Hexagonal Plates Research Articles

A metastable Cr4+-compound AlCrO3+δ, δ ≤ 0.5, grown at a nanocolloid, and its ultraviolet absorption, phonon bands, and dielectric properties

AlCrO3+δ, δ ≤ 0.5, is a Cr4+:CrO2 product of a metastable compound of two types Cr4+−3d2 electrons that determine its spin degree of freedom and allied magnetic/optical properties at a magnetic semiconductor. A nanocolloid of Cr6+ bonded via Al3+ and O2– in small micelles (a hydrogel) in water is explored to grow up AlCrO3+δ, δ ≤ 0.5, at hydrothermal reactions at microwave irradiation. It forms hexagonal plates (20–40 nm thickness) as annealed at 500 °C − 1000 °C (microwave). It has 4.69% larger X-ray crystal density of 4.848 g/cm3 than a usual phase, AlCrO3.5 → AlCrO3 + ¼O2↑, turned up on anneals at ≥ 1000 °C, at a larger bandgap, ≥ 4.2 eV, of a Cr3+−3d3 insulator. X-ray diffraction, XPS, electronic absorption, and phonon bands studied at duly annealed samples confer a Cr5+ → Cr4+ → Cr3+ charge ordering at anneals. A 700 °C annealed sample (others behave as an antiferromagnet, AFM) exhibits a ferromagnetic (FM) loop, with an unsaturated magnetization 9.2 emu/g (at 50 kOe fields), a coercivity 3.67 kOe, and a 0.1 MGOe energy-product at room temperature. The two types FM−AFM spins channels govern electrical conduction at major charge carriers Cr4+ → Cr3+ − e–, O2– vacancies, and ‘e–−h+’ electron-hole pairs as per applied frequencies. The results have renewed interest to design and develop spintronics-photonics at Cr4+−3d2 spin doped Al2O3 type oxides.

Structural ordering at magnetic seeds with twins at boundaries of a core–shell alloy Mn60Bi40 and tailored magnetic properties

A spin Mn3d5-rich Mn60Bi40 alloy reveals a model system in order to tailor profound magnetic properties at unpaired 3d5 spins in such alloys of a core–shell structure. As annealed (at a critical temperature 573 K in H2 gas), a refined powder (in glycine) grows on α-MnBi seeds (crystallites) present in it at Mn/Bi atoms order over topological layers, preferentially along (110) planes, at a self-confined structure at seeds of an anisotropic shape of hexagonal (h) plates (25–85 nm widths). In terms of the HRTEM images, the atoms turn down at edges (at the plates grow up) in a spiral layer, ≤ 2.1 nm thickness, of small core–shells. A spin model is proposed to delineate a way at the spins can pin down at the edges, form single magnetic domains, and raise coercivity (H c), with no much loss of net magnetic moment. The X-ray diffraction and HRTEM images corroborate the results of topological pacing of atoms at the h-plates at anneals. A novelty is that a core–shell leads to tailor a superb H c, as much as 11.110 kOe (16.370 kOe at 350 K), with a fairly large magnetization, 76.5 emu g−1, at near 300 K. An enhanced Curie point 650.1 K (628 K at Mn50Bi50 alloy) confers a surplus 3d5-Mn spin sensitively tunes α-MnBi stoichiometry and so its final magnetic structure. A refined alloy powder so made is useful to make powerful magnets and devices in the forms of films and bonded magnets in different shapes for uses as small tools, tweezers, and other devices.

Stabilizing Metallic Zn Electrode Using Organic Acid Additives in Aqueous Zinc-Ion Batteries

Aqueous zinc (Zn)-ion batteries (AZIBs) have been paid attention to as safe, economical, and high-energy-density storages through multiple electron transfer. Although conventional alkaline solution-based AZIBs are primary batteries, recent studies demonstrated the reversible Zn2+ deposition and stripping processes enabled in mildly acidic solutions. It promises the development of rechargeable AZIBs and viable applications for energy storage systems (ESSs). However, metallic Zn employed as the negative electrode has suffered from severe corrosion and precipitation of electrolyte salts in this low pH condition. The Zn electrode undergoes a hydrogen evolution reaction (HER) as Zn2+ is dissolved from the Zn surface. The corrosion leads to a pH rise, precipitating electrolyte salt as zinc hydroxide forms. For example, hexagonal plates of zinc hydroxide sulfate hydrate (Zn4SO4(OH)6∙xH2O, indicated as ZHS) grew on the Zn electrode in 1 M ZnSO4 solution when pH approached ~5.4. The insulating and randomly oriented ZHS increased the surface resistance and caused the non-uniform Zn deposition.These challenges are mitigated by adding organic acid to the 1 M ZnSO4 solution. As the HER raised pH, the acid was promptly deprotonated, then coordinated with Zn2+. This process caused the thin film formation consisting of three-dimensional zinc glutarate. The zinc glutarate protected the Zn electrode and impeded the electrode corrosion and the ZHS precipitation. We demonstrated a uniform Zn plating and stripping process with 10 mM of organic acid in contrast with dendritic and dead Zn growth in the absence of the additive. Galvanostatic tests of symmetric Zn cells revealed over 1000 h cycles with the additives at a current density of 1 mA cm-2 and a limited capacity of 1 mAh cm-2. In contrast, the Zn cells with the additive-free electrolyte solution exhibited 15 times lower cyclability as micron-scale ZHS plates covered the electrode surface. Our strategy using the cheap additives is feasible to use grid-scale ESSs and shows significantly improved cycling performances. I will present details of Zn surface reactions using organic acid additive and corresponding electrochemical performances in this presentation.

Free transverse vibration analysis of general polygonal plate with elastically restrained inclined edges

In this study, a semi-analytical solution for the free transverse vibration of polygonal isotropic thin plates with arbitrary shapes and elastically restrained edges is obtained. All edges including inclined edges are elastically restrained by setting two groups of boundary springs along each edge of the polygonal plate to simulate the boundary forces and moments. Specifically, the complex surface integrals over the irregular plate area are simplified into a summation of plate boundary points by introducing the divergence theorem. The Chebyshev polynomial series are adopted to expand the displacement of the polygonal plate. Then, the Ritz method is performed to obtain the natural frequencies and mode shapes of several polygonal plates, such as triangular plates, quadrilateral plates, hexagonal plates, and irregular polygonal plates. An experiment study is performed and the validated comparisons between the current results and the reference results demonstrate that the proposed method can obtain accurate eigenpairs for general polygonal plates. The present method offers a unified procedure to address the vibration of polygonal plates, in which the change in the geometrical shape of plates can be readily converted with the increase or decrease in the corresponding boundary points. The results show that when the geometry and boundary restraints of a general polygonal plate are axisymmetric, the vibration modes will also present the feature of axial symmetry. Furthermore, cutting off a small part of the plate shows little influence on the modal shape whereas the influence on natural frequencies depends on the boundary conditions.

Formation of stacking fault pyramid in zirconium

Zirconium alloys were widely used as fuel cladding in nuclear reactors. Stacking fault pyramid (SFP) is an irradiation-induced defect in zirconium. In this work, the formation process of SFP from a hexagonal vacancy plate on basal plane is studied by molecular dynamics (MD) simulations. The results show that, during the SFP formation from a basal vacancy plate, the 12[0001] (<c>/2) dislocation is firstly dissociated into two partial dislocations 118<202¯3> and 19<1¯013>. The former one resides on the basal plane, while the latter one glides on the first-order pyramidal plane. The partials on adjacent pyramidal planes react further and form a partial dislocation on the pyramidal edge, i.e. 19[101¯3¯]+19[01¯13]→19[11¯00]. A critical edge length of the initial vacancy plate is observed, below which perfect SFP is formed while above which truncated SFP is formed. The critical edge length increases with the increasing temperature. Under a compressive stress, the SFP collapses into an <c>/2 dislocation loop and then becomes a faulted loop. Under shear stress, the formation of SFP is facilitated, i.e. the critical edge length increases with the increasing shear stress. The current work is useful for understanding the irradiation effects in zirconium alloys.

An analytical method for vibration analysis of arbitrarily shaped non-homogeneous orthotropic plates of variable thickness resting on Winkler-Pasternak foundation

A highly applicable analytical approach is proposed for the dynamic analysis of composite plate structures with complex variation of geometric characteristics (shape/boundary and thickness) and material characteristics (Young's modulus, shear modulus and density) resting on Winkler-Pasternak foundation with general elastic boundary conditions. Boundary conditions of the plates are treated by the penalty method, so that the admissible functions can use any complete set of orthogonal polynomials, which is obtained by Gram-Schmidt orthogonalization process. The interval where the in-plane coordinate variables of the plate domain are located can be selected as the orthogonalization intervals, so as to avoid the normalization procedure of coordinates and simplify the operation process. In order to calculate the energy integral of the arbitrarily shaped plate, the plate domain segmentation strategy is introduced. To verify the effectiveness and accuracy of the proposed method, convergence study and numerical verifications for different orthogonalization intervals, weight functions, penalty spring stiffness and the truncation number of orthogonal polynomials are carried out. Taking regular hexagonal plates as examples, the effects of the parameters of thickness, nonhomogeneity and foundations on the vibration characteristics of the plates are studied. These results can be used as reference data for future research.

Multilayers of avidin–biotin complexes as spacers used in the study of the effect of metal‐enhanced fluorescence

AbstractThe effects of metal‐enhanced fluorescence (MEF) of rhodamine dye by gold sub‐micro hexagonal plates were studied. A multilayered avidin–biotin complex was designed and used as a spacer to connect the fluorophore and the sub‐microplate. Fluorescence lifetime image microscopy (FLIM) combined with time‐correlated single‐photon counting was used to obtain lifetime images and intensities of dye on single particles. Gold hexagon plates ~900 nm were synthesized, and the avidin–biotin complexes were placed layer‐by‐layer for up to 4 layers onto the sub‐microplates. All emission curves of fluorophore displayed biexponential decay with short lifetimes of 18–23 ps and long lifetimes of 249, 271, 304, and 348 ps for 1–4 layers on gold sub‐microplates, respectively. Using the kinetic model of energy transfer between fluorophore and nanoparticles to explain the coupling mechanism, we found that the excited fluorophore transferred energy mostly to the high‐order modes for the 1‐layered avidin–biotin complexes enclosing gold nanospheres, consequently resulting in a non‐emissive pathway. The 4‐layered samples had the highest emission intensity because, at those distances, the enhancement by the gold sub‐microplates during plasmonic excitation remained high and became comparable to the energy quenching rate. Using the composed complexes, the MEF effect achieved the maximal enhancement in this system.

Benign approach for the synthesis of ZnO hexagonal plates for electrochemical sensing of l-tryptophan

L-tryptophan is amino acid which can significantly affects metabolic activities in humans and herbivore animals. l-tryptophan also known as precursor for melatonin, and serotonin and its level should be controlled in the human body. Thus, it is required to develop the cost-effective, simple processed, sensitive and selective l-tryptophan. In this paper, we reported benign approach for the synthesis of ZnO hexagonal plates. Various advanced physiochemical techniques such as powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), and X-ray photoelectron spectroscopic (XPS) were adopted to characterize the synthesized of ZnO hexagonal plates. Glassy carbon electrode (GCE) was modified with ZnO hexagonal plates using drop cast method. This modified GCE (ZnO/GCE) was applied as tryptophan sensor. Cyclic voltammetry (CV) and linear sweep voltammetry (LSV) techniques were adopted for the detection of tryptophan (TRP). The limit of detection (LOD) of 1.49 μM and 0.94 μM were obtained using CV and LSV, respectively. The fabricated electrode (ZnO/GCE) also exhibited excellent stability, reproducibility, repeatability, and selectivity towards the determination of l-tryptophan.

Synthesis, Structure and Properties of Barium Ferrites BaFe&lt;sub&gt;11&lt;/sub&gt;M&lt;sub&gt;1&lt;/sub&gt;O19 (M= Al, Ti and Mn) Ceramics

The article shows the results of a research in which barium hexaferrite samples of the BaFe11M1O19 (M= Al, Ti and Mn) composition were obtained by solid-state synthesis. Samples substituted with titanium, aluminum, and manganese were obtained in a tubular furnace at an exposure time of 5 hours at a temperature of 1350°C, the sample, substituted with manganese, it was obtained at a temperature of 1250°C. The chemical composition was controlled using electron microscopy the samples obtained correspond to the initial composition with sufficient accuracy. Hexagonal plates represent the structure of all the obtained samples. According to X-ray phase analysis, all samples are monophasic and have the structure of barium hexaferrite. Using the data of powder X-rays, the parameters of the unit cell of the studied samples were calculated, when iron atoms are substituted by titanium or aluminum or manganese atoms, the crystal lattice is distorted, while its change is not the same for different crystallographic directions. During the doping of barium hexaferrite with titanium, aluminum or manganese atoms, the Curie temperature decreases. This is due to a decrease in the exchange interaction forces during the modification of the barium hexaferrite matrix. The aim of this study was to study the structure and change of the lattice parameters, the Curie temperature, depending on the substitution element.

Laser reshaping of gold nanoparticles for highly sensitive SERS detection of ciprofloxacin

Laser reshaping of hexagonal gold plates is demonstrated to generate particles with different size and shape, which is further used for highly sensitive label-free surface-enhanced Raman scattering detection of synthetic antibiotic ciprofloxacin. A nanosecond laser can be used to reshape gold particles to 120-nm diameter and form a spherical-hexagonal combined structure, while a femtosecond laser can reshape the particles into spherical and triangle shapes with an average size of 6 nm. The nano-sized particles can help to enhance the Raman signal and demonstrate a superior performance with a lowest detection limit of 7.5 × 10−8 M for the ciprofloxacin sensing in milk. The presented ultrafast laser reshaping of gold nanoparticles can be exploited in a wide range of plasmonic enhanced sensing applications for a simple, fast, flexible, and portable biomaterial detection.

Morphological evolution of cadmium oxide crystals showing color changes and facet-dependent conductivity behavior

CdO stellated octahedra, octahedra, truncated octahedra, and Cd(OH)2 hexagonal plates have been synthesized. These CdO crystals exhibit size-dependent colors, and the {111} faces of CdO are much more electrically conductive than the {100} faces.

Surfactant assisted solvothermal synthesis of Bi2Te3 nanostructure for thermoelectric applications

Solvothermal method was used to synthesize Bi2Te3 nanostructures for thermoelectric applications. The structural, morphological and chemical composition was studied using X- ray diffractometer (XRD), Field emission scanning electron microscope (FESEM) and Energy dispersive X-ray spectroscopy (EDS) respectively. XRD study reveals the polycrystalline nature of the prepared samples. Defects present in the EDTA assisted sample can reduce the lattice thermal conductivity. The morphological studies show that irregular and hexagonal plate like nanostructures were obtained. The quantum confinement effect in these nanostructures improves the Seebeck coefficient.

The sequential structural transformation of a heptanuclear zinc cluster towards hierarchical porous carbon for supercapacitor applications.

The peripheral N/O chelating of Schiff base ligands, inner bridges, counterions, and metal centers gave rise to a brucite disk cluster [Zn7L6(OCH3)6](NO3)2 (Zn7, (HL = 2-methoxy-6-((methylimino)-methyl)phenolate)) which crystallized into hexagonal prismatic plates. The combination of crystallographic studies, in situ TG-MS, and other characterization techniques showed that with a fixed metal and ligand composition in the precursors, weak correlative interactions (e.g., electrostatic interactions) and shape matching between the cluster core and counterions determine the cluster packing modes in the crystals and affect their phase and morphological changes during pyrolysis. The tracking of the pyrolysis process showed that the peripheral ligands, inner bridge, and counterion decompose first, followed by the Zn7O6 core merging with cubic ZnO, which was then reduced by carbon and eventually evaporated, leaving behind a porous carbon structure. In this process, the solid material composition change was in the sequence {Zn7}-{Zn-O core@C}-{ZnO@C}-{Zn@C}-{C}, which was accompanied by a porosity change from micropores to hierarchical pores, and then to micropores again. The core structure and packing modes of Zn7 evolved into micropores and mesopores, respectively. Micro-mesoporous carbon Zn7-1000 featured a capacitance of 1797 F g-1 at 1 A g-1, where the BET specific surface area was 3119.18 m2 g-1, which, to the best of our knowledge, is the highest value reported for a porous carbon electrode. This work represents an important benchmark for the analysis of dynamic chemical processes involving coordination clusters at high temperatures, and it could lead to important applications in high-performance devices.

Effect of milling duration on structural properties of polycrystalline bulk barium hexaferrite

Polycrystalline bulk Barium hexaferrite, BaFe12O19 were synthesised by ball milling for different milling duration followed by sintering at high temperature. Effect of milling duration on structural, morphological and dc electrical properties were studied for 4, 8, 12 and 16 h of milling using planetary ball mill. X-ray diffraction measurement data shows the formation of single phase barium hexaferrite which belongs to P63/mmc group for 8, 12 and 16 h milled samples. There is formation of intermediate phase along with M−phase of barium hexaferrite in 4 h milled sample. Inverse relation of the crystallite size and lattice strain was observed. The saturation value of crystallite size and maximum lattice strain were observed for 12 h milled sample. Morphological studies for 8 and 16 h milled samples reveals the formation of hexagonal plate like grains for the former and agglomerates with different grain size for the latter. High porosity for 8 h milled sample was observed by density measurements. Resistivity of the samples measured from I-V characteristics using 2 probe method exhibits maximum resistivity for 8 h milled sample and minimum resistivity for 12 h milled samples. Linear relationship was observed between electrical resistivity and porosity.

Morphological features of micro- and nanoporous silver and copper films synthesized by the substitution reaction method

The results of a study of the structural features of thin silver and copper films synthesized by the chemical substitution reaction are presented. Silver films were obtained by immersing copper substrates in a solution of silver nitrate. Copper films were synthesized by immersing iron and tin-plated iron substrates in a copper sulfate solution. The study of the morphology and composition of the synthesized layers was carried out using a scanning electron microscope. It has been shown that metal nanoporous layers up to 1 μm thick are formed on the substrates as early as 2-3 s after the start of the reaction. The layers consist of microcrystalline hexagonal plates and micro- and nanodendrites. As the reaction time increases, the layers become denser. In this case, the minimum pore size is 20 nm. The synthesized nanoporous films can be used for photocatalytic decomposition of water and enhancement of Raman scattering. Keywords: morphology, porous film, silver, copper, substitution reaction.

Морфологические особенности микро- и нанопористых пленок из серебра и меди, синтезированных методом реакции замещения

The results of a study of the structural features of thin silver and copper films synthesized by the chemical substitution reaction are presented. Silver films were obtained by immersing copper substrates in a solution of silver nitrate. Copper films were synthesized by immersing iron and tin-plated iron substrates in a copper sulfate solution. The study of the morphology and composition of the synthesized layers was carried out using a scanning electron microscope. It has been shown that metal nanoporous layers up to 1 μm thick are formed on the substrates as early as 2–3 s after the start of the reaction. The layers consist of microcrystalline hexagonal plates and micro- and nanodendrites. As the reaction time increases, the layers become denser. In this case, the minimum pore size is 20 nm. The synthesized nanoporous films can be used for photocatalytic decomposition of water and enhancement of Raman scattering.

Tuning the Structure, Magnetic, and High Frequency Properties of Sc‐Doped Sr0.5Ba0.5ScxFe12‐xO19/NiFe2O4 Hard/Soft Nanocomposites

AbstractThe Sr0.5Ba0.5ScxFe12–xO19(SrBaSc)/NiFe2O4(NiFe) hard–soft nanocomposites (NCs) are synthesized by in situ sol–gel route. Impact of Sc3+ doping on their structure, morphology, and magnetic properties are examined. X‐ray diffraction confirms the coexistence of SrBaSc and NiFe phases without any impurity. Morphology of NCs reveals a cluster of hexagonal plate decorated by spherical grains. Magnetic characteristics of the NCs are examined by using a vibration sample magnetometer at room temperature and 10 K. The x = 0.000 sample shows some kinks in their M–H loops and the occurrence of two peaks in dM/dH(H). All the NCs with Sc3+ exhibit smooth shapes of M–H curves with single peak, revealing the complete and perfect exchange coupling behavior. The diverse magnetic parameters at both temperatures are determined. The values of saturation and remanent magnetizations are decreasing with the Sc content increase. The intensive electromagnetic absorption is observed in all the samples. Reflection loss (RL) of more than ‐18 dB is observed above 3 GHz. Strong coupling between Sc concentration and amplitude–frequency characteristics of the RL can be used for developing of the functional media for high‐frequency devices and will open broad perspectives for practical application in radar‐absorbing technology and electromagnetic compatibility.

In English

X-ray phase and thermogravimetric analysis, scanning electron microscopy and energy-dispersion spectroscopy were used to study the products of phase formation during the precipitation of lanthanum and cerium salts in the presence of silver nitrate and recipients of precipitators, nucleating agents and hydrolysis regulators. Thermogravimetric analysis shows the completion of the La(OH)3 lattice dehydroxylation process at a temperature of ~ 300 °С and probable destruction of sulfates at a temperature of ~ 340 °С. The phase interaction of lanthanum oxide(III) with silver ends at T ~ 400 °C. The DTG curve shows a two-stage weight loss, which characterizes the destruction of lanthanum and silver hydroxides (250 °C) and the removal of sulfates (~ 340 °C), respectively. According to the TG, the total weight loss is 21.6 %. For the cerium-containing system the only endothermic effect of dehydroxylation of cerium hydroxide at T = 250 °C with its conversion into cerium dioxide is observed. The destruction of nitrates (anionic component of solutions) takes place at the temperature of 400 °C. Weight loss takes place at T = 150 °C and is 53.9 %. Thus, on the basis of TG-DTA data, it can be assumed that the formation of composites particles based on lanthanum and cerium oxides, modified with silver, ends at the temperature of 400 °C. The X-ray diffraction data shows that at the initial stage the system undergoes the formation of cerium and lanthanum hydroxides, and during lyophilization of the precipitate (T = 160 °C) the crystal lattice of hydroxides partial dehydroxylation takes place with the formation of trigonal oxides La2O3 and Ce2O3. It has been found that the presence of silver cations in the solution can affect the phase composition of lyophilized structures and the formation of the CeO2 phase. It is shown that the hydroxylamine chloride injection into the system can initiate the silver restoration on the lanthanum oxide surface and also partially restore it to the LaO phase. Temperature treatment of the samples (T = 400 °С) promotes homogenization of the precipitate composition: formation of 30 nm cerium dioxide particles with silver clusters evenly distributed on its surface, and hexagonal lanthanum oxide plates with individual silver particles as the second phase. In three-component systems, two modifications of lanthanum oxides (trigonal and cubic), cerium dioxide and metallic silver are formed. It is found that the chemical composition of the precipitates contains the main elements – La, Ce, O, Ag and impurity – S or Cl, as the anionic component of the initial solutions, N and K in the composition of the initial suspension. It is shown that the morphology of the samples is represented by hexagonal structures of lanthanum hydroxide and oxide, spherical and pseudocubic particles of cerium dioxide and lanthanum oxide, spherical clusters of silver.

Guided waves in a functionally graded 1-D hexagonal quasi-crystal plate with piezoelectric effect

For the purpose of design and optimization for piezoelectric quasi-crystal transducers, guided waves in a functionally graded 1-D hexagonal piezoelectric quasi-crystal plate are investigated. In this paper, a model combined with the Bak’s and elastohydrodynamic models is utilized to derive governing equations of wave motion, and real, pure imaginary, and complex roots of governing equations are calculated by using the modified Legendre polynomial method. Subsequently, dispersion curves and displacements of phonon and phason modes are illustrated. Then, guided waves in functionally graded 1-D hexagonal piezoelectric quasi-crystal plates with different quasi-periodic directions are studied. And the phonon-phason coupling effect on Lamb and SH waves are analyzed. Accordingly, some interesting results are obtained: The phonon-phason coupling just affects Lamb waves in the x- and z-direction quasi-crystal plates, and SH waves in the y-direction quasi-crystal plate. Besides, frequencies of propagative phason modes decrease as phonon-phason coupling coefficients Ri increase. Furthermore, a variation in the polarization has a more significant influence on phonon modes, and a variation in the quasi-periodic direction has a more significant influence on phason modes.

Electric-Field Assisted Hydrolysis-Oxidation of MOFs: Hierarchical Ternary (Oxy)hydroxide Micro-Flowers for Efficient Electrocatalytic Oxygen Evolution.

Water oxidation is the key process of electrocatalytic water splitting owing to its inherently slow kinetics. The ingenious design of microstructures for oxygen evolution reaction (OER) catalysts is an important way to accelerate the kinetics of the water splitting reaction. In this work, a facile electric-field assisted alkaline hydrolysis-oxidation strategy is proposed to prepare 3D layered micro-flowers in situ constructed from ultra-thin CoNiFe (oxy)hydroxide (CoNiFe-OH) hexagonal plates by using Co/Ni/Fe metal-organic frameworks (MOFs) as sacrificial templates and metal sources. The growth of the ballflowers can be accurately controlled by matching the hydrolysis rate of MOFs templates and the coprecipitation rate of metal ions. More importantly, continuous oxidation voltage can drive transformation of some hydroxides into oxyhydroxide with abundant oxygen vacancies. Benefiting from the open structure with multiple electroactive sites and optimized chemical composition, the layered CoNiFe-OH micro-flowers show appealing OER electrocatalytic performance with a low overpotential of 207 mV@10mA cm-2 and robust durability over 60 h. This work provides a strategy to prepare non-noble hierarchical nanostructured electrocatalysts for electrochemical energy conversion.