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Like other aqueous batteries, aqueous rechargeable Al‐ion batteries (ARAIBs) have attracted much attention due to their high safety and low cost. However, the low energy density of ARAIBs limits its popularization and application. In order to solve this problem, in addition to choosing Al metal as the negative electrode, it is also necessary to choose a suitable positive electrode material. Here, a cubic phase cobalt hexacyanoferrate (CoHCF) with excellent rate and cycling performance is used as the positive electrode material. Due to the reversible catalysis of the Cl−/Cl0 reaction at high potential in saturated AlCl3 solution, it has the characteristics of high capacity up to 103.5 mAh g−1. Combined with the Al metal as negative electrode, an ARAIB with an average discharge voltage of 1.56 V and an energy density of 155 Wh kg−1 is constructed, which shows outstanding cycling and rate performances. [ABSTRACT FROM AUTHOR]

In this work the influence of the molar ratio on the dimensional and structural characteristics of cobalt hexacyanoferrate nanoparticles was studied. The synthesis was carried out by chemical method in an aqueous medium using potassium hexacyanoferrate and cobalt nitrate. As a result of the study of samples by the method of dynamic light scattering, the values of the hydrodynamic radius of the samples were obtained. It was found that the minimum size (R = 76 nm) has a sample with a molar ratio K3[Fe(CN)6] : Co(NO3)2= 4 : 1. Scanning electron microscopy revealed that cobalt hexacyanoferrate samples are irregularly shaped aggregates consisting of nanoparticles with a diameter of 50 to 150 nm. As a result of X-ray phase analysis, it was found that the samples have a face-centered cubic crystal structure (Fm 3 m). According to the Debye-Scherrer equation, the average size of crystallites in the samples is from 17 to 20 nm.

In this paper, a novel electrochemical sensing platform for the sensitive detection of interleukin 6 (IL-6) was designed and fabricated. A label-free aptasensor was fabricated by modifying the glassy carbon electrode (GCE) using a nanocomposite composed of carboxylated multi-walled carbon nanotubes (cMWCNTs), cobalt hexacyanoferrate (CoHCF) and gold nanoparticles (AuNPs). The nanocomposite improved electron transfer rate and increased intercalation of signaling molecules. Moreover, it also offers desirable capabilities for the immobilization of biomolecules. The cMWCNTs/CoHCF/AuNPs modified electrode showed good electrochemical characteristics and biocompatibility, thus achieving excellent sensor performance. The differential pulse voltammetry (DPV) was used to detect the peak current of CoHCF in the redox process. The peak current is proportional to the concentration of IL-6 on the electrode surface. Under optimal conditions, the proposed aptamer sensor exhibits a linear range from 0.5 pg/mL to 1000 pg/mL and has a low detection limit of 0.17 pg/mL. In addition, the IL-6 aptamer sensor has good selectivity, high stability, and satisfactory reproducibility, showing broad potential in clinical research and diagnostic applications.

[Display omitted] • The CoHCF/PANI composite with regular structure was finely customized. • The synergistic redox reactions of CoHCF and PANI layers improve HCDI performance. • The CoHCF/PANI electrode is more suitable as the negative electrode. In order to realize high desalting capacity of capacitive deionization (CDI) system, cobalt hexacyanoferrate/polyaniline (CoHCF/PANI) composite with hollow hierarchical tubular structure was finely prepared by employing conductive hollow PANI tube as the interconnection skeleton for CoHCF cubic particles grown in situ, thereby endowing this composite with good conductivity, abundant redox active sites and stable structure. The synergistic effect between the CoHCF layer and PANI layer makes the CoHCF/PANI electrode possess superior specific capacitance (263.8F·g−1) and high contribution of the capacitance behavior (87.8 %) at 5 mV·s−1. Compared with either the single PANI or CoHCF electrode, the CoHCF/PANI electrode exhibits outstanding salt adsorption capacity (30.48 mg·g−1), rapid salt adsorption rate (3.66 mg·g−1·min−1) and excellent cycle stability (retention rate 98.1 %). Different from the CoHCF/PANI(+)‖AC(−) cell, there is no inversion peak in the AC(+)‖CoHCF/PANI(−) cell, which testifies that the CoHCF/PANI electrode is easier to capture Na+ ions. Based on the XPS spectra before and after desalination tests, the Na+ adsorption mechanism of the CoHCF/PANI electrode as cathode for the hybrid capacitive deionization (HCDI) system was further explored. It is found that the change of element valence in CoHCF/PANI composites (reduction of Fe3+ to Fe2+ and Co3+ to Co2+ in CoHCF, partial reduction of −C = N+ to −N–H- in PANI) is the main factor leading to Na+ intercalation. This study emphasizes the significance for fine design of the electrode material and strategic configuration of the HCDI cell. [ABSTRACT FROM AUTHOR]

• A series of trimetallic (Co/Ni/Fe) PBAs were synthesized by a co-precipitation method. • The color change of the PBAs is readily modified by changing the Co/Ni molar ratio. • The lithium storage capacity and reaction potential are tuned by adjusting the Co/Ni molar ratio. • The series of PBAs exhibit a short response time and excellent cycling stability. Prussian blue (PB) and its analogs (PBAs) have become a research hotspot in the fields of electrochemical energy storage and electrochromism due to their good reversible redox activity, and reversible color change response in different redox states. Herein, a series of trimetallic PBAs (Co/NiHCF with Co to Ni molar ratios of 1:0, 3:1, 1:1, 1:3, and 0:1) are synthesized by a facile co-precipitation method. In particular, the impact of Co to Ni molar ratio on the lithium storage and electrochromic properties of Co/NiHCF materials are systemically investigated. All five samples possess good crystallinity but the particle size decreases with the reduction of Co/Ni molar ratio. The color change, redox reaction potential, and lithium storage activity of the samples can be readily controlled by adjusting the molar ratio of Co to Ni. The lithium storage activity of the samples strengthens with the increase of Ni content in Co/NiHCF, accompanied by a decrease in redox potentials. With the increase of Ni content, the color of the Co/NiHCF film in the oxidation state changes from purple-red to orange, and finally to yellow; in the reduction state, the color of the film changes from green to light green and then to colorless. All the samples exhibit superior rate capability, excellent cycling stability, and short switching time (in the range of 1.6 to 4.3 s). The present work demonstrates a facile strategy for readily tunning the lithium storage activity, redox reaction potentials, and realizing rich color changes of PBA-based bifunctional materials. [Display omitted] TOC Graphic [ABSTRACT FROM AUTHOR]

In-situ electrochemical deposition of cobalt hexacyanoferrate (CoHCF) on graphene oxide (GO) and its application for the electrocatalytic hydrazine determination in real samples are described in this research study. Co2+ is immobilized on GO and the resulting material, GO-Co2+ is coated on the surface of glassy carbon (GC) electrode. The fabricated electrode (GC/GO-Co2+) is subjected to a continuous potential cycling in the range of 0.0–1.0 V which results in the formation of a thin CoHCF film on the surface of GO coated on the GC electrode (abbreviated as GC/GO-CoHCF). The synthesized GO-CoHCF composite material is characterized by Fourier transform infrared and scanning electron microscopy. GC/GO-CoHCF electrode electrocatalytically oxidizes hydrazine at low overpotential (0.63 V) and this phenomenon is subsequently utilized for the sensitive determination of hydrazine in aqueous solutions. It exhibits a wide linear calibration range (0.1–400 µM), high sensitivity (0.93 µA µM−1 cm−2) and low limit of detection (17.5 nM) for the determination of hydrazine. Further, this electrode is employed for hydrazine determination in real samples. [ABSTRACT FROM AUTHOR]

Ni-doped cobalt hexacyanoferrate (NiCoHCF) microcubes were fabricated through co-precipitation method at room temperature. The doping of nickel ions shows positive effect on the nanostructure and electrochemical properties of the cobalt hexacyanoferrate (CoHCF). The results of scanning electron microscopy (SEM) and X-ray diffractometer (XRD) indicate that the doping of nickel ions can reduce the grain size of CoHCF microcubes. The as-synthesized NiCoHCF microcubes are studied as electrode materials for supercapacitor showing a high specific capacitance of 129.4 mAh g−1 (466 F g−1) at a scan rate of 5 mV s−1 and good cycling stability of retaining 87.9% after 2000 cycles in 1 M Na 2 SO 4 under 0–1 V at 2 A g−1 when the molar ratio of nickel-cobalt is 1:2 mmol. The enhanced electrochemical performance of NiCoHCF benefits from the strong synergistic utilization of nickel ions and cobalt ions. • The effect of nickel ions on CoHCF was systematically studied. • The grain size of CoHCF can be significantly controlled by doping nickel ions. • The maximum specific capacitance of NiCoHCF is 129.4 mAh g−1 at 5 mV s−1. [ABSTRACT FROM AUTHOR]

Prussian blue analogues (PBAs) have been proven to be a kind of seawater battery cathode due to the accommodation of electrons upon the intercalation of Na+ in seawater. In the current work, Ni-doped cobalt hexacyanoferrate (Co x Ni 1-x HCF) was fabricated by using co-precipitation method at room temperature. Results have shown that with increasing the molar ratio of Co: Ni, the specific capacity of the cathode initially increases and then decreases. The best battery properties were obtained when the molar ratio of Co: Ni was 1:2. The specific capacity was up to 76.5 mAh·g−1 at 0.1 A g−1, the capacity retention was up to 63.5 % at a current density of 10 A g−1, and the capacity retention of 81 % was obtained after 100 cycles. The introduction of Ni2+ increases the specific surface area leading to the additional active sites for the redox reaction. At the same time, the specific capacity decreased due to the Ni doping. The enhanced electrochemical performance of Co x Ni 1-x HCF cathode for seawater battery was achieved by considering the synergistic effects of specific surface and elemental composition. Furthermore, seawater battery was successfully assembled by matching the Co 0.86 Ni 0.14 HCF cathode with Mg anode, which demonstrates the promising application of PBAs for seawater batteries. • Seawater Battery (SWB) based on Prussian blue analogues. • Specific surface could be controlled by adjusting Ni doping content. • Satisfied specific capacity and cycle stability SWB was achieved by doping Ni2+. • SWB properties depend on synergetic effect of specific surface and composition. [ABSTRACT FROM AUTHOR]

• Controllable structure of CoSe 2 /FeSe 2 @C composites were fabricated. • The CoSe 2 /FeSe 2 @C composites with different structures exhibited various electrochemical performance. • The toughness of the carbon layer alleviates the volume expansion of bimetallic materials in long cycles. • CoSe 2 /FeSe 2 @C-2||AC all-solid-state flexible asymmetrical supercapacitors have the practicability of powering wearable electronic products. Designing and manufacturing novel energy storage device electrode materials, particularly for supercapacitors, are of critical importance. Here, structure-adjustable porous bimetallic selenides (CoSe 2 /FeSe 2) and carbon composites (CoSe 2 /FeSe 2 @C), derived from Co/Fe-Prussian Blue analogs, were successfully designed and fabricated as a high-performance positive electrode material. The results demonstrated the size and structure are crucial for electrochemical performance. Specially, the CoSe 2 /FeSe 2 @C-2 composite exhibits exceptional performance, with a specific capacitance of 1010 F g−1 at 0.5 A g−1 and prolonged lifespan (maintains 95.5% of its initial capacity after 15,000 cycles at 5 A g−1). The all-solid-state flexible asymmetrical supercapacitors (CoSe 2 /FeSe 2 @C-2//AC) were assembled with the positive electrode of CoSe 2 /FeSe 2 @C-2, which delivered a high energy density (13.13 Wh kg−1), and exceptional cycling stability (91.17% of the initial capacity after 7000 cycles at 2 A g−1). This work opens up an avenue to synthesize bimetallic selenides with different sizes and structures rationally and environmentally. [Display omitted] [ABSTRACT FROM AUTHOR]

Futuristic wearable electronics desperately need power sources with similar flexibility and durability. In this regard, the authors, therefore, propose a scalable PAN-PMMA blend-derived electrospinning protocol to fabricate free-standing electrodes comprised of cobalt hexacyanoferrate nanocube cathode and tin metal organic framework-derived nanosphere anode, respectively, for flexible sodium-ion batteries. The resulting unique inter-networked nanofiber mesh offers several advantages such as robust structural stability towards repeated bending and twisting stresses along with appreciable electronic/ionic conductivity retention without any additional post-synthesis processing. The fabricated flexible sodium ion full cells deliver a high working voltage of 3.0 V, an energy density of 273 Wh·kg -1 , and a power density of 2.36 kW·kg -1 . The full cells retain up to 86.73% of the initial capacity after 1000 cycles at a 1.0 C rate. After intensive flexibility tests, the full cells also retain 78.26% and 90.78% of the initial capacity after 1000 bending and twisting cycles (5 mm radius bending and 40 o axial twisting), respectively. This work proves that the proposed approach can also be employed to construct similar robust, free-standing nanofiber mesh-based electrodes for mass-producible, ultra-flexible, and durable sodium ion full cells with commercial viability., (© 2023 Wiley-VCH GmbH.)

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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) C N Co(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. [ABSTRACT FROM AUTHOR]

In the proposed work, we present a novel, high performance ternary hybrid nanocomposite material based on cobalt hexacyanoferrate/carbon nanofibers/polypyrrole (CoHCF/CNF/PPY). The nanocomposite is fabricated by in situ oxidative polymerization of pyrrole in presence of CoHCF and CNF utilizing simple, cost effective and environmentally friendly approach. The structural and elemental characterizations of the nanocomposite are carried out by various characterization techniques which revealed formation of PPY layer on CNF surface to which CoHCF nanoparticles are linked. Also, the thermal stability of nanocomposite is found to be increased due to presence of CNF backbone. The electrochemical performances of the nanocomposite are investigated by cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS) techniques, which resulted into specific capacitance of 512 F g −1 at the current density of 0.5 A g −1 . Moreover, it exhibits notable energy density of 102 W h. kg −1 and power density of 628 W kg −1 . It also shows capacitive retention up to 87.8% after 2000 cycles indicating excellent cyclic stability. The structural stability of CoHCF framework is maintained due to ion diffusion through the cavities and its combination with interlinking network of PPY chains on the surface of CNF enhances electron transport. This charge storage mechanism is responsible for improved charge storage capacity resulting into high energy density. Thus, proposed ternary hybrid nanocomposite of CoHCF/CNF/PPY can be considered to overcome the gap between supercapacitors and batteries, thus can serve as a promising candidate for the future energy storage technologies. [ABSTRACT FROM AUTHOR]

Flexible solid-state supercapacitor (FSSC) holds great promise as power source to supply the next generation of portable and wearable electronics. Assembling asymmetric supercapacitor constructed with broadening cell voltage ( V ) is the promising way to increase the energy density. However, the imparity reaction kinetics between EDLC and pseudocapacitive materials will further lead to inferior power density. Hence, to pursue higher working voltage and energy density, a hybrid configuration of cobalt hexacyanoferrate/reduced graphene oxide hydrogels (PB-Co/rGOH) is prepared through a one-pot hydrothermal method. With highly interconnected 3D network structure, excellent mechanical robustness and the synergistic effects between the graphene and PB-Co, the resultant PB-Co/rGOH exhibits a high specific capacitance of 220 F g −1 and well cycle stability (83% capacitance retention after 10,000 cycles at 5 A g −1 ). Moreover, the assembled PB-Co/rGOH//PB-Co/rGOH symmetric flexibly solid-state supercapacitor exhibits an amazing higher working voltage of 2.0 V and a remarkable energy density of 57.5 Wh kg −1 , which is comparable with that of Ni/MH batteries (60–120 Wh kg −1 ). These excellent electrochemical performances of the hybrid electrode provide a rational design strategy for developing supercapacitors with high energy density. [ABSTRACT FROM AUTHOR]

Supercapacitors are energy storage devices with remarkable properties including high power density, prolonged operational life, and hasty charging/discharging profile; however, a primary barrier to broad development is reduced energy density. Consequently, efforts have been undertaken to fabricate supercapacitors electrodes that resemble battery-type behavior. Owing to the unique structural characteristics and redox active sites, Prussian blue analogs (PBAs) are becoming attractive electrode materials. Herein, we presented the fabrication of ternary PBA-based electrode i.e., cerium cobalt hexacyanoferrate (CeCoHCF) with improved electrical properties and their characterization through different analytical techniques (SEM, FTIR, EDX, XPS, and XRD). The incorporation of cerium and cobalt together in PBA framework imparts a positive effect on the electrochemical properties. The as-synthesized CeCoHCF exhibits a significant specific capacity of 268.8 mA h g−1 at 1 A g−1 under alkaline conditions (3 M KOH) along with 88.6 % of capacity retention over 1000 cycles. Furthermore, the fabricated electrode exhibited the specific capacity 159.4 mA h g−1 at 1 A g−1 in neutral media (1 M Na 2 SO 4). To investigate the practical application, symmetric supercapacitor device was fabricated that provides improved energy and power density as well as a wide operational voltage of around 1.2 V. Conclusively, PBA-based material can be potential candidates for future storage applications, owing to their outstanding electrochemical performance, chemical resilience, simplicity of synthesis, and low cost. Due to the unique structural architecture and multiple redox active sites, PBAs are becoming attractive electrode materials. Herein, we have reported the synthesis of ternary PBAs based on CeCoHCF through a facile co-preparation procedure with improved electrochemical properties. The as-synthesized CeCoHCF exhibits a remarkable specific capacity of 268.8 mA h g−1 at 1 A g−1 in 3 M KOH along with good cyclic stability and capacity retention over 1000 cycles. Additionally, in 1 M Na 2 SO 4 , CeCoHCF exhibits a high specific capacitance of 159.4 mA h g−1 at 1 A g−1. Furthermore, the symmetric supercapacitor device was fabricated that displayed energy density of 16.36 Wh kg−1 at the power density of 500 W kg−1 with appreciable capacity retention. Conclusively, PBAs can be potential candidates for future storage applications owing to their outstanding electrochemical performance, chemical resilience, simplicity of synthesis, and low cost. [Display omitted] • The CeCoHCF composite was synthesized by a facile coprecipitation method. • It exhibited the specific capacity of 268.8 and 159.4 mA h g−1 at 1 A g−1 in 3 M KOH and 1 M Na 2 SO 4 , respectively. • The symmetric supercapacitor device displayed energy density of 16.36 Wh kg−1 at the power density of 500 W kg−1. [ABSTRACT FROM AUTHOR]

Vast improvement of the capacitance of supercapacitors without sacrificing high power density and cycle performance brings bright application prospect. Here, a novel cobalt hexacyanoferrate/multi-walled carbon nanotubes (CoHCF/MWCNTs) nanocomposite is prepared by a simple and facile approach and further investigated as electrode materials for supercapacitors. The physical properties of as-prepared materials are characterized by XRD, FTIR, Raman and FE-SEM techniques. Furthermore, electrochemical performances of as-prepared materials are investigated by cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy in 1.0 M Na 2 SO 4 electrolyte. It is shown that as-prepared CoHCF/MWCNTs (25.0 wt% of MWCNTs) nanocomposite based electrode exhibits the best electrochemical performances, including higher specific capacitance/capacity (648.5 F g −1 /810.6 C g −1 at 1.4 A g −1 ), good rate capability (648.5 F g −1 /810.6 C g −1 and 436.3 F g −1 /545.3 C g −1 at 1.4 A g −1 and 15 A g −1 , respectively) and excellent cycling stability (94.3% capacitance retention after 3000 cycles at 2.0 A g −1 ) in all as-prepared electrodes. The results demonstrate that as-prepared CoHCF/MWCNTs nanocomposite is a promising candidate for electrochemical energy storage. [ABSTRACT FROM AUTHOR]

A simple strategy has been proposed for the covalent anchoring of cobalt hexacyanoferrate (CoHCF) particles on graphitic carbon substrate using p-phenylenediamine as a linker molecule. The covalent anchoring was confirmed by X-ray diffraction, Fourier transform infrared spectroscopy and electrochemical studies. A robust pellet electrode was fabricated using CoHCF particles modified graphitic carbon and it has been applied in the electrocatalytic oxidation of sulfite. The proposed sensor showed a linearity in the concentration range 4–128 μM of sulfite with a limit of detection (LOD) 1.7 μM and limit of quantification (LOQ) 5.8 μM. Proposed sensor has been successfully applied to measure sulfite levels from a variety of food sample matrices. The results obtained by the proposed electrochemical sensor have been compared with the iodimetric method. [ABSTRACT FROM AUTHOR]

This paper examines the results of the characterization of two functional composites: Poly(methyl methacrylate) (PMMA)-Ce:YAG (yttrium aluminium garnet doped with cerium) and PMMA-cobalt hexacyanoferrate (CoHCF). The composites were prepared as possible emitters in the fields of lighting thermal sensors. The prepared composites were characterized using transmission electron microscopy (TEM), nuclear magnetic resonance (NMR) spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) analyses to study the correlation between micro and macro characteristics. We found that the molecular interactions of the two different fillers with the matrix were localized in different sites of the polymer chains. Moreover, the composites showed an increased thermal strength and stiffness, in particular the PMMA-Ce:YAG composite.

The electrocatalysis of dopamine has been studied using a cobalt hexacyanoferrate film (CoHCFe)-modified glassy carbon electrode. Using a rotating disk CoHCFe-modified electrode, the reaction rate constant for dopamine was found to be 3.5 × 105 cm3 mol-1 s-1 at a concentration of 5.0 × 10-5 mol L-1. When a Nafion® film is applied to the CoHCFe-modified electrode surface a high selectivity for the determination of dopamine over ascorbic acid was obtained. The analytical curve for dopamine presented linear dependence over the concentration range from 1.2 × 10-5 to 5.0 × 10-4 mol L-1 with a slope of 23.5 mA mol-1 L and a linear correlation coefficient of 0.999. The detection limit of this method was 8.9 × 10-6 mol L-1 and the relative standard deviation for five measurements of 2.5 × 10-4 mol L-1 dopamine was 0.58%.

A Prussian blue analogue, cobalt hexacyanoferrate Co 3 [Fe(CN) 6 ] 2 , was used for the first time to prepare a magnetic carbon/cobalt/iron (MCCI) nanocomposite via one-step carbonization of Co 3 [Fe(CN) 6 ] 2 . The resulting MCCI consisted of evenly-distributed cobalt and cobalt ferrite in a porous carbonaceous matrix, making it an attractive magnetic heterogeneous catalyst for activating peroxymonosulfate (PMS). As Rhodamine B (RhB) degradation was adopted as a model test for evaluating activation capability of MCCI, factors influencing RhB degradation were thoroughly examined, including MCCI and PMS dosages, temperature, pH, salt and radical scavengers. A higher MCCI dosage noticeably facilitated the degradation kinetics, whereas insufficient PMS dosage led to ineffective degradation. RhB degradation by MCCI-activated PMS was much more favorable at high temperatures and under neutral conditions. The presence of high concentration of salt slightly interfered with RhB degradation by MCCI-activated PMS. Through examining effects of radical scavengers, RhB degradation by MCCI-activated PMS can be primarily attributed to sulfate radicals instead of a combination of sulfate and hydroxyl radicals. Compared to Co 3 O 4 , a typical catalyst for PMS activation, MCCI also exhibited a higher catalytic activity for activating PMS. In addition, MCCI was proven as a durable and recyclable catalyst for activating PMS over multiple cycles without efficiency loss and significant changes of chemical characteristics. These features demonstrate that MCCI, simply prepared from a one-step carbonization of Co 3 [Fe(CN) 6 ] 2 is a promising heterogeneous catalyst for activating PMS to degrade organic pollutants. [ABSTRACT FROM AUTHOR]

Cobalt hexacyanoferrate (CoHCF) was electrodeposited into an organically modified silica (ormosil) film with a nanoarray of parallel, cylindrical channels, which were obtained using 20-nm poly(styrene sulfonate), PSS, beads as a templating agent. The PSS was bound to the electrode surface with 3-aminopropyltriethoxysilane, APTES. Methoxytrimethylsilane was the ormosil precursor. Electrochemically assisted processing at a positive potential where the hydrogen ion catalyst was generated was used to deposit the ormosil film. Subsequently, the PSS and APTES were removed to provide the pores. The CoHCF was deposited in the 20-nm channels by cyclic voltammetry of a freshly prepared KFe(CN), CoCl mixture with 1.0 mol dm KCl as the supporting electrolyte. Limiting the number of electrodeposition cycles to 10-20 resulted in CoHCF nanorods in the pores, whereas with 50 cycles bulk-form CoHCF spilled over the outer ormosil surface. Electrocatalytic oxidation of cysteine was successfully performed on these nanorod arrays, which showed greater catalytic activity than bulk-form CoHCF. [ABSTRACT FROM AUTHOR]

In this work, Co 2+ ions were initially intercalated into the layers of laponite and then cobalt hexacyanoferrates (CoHCFe) were electrogenerated on the surface of laponite-Co 2+ modified ITO via square wave voltammetry (SWV). At scan rate of 10 mV s −1 , the electrochemical response of the ITO/laponite/CoHCFe showed two pairs of well-defined redox peaks located about 0.44 and 0.672 V vs.SCE, attributed to the redox reaction of Co II /Co III and Fe II /Fe III , respectively. The modified electrode was highly electrocatalytic to the captopril oxidation. Moreover, the ITO/laponite/CoHCFe exhibited an enhanced analytical performance for amperometric detection of captopril with two enlarged linear ranges from 3.0 × 10 −7 to 1.27 × 10 −4 M and 1.63 × 10 −4 to 3.76 × 10 −4 M and a low detection limit (0.29 μM). The modified electrode was used for electrocatalytic determination of captopril in some real samples. [ABSTRACT FROM AUTHOR]

Cobalt hexacyanoferrate (CoHCF) suffers from low rate capability and lifespan because of the dissolution and structural instability of Co during cycling. A smaller active material can relieve the stress caused by volume change during cycling and enable shorter transport pathways. Here, particle size reduction is performed by reducing the mixing time or citrate concentration in the coprecipitation reaction to improve the rate capability and lifespan of CoHCF. The reduced mixing time produces smaller particles with enlarged active sites, thus improving the capacity. Upon coprecipitation at a low citrate concentration, particle precipitation at reduced sizes is achieved by preferential nucleation versus growth. Although lowering the citrate concentration enlarges the external surface area, the reduced redox-active Fe degrades the capacity. All CoHCF samples with small sizes achieved enhance rate capability and stability. In particular, the sample synthesized with a short mixing time (0 h) achieve a specific capacity of 122 mAh g−1 with improved rate capability (79.4%) and stability (79.3%) over 500 cycles. Structural distortions are relaxed because of the shortened transport pathways and relieved distortion owing to particle size reduction. This study paves the approach for fast rechargeable and long-lasting aqueous Na-ion batteries using CoHCF electrodes. [Display omitted] • A decreased mixing time or citrate concentration yielded smaller CoHCF particles. • The capacity, rate capability, and lifespan were improved with shorter mixing times. • The low citrate ion concentration increased Fe vacancies and decreased the capacity. • Fe vacancies limited Na access in the lattice, thus improving structural stability. • The reduced CoHCF particle size improved rate capability and lifespan. [ABSTRACT FROM AUTHOR]

[Display omitted] • KCoFe(CN) 6 shows superior cycling stability as K-ion storage host. • Co(NO 3) 2 is added into the electrolyte to consolidate the lattice structure. • K+ storage mechanism is released by various ex-situ methods. Aqueous potassium-ion batteries (APIBs) are emerging as candidates for large-scale energy storage in virtue of their cost-efficiency, environmental friendliness and intrinsic security. Nevertheless, the shortage of high-capacity and long-cycle K+ hosts imposes restrictions on developing advanced APIBs. Herein, KCo[Fe(CN) 6 ] (K-CoHCF) is synthesized through simple co-precipitation and applied as a novel cathode material for storage of K+ in APIBs. For building a strong host, Co(NO 3) 2 is introduced into the electrolyte to suppress the dissolution of Co ions and consolidate the lattice structure on account of "common ion effect". Thus, benefitting from its firm open structure as well as two active redox couples, K-CoHCF exhibits desirable capacity of 89.2 mAh g−1 at 100 mA g−1, excellent rate performance and superior cycling stability with 87.0% capacity retention upon 1400 cycles. In addition, the highly reversible structural evolution and single-phase reaction mechanism of K-CoHCF are unraveled by a series of ex-situ tests during K+ insertion/extraction. Thus, this work establishes a feasible battery system with K-CoHCF as cathode and sheds light on further development of advanced APIBs for practical utilization. [ABSTRACT FROM AUTHOR]

Sodium-based intercalation aqueous pseudocapacitive energy systems are attractive because of their obvious advantages including improved safety, low cost and environmental friendliness. Herein, an aqueous sodium-ion capacitor with the cobalt hexacyanoferrate (CoHCF) as the cathode electrode and carbon micro-spheres (CMS) as the anode electrode was fabricated, showing an extended operating voltage window (2 V), excellent capacitance behaviour, and high energy density (54.4 Wh kg −1 ). The present results provide meaningful clues to design new intercalation pseudocapacitor for future practical applications. And these remarkable features may pave the way to next-generation large-scale production of high performance hybrid supercapacitors performed as regulation or complementary devices. [ABSTRACT FROM AUTHOR]

ABSTRCT A three-dimensional graphene oxide/carbon nanotubes-COOH hybrid (GO/CNTs-COOH) consisted of two-dimensional graphene oxide (GO) and one-dimensional carbon nanotubes-COOH (CNTs-COOH) was synthesized. The GO/CNTs-COOH hybrid exhibited excellent water-solubility owing to the high hydrophilicity of GO components and the carboxylation of carbon nanotubes. The cobalt hexacyanoferrate decorated GO/CNTs-COOH (CoHCF/GO/CNTs-COOH) has been prepared using electrostatic adsorption of Co 2+ on GO/CNTs-COOH and K 4 [Fe(CN) 6 ] as an in-situ chemical precipitant. FT-IR, Raman spectroscopy, TEM, SEM, and cyclic voltammetry were utilized to characterize the nanohybrid. The electrochemistry behavior of hydrazine on different modified electrodes was also studied. The CoHCF/GO/CNTs-COOH modified GCE (CoHCF/GO/CNTs-COOH/GCE) exhibited greatly enhanced electrocatalytic performance towards electro-oxidation of hydrazine. The oxidation peak currents showed good linear relationships with concentration of hydrazine. It can be applied to detect hydrazine in samples sensitively. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Investigation of the redox properties of drugs and their determination are performed by electrochemical techniques. Data obtained from electrochemical techniques are often correlated with molecular structure and pharmacological activity of drugs. In this regard, different modified electrodes were applied as sensors for quantification of different drugs. A nanocomposite of reduced graphene oxide-cobalt hexacyanoferrate was synthesized by a simple precipitation route. Scanning electron microscopy revealed that the nanocomposite comprised nanoparticles of cobalt hexacyanoferrate attached to the reduced graphene oxide nanosheets. A nanocomposite-modified carbon paste electrode was then fabricated. It represented prominent activity toward the electrocatalytic oxidation of ascorbic acid, and the kinetics of the electrooxidation process was evaluated. Finally, an amperometric method was developed for the quantification of ascorbic acid in different pharmaceutical formulations. [ABSTRACT FROM AUTHOR]

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. [Display omitted] • 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. [ABSTRACT FROM AUTHOR]

The electrochemical modification of solid electrodes with metal hexacyanoferrate thin films for enhancing the interfacial properties has created interest for over the past three decades. The preparation of Prussian blue (PB) Au nano composites for the enhancement in the electrocatalytic properties of PB on glassy carbon electrode has been reported by us. The incorporation of Au nano particles in Cobalt hexacyanoferrate (CoHCF) films on Glassy carbon by co-electrodeposition is expected to benefit its interfacial electron transfer properties. The present work describes the effect on the interfacial properties by incorporated Au particles in CoHCF (CoHCF(Au)) modified electrodes. The CoHCF(Au) modified electrodes were characterized by UV-Vis spectrophotometry, Cyclic Voltammetry, AC Impedance, FE-SEM etc., Influence on the electrocatalytic properties of CoHCF(Au) films have been explored by performing two important reactions i) Hydrazine elecrtro-oxidation ii) Oxygen evolution reaction. Our results reveal that CoHCF(Au) modified GC electrode perform better in terms of charge transport in the redox film and also for the electrooxidation of hydrazine in comparision with simple CoHCF modified electrodes. By using the current-transient technique (chrono method i vs t curve) the hydrazine diffusion coefficient (D 0 ) were calculated. Diffusion coefficient of hydrazine was approximately three times higher on CoHCF(Au) electrode, 9.5 × 10 −5 cm 2 s −1 compared with simple CoHCF modified electrode, 3.3× 10 −5 cm 2 s −1 . Similarly, we also discuss results which reveal that CoHCF(Au) electrodes enhances electrocatalytic activity in splitting water to oxygen in 0.1 M NaOH solution compared to simple CoHCF and Au deposited on GC electrodes. [ABSTRACT FROM AUTHOR]

Highlights: [•] Iron oxyhydroxide@cobalt hexacyanoferrate coaxial nanostructure was synthesized. [•] The nanostructure showed an excellent pseudocapacitive behavior. [•] The electrode is biocompatible. [ABSTRACT FROM AUTHOR]

Highlights: [•] Redox state of cobalt hexacyanoferrate layer at electrode can be estimated by Raman spectroscopy. [•] Redox processes within this layer are limited by intrinsic electron transfer rate. [•] Electroreduction of hydrogen peroxide is limited by slow redox transformations within the modifier layer. [ABSTRACT FROM AUTHOR]

• Cobalt hexacyanoferrate nanocubes were electrodeposited on graphitized porous silicon to achieve a hybrid electrode for supercapacitor assembly. • CoHCF phase brought enhanced capacitive properties for the hybrid silicon electrode. • The supercapacitor was able to reach remarkable power density with high energy density. In this work, we report a scalable route to wafer-size processing for fabrication of hybrid nanocomposite electrodes based on cobalt hexacyanoferrate /carbon / porous silicon (CoHCF/C/Si) to improve the performances of silicon-based supercapacitors via electrochemical processes. First, an electrochemical etching process was used to obtain a 3D nanoporous matrix on the top of silicon wafer, and the resulted huge surface was then covered with active nanomaterials by the successive electrochemical deposition of an ultra-thin carbon layer and CoHCF nanocubes, respectively. The fabricated symmetric supercapacitor device showed excellent volumetric capacitance of about 5 F cm−3 at the current density of 0.7 mA cm−2, an outstanding volumetric power density of 19.42 W cm−3 with a high energy density of 0.98 mWh cm−3, achieving good cycling stability with a capacitance retention of 61% after 5000 cycles at a high rate of discharge current density, 100 A g−1. The nanosized CoHCF phase favors migration of Li+ ions into the material, followed by charge transfer reactions via insertion/extraction of alkaline ions into/from the cyano-bridged framework during the redox reactions of FeII/III and CoII/III ions as evidenced by CV and GCD. These results support the successful integration of CoHCF nanocubes with carbonaceous and silicon material using electrochemical methods, rendering synergistic effects over the electrochemical performances. [Display omitted] [ABSTRACT FROM AUTHOR]

A cobalt hexacyanoferrate modified electrode has been prepared following an "insertionsubstitution" mechanism based procedure and tested as an amperometric ascorbate sensor. The sensitivity of the sensor grows up with increasing pH of the solution from 5.5 to 7.3 and with increasing the operating potential from 0.1 to 0.3 V vs. Ag/AgCl. The decrease of the sensor response has been studied, and attempts have been made towards its stabilization. [ABSTRACT FROM AUTHOR]

Abstract: A nanocomposite of cobalt hexacyanoferrate/reduced graphene oxide was synthesized by a facile precipitation route. The nanocomposite morphology was characterized by scanning electron microscopy. A nanocomposite-modified carbon paste electrode was then fabricated and its redox behavior was characterized. In the voltammograms of the modified electrode recorded in phosphate buffer solution, pH 7.4, two quasi-reversible redox transitions appeared related to the Co(II)/Co(III) and Fe(II)/Fe(III) transitions. The diffusion of the counter cation into the nanocomposite and the charge transfer kinetics across the electrode/electrolyte interface were studied. The modified electrode showed an efficient electrocatalytic activity toward the electrooxidation of captopril. In the presence of captopril, the anodic peak current of the Fe(II)/Fe(III) transition increased and the cathodic one decreased, while, the peak currents of the Co(II)/Co(III) transition remained almost constant. This indicates that captopril was oxidized on the modified electrode surface through a surface mediated electron transfer (an electrocatalytic reaction). The catalytic rate constant and the electron transfer coefficient for the electrooxidation process and the captopril diffusion coefficient were reported. A sensitive and time-saving amperometric method was developed for the analysis of captopril. Based on the developed method, captopril was determined with a detection limit of 0.331μM. The proposed amperometric method was also applied to the analysis of captopril in tablets. [Copyright &y& Elsevier]

Abstract: By depositing a film of cobalt hexacyanoferrate (CoHCF) on silicon electrode coated by a platinum layer, a novel photoelectrochemical sensor for the detection of ascorbic acid (AA) has been developed. The stable film of CoHCF was electrochemically deposited onto a phosphorus heavy doped silicon (n+-Si) with 9μm epitaxial layer (n–n+-Si) wafers coated with about 40nm platinum layer (Pt/n–n+-Si). Scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectra, X-ray diffraction (XRD) and cyclic voltammetry (CV) were used to characterize the CoHCF film on the Pt/n–n+-Si electrode. The CoHCF modified Pt/n–n+-Si electrode has been used for determination of AA with a two-electrode cell in absence of reference electrode by photocurrent measurement at a zero bias. The composite modified electrode demonstrated good photocurrent responses by adding different concentrations of AA with a good stability. The linear range for the detection of AA was 1.0×10−6 to 1.0×10−3 M, with a detection limit (S/N = 3) of 1.0×10−6 M. This provides a facile way of detecting AA and succeeds in averting from inconvenient reference electrode. [Copyright &y& Elsevier]

Abstract: Cobalt hexacyanoferrate (CoHCF) nanostructure was synthesized by anodic oxidation of metallic cobalt nanoflowers in a solution of K3Fe(CN)6. The synthesized CoHCF sample was then employed to prepare a modified carbon paste electrode. The modified electrode was characterized electrochemically in a phosphate buffer solution at physiological pH. Two redox transitions were appeared in the voltammograms which were related to the redox processes of CoII/CoIII and FeII/FeIII in the solid state of CoHCF. The modified electrode was successfully applied to the electrooxidation of nitrite and sulfite and these substrates were oxidized electrocatalytically on the modified electrode surface via the active FeIII species. The catalytic rate constants, the electron transfer coefficients and diffusion coefficients involved in the electrocatalytic oxidation of the compounds were reported. The modified electrode was applied to the amperometric determination of nitrite and sulfite. [Copyright &y& Elsevier]

Abstract: Nanomaterial-based electrochemical sensor has received significant interest. In this work, cobalt hexacyanoferrate modified multi-walled carbon nanotubes/graphite composite electrode was electrochemically prepared and exploited as an amperometric detector for microchip electrophoresis. The prepared sensor displayed rapid and sensitive response towards hydrazine and isoniazid oxidation, which was attributed to synergetic electrocatalytic effect of cobalt hexacyanoferrate and multi-walled carbon nanotubes. The sensitivity enhancement with nearly two orders of magnitude was gained, compared with the bare carbon paste electrode, with the detection limit of 0.91μM (S/N =3) for hydrazine. Acceptable repeatability of the microanalysis system was verified by consecutive eleven injections of hydrazine without chip and electrode treatments, the RSDs for peak current and migration time were 3.4% and 2.1%, respectively. Meanwhile, well-shaped electrophoretic peaks were observed, mainly due to fast electron transfer of electroactive species on the modified electrode. The developed microchip-electrochemistry setup was successfully applied to the determination of hydrazine and isoniazid in river water and pharmaceutical preparation, respectively. Several merits of the novel electrochemical sensor coupled with microfluidic platform, such as comparative stability, easy fabrication and high sensitivity, hold great potential for hydrazine compounds assay in the lab-on-a-chip system. [Copyright &y& Elsevier]

A composite electrode comprised of graphite, Nujol, and nanoparticles of FeO core-cobalt hexacyanoferrate shell was prepared and the charge transport processes in the bulk of this composite were studied. The electrode/solution interface was assumed as a binary electrolyte whose charge transport occurred between redox sites of the nanoparticles present in the composite and counter cations present in the solution. Using cyclic voltammetry, the diffusion of counter cation in the shell was investigated. Using chronoamperometry, an effective diffusion coefficient and its dependency on the applied potential was obtained. In the Nyquist diagrams, different time constants were appeared with relation to different physical and electrochemical processes. Percolation of electron in the shell of the nanoparticles appeared at very high frequencies and exhibited the feature of a diffusion process with a transmissive boundary condition at interface of core-shell structure/graphite particles. The diffusion coefficients of electron and counter cation and the standard rate constants of each individual electrochemical reaction were obtained. [ABSTRACT FROM AUTHOR]