Cobalt Hexacyanoferrate Nanoparticles Research Articles

PEDOT/Cobalt hexacyanoferrate free-standing films for high-performance quasi-solid-state asymmetric supercapacitor

Recently, with the increasing number of electronic devices and electric vehicles, supercapacitors have been investigated as high-performance energy storage devices. However, most electrodes fabricated with inactive additives (binder and conductive agent) have a problem with dead mass in the electrodes, which limits the application of lightweight energy storage devices. Herein, poly[3,4-ethylenedioxythiophene] nanowires (PEDOT NWs)/Cobalt hexacyanoferrate nanoparticles (CoHCF NPs) free-standing films (PCF films) were prepared using a vacuum-assisted filtration process. The PEDOT NWs acted not only as active materials but also as conductive substrates and provide numerous sites for the CoHCF NPs to achieve enriched redox reactions. The as-prepared free-standing PCF-4 electrode displays a high areal capacity of 386.4 µA h cm −2 at a current density of 1 mA cm −2 and the long-term stability in 1 M Na 2 SO 4 electrolyte. The fabricated quasi-solid-state asymmetric capacitor (PCF-4//activated carbon) shows a high energy density of 0.126 mW h cm −2 and power density of 0.82 mW cm −2 . • Free-standing PEDOT NWs/CoHCF NPs film was prepared by a vacuum-assisted filtration process. • The Free-standing film was studied as electrode material for supercapacitors. • The capacitive PEDOT NWs act as not only an active material but also a conductive substrate. • The fabricated film displays the good electrical conductivity and excellent areal capacity.

Synthesis, characterization, and the effectiveness of cobalt hexacyanoferrate nanoparticles in Cs+ adsorbent application

Synthesis, characterization, and the effectiveness of cobalt hexacyanoferrate nanoparticles in Cs+ adsorbent application

Alternately Dipping Method to Prepare Graphene Fiber Electrodes for Ultra-high-Capacitance Fiber Supercapacitors.

SummaryFlexible fiber supercapacitors are promising candidate for power supply of wearable electronics. Fabrication of high-performance fibers is in progress yet challenging. The currently available graphene fibers made from wet-spinning or electro-deposition technologies are far away from practical applications due to their unsatisfactory capacitance. Here we report a facile alternately dipping (AD) method to coat graphene on wire-like substrates. The excellent mechanical properties of the substrate with greatly diverse choices can be carried over to the fiber supercapacitors. Under such guideline, the graphene fiber with a titanium core made by our AD method (AD:Ti@RGO) shows an ultra-high specific capacitance of up to 1,722.1 mF cm−2, which is ∼1,000 times that of wet-spinning- and electro-deposition-fabricated neat graphene fibers and presents the highest specific capacitance to date. With excellent mechanical properties and striking electrochemical performances, the AD:Ti@RGO-based supercapacitors light the path to the next-generation technologies for wearable devices.

Self-assembled globular clusters-like cobalt hexacyanoferrate/carbon nanotubes hybrid as efficient nonprecious electrocatalyst for oxygen evolution reaction

For the first time, a novel of self-assembled globular clusters-like cobalt hexacyanoferrate/carbon nanotubes electrocatalyst has been synthesized by a facile one-pot chemical co-precipitation method. Compared to bare cobalt hexacyanoferrate with higher onset overpotential of 296 mV vs. RHE, a larger Tafel slope of 107.27 mV dec−1 and higher overpotential of 411 mV at 10 mA cm−2 for OER, the optimized cobalt hexacyanoferrate/carbon nanotubes hybrid exhibits a much lower Tafel slope of 62.43 mV dec−1 and smaller onset overpotential of 152 mV, and its overpotential at 10 mA cm−2 is only 274 mV. Most importantly, at a fixed overpotential of 400 mV, cobalt hexacyanoferrate/carbon nanotubes hybrid with 20 mg carbon nanotubes delivers a large current density of 95.02 mA cm−2, which is over ten times than that of bare cobalt hexacyanoferrate (8.52 mA cm−2). The dramatically enhanced OER performances are mainly assigned to the unique globular clusters-like structure and the good synergistic effect between cobalt hexacyanoferrate nanoparticles and highly conductive carbon nanotubes skeleton, leading to producing the higher electrochemical active surface area and much lower impedance. This work provides a simple strategy to rationally design and synthesize transition metal hexacyanoferrate-based catalysts as highly efficient nonprecious electrocatalysts for OER.

Electrochemical properties of Langmuir-Blodgett films containing cobalt hexacyanoferrate nanoparticles

Langmuir-Blodgett films modified by an electrochemically active compound, such as cobalt hexacyanoferrate, are of interest to create water-insoluble film electrodes with a high concentration of active centers and a low response time. The possibility of introducing cobalt hexacyanoferrate nanoparticles stabilized by sodium hexametaphosphate in octadecylamine monolayers with subsequent transfer them to a solid substrate by the Langmuir-Blodgett method is shown. Cobalt hexacyanoferrate nanoparticles were obtained by gradual mixing of an equimolar reagents mixture with the addition of sodium hexametaphosphate as a stabilizer. The size of nanoparticles were determined by the laser diffraction method, the size of their main number was about 12 nm. The hydrosol of the nanoparticles stability was studied photometrically in the pH range 2–4. The π-A octadecylamine monolayers isotherms on a subphase containing cobalt hexacyanoferrate nanoparticles were studied at the same pH values. According to the obtained data, optimal conditions for the monolayers transfer to a solid substrate by the Langmuir-Blodgett method were chosen. The morphology of the resulting films was studied on the surface of solid substrates. The electrochemical properties of electrodes based on Langmuir-Blodgett films in various solutions of electrolytes were studied by using the cyclic voltammetry and potentiometry.

High-performance counter electrode of carbon nanocubes with embedded cobalt-iron alloy nanoparticles for dye-sensitized solar cells

High concentration of polyvinylpyrrolidone (PVP) favored the growth of cobalt hexacyanoferrate (CoHCF) nanocubes with sharp corners and small particle size during synthesis. The cobalt-iron (CoFe) alloy nanoparticles were embedded in the carbon matrix through pyrolysis of the CoHCF powder. The presence of PVP in CoHCF also changed the morphology and microstructure of the resultant carbon-CoFe composite. Bare CoHCF formed bamboo-like hollow nanotubes, while CoHCF nanoparticles capped with large and small amounts of PVP tended to form porous nanocubes and aggregated nanoparticles, respectively. Cyclic voltammetry and electrochemical impedance measurements indicated that the carbon-CoFe nanocube electrode exhibited better catalytic performance than the nanotube, nanoparticle, and Pt electrodes, mostly due to its higher surface area and suitable pore size distribution for facilitating the iodide/triiodide couple. Dye-sensitized solar cells (DSSCs) employing the nanocube counter electrode (CE) exhibited a high photovoltaic conversion efficiency of 9.20%, which was greater than those obtained using Pt (8.94%), nanotube (8.48%), and nanoparticle (8.40%) CEs. The enhanced performance of the DSSC using the nanocube CE was due to the low charge-transfer resistance of the porous nanocubes with embedded CoFe nanoparticles compared to the other CEs.

Synthesis of cobalt hexacyanoferrate nanoparticles and its hydrogen storage properties

In the present paper, we report hydrogen storage properties of cobalt hexacyanoferrate nanoparticles as a function of temperature. Cobalt hexacyanoferrate nanoparticles were synthesized by facile chemical precipitation method. The resulted compound forms FCC structure analogous to Prussian blue and is found to be stable up to 550 K. Presence of characteristic absorption bands in the range of 2000–2300 cm−1 in IR spectra corresponds to the CN stretching frequency of Fe(III)CNCo(II) sequence and this confirms the formation of Prussian blue analogues. Hydrogen adsorption studies were performed at variable temperatures. The effect of precursor concentration on hydrogen storage property has been investigated and interestingly, with increase in cobalt precursor concentration, hydrogen storage capacity is found to decrease. This correlates well with openness of the crystal structure. To the best of our knowledge, this is the first report on hydrogen storage properties of cobalt hexacyanoferrate.

Electron transfer in cobalt hexacyanoferrate nanoparticles promoted by reverse microemulsions prepared with Cetyltrimethylammonium surfactants

Reverse microemulsions (RME) formed with the systems CTAX + pentanol/hexane/water (where X = Br−, Cl− or p-toluensulfonate) were used as synthesis media of cobalt hexacyanofarrate nanoparticles (CoHCF-NP). In this work, the effect that these RME have on the final structure of the CoHCF-NP is presented. Starting with a reaction between the reactant ions (RI) Co2+ and [Fe(CN)6]3−, CoHCF-NP with the expected structure based on the chain FeIII-CN-CoII can be obtained. By changing variables that defines the RME, it is possible to promote an electron transfer inside the CoHCF-NP to change the structure from FeIII-CN-CoII to FeII-CN-CoII. Variables as water concentration, distribution of the RI in the RME droplets, the surfactant counterion, and the concentration ratio of the RI showed a remarkable effect on the CoHCF-NP. CoHCF-NP in which the chain FeIII-CN-CoII predominates in the structure can be synthesized using RME formed with: i) CTAB at high RI and water concentration; ii) CTAT, when the concentration of RI is higher than 0.02 M. On the other hand, CoHCF-NP with predominance of FeII-CN-CoII can be synthesized using RME formed with: i) CTAB at low RI and water concentration; ii) CTAC, regardless the RI and water concentrations. This information is summarized in a concentration diagram where it is possible to predict the structure of the CoHCF-NP. To the best of our knowledge, this type of diagrams has not been constructed before for any of the Prussian blue analogues synthesized in RME.

Cobalt hexacyanoferrate nanoparticles and MoO3 thin films grown on carbon fiber cloth for efficient flexible hybrid supercapacitor

For the wearable and flexible applications, solid-state supercapacitors have been attracted significant attention owing to their unique features. Herein, we demonstrated the fabrication of a high-energy solid-state hybrid supercapacitor by using cobalt hexacyanoferrate nanoparticles and molybdenum oxide thin films grown on the flexible carbon fiber cloth. The flexible hybrid supercapacitor using a neutral gel electrolyte can be operated in a stable potential window of 2.0 V and delivers a maximal energy density of 67.8 Wh kg−1 at the power density of 1003 W kg−1, outstanding reliability without capacitance degradation under various twisting rates, and remarkable cycling stability retaining 74% of initial capacitance after 10000 cycles.

Cobalt hexacyanoferrate nanoparticles for wet-processed brown–bleached electrochromic devices with hybridization of high-spin/low-spin phases

A brown–bleached electrochromic device with inorganic printed nanoparticles and an appropriate mixture of a low-spin and a high spin state.

An electrochemical sensor for hydrazine and nitrite based on graphene–cobalt hexacyanoferrate nanocomposite: Toward environment and food detection

Hydrazine and nitrite are well known as carcinogenic substances, which however, are commonly used in chemical industry and food processing. Monitoring of such two species in water and food is necessary. Here, we report a convenient electroanalytical method for detection of hydrazine and nitrite by facile preparation of graphene–cobalt hexacyanoferrate nanocomposite through a two-step electrode surface functionalization. The morphology and constituent of the prepared nanocomposite were characterized by scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. Cyclic voltammetry was used to profile the electrochemical behaviors of hydrazine and nitrite, revealing the synergetic electrocatalytic function of reduced graphene oxide and cobalt hexacyanoferrate nanoparticles. This was confirmed by the decreased oxidation overpotentials and increased current response of the target analytes, and thus offered a premise for electroanalysis. The quantitative measurements were carried out by amperometry and differential pulse voltammetry, respectively. Moreover, the analytical utility was demonstrated by determination of water samples and pickled food; the average recovery was found to be from 92.2% to 108%, with the relative standard deviation (RSD) less than 7.8%. The present method opens an avenue for detection of potential carcinogens in relation to environment and food territory.

A novel nonenzymatic H2O2 sensor based on cobalt hexacyanoferrate nanoparticles and graphene composite modified electrode

A nanocomposite of cobalt hexacyanoferrate nanoparticles (CoHCFNPs) and graphene was synthesized by using a facile precipitation method. As a kind of modified electrode materials, CoHCFNPs/graphene nanocomposite was used to fabricate a nonenzymatic H2O2 sensor. Several techniques, such as Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM) and inductive coupled plasma emission spectrometry (ICP) and electrochemistry, were performed to characterize the modified electrode. Experimental results demonstrated that the prepared sensor exhibited intensive electrocatalytic activity toward the oxidation of H2O2. Under the optimum conditions, the proposed nonenzymatic sensor can be applied to the detection of H2O2 with a wide linear range of 0.6–379.5μM and a low detection limit of 0.1μM.

Cobalt hexacyanoferrate nanoparticles as a high-rate and ultra-stable supercapacitor electrode material.

Although great recent efforts have been invested to improve the performance of supercapacitors, these energy storage devices still fall short of meeting our expectations because of their limited working voltage, insufficient cycle life, and high manufacturing cost. Here, we report the facile preparation of cobalt hexacyanoferrate (CoHCFe) nanoparticles, which have an analogous structure to Prussian blue but with many vacant ferricyanide sites. In 0.5 M Na2SO4, CoHCFe exhibits specific capacitance of >250 F/g, excellent rate capability, and ultrahigh cycling stability with capacitance retention of 93.5% after 5000 cycles. Furthermore, CoHCFe was paired up with a carbon black modified graphene (mRGO) negative electrode to form asymmetric supercapacitors. They deliver a wide working voltage of ∼2.4 V in Na2SO4, large energy density and power density. Given its high electrochemical performance, chemical robustness, environmental benignity, ease of preparation and low cost, CoHCFe as well as other Prussian blue analogues clearly deserve more attention for future energy storage applications.

Amperometric detection of hydrogen peroxide utilizing synergistic action of cobalt hexacyanoferrate and carbon nanotubes chemically modified with platinum nanoparticles

In this study, a novel composite of cobalt hexacyanoferrate nanoparticles (CoNP) and platinum nanoparticles (Pt) on carbon nanotubes (CNTs) is obtained by ultrasonically mixing CoNP synthesized in a microemulsion with CNTs chemically modified with platinum nanoparticles (Pt/CNTs). Cyclic voltammetric and amperometric measurements on a glass carbon electrode showed that the composite (called CoNP–Pt/CNTs) exhibits a well-defined pair of redox peaks and a prominent electrocatalytic activity toward hydrogen peroxide (H2O2) reduction. Besides, the current response of CoNP–Pt/CNTs is 2 orders of magnitude higher than the response of CoNP alone and 1 order of magnitude higher than the response of Pt/CNTs or CoNP/CNTs alone. This higher efficiency can be attributed to a remarkable synergistic effect between CoNP, Pt and CNTs. This sensor shows a linear response to H2O2 concentrations ranging from 0.2 μM to 1.25 mM with a detection limit of 0.1 μM, a maximum sensitivity of 0.744 A·M−1 and a fast response time below 2 s.

Electrochemical preparation of cobalt hexacyanoferrate nanoparticles under the synergic action of EDTA and overoxidized polypyrrole film

The cobalt hexacyanoferrate nanocrystals (Nano-CoHCF) with uniform shape and size were electrochemical deposited on the electrode surface modified with the overoxidized polypyrrole (OPyox) film in the presence of ethylene diamine tetraacetic acid (EDTA). The conceivable effect of EDTA and OPyox film was studied using SEM and electrochemical techniques. The experiment results showed that the nucleation and deposition rate of CoHCF on the electrode surface were controlled by the synergic action of EDTA and OPyox film, which resulted in the formation of uniform Nano-CoHCF. Moreover, some electrodeposition conditions for Nano-CoHCF film had been optimized such as pH, concentration of EDTA, as well as deposition cycles. The resulting modified electrode exhibited excellent catalytic activity and improved stability for the oxidation of hydrazine. Hydrodynamic amperometry was applied for the determination of hydrazine with a linear range of 2.0×10−7 to 1.1×10−5molL−1 and 1.1×10−5 to 4.1×10−4molL−1 with the maximum sensitivity of 2719.5μAmM−1cm−2.

Nano-Prussian blue analogue/PEDOT:PSS composites for electrochromic windows

Owing to the redox reversibility and color-tunable property, Prussian blue (PB) and its analogs (PBAs) have been of interest in the field of electrochromics. However, most PBAs have long lacked an effective method for processing them as uniform and robust thin films on transparent conductive substrates, so the applications of most PBAs for electrochromic windows are not yet realized. Here we propose a composite film approach to tackle this bottleneck. We employ poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) ink as a dispersive medium for spin coating of PBA nanoparticles on indium tin oxide (ITO) glasses. Two kinds of PBAs, highly transparent zinc hexacyanoferrate (ZnHCF) and electrochromically active cobalt hexacyanoferrate (CoHCF) nanoparticles, are prepared and used to prove this idea. From SEM pictures, we find that a uniform nano-ZnHCF film up to 1.76μm in coating thickness can be deposited on the ITO slide, and the morphology of cuboid-shape ZnHCF nanoparticles (200–500nm) is highly dependent on the co-precipitation concentration. Enhanced charge capacity, cycle life and diffusion characteristics for nano-ZnHCF through networking with PEDOT:PSS are demonstrated with cyclic voltammetric (CV) analyses. According to the AC impedance characterization by a new Randles circuit model, it is found that PEDOT:PSS not only serves as a transparent conductive binder for nano-ZnHCF but also acts like a pseudo-capacitor that holds electric charge for facile electron transfer between the nanoparticles. To demonstrate practical devices, a 10×10cm2 WO3 window prototype with a maximum transmittance modulation of 61.6% at 700nm and a polymeric red-green-blue (RGB) device prototype with a low driving voltage of 1.6V are successfully fabricated with the nano-ZnHCF/PEDOT:PSS counterelectrode. The PEDOT:PSS-assisted spin coating also attains a reliable nano-CoHCF thin film that shows vivid red-to-green electrochromism and has an AC impedance feature perfectly explained by the new Randles circuit. To sum up, we believe that the PEDOT:PSS-assisted spin coating can be applied to other nano-PBAs and may help realize the PBA-based electrochromic windows.

Electrochemical imprinted sensor for determination of oleanic acid based on poly (sodium 4-styrenesulfonate-co-acrylic acid)-grafted multi-walled carbon nanotubes-chitosan and cobalt hexacyanoferrate nanoparticles

A novel sensitive and selective imprinted electrochemical sensor for the determination of oleanic acid was constructed on a carbon electrode by stepwise modification of functional multi-walled carbon nanotubes, cobalt hexacyanoferrate nanoparticles and a thin imprinted sol–gel film. The fabrication of a homogeneous porous poly (sodium 4-styrenesulfonate-co-acrylic acid)-grafted multi-walled carbon nanotubes/SiO2–chitosan nanocomposite film was conducted by controllable electrodeposition technology. The surface morphologies of the modified electrodes were characterized by scanning electron microscope. The performance of the imprinted sensor was investigated by cyclic voltammetry, square wave voltammetry and electrochemical impedance spectroscopy in detail. The imprinted sensor displayed high sensitivity and selectivity towards oleanic acid. A linear relationship between the sensor response signal and the logarithm of oleanic acid concentrations ranging from 1.0×10−8 to 1.0×10−3molL−1 was obtained with a detection limit of 2.0×10−9molL−1. It was applied to the determination of oleanic acid in real capsule samples successfully.

An electrocatalytic transducer for l-cysteine detection based on cobalt hexacyanoferrate nanoparticles with a core–shell structure

The electrocatalytic oxidation of l-cysteine (CySH) was studied on cobalt hexacyanoferrate nanoparticles with a core–shell structure (iron(III) oxide core–cobalt hexacyanoferrate shell) using cyclic voltammetry and chronoamperometry. Voltammetric studies represented two quasi-reversible redox transitions for the nanoparticles in phosphate buffer solution (pH 7.4). In the presence of CySH, the anodic peak current of the Fe(II)/Fe(III) transition was increased, followed by a decrease in the corresponding cathodic peak current, whereas the peak currents related to the Co(II)/Co(III) transition almost remained unchanged. The results indicated that the nanoparticles oxidized CySH via a surface mediation electrocatalytic mechanism. The catalytic rate constant, the electron transfer coefficient, and the diffusion coefficient involved in the electrooxidation process of CySH are reported here. Ultrasensitive and time-saving determination procedures were developed for the analysis of the CySH, and the corresponding analytical parameters are reported. According to the proposed methods, CySH was determined with detection limits of 40 and 20 nm in batch and flow systems, respectively. The proposed amperometric method was also applied to the analysis of CySH in human urine and serum blood samples.

Synthesis and Characterization of Nanostructured Cobalt Hexacyanoferrate

Cobalt hexacyanoferrate (CoHCF) nanoparticles have been synthesized by mixing aqueous solutions of K3Fe(CN)6 and CoCl2 under vigorous stirring at different temperatures and following two different procedures, drop-by-drop or immediate mixing. The resulting CoHCF nanoparticles, with dimensions of several tens of nanometers, were characterized using TEM, SEM-EDX, IR, and XRD. Their electrochemical behavior was investigated in comparison with the CoHCF powder bulk compound. The CoHCF nanoparticles exhibit an electrochemically driven conversion to the bulk one that has been investigated by a chemometric approach in order to establish the best synthetic parameters. The rate and the degree of conversion depend on the synthesis temperature.

Cobalt hexacyanoferrate–poly(methyl methacrylate) composite: Synthesis and characterization

The preparation of cobalt hexacyanoferrate nanoparticles–poly(methyl methacrylate) (CoHCF–PMMA) composites are described together with their characterization and thermochromic properties. CoHCF nanoparticles – investigated by dynamic light scattering – were prepared by optimizing solvent composition and temperature to obtain nanoparticles with a reduced degree of aggregation. The nanoparticles were embedded in a PMMA matrix to obtain a transparent coloured composite which was studied by transmission electron microscopy. The nanoparticle chromic features, enhanced by their reduced sizes, were investigated by UV–vis and FT-IR spectroscopy.