Nanocrystalline FeWO4 as a pseudocapacitive electrode material for high volumetric energy density supercapacitors operated in an aqueous electrolyte

Iron tungstate (FeWO₄) has been synthesized using two low-temperature synthetic routes and investigated as a new pseudocapacitive electrode material for supercapacitors operating in a neutral aqueous electrolyte. Its electrochemical properties are clearly related to the specific surface area and seem to originate from Fe^3 +/Fe^2 + fast surface reactions. For FeWO₄ obtained by polyol-mediated synthesis, a high volumetric capacitance of 210 F·cm^− 3 (i.e. more than two times higher than that of activated carbon) was measured at 20 mV·s^− 1 with less than 5% fade over 10,000 cycles. Furthermore, unlike most of the previously investigated iron based electrodes, a unique pseudocapacitive behavior is observed, thus emphasizing the role of the crystallographic structure on the electrochemical signature.     

Direct measurement of electrochemical reaction kinetics in flow-through porous electrodes

This work demonstrates the feasibility of measuring electrochemical reaction rates on common flow-through porous electrodes by traditional Tafel analysis. A customized microfluidic channel electrode was designed and demonstrated by measuring the intrinsic kinetics of the V^2 +/V^3 + and VO^2 +/VO₂⁺ redox reactions in carbon paper electrodes under forced electrolyte flow. The exchange current density of the V^2 +/V^3 + reaction was found to be nearly two orders of magnitude slower than the VO^2 +/VO₂⁺ reaction, indicating that this may be the limiting reaction in vanadium redox flow batteries. The forced convection in this technique is found to generate reproducible exchange current densities which are consistently higher than for conventional electrochemical methods due to improved mass transport.     

High performance mesoporous Pt electrode for methanol electrooxidation. A DEMS study

Electrodeposited mesoporous (MP) Pt electrodes were evaluated as catalysts for CO and methanol electrooxidation. Electrochemical analysis reveals a mass activity of 41 Ag⁻¹ at 0.55 V in 1 M CH₃OH, similar to carbon supported catalysts. However, the high current densities are related to low CO₂ conversion efficiencies, as was established by using differential electrochemical mass spectrometry in a thin layer flow cell configuration (TLFC-DEMS). These results can be understood taking into account the especially accessible porous structure of the MP Pt, where the possibility of readsorption of partially oxidized products is low.     

Preparation of monodisperse carbon nanospheres for electrochemical capacitors

The efficiently hydrothermal route using sucrose without any catalysts is employed to prepare the uniform carbon spheres. The monodisperse 100–150 nm carbon spheres are obtained with the activation treatment in molten KOH. The carbon spheres are characterized by transmission electron microscope, X-ray diffraction, N₂ adsorption, Raman spectroscopy and electrochemical techniques. The relationships of specific capacitance and surface properties of carbon spheres are investigated. A single electrode of carbon nanosphere materials performs excellent specific capacitance (328 F g⁻¹), area capacitance (19.2 μF cm⁻²) and volumetric capacitance (383 F cm⁻³).     

Hydrogen bubble dynamic template synthesis of porous gold for nonenzymatic electrochemical detection of glucose

Gold (Au) films with open interconnected macroporous walls and nanoparticles have been successfully sculptured using the hydrogen bubble dynamic template synthesis followed by a galvanic replacement reaction. Copper (Cu) films with open interconnected macroporous walls and nanoparticles were synthesized using the electrochemically generated hydrogen bubbles as a dynamic template. Then through a galvanic replacement reaction between the porous Cu sacrificial templates and KAu(CN)₂ in solution, the porous Cu films were converted to porous Au films with the similar morphologies. Additional electrochemical dealloying process was introduced to remove the remaining Cu from the porous Au films. X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), Energy-dispersive X-ray (EDX), X-ray diffraction (XRD) and electrochemical methods were adopted to characterize the porous Au films. The resulted porous Au films show excellent catalytic activity toward the electrooxidation of glucose. A nonenzymatic glucose sensor based on those Au film electrodes shows a linear range from 2 to 10 mM with a sensitivity of 11.8 μA cm⁻² mM⁻¹, and a detection limit of 5 μM.     

Insoluble metal hexacyanoferrates as supercapacitor electrodes

Nano-sized insoluble iron, cobalt and nickel hexacyanoferrates (Mhcf) were prepared by a simple co-precipitation method. The potential of using these materials for supercapacitor was examined by cyclic voltammogram and constant charge/discharge. Due to the different types of the second metal (M), the Mhcf electrodes showed different electrochemical capacitive performances. The specific discharge capacitances of Fehcf, Nihcf and Cohcf electrodes at the current density of 0.2 A g⁻¹ were 425 F g⁻¹, 574.7 F g⁻¹ and 261.56 F g⁻¹, respectively. Meanwhile, the Mhcf electrodes showed good cyclic performance.     

Outstanding room-temperature capacitance of biomass-derived microporous carbons in ionic liquid electrolyte

A remarkable capacitance of 180 F·g^− 1 (at 5 mV·s^− 1) in solvent-free room-temperature ionic liquid electrolyte, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, was achieved in symmetric supercapacitors using microporous carbons with a specific surface area of ca. 2000 m²·g^− 1 calculated from gas sorption by the 2D-NLDFT method. The efficient capacitive charge storage was ascribed to textural properties: unlike most activated carbons, high specific surface area was made accessible to the bulky ions of the ionic liquid electrolyte thanks to micropores (1–2 nm) enabled by fine-tuning chemical activation. From the industrial perspective, a high volumetric capacitance of ca. 80 F·cm^− 3 was reached in neat ionic liquid due to the absence of mesopores. The use of microporous carbons from biomass waste represents an important advantage for large-scale production of high energy density supercapacitors.     

Highly porous electrodes from novel corn grains-based activated carbons for electrical double layer capacitors

In this study, novel corn grains-based activated carbons (CG-ACs) were prepared and their use as electrodes in the electrical double layer capacitor (EDLC) performed successfully. The structural properties, energetic heterogeneities and surface functional groups of CG-ACs were characterized using different techniques like nitrogen sorption data, adsorption energy distribution (AED) and X-ray photoelectric spectroscopy (XPS). The electrochemical properties of various CG-ACs were evaluated by using cyclic voltammetry. The maximum specific capacitance value as 257 F g⁻¹ was obtained in 6 M KOH electrolyte solution. The effects of various properties of the porous carbon materials on the EDLC performance were discussed.     

Synthesis of coin-like hollow carbon and performance as Pd catalyst support for methanol electrooxidation

The coin-like hollow carbon (CHC) has been synthesized by only using ethanol as the carbon source with a novel Mg/NiCl₂ catalytic system via a facile solvothermal method for the first time. The CHC synthesized at optimized conditions shows an average thickness of less than 154 nm and the coin diameter of 1–3 μm. The CHC is characterized by SEM, TEM, XRD and electrochemical techniques. Pd on CHC (denotes as Pd/CHC) electrocatalysts are prepared for methanol oxidation in alkaline media. The Pd/CHC electrocatalyst gives a mass activity of 2930 A g⁻¹ Pd for methanol oxidation against 870 A g⁻¹ Pd on Pd/C electrocatalyst. One main reason for the higher mass activity of the Pd/CHC is the higher electrochemical active surface area (EASA) of the Pd/CHC.     

A microfluidic flow-through electrochemical reactor for wastewater treatment: A proof-of-concept

In this work, a microfluidic flow-through electrochemical reactor for wastewater treatment is presented which simultaneously minimizes ohmic drop and mass transfer limitations, two of the most important bottlenecks in electrochemical wastewater treatment. A proof-of-concept comparison versus a state-of-the-art flow-by commercial reactor revealed that the proposed reactor greatly outperforms the commercial system. The novel system requires only 2.4 Ah dm^− 3 (vs. 11.4 Ah dm^− 3) and 12.5 kWh m^− 3 (vs. 75.0 kWh m^− 3) to completely mineralize 100 mg dm^− 3 of clopyralid spiked in a low-conductive (1 mS cm^− 1) matrix with both systems using diamond anodes. The microfluidic flow-through configuration represents a promising approach to the development of cost-effective electrochemical technologies for wastewater treatment.     

Gold surface patterned with cyclodextrin-based molecular nanopores for electrochemical assay of transglutaminase activity

A novel electrochemical method for measuring transglutaminase activity was reported. This approach was based on the patterning of gold electrodes with a mixed self-assembled monolayer of perthiolated β-cyclodextrin and 1-octanethiol. The proper functionalization of β-cyclodextrin with primary amino groups allowed it to act as amino-donor substrates for transglutaminase and molecular nanopores for the enzyme-controlled diffusion of Fe(CN)₆^{3 −/4 −} to the electrode surface. Voltamperometric measurements allowed detection of transglutaminase in the range of 1.9–37 mU/mL with a sensitivity of 1.42 nA μL U^− 1 s^− 1.     

Electroless decoration of macroscale foam with nickel nano-spikes: A scalable route toward efficient catalyst electrodes

Electroless deposition of anisotropic catalyst layers is introduced as an efficient approach to fabricate high-performing multiscale electrode architectures. In the present study, a biomass-derived, solidified foam is coated with nickel nano-spikes. This results in an amplification of the surface area and an introduction of catalytic functionality, while the favorable mass transfer properties of the porous support are retained. Both the substrate and the metal film are produced using simple, readily scalable processes. The support is prepared from liquefied sawdust by self-foaming, and nickel deposition is performed by immersion in a hydrazine-based plating bath. The favorable functional properties of the nickel-coated foam are demonstrated in enzyme-free glucose sensing. Due to the large surface area and the high activity of the nickel nanofilm, an outstanding sensitivity of 8.1 mA mM^− 1 cm^− 2 and a low detection limit of 60 nM were achieved.     

A novel process to prepare porous membranes comprising SnO2 nanoparticles and P(MMA-AN) as polymer electrolyte

We have successfully developed a new process to prepare porous poly(methyl methacrylate-co-acrylonitrile) (P(MMA-AN)) copolymer based gel electrolyte. The porous structure in the polymer matrix is achieved by adding SnO₂ nanoparticles which are mostly used as gas sensor materials. The quasi-aromatic solvent, NMP, has an electron-repulsion effect with the space charge layer on the surface of SnO₂ nanoparticles and forms a special gas–liquid phase interface. Once the cast polymer solution is stored at an elevated temperature to evaporate the solvent, gas–liquid phase separation happens and spherical pores are obtained. The ionic conductivity at room temperature of the prepared gel polymer electrolyte based on the porous membrane is as high as 1.54 × 10⁻³ S cm⁻¹ with the electrochemical stability up to 5.10 V (vs. Li/Li⁺). This method presents another promising way to prepare porous polymer electrolyte for practical use.     

Hollow fiber supported liquid membrane: a novel technique for separation and recovery of plutonium from aqueous acidic wastes

Low plutonium content acidic waste is generated in nuclear chemical facilities. Study was initiated to develop hollow fiber supported liquid membrane (HFSLM) technique for quantitative separation and recovery of plutonium (Pu) from such wastes using tri-n-butyle phosphate (TBP) in dodecane as carrier. Hollow fiber test module was fabricated using 20 lumens of 33.91 cm² surface area and 9 cm length. After satisfactory testing of the hydrodynamic condition of the module, it was operated at a flow rate of 3 ml min⁻¹ on recycling mode with acidic waste solution containing Pu=8 mg dm⁻³, uranium=15 dm⁻³, gross β⁻=49.33 mCi dm⁻³, gross γ=15.73 mCi dm⁻³ and acidity 3 M HNO₃. In presence of various fission products, selective permeation of Pu(IV) through the bundle of hollow fiber test module was observed to be more than 90% into a stripping phase consisting 0.1 M NH₂OH·HCl in 0.3 M HNO₃. A model is presented to describe the transport mechanism and to evaluate the mass transfer coefficient. The radiation stability was also tested by exposing the membrane upto irradiation level of 1 M rad. Potentiality of the method for the selective separation of plutonium from acidic waste is, thus, clearly seen.     

Mucin 4 detection with a label-free electrochemical immunosensor

Mucin 4 (MUC4) is a useful biomarker for endometriosis and cancers of the pancreas, esophagus and breast. The very first electrochemical immunosensor for the detection of MUC4 is reported, using carbon-based screen-printed electrodes modified by reaction with the diazonium salt of p-aminophenylacetic acid. Electrochemical impedance spectroscopy and cyclic voltammetry were used to characterize and optimize the electrografting process. The in situ surface modification through diazotation with phenylacetic groups enables the chemical binding of the specific antibody, followed by its affinity reaction with MUC4. The immunosensor was optimized with respect to several parameters and is very promising for clinical applications, having a limit of detection of 0.33 μg mL^− 1 and a linear domain between 1 and 15 μg mL^− 1 obtained by electrochemical impedance spectroscopy measurements.     

Gelatin-functionalized carbon nanotubes for the bioelectrochemistry of hemoglobin

In this paper, we compared the use of gelatin-functionalized carbon nanotubes (CNTs) as substrates for Hemoglobin (Hb) immobilization and as electrodes for electrochemical reduction of the absorbed Hb. The non-covalently gelatin-functionalized CNTs possessed an improved solubility in aqueous solution and may have an enhanced biocompatibility with Hb. The characteristics of Hb/gelatin-CNTs composite films were studied by using UV–vis spectroscopy, FTIR spectroscopy and electrochemical methods. The immobilized Hb showed a couple of quasi-reversible redox peaks with a formal potential of −0.35 V (vs. SCE) in 0.10 M pH 7.0 phosphate buffer solution (PBS). The surface concentration of electroactive Hb immobilized on gelatin-CNT/GC electrode was about 4.34 × 10⁻¹⁰ mol cm⁻².     

In situ quantification of electrochemical dissolution of hafnium-tantalum alloys in acidic media

A thin film hafnium-tantalum combinatorial library with a compositional spread of over 70 at.% was used for electrochemical dissolution experiments in nitric acid. Surface microstructure analysis and crystallographic characterization of individual Hf–Ta alloys confirmed a hexagonal to tetragonal transition from pure Hf to pure Ta accompanied by a change in the surface grain structure. A flow-type scanning droplet cell microscope coupled to downstream analytics was used for the quantification of Hf and Ta dissolution rates along the entire compositional spread. Potentiostatically applying 3 V vs. SHE for 120 s for an electrolyte flow of 0.46 ml min^− 1 resulted in dissolution rates of pure Hf and pure Ta in the ng s^− 1 cm^− 2 and pg s^− 1 cm^− 2 range, respectively. For both species, the average dissolution rate was independent of the compositional gradient, indicating a dissolution enhancement of minor species. A decrease in their activation energy for dissolution triggered by a surface energy modification was the reason for the observed behavior.     

A lotus root-like porous nanocomposite polymer electrolyte

A lotus root-like porous nanocomposite polymer electrolyte (NCPE) based on poly(vinylidene difluoride-co-hexafluoropropylene) [P(VDF-HFP)] copolymer and TiO₂ nanoparticles was easily prepared by a non-solvent induced phase separation (NIPS) process. The formation mechanism of the lotus root-like porous structure is explained by a qualitative ternary phase diagram. The resulting NCPE had a high ionic conductivity up to 1.21 × 10⁻³ S cm⁻¹ at room temperature, and exhibited a high electrochemical stability potential of 5.52 V (vs. Li/Li⁺), lithium ion transference number of 0.65 and 22.89 kJ mol⁻¹ for the apparent activation energy for transportation of ions. It is of great potential application in polymer lithium ion batteries.     

Quantum dot-based electrochemical DNA biosensor using a screen-printed graphite surface with embedded bismuth precursor

This work reports the development of screen-printed quantum dots (QDs)-based DNA biosensors utilizing graphite electrodes with embedded bismuth citrate as a bismuth precursor. The sensor surface serves both as a support for the immobilization of the oligonucleotide and as an ultrasensitive voltammetric QDs transducer relying on bismuth nanoparticles. The utility of this biosensor is demonstrated for the detection of the C634R mutation through hybridization of the biotin-tagged target oligonucleotide with a surface-confined capture complementary probe and subsequent reaction with streptavidin-conjugated PbS QDs. The electrochemical transduction step involved anodic stripping voltammetric determination of the Pb(II) released after acidic dissolution of the QDs. Simultaneously with the electrolytic accumulation of Pb on the sensor surface, the embedded bismuth citrate was converted in situ to bismuth nanoparticles enabling ultra-trace Pb determination. The biosensor showed a linear relationship of the Pb(II) peak current with respect to the logarithm of the target DNA concentrations from 0.1 pmol L^− 1 to 10 nmol L^− 1, and the limit of detection was 0.03 pmol L^− 1. The biosensor exhibited effective discrimination between a single-base mismatched sequence and the fully complementary target DNA. These “green” biosensors are inexpensive, lend themselves to easy mass production, and hold promise for ultrasensitive bioassay formats.     

VO2 nano-sheet negative electrodes for lithium-ion batteries

Vanadium dioxide (VO₂) nano-sheets were directly synthesized via a continuous hydrothermal process and were investigated as electrodes in a wide potential range of 0.05–3 V vs. Li/Li⁺. The nano-sheets showed excellent capacity retention, with a specific capacity of 350 mAh g^− 1 at an applied current of 0.1 A g^− 1 and 95 mAh g^− 1 at 10 A g^− 1. Further electrochemical testing suggested that a significant proportion of the charge storage in the cells was due to pseudocapacitive processes.