Transition Metal Hydroxides Research Articles

CTAB improves the performance of NiMoO4@NF grown NiCoZn-LDH for supercapacitor

Transition metal hydroxides have attracted wide attention as promising composite nanomaterials due to their numerous active sites and large specific surface areas. In this study, a two-step hydrothermal synthesis method is proposed to generate a heterostructure (NiCoZn-LDH@NiMoO4@NF) consisting of nanoflowers coated with nanoneedles on a foam nickel substrate. The aggregation issue of NiCoZn-LDH is effectively improved by immersing it in CTAB solution after one-step hydrothermal synthesis of NiMoO4 nanoneedles on Ni Foam (NF). The heterostructure between NiMoO4 nanoneedles and NiCoZn-LDH significantly enhances the material stability and electrochemical performance. Activated carbon is used as the negative electrode, and the NiCoZn-LDH@NiMoO4@NF composite material is used as the positive electrode to assemble an asymmetric supercapacitor (ASC) device for electrochemical testing. The device exhibits a specific capacitance of 3541 mF/cm2 at a current density of 6 mA/cm2. Furthermore, the capacity retention rate remains at 83.04 % after 10,000 cycles of charge and discharge, and a high specific energy density of 0.735 mWh/cm2 is achieved at a power density of 1.6 mW/cm2. The experimental results demonstrate that transition metal hydroxides play a crucial role in enhancing the electrochemical performance of supercapacitors. This study provides new insights into Supercapacitor (SC) active materials and offers a promising experimental approach for synthesizing new nanomaterials.

Cooperative Fe sites on transition metal (oxy)hydroxides drive high oxygen evolution activity in base

Fe-containing transition-metal (oxy)hydroxides are highly active oxygen-evolution reaction (OER) electrocatalysts in alkaline media and ubiquitously form across many materials systems. The complexity and dynamics of the Fe sites within the (oxy)hydroxide have slowed understanding of how and where the Fe-based active sites form—information critical for designing catalysts and electrolytes with higher activity and stability. We show that where/how Fe species in the electrolyte incorporate into host Ni or Co (oxy)hydroxides depends on the electrochemical history and structural properties of the host material. Substantially less Fe is incorporated from Fe-spiked electrolyte into Ni (oxy)hydroxide at anodic potentials, past the nominally Ni2+/3+ redox wave, compared to during potential cycling. The Fe adsorbed under constant anodic potentials leads to impressively high per-Fe OER turn-over frequency (TOFFe) of ~40 s−1 at 350 mV overpotential which we attribute to under-coordinated “surface” Fe. By systematically controlling the concentration of surface Fe, we find TOFFe increases linearly with the Fe concentration. This suggests a changing OER mechanism with increased Fe concentration, consistent with a mechanism involving cooperative Fe sites in FeOx clusters.

Magnetic field-assisted microbial corrosion construction iron sulfides incorporated nickel-iron hydroxide towards efficient oxygen evolution

Nickel iron (hydroxyl) hydroxide with unique layered structure and controllable composition is widely regarded as typical oxygen evolution reaction (OER) catalysts. Recently, developing top-down approaches to realize the facile preparation of transition metal hydroxide catalyst has received wide attention. Based on the natural microorganism corrosion behavior, this work demonstrates the external magnetic field-assisted microbial corrosion strategy to construct advanced transition metal hydroxide OER catalyst, and the prepared biofilm electrode presents superior OER performance in the existence of magnetic field, which needs an overpotential of 287 ​mV at 100 ​mA ​cm−2. Experimental and theoretical calculations show the applied magnetic field can accelerate sulfate reducing bacteria (SRB) corrosion and chemical corrosion. The additional magnetic field can promote SRB corrosion to produce FeS, which can facilitate the optimization of O intermediate desorption from the NiOOH catalyst during OER process, reducing the reaction energy barrier for O→OOH. The synergistic effect between the nickel-iron oxyhydroxides originated from the accelerated chemical corrosion and FeS produced from the accelerated SRB corrosion interprets the improved OER activity. This work explores the influence of magnetic field on the construction of advanced OER materials, which can provide an effective magnetic field-assisted corrosion engineering strategy, and promote the development of multidisciplinary fields of physics, biology, and emerging energy conversion technologies.

Research Progress on Metal–Organic Framework-Based Electrode Materials for Supercapacitors

Supercapacitors play an important role in power systems since they are a key part of electrochemical energy storage devices. To assemble high-performance supercapacitors, it is crucial to discover and innovate high-capacitive electrode materials. Recently, metal–organic frameworks (MOFs) and their derivatives have received wide concerns as electrode materials for supercapacitors, not only because of their high pore volume and large surface area for ions and electrons insertion and transportation, but also due to the intrinsic metal active sites that possibly offer extra faradaic pseudocapacitance. Additionally, the abundant species of MOFs with various morphologies also feature advantages in enriching the structural diversity of electrodes. In this paper, we first report the latest research progress and demonstrate the feasibility of pure MOFs for directly constructing supercapacitor electrodes. Furthermore, different MOF derivatives, including porous carbons, transition metal oxides, metal hydroxides and MOF composites for supercapacitors, are summarized, and their electrochemical performances with corresponding energy storage mechanisms are presented in detail. Finally, the perspectives for MOF-based materials applied in supercapacitors are discussed, aiming to provide a guideline for further research based on these promising materials.

Development of a lead-free, high-frequency ultrasound transducer with broad bandwidth and enhanced pulse-echo response, employing β-Ni(OH)2/PVDF-TrFE piezoelectric composite

Piezoelectric composite-based high-frequency ultrasound transducers (USTs) have gained significant prominence as a leading and effective tool in non-invasive medical diagnosis, non-destructive testing and diverse industrial applications. In this study, we present the fabrication of a lead-free, high-frequency ultrasound transducer (P-UST), having a very simple and unique assembly procedure. To achieve this, we employed PVDF-TrFE based piezoelectric composite thin film (NTr5) integrated with a transition metal hydroxide (β-Ni(OH)2 nanoplates) and demonstrated its outstanding performance, thereby showcasing its potential in various applications. The composite exhibited exceptional β-phase crystallization, reaching impressive maximum value of 90.04%, owing to the favorable interaction between electrostatic ions and dipoles, along with the presence of strong surface polarization. Upon analysis, remarkable piezoelectric (d33∼50.22 pm/V) and ferroelectric properties were observed in the composite material, accompanied by significant enhancement in surface roughness. Here, the piezoelectric property's impact on UST output is well-explained using Maxwell's equation. P-UST, being a versatile system, is capable of generating and receiving pulse signals. By conducting a pulse-echo test on an aluminium block with ultrasound gel, we achieved a peak-to-peak output voltage of 5.19 V, surpassing the output voltage magnitude of any previously reported UST in this field. The Fast Fourier transformed data of the voltage output revealed an impressive −6 dB bandwidth of 51.22 MHz (102.4%) with a high central frequency of 50.01 MHz. Hence, our P-UST's exceptionally high central frequency promises significantly enhanced ultrasound image resolution, which expands the potential for highly accurate medical assessments for advanced healthcare outcomes and improving patient well-being.

Metal Chalcogenide-Hydroxide Hybrids as an Emerging Family of Two-Dimensional Heterolayered Materials: An Early Review.

Two-dimensional (2D) materials and phenomena attract huge attention in modern science. Herein, we introduce a family of layered materials inspired by the minerals valleriite and tochilinite, which are composed of alternating "incompatible", and often incommensurate, quasi-atomic sheets of transition metal chalcogenide (sulfides and selenides of Fe, Fe-Cu and other metals) and hydroxide of Mg, Al, Fe, Li, etc., stacked via electrostatic interaction rather than van der Waals forces. We survey the data available on the composition and structure of the layered minerals, laboratory syntheses of such materials and the effect of reaction conditions on the phase purity, morphology and composition of the products. The spectroscopic results (Mössbauer, X-ray photoelectron, X-ray absorption, Raman, UV-vis, etc.), physical (electron, magnetic, optical and some others) characteristics, a specificity of thermal behavior of the materials are discussed. The family of superconductors (FeSe)·(Li,Fe)(OH) having a similar layered structure is briefly considered too. Finally, promising research directions and applications of the valleriite-type substances as a new class of prospective multifunctional 2D materials are outlined.

Clusters of Fe–Co–Cd nanosheets grow on the surface of nickel foam to enhance the oxygen evolution reaction

To enhance the efficiency of water electrolysis for hydrogen energy production, it is essential to synthesize oxygen evolution reaction (OER) catalysts that are both high-performing and low-cost. In this study, a self-supporting electrocatalyst denoted as was synthesized using the hydrothermal method by growing trimetallic nanosheets FeCoCd@C in situ on nickel foam. This electrocatalyst is composed of transition metal hydroxides and carbon materials, which exhibit a specific interaction between them. The electrocatalyst demonstrates outstanding OER performance, achieving a current density of 10 mA cm−2 in a 1.0 M KOH electrolyte with only 216 mV overpotential and a Tafel slope of 75.86 mV dec−1. Furthermore, carbon materials can prevent direct contact between the electrolyte and transition metal hydroxide, effectively impeding electrocatalyst corrosion, and providing long-term stability. Additionally, a comprehensive analysis of the physical and chemical properties of the composite catalyst was carried out to elucidate its mechanism of action. This study confirms that the combination of transition metal hydroxides and carbon materials can effectively enhance the catalytic activity of electrocatalysts, providing a clear direction for the development of composite OER catalysts.

Simultaneous Single Crystal Growth and Segregation of Ni-Rich Cathode Enabled by Nanoscale Phase Separation for Advanced Lithium-Ion Batteries

A novel nanoscale phase separation process has been discovered to promote the growth and segregation of single-crystal LiNi0.8Mn0.1Co0.1O2 (NMC811). This process occurs directly during high-temperature calcination without significant agglomeration. The key lies in converting transition metal hydroxide (TM(OH)2) precursors with well-controlled morphology into transition metal oxide (TMO) intermediates before reacting them with lithium salt. The nanoscale redistribution of Ni in TMO, resulting from the concurrent formation of spinel and rock salt phases, helps to deagglomerate the clusters of later-formed NMC811 crystals. The as-prepared single-crystal NMC811 is further validated in a 2Ah pouch cell, demonstrating 1,000 stable cycles. The fundamentally new reaction mechanism of single-crystal growth and segregation provides a new direction for large-scale synthesis of a broad range of single crystals for advanced energy storage.

Cobalt hydroxide supported nickel nanoparticles for an efficient electrocatalytic urea oxidation reaction

An efficient electrochemical urea oxidation reaction (UOR) could be used in energy production technology. Metallic nickel nano-particles (Ni NPs) are incorporated in cobalt hydroxide layered material to form Ni/Co(OH)2. The synthesized material is utilized as an electrocatalyst in UOR. It has been revealed that the incorporation of Ni NPs into cobalt hydroxide significantly enhances their electrocatalytic activity toward UOR. Ni/Co(OH)2 catalyzes UOR at a very low anodic potential of 1.15 V vs RHE with a peak current density of 14.2 mAcm−2 and Tafel slope of 75 mVdec−1. The current work is a step ahead towards use of transition metal hydroxide (TMH) as support in the electrocatalytic oxidation applications especially UOR.

Effect of Microwave Synthesis Conditions on the Structure of Nickel Hydroxide Nanosheets.

A protocol for rapid, microwave-assisted hydrothermal synthesis of nickel hydroxide nanosheets under mildly acidic conditions is presented, and the effect of reaction temperature and time on the material's structure is examined. All reaction conditions studied result in aggregates of layered α-Ni(OH)2 nanosheets. The reaction temperature and time strongly influence the structure of the material and product yield. Synthesizing α-Ni(OH)2 at higher temperatures increases the reaction yield, lowers the interlayer spacing, increases crystalline domain size, shifts the frequencies of interlayer anion vibrational modes, and lowers the pore diameter. Longer reaction times increase reaction yields and result in similar crystalline domain sizes. Monitoring the reaction pressure in situ shows that higher pressures are obtained at higher reaction temperatures. This microwave-assisted synthesis route provides a rapid, high-throughput, scalable process that can be applied to the synthesis and production of a variety of transition metal hydroxides used for numerous energy storage, catalysis, sensor, and other applications.

Elucidating the Geometric Active Sites for Oxygen Evolution Reaction on Crystalline Iron-Substituted Cobalt Hydroxide Nanoplates.

Transition-metal (oxy)hydroxides are among the most active and studied catalysts for the oxygen evolution reaction in alkaline electrolytes. However, the geometric distribution of active sites is still elusive. Here, using the well-defined crystalline iron-substituted cobalt hydroxide as a model catalyst, we reported the scanning electrochemical cell microscopy (SECCM) study of single-crystalline nanoplates, where the oxygen evolution reaction at individual nanoplates was isolated and evaluated independently. With integrated prior- and post-SECCM scanning electron microscopy of the catalyst morphology, correlated structure-activity information of individual electrocatalysts was obtained. Our result reveals that while the active sites are largely located at the edges of the pristine Co(OH)2 nanoplates, the Fe lattice incorporation significantly promotes the basal plane activities. Our approach of correlative imaging provides new insights into the effect of iron incorporation on active site distribution across nano-electrocatalysts.

Synthesis, structure and canted antiferromagnetism of layered cobalt hydroxide sorbate

Layered hybrid organic–inorganic compounds of the transition metal hydroxides, in which part of the hydroxide ions are exchanged for organic ligands that act as spacers of the 2-dimensional inorganic layers, elicit new or enhanced properties. The interlayer ligands enable fine-tuning of the physicochemical properties of the metal hydroxide layers, including their magnetism. Specifically, within the Co(OH)2 family of transition ion hydroxides, this approach has been leveraged to stabilize antiferromagnetic and ferrimagnetic ground states for pillared and layered complexes, respectively. Here, we further investigate the effects of changing dimensionality, local Co coordination, and interlayer spacing on the magnetic ground state of brucite-like β-Co(OH) layered complexes. We report the hydrothermal synthesis of a new crystalline material, Co(OH)(sorb), where the inorganic layers are spaced by monotopic, doubly unsaturated sorbate ligands (sorb = [C6H7O2]−). The material was structurally characterized using powder X-ray and neutron diffraction measurements and the crystal structure was solved ab initio from powder diffraction data and refined using the Rietveld method. The magnetic susceptibility and magnetization measurements reveal canted antiferromagnetic ordering with TN = 41.7 K. This report augments our understanding of tuning magnetism through dimensionality in layered complexes and represents a step forward in the design of new 2D layered hybrid compounds.

Real-time observation of phase transition from layered to spinel phase under electron beam irradiation

Transition metal hydroxides (TM(OH)2) have drawn significant attention for their potential applications in the environmental and energy field. In this study, we investigated the phase transition of cobalt hydroxide (Co(OH)2) under electron beam irradiation using in situ high-resolution transmission electron microscopy. Both the α- and β-Co(OH)2 phases underwent a phase transition to a spinel Co3O4 phase, forming nanograins with a porous morphology. However, the α-Co(OH)2 showed a faster phase transition and dramatic volume shrinkage during the phase transition. Our results provide a detailed explanation of the mechanism behind the deterioration of the layered structure and the emergence of defects during the phase transition.

Co(OH)2 nanoneedles grown on Cu/NF current collector with high areal capacitance for supercapacitors

Despite the demand for high energy-density supercapacitors has been realized when transition metal hydroxides are used as electrode materials, the ion diffusion dynamics are still limited by its high impedance. In this work, Cu is deposited on nickel foam (NF) by filtered cathodic vacuum arc (FCVA) technology to serve as an ion-diffusion-favored surface state. Co(OH)2 synthesized hydrothermally on this Cu/NF exhibits remarkably enhanced electrochemical properties compared with Co(OH)2 grown on pristine NF. The resultant electrode can deliver a large area capacity of 0.772 C cm−2 at 1 mA cm−2 and retain 80.92% of initial capacitance after 4000 cycles. Moreover, an assembled asymmetric supercapacitor shows a high energy density of 0.086 mW cm−2 at 0.4 mWh cm−2 with a long lifespan (80.67% retention after 3000 cycles). Our strategy may provide a new insight to prepare electrodes for assembling high areal capacitance supercapacitors.

A Liquid and Waste-free Method for Preparing Single Crystal Positive Electrode Materials for Li-ion Batteries

Nickel-rich layered positive electrode materials are normally made by a “co-precipitation-sintering” method. Mixed transition metal hydroxides called “precursors” are prepared by co-precipitation to ensure homogeneous cation mixing at the atomic level and to create spherical particles which ensure high-performance poly-crystalline materials. Single crystal materials, which show better capacity retention in long-term cycling can be made from the same mixed transition metal hydroxide precursors by sintering at a higher temperature which inevitably destroys the spherical morphology present in the initial precursors. Here we describe a method for single crystal positive electrode material production which we call “all-dry synthesis” since it does not require the use of any liquid and creates no waste unlike the co-precipitation method. The exemplary reaction between Ni, MnCO3, and LiOH·H2O was studied in situ by synchrotron XRD in order to define a proper heating scheme for the all-dry process. The crystal structure, particle morphology, surface residual impurities, and electrochemical performance of materials prepared by the “all-dry synthesis” method are equivalent to or even better than those of materials made using a conventional co-precipitation method.

The identification of dual active routes for highly efficient furfural oxidation reaction coupling with hydrogen production over Re modulated Co(OH)2/CC

It is of great significance and challenge to tune the active sites of two-dimensional materials and identify the exclusive active sites for separate reaction toward hydrogen evolution reaction (HER) coupled with electrochemical oxidation (ECO) reaction. Herein, Re was introduced to tune d band charge density of Co, which reduced the energy barrier of water splitting for HER. Meanwhile, the abundant oxygen vacancies (Ov) caused by Re introduction resulted in a new reaction route for furfural oxidation reaction (FOR). That is, the adsorbed OH− on Ov accelerates the dehydrogenation of Co(OH)O, and the active site further promotes the nucleophile dehydrogenation, thus improving the catalytic performance of FOR. In conclusion, Re-Co(OH)2/CC with Re modified Co-centered sites displays dual active routes, which simultaneously enhance FOR and HER with a cell voltage (1.36 V) at 10 mA cm−2, surpassing the most two-dimensional transition-metal hydroxides (2D TMHs) results reported as we known. This work provides new insights into the modulation of Co electronic structure and Ov concentration, which results in enhanced bifunctional electrocatalytic reactions.

Cu@S-Co(OH)2 hybrid electrocatalysts with high performance for alkaline hydrogen evolution reaction

Transition metal hydroxides have superior oxygen evolution reaction (OER) activity but poor hydrogen evolution reaction (HER) performance, which greatly limits the water splitting for hydrogen production. Herein, copper modification of sulfur doped Co(OH)2 hybrid catalyst (Cu@S-Co(OH)2) was prepared by one-step of electrodeposition method which can serve as efficient hydrogen evolution reaction catalyst. In the presence of sulfur and copper, Cu@S-Co(OH)2 hybrid catalyst exhibits the best catalytic activity, showing ultralow overpotential of 42 mV at a current density of 10 mA cm−2. Compared with Co(OH)2, the overpotential is improved by nearly 100 mV as well as enhanced stability. In addition, the active site poison experiments proved that the active center is cobalt metal. Combined with the adsorption strength of the catalyst for OH and H species, it is considered that both S and Cu can enhance the adsorption of OH for Co(OH)2, while S is contributed to the adsorption of H, and Cu can promote the desorption of H. This work provides a facile method and new insight to enhance the HER activity for transitional metal hydroxides via metal and non-metallic elements co-modulation.

Potential modulation of Nickel-Cobalt hydroxide nanosheets with conductive Poly(3,4-Ethylenedioxythiophene) skin for aqueous hybrid supercapacitors

Transition metal hydroxides with tuned structure and superior electrochemical activities are of potential as positive electrodes for aqueous hybrid supercapacitors (AHSs), yet their conductivities and stacking behaviors need to be optimized to further improve the electrical potential distribution from the electronic multi-contact border to the electroactive center. Herein, we report a new approach to coat poly(3,4-ethylenedioxythiophene) (PEDOT) skin with a controlled thickness on nickel–cobalt layered double hydroxide (NiCo-LDH) nanosheets via a simple yet efficient oxidative chemical vapor deposition (oCVD). The conductive PEDOT skin is ionically permeable, resulting in uniform distribution of the electrical potential and fast transport of ions to active sites. The density functional theory (DFT) calculations reveal that the PEDOT layer can build an embedded electric field at the interface and enable a low desorption energy of hydrogen for electrochemical redox reactions. The as-obtained NiCo-LDH nanosheets with the PEDOT skin of 10 nm thick (LDH/PEDOT-10) as the battery-type electrode deliver a high specific capacity of 167 mAh g−1 (1250F g−1) with a greatly improved rate capability of 79 % at 50 A g−1 and cycling stability of 92 % for 6000 cycles, which endows AHS devices with superior charge-storage performance. This study has demonstrated for the first time that the modulation of electrical potential for redox electrodes via an interface engineering strategy can achieve simultaneously fast reaction kinetics and excellent structure stability for aqueous energy-storage devices.

Effect of Transport Properties of Crystalline Transition Metal (Oxy)hydroxides on Oxygen Evolution Reaction.

Electronic transport plays a pivotal role in the electrolysis of semiconducting electrocatalysts for oxygen evolution reaction (OER), while it is mostly underestimated and largely unexplored. Here, by investigating the electronic transport behavior of seven archetypical crystalline Co/Ni/Fe-based (oxy)hydroxides (unary, binary, and ternary) under OER potential, we study how and the extent to which it affects the apparent catalytic performances. The electronic transports of unary metal (oxy)hydroxides follow the order of Co > Ni > Fe, and their binary or ternary compounds can generally impose one order of magnitude higher electrical conductivity. By studying the dependence of catalytic performances on electrical conductivities, we further unveil that charge transportability not only determines the electronic accessibility of catalytic nanoparticles but also, to our surprise, regulates the reaction kinetics of the electronically accessible active sites. Remarkably, the regulation extent of reaction kinetics correlates with the electrical conductivities of electrocatalysts, suggesting that the electrocatalytic process is strongly coupled with electronic transport. The work presents an overview of electronic transports of crystalline (oxy)hydroxides under OER potentials and highlights their pivotal role in unfolding catalytic potential, holding both fundamental and technical implications for the screen and design of efficient electrocatalysts.

Fluorescence nanoplatform based on conjugated polymer nanoparticles-transition metal hydroxide composite for the detection of Butyrylcholinease

Butyrylcholinesterase (BChE) as a valuable biochemical indicator could evaluate liver's function in clinical diagnosis by blood. The traditional Ellman colorimetric method needs enzymatic cascades and additional substances, which greatly limits its practical application. The fluorescence strategy was broadly applied because of great selectivity, sensitivity and convenience. Here, a novel fluorescence sensing platform was built by internal filtering effect (IFE) based on conjugated polymer nanoparticles (CPNsPBOC-COOH) and transition metal hydroxides (MOOH) for the detection of BChE. In order to get an optimized detection platform, three different MOOH (FeOOH/ CoOOH/ NiOOH) were selected, and their preparation conditions, water solubility, the morphology, the absorption and the fluorescence quenching efficiency were investigated. The results showed FeOOH preparated at 120°C for 4 h have the better water solubility and size uniform, the broad absorption and the high quenching efficiency of 95.3%. At the same time, the fluorescence platform of CPNsPBOC-COOH@FeOOH is highly selective with lower interference. So the optimized fluorescence detection platform of CPNsPBOC-COOH@FeOOH (CCPNsPBOC-COOH =1 µg·mL−1, CFeOOH =60 µg·mL−1) was selected and obtained. Furthermore, the fluorescence platform of CPNsPBOC-COOH@FeOOH has a detection range of 0.02∼2.6 µg·mL−1 and a very low detection limit of 3.5 ng·mL−1, showing it very sensitive for the BChE. The determination of BChE in human serum and plasma was applied using this detection technology, and the result was satisfactory. At the same time, the detection mechanism was explored. The result data indicate that FeOOH is decomposed by thiocholine (TCh), an enzymatic digestion product from acetylcholine (ATCh) hydrolyzed by BChE, and then the fluorescence of CPNsPBOC-COOH@FeOOH platform is recovered. The Fe2+ in products can be verified by specifically reacting with [Fe (CN)6]3−.