(0)-CoNi-OH/NF electrode exhibits extraordinarily electrocatalytic activity for HER and it only requires an overpotential of 47 mV to reach a benchmark HER current density of 10 mA cm−2 in 1.0 M KOH. The prepared Cu(0)-CoNi-OH/NF electrode also exhibits extraordinary stability and fast reaction kinetics with a small Tafel slope of 48 mV dec−1. The excellent activity is attributed to the unique metal/hydroxide interfaces and the increased electrochemical activity surface area after Cu doping.

The properties investigation of the faradaic supercapacitor electrode formed on foamed nickel substrate with polyvinyl alcohol using

The electrode materials for positive electrodes of hybrid supercapacitors were deposited on the nickel foam substrate using cathodic template method. It has been demonstrated that prepared materials are composed of polyvinyl alcohol and X-ray amorphous α-like nickel hydroxide with a large number of lattice defects, that have a flat morphology with a grid of cracks. The optimal deposition times were found to be 10 and 20 minutes. It has also been demonstrated that the greatest effect on the capacity of nickel foam substrates was caused by the treatment itself and to not by its duration or polarization with the cathodic current. It has been demonstrated that with such deposition method, the resulting capacity is constituted by two components – the capacity of PVA-Ni(OH) 2 composite material and capacity of the nickel foam substrate. The maximum specific capacity obtained at a current density of 320 mA/cm 2 is 2.26 F/cm 2 . The maximum substrate capacity was achieved after treatment with KNO 3 solution for 10 minutes and is 1.58 F/cm 2 at a current density of 160 mA/cm 2

Amorphous Nickel Hydroxide Nanosheets with Ultrahigh Activity and Super-Long-Term Cycle Stability as Advanced Water Oxidation Catalysts

Good conductivity is conventionally considered as a typical reference standard in terms of selecting water electrolysis catalysts. Electrocatalyst research so far has focused on crystal rather than amorphous due to poor conductivity. Here, we demonstrate that the amorphous electrocatalyst made of 3D honeycomb-like amorphous nickel hydroxide (Ni(OH)2) nanosheets synthesized by a simple, facile, green, and low-cost electrochemistry technique possesses ultrahigh activity and super-long-term cycle stability in the oxygen evolution reaction (OER). The amorphous Ni(OH)2 affords a current density of 10 mA cm–2 at an overpotential of a mere 0.344 V and a small Tafel slope of 46 mV/dec, while no deactivation is detected in the CV cycles even up to 5000 times. We also establish that the short-range order, i.e., nanophase, of amorphous creates a lot of active sites for OER, which can greatly promote the electrochemical performance of amorphous catalysts. These findings show that the conventional understanding of sel...

Facile synthesis of amorphous Ni(OH)2 for high-performance supercapacitors via electrochemical assembly in a reverse micelle

The specific and unique amorphous nickel hydroxide nanostructures were synthesized via a simple and straightforward electrochemical way. By simply tuning the soft templates and applying a suitable current density, a specific and unique microstructure is obtained. The diameter of the Ni(OH)2 nano-sphere is greatly influenced by the current density, the sample obtained at 1 mA•cm−2 is about 200nm while the size of that assembled at 6 mA•cm−2 is less than 20nm. However, the Ni(OH)2 film prepared at the current density of 2 mA•cm−2 showed the best electrochemical performance for the highly porous surface morphology which contributed to the uniform morphology obtained at this current density. The maximum specific capacitance can be achieved as high as 1460F•g−1 in 2M NaOH at the scan rate of 2mV•s−1. Such impressive electrochemical properties can be ascribed to the highly porous microstructures and disorder of the amorphous phase which was considered for the better accommodation of repeated volume changes associated with doping-undoping process. The high specific capacitance and remarkable rate capability of amorphous transition metal oxides nanostructures show broad prospect for potential applications in energy conversion and storage devices.

Ternary Hybrids of Amorphous Nickel Hydroxide–Carbon Nanotube‐Conducting Polymer for Supercapacitors with High Energy Density, Excellent Rate Capability, and Long Cycle Life

The utilization of Ni(OH)2 as a pseudocapacitive material for high performance supercapacitors is hindered by its low electrical conductivity and short cycle life. A coaxial ternary hybrid material comprising of amorphous Ni(OH)2 deposited on multiwalled carbon nanotubes wrapped with conductive polymer (poly (3,4‐ethylenedioxythiophene)‐poly(styrenesulfonate)) is demonstrated. A thin layer of disordered amorphous Ni(OH)2 is deposited by an effective “coordinating etching and precipitating” method, resulting in an ultrahigh specific capacitance of 3262 F g−1 at 5 mV s−1 and excellent rate capability (71.9% capacitance retention at 100 mV s−1). More importantly, the polymer layer prevents the degradation of the nanostructure and dis­solution of Ni ion during repeated charge–discharge cycling for 30 000 cycles, a phenomenon which often plagues Ni(OH)2 nanomaterials. Using the ternary Ni(OH)2 hybrid and the reduced graphene oxide/carbon nanotube hybrid as the positive and negative electrodes, respectively, the assembled asymmetric supercapacitors exhibit high energy density of 58.5 W h kg−1 at the power density of 780 W kg−1 as well as long cycle life (86% capacitance retention after 30 000 cycles). The ternary hybrid architecture design for amorphous Ni(OH)2 can be regarded as a general approach to obtain pseudocapacitive materials for supercapacitors with both high energy density, excellent rate capability, and long cycle life.