Amorphous Fe-P Research Articles

Modelling and optimization of electrodeposited amorphous Fe-P alloys using central composite design and response surface method

Central composite circumscribed (CCC) design and response surface methodology (RSM) were used to model and optimize the electrodeposition of amorphous Fe-P alloys. Based on our previous single-factor experimental results, the significance of influencing factors was ranked using analysis of variance (ANOVA) method. Three factors, significantly impacting the P content in deposits, hardness and corrosion current density, were identified, including bath temperature, pH values and H2PO2− concentration. The statistic relationships between process parameters and individual responses were established based on the CCC experimental data and RSM. The optimal parameters for each response were derived and the influences of interaction terms were investigated. The predicted maximum P content of 26.35 wt% was achieved at a bath temperature of 60℃, a pH of 1.2 and H2PO2− concentration of 60 g/L. The predicted highest microhardness was 534 HV0.1 under the optimal conditions of temperature of 60 ℃, pH value of 1.6 and H2PO2− concentration of 49 g/L. The lowest corrosion current density was predicted to be 1.34 μA·cm−2 under the conditions of a bath temperature of 60℃，a pH value of 1.2, and a H2PO2− concentration of 53 g/L. A desirability function was applied to explore the optimal comprehensive performance of both high hardness and low corrosion current density. The optimal parameter combination for comprehensive performance was bath temperature of 60℃, pH of 1.4, and H2PO2− concentration of 49 g/L, and the resulting hardness and corrosion current density were 527 HV0.1 and 2.40 μA·cm−2, respectively. Due to the complex electrodeposition mechanism of amorphous Fe-P alloys, the predicted P content in deposits largely deviated from the experimental result, but the hardness, corrosion current density and comprehensive performances show high prediction accuracy.

Modulating Fe/P ratios in Fe-P alloy through smelting reduction for long-term electrocatalytic overall water splitting

Owing to strong Fe-P interaction that differs the electron distribution beneath metal/phosphide interface of Fe-P alloy, the charge transfer of Fe-P alloy has been accelerated during the electrocatalytic oxidation process and improved the efficiency and durability of overall water splitting. In this work, a novel metallurgical technology in combination with smelting reduction and Single Roller Melting Spinning (SRMS) for the purpose of electrochemical overall water splitting where High-phosphorus Oolitic Iron Ore (HPOIO) has been directly used as the main raw material is developed for preparing amorphous Fe-P alloys strips. The rational modulation on the Fe/P ratio can alter the crystal structure and crystallinity of Fe-P alloy, favor electron transfer, and further trap the positively charged H+. The obtained FeP electrocatalyst exhibits 436 and 527 mV at 10 mA cm−1 with Tafel slopes of 102.3 and 77.2 mV dec−1 for HER and OER in 1.0 mol/L KOH solution, respectively, especially with long-term stability (∼207 h for HER and ∼42 h for OER). Specifically, the DFT calculation displaying structural advantages and componential superiorities exhibited that P in Fe-P amorphous alloy regulated by systematic P addition optimization might increase the energy density in the Fermi level. Furthermore, the phosphorus content brought about high active surface areas, low impedance, and variable reaction paths-caused low reaction energy barriers with the improved amorphicity and absorption and desorption of intermediates, thereby boosting the overall water splitting activity. This study displays a novel strategy to develop Fe-P amorphous alloy for the stable and efficient overall water splitting.

Phosphorus controls on the formation of vivianite versus green rust under anoxic conditions

The formation of green rust (GR; a mixed ferric/ferrous hydroxide) and vivianite (ferrous phosphate) are likely to have exerted a major control on phosphorus (P) cycling in ancient anoxic oceans. However, the factors that influence the formation of these minerals under different chemical conditions are poorly constrained, which limits understanding of the pathways that ultimately result in P drawdown and retention in anoxic sediments. This, in turn, limits understanding of P cycling in anoxic oceans and hence potential productivity feedbacks. Here we explore the effect of dissolved P concentration on the formation of sulfate GR (FeIII2FeII3(OH)12SO4) versus vivianite (FeII3(PO4)2·8H2O) under anoxic conditions. Our results show that at low dissolved P concentrations and with P:Fe(II) molar ratios <1:30, P drawdown is effectively controlled by interlayer anion exchange and adsorption onto GR species, via the formation of amorphous Fe-P precursors. Such precursors may delay the precipitation of crystalline GR, but vivianite was not detected under these conditions. At higher dissolved P concentrations and P:Fe(II) ratios, GR also forms. However, the GR formed under these conditions rapidly dissolves, likely forming amorphous ferric hydroxides together with dissolved Fe(II) and phosphate, with the dissolved species subsequently reacting to form crystalline vivianite. Our observations agree with studies showing the water column formation of GR in modern oligotrophic, anoxic Fe-rich (ferruginous) settings, and provide support for a major role for GR in controlling P cycling in ancient oligotrophic ferruginous oceans. By contrast, in more productive ancient anoxic settings, enhanced redox-controlled P recycling and/or increased weathering inputs would have led to higher dissolved P concentrations in the water column and sediments. Our observations show that such conditions ultimately promote the formation of vivianite, which would have exerted a limiting control on the extent of P recycling in ancient, more productive settings, via the long-term fixation of P in the sediments.

Amorphous transformation of FeP enabling enhanced sulfur catalysis and anchoring in High-performance Li-S batteries

• Amorphous transformation of FeP enables enhanced catalytic activities in sulfur cathodes. • aFeP overcomes the downsides of structural anisotropy in sulfur catalysis. • aFeP presents abundant and stronger binding sites for active sulfur species. • aFeP enhances the liquid–solid conversions for higher sulfur utilization. • A high-capacity pouch cell (6.3 mAh cm −2 and 305 mAh in total) is demonstrated. Catalytic materials have recently been demonstrated to be effective in addressing the critical challenges of polysulfide shuttling and low utilization of sulfur in Li-S batteries. Although amorphous materials show advantages in typical electrocatalysis processes such as water splitting, the vast majority of catalytic materials developed for the sulfur cathodes are crystalline. Herein, we demonstrate the enhanced electrochemical performance of the amorphous FeP phase (aFeP) derived from a self-oxidation process of its crystalline counterpart. Electrochemical measurements and theoretical calculation reveal that the structural anisotropy of crystalline FeP is not in favour of important properties such as polysulfide binding energy, catalytic activity and electrical conductivity. Amorphous aFeP effectively overcomes these issues. Moreover, amorphous aFeP provides additional and stronger binding sites, enhanced electron exchanging between Fe-S and P-S atoms, as well as reduced HOMO-LUMO gap of the aFeP-Li 2 S 4 adsorption system, leading to significantly improved catalytic effects especially for the capacity-limiting liquid–solid conversions. High specific capacities are achieved up to 5C and pouch cells with a high areal capacity (6.3 mAh cm −2 ) are also demonstrated. This study provides useful insights for the future development of amorphous catalytic materials in high-performance Li-S cathodes.

Achieving Fast and Durable Lithium Storage through Amorphous FeP Nanoparticles Encapsulated in Ultrathin 3D P-Doped Porous Carbon Nanosheets.

Conversion-type transition-metal phosphide anode materials with high theoretical capacity usually suffer from low-rate capability and severe capacity decay, which are mainly caused by their inferior electronic conductivities and large volumetric variations together with the poor reversibility of discharge product (Li3P), impeding their practical applications. Herein, guided by density functional theory calculations, these obstacles are simultaneously mitigated by confining amorphous FeP nanoparticles into ultrathin 3D interconnected P-doped porous carbon nanosheets (denoted as FeP@CNs) via a facile approach, forming an intriguing 3D flake-CNs-like configuration. As an anode for lithium-ion batteries (LIBs), the resulting FeP@CNs electrode not only reaches a high reversible capacity (837 mA h g-1 after 300 cycles at 0.2 A g-1) and an exceptional rate capability (403 mA h g-1 at 16 A g-1) but also exhibits extraordinary durability (2500 cycles, 563 mA h g-1 at 4 A g-1, 98% capacity retention). By combining DFT calculations, in situ transmission electron microscopy, and a suite of ex situ microscopic and spectroscopic techniques, we show that the superior performances of FeP@CNs anode originate from its prominent structural and compositional merits, which render fast electron/ion-transport kinetics and abundant active sites (amorphous FeP nanoparticles and structural defects in P-doped CNs) for charge storage, promote the reversibility of conversion reactions, and buffer the volume variations while preventing pulverization/aggregation of FeP during cycling, thus enabling a high rate and highly durable lithium storage. Furthermore, a full cell composed of the prelithiated FeP@CNs anode and commercial LiFePO4 cathode exhibits impressive rate performance while maintaining superior cycling stability. This work fundamentally and experimentally presents a facile and effective structural engineering strategy for markedly improving the performance of conversion-type anodes for advanced LIBs.

A Single Molecular Stoichiometric P‐Source for Phase‐Selective Synthesis of Crystalline and Amorphous Iron Phosphide Nanocatalysts

AbstractThe formation of iron phosphide nanoparticles (FexP NPs) is a well‐studied process. It usually uses air‐sensitive phosphorus precursors such as n‐trioctylphosphine or white phosphorus. In this study, we report the synthesis and characterization of a remarkably stable tetrakis(acyl)cyclotetraphosphane, P4(MesCO)4. We demonstrate that this compound can be used as a stoichiometric source of P(0) species in order to synthesize FeP and Fe2P nanoparticles at only 250 °C. This tunable process provides a route to monodisperse nanoparticles with different compositions and crystallinities. We combine X‐Ray photoelectron spectroscopy (XPS) and atomic pair distribution function (PDF) in order to study the local order and bonding in the amorphous and crystalline materials. We show that crystalline FeP forms via an intermediate amorphous phase (obtained at a lower temperature) that presents local order similar to that of the crystalline sample. From the results of this work, a better understanding of the mechanism of the formation of amorphous and crystalline FexP NPs is provided which relies on the use of a stoichiometric and single P‐source. We then explore the electrocatalytic properties of FexP nanoparticles for the hydrogen evolution reaction (HER) in acidic and neutral electrolytes. In both electrolytes, amorphous FeP is a more efficient catalyst than crystalline FeP, itself more efficient than crystalline Fe2P. Our study paves the way for a more systematic investigation of amorphous metal phosphide phases in electrocatalysis. It also shows the beneficial properties of PDF on the characterization of such nanomaterials, which is highly challenging.

Ni-doped amorphous iron phosphide nanoparticles on TiN nanowire arrays: An advanced alkaline hydrogen evolution electrocatalyst

Efficient and low-cost non-precious-metal-based electrocatalysts are crucial to the commercial success of the hydrogen evolution reaction (HER) under alkaline conditions. Herein, a step-by-step strategy to prepare a hierarchical structure assembled from Ni-doped amorphous FeP nanoparticles, porous TiN nanowires, and graphitic carbon fibers (Ni-FeP/TiN/CC) is described. The FeP/TiN/CC composite is plasma-implanted with Ni ions to modify the electronic structure and produce an amorphous surface. Simultaneous doping and amorphization of FeP by Ni ion implantation to enhance the HER activity is achieved for the first time. The flexible and freestanding Ni-FeP/TiN/CC catalyst produced on a carbon cloth can serve directly as an electrode in HER in an alkaline medium. The Ni-FeP/TiN/CC catalyst delivers excellent HER performance including an overpotential of 75 mV to generate a cathodic current density of 10 mA cm−2, a Tafel slope close to that of commercial Pt/C catalysts, and long lifetime indicated by a more constant cathodic current density during continuous operation for 10 h. The remarkable HER activity is attributed to the combined effects rendered by the Ni and Fe atoms in the Ni-doped FeP nanoparticles, active amorphous surface, as well as conductive nanowire scaffold, which expose a large amount of active sites, enhance the charge transfer efficiency, and prevent the catalysts from migration and aggregation.

Electrodeposited Fe-P nanowire arrays in hard-anodic aluminum oxide templates with controllable magnetic properties by thermal annealing

The highly ordered uniform amorphous Fe-P alloy nanowire arrays are fabricated by potentiostatic electrodeposition in hard-anodic aluminum oxide (H-AAO) templates with diameter and pore distance about 110 nm and 265 nm, respectively. The deposited Fe-P nanowire arrays gradually change from crystalline to amorphous phase as the phosphorus content in the nanowire arrays increases. The phosphorus content and nanowire growth rate are sensitive to the applied potential and sodium hypophosphite concentration in electrolyte. Subsequently, the as-deposited amorphous Fe-P alloy nanowire arrays are annealed with different temperature. And the original and annealed samples reveal different crystallographic structures and magnetic properties. The results show that both the coercivity and squareness have been improved significantly, while the magnetic anisotropy become weak with the increasing of annealing temperature, which mainly attributes to the competition of shape anisotropy, stress anisotropy and the strengthening of magnetocrystalline anisotropy.

Low-Temperature Synthesis of Amorphous FeP2 and Its Use as Anodes for Li Ion Batteries

The reaction of Fe(N(SiMe(3))(2))(3) with PH(3) in THF at 100 °C gives amorphous FeP(2) in high yield. As an anode material in a Li ion battery, this material shows remarkable performance toward electrochemical lithiation/delithation, with gravimetric discharge and charge capacities of 1258 and 766 mA h g(-1), respectively, translating to 61% reversibility on the first cycle and a discharge capacity of 906 mA h g(-1) after 10 cycles. This translates to 66% retention of the theoretical full conversion capacity of FeP(2) (1365 mA h g(-1)).

Electrodeposited Thick Amorphous Fe-P Foils Having Improved Soft Magnetic Properties

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Pulse Plated Amorphous Fe-P Thin Layers for High Frequency Magnetic Applications

Amorphous and partly nanocrystalline amorphous iron-phosphorus (Fe-P) layers have been deposited by pulse electrochemical technique. X-ray Diffraction (XRD) and Transmission Electron Microscopy (TEM) have been used to characterize the structure in the layers. Depending on the pulse parameters, the structure of Fe-P layers changed from mostly amorphous to partly nanocrystalline amorphous. The magnetic coercivity and the frequency limit of the samples are discussed in terms of the structure of the Fe-P layers. The frequency limit as determined from the permeability spectra is above 10 MHz, which makes these layers suitable for high frequency inductive element applications.

Comparative study of the structure and magnetic properties of Co-P and Fe-P amorphous alloys

We present the structural parameters of a complete series of ${\mathrm{Co}}_{1\ensuremath{-}x}{\mathrm{P}}_{x}$ $(x=0.17\ensuremath{-}0.26)$ amorphous alloys as obtained by the analysis of x-ray absorption fine structure measurements. To investigate their correlation with the magnetic properties, we have performed magnetization measurements in the same set of samples, obtaining the concentration dependence of the saturation magnetization, Curie temperature, and the behavior of the low-temperature magnetization. The results for the Co-P system are then compared with the ones of amorphous Fe-P, in order to clarify whether the different structural features found can be used to explain the different behavior of the magnetic properties that these systems exhibit. The evolution of the spontaneous magnetization with the metalloid content is the same for both systems. The Curie temperature decreases appreciably in Co-P, while remaining unchanged in Fe-P. The main result of the structural analysis shows that the bonding distances between metal atoms increases in the Co-P system, whereas they do not change in Fe-P. These magnetic and structural differences are correlated in basis of simple magnetic models.

The Anodic Behaviour of Electrodeposited Amorphous Fe-P and Ni-Fe-P Coatings Studied by X-ray Photoelectron Spectroscopy

SUMMARYThe relationship was studied between the corrosion-electrochemical state of Fe-P and Ni-Fe-P alloys containing different amounts of Fe and the composition of the surface film, which plays a crucial role in the corrosion resistance. The electrodeposited amorphous alloys Fe-P, Ni-Fe29-P18 and Ni-Fe0. 7-P18.7 are not passivated in 0.1N H2SO4 The anodic dissolution rate in the active state is abruptly reduced with a increase in the percentage of Ni content in the alloy. The elemental composition of the surface layers and the type of chemical compounds corresponding to depths down to 1000 Å after treatment at the stationary corrosion potential and after anodic dissolution in active state at the maximum rate were determined by XPS methods. The ratio between the basic components of the Ni, Fe and P alloys in the surface films (especially as a result of the treatment) is quite different from that in the bulk. In the case of Ni-Fe-P alloys the surface film is enriched with Fe, which is very pronounced in alloys with low Fe content, in Fe-P alloys Fe is depleted in the film. This phenomenon is due to the different degree of oxidation on the surface where iron oxides of the types Fe2O3 and Fe3O4 are registered. It is presumed that in alloys Fe-P and Ni-Fe29-P18 after anodic treatment in 0.1N H2SO4 a relatively thick diffusion-barrier film is formed, which consists mainly of Fe oxides and P compounds and displays good ionic conductivity, offering a possibility for high anodic dissolution rates.

Biomineralization at hot springs and mineral springs, and their significance in relation to the Earth's history

Recently, there is strong interest on microbe-mineral interactions. This is related also to recent expanded knowledges on extremely severe environments in which microbes live. Interaction between microbes and minerals contains biomineralization processes. Varieties of biomineralization products are found not only in various geologic materials and processes in the earth's history but also in present surface environments. Some hot springs represent such environments similar to those of unique and extremely severe environments for life. In this short review, the author briefly shows some examples of biomineralizations at some hot springs and mineral springs, Japan. In such environments, iron ore was formed and some varieties of growing stromatolites were found. The varieties of stromatolite are siliceous, calcic and manganese types. Cyanobacteria and the other bacteria are related to form the stromatolite structure. In the Gunma iron ore, sedimentary iron ores were mineralogically described in order to evaluate the role of microorganisms and plants in ore formation. The iron ore is composed of nanocrystalline goethite. Algal fossils are clearly preserved in some ores. Various products of biomineralization are found in the present pH 2-3, Fe2(+)- and SO4(2-)-rich streams. Bacterial precipitation had variations from amorphous Fe-P-(S) precipitates near the outlet of mineral spring, to Fe-P-S precipitates and to Fe-S-(P) precipitates. Mosses and green algae are also collecting Fe precipitates in and around the living and dead cells. The Gunma Iron Ore can be said as Biologically Induced Iron Ore. At Onikobe and Akakura hot springs, growing stromatolites of siliceous and calcareous types, were found, respectively. At Onikobe, The stromatolites grow especially near the geyser. Cyanobacterial filaments in stromatolite were well preserved in the siliceous and calcic stromatolites. The filaments oriented in two directions which form the layered structures were found. At Yunokoya hot spring, black and brittle stromatolitic structures which were composed of amorphous Mn minerals are growing. The form of these structures are hemispherical. Many bacteria that were coated with amorphous Mn minerals were found on these structures. Furthermore, Precambrian (Proterozoic : Wittenoom-Chichester region, western Australia) manganese stromatolite was briefly shown in comparison. The black stromatolite has been clarified to be composed of todorokite. Small spotty and donuts-like shaped todorokite aggregates which are very similar to biologically induced Mn-precipitates were found in massive dolomite layers.

Biologically induced iron ore at Gunma iron mine, Japan

The mineralogy of sedimentary iron ores from the Gunma iron mine are described to evaluate the role of microorganisms and plants in ore formation. The iron ore is composed of nanocrystalline goethite, well-crystallized jarosite and very small amounts of strengite. The ore characteristically occurs as thick-bands of alternating goethite and jarosite bands, thin-bands of different goethite grain sizes, and fossil-aggregate ore rich in moss and/or leaves. Algal fossils are clearly preserved in the goethite bands in the thick-banded ore. Lattice imaging showed characteristic crystallographic orientations of the goethite nanocrystals. The thin-banded iron ores consist of micrometer-sized chestnut-burr-like goethite aggregates, probably formed by bacterial iron biomineralization. The bands may be attributed to biological or seasonal rhythms. Various products of biomineralization are found in the present-day pH 2‐3, Fe 21 -, and SO -rich streams. Bacterial precipitation had var22 4 iations from amorphous Fe-P-(S) precipitates near the outlet of mineral spring to Fe-P-S precipitates and to Fe-S-(P) (schwertmannite-like) precipitates in the midstream. Mosses and green algae are also collecting Fe precipitates in and around the living and dead cells. Comparison of the processes occurring in the present-day streams and the iron-ore specimens supports the interpretation of these ores as the product of biomineralization.

Internal stress and magnetic properties of electrodeposited amorphous Fe-P alloys

Amorphous Fe–P alloys were electrodeposited under galvanostatic conditions at a current density of 10Adm–2 from sulfate–chlorine solutions containing β-alanine and glycine, as well as hypophosphoric acid. It was established that an increase in the deposition temperature from 50 to 60°C causes an increase in the deposition rate and a substantial rise in current efficiency and internal stress (IS). With pH increase from 2.0 to 3.0 the phosphorus content decreases, current efficiency almost doubles and there is a substantial drop in IS. It is assumed that a higher electrolyte acidity enhances hydrogen occlusion in the coating, which then desorbs from the deposit creating tensile IS. The same correlation between IS and current efficiency is observed when glycine concentration varies. A profile of residual IS is plotted illustrating the IS distribution throughout the deposit thickness. When the samples are magnetized in the coating plane, the shape of the hysteresis loop indicates perpendicular magnetic anisotropy. This is due to the columnar structure observed in scanning electron micrographs of the coating cross-sections. There is a linear dependence between IS and coercivity of amorphous Fe–P alloys deposited under different conditions.

Direct production of ultrafine amorphous Fe-P alloy particles by the plasma method

Ultrafine amorphous Fe-P alloy particles were directly synthesized by the plasma using cyclopentenyl iron and phosphorous trichloride as starting materials. The plasma gas greatly influenced the morphology, dispersion and composition.The particles were roughly spherical with a diameter of 40–200 nm and had the composition of Fe106P50. Elemental chlorine was found in the surface of the particle especially prepared under argon plasma conditions. It was bonded with phosphorus and carbon in Fe-P particles prepared in argon plasma and mainly with carbon in Fe-P particles deposited under a hydrogen plasma. Formation of Fe-P improves the stability of phosphorus in air. Phosphorus enrichment in the surface of Fe-P particles was also found. The particles were characterized by TEM, SEM, infrared-spectroscopy, X-ray photoelectron spectroscopy quantitative analysis, differential scanning colorimetry, inductively coupled plasma, X-ray diffraction and X-ray microprobe analysis. The formation mechanism of Fe-P amorphous particles was also discussed.

EXAFS study of compositional dependence of short range order in amorphous FeP electrodeposited alloys

Fe and P K-edges have been studied in a series of Fe 100− x P x (16 ⩽ x ⩽ 22) amorphous alloys. Changes of short range order with sample composition have been correlated with magnetic properties.

Average and local magnetic moments on Fe atoms in microcrystalline and amorphous Fe 100− xP x alloys

We have measured the concentration dependence of the average magnetic moment per Fe atom m̄ Fe( x) in microcrystalline and amorphous Fe-P alloys obtained over a wide concentration range using electrochemical deposition. The model of local magnetic moments has been used to described m̄ Fe( x). On the basis of this model the effects of phosphorus on the value m̄ Fe are explained in terms of the parameters of the local environment of the Fe atom.

The investigation of magnetic state variations in α-Fe and its alloys by means of continuous temperature scanning of the Mössbauer effect

A new method for continuous temperature scanning of the Mossbauer effect was developed permitting the measurement in a broad temperature range with satisfactory precision. The temperature dependence of Mossbauer radiation transmission for α-Fe, amorphous Fe-P and for alloys was measured from 20–800°C. A region of anomalous transmission was observed for crystalline α-Fe and its alloys and a new method of Debye-temperature determination was proposed.