Using flowerlike polymer–copper nanostructure composite and novel organic–inorganic hybrid material to construct an amperometric biosensor for hydrogen peroxide

A new type of amperometric hydrogen peroxide biosensor was fabricated by entrapping horseradish peroxidase (HRP) in the organic–inorganic hybrid material composed of zirconia–chitosan sol–gel and Au nanoparticles (ZrO₂–CS–AuNPs). The sensitivity of the biosensor was enhanced by a flowerlike polymer–copper nanostructure composite (pPA–FCu) which was prepared from co-electrodeposition of CuSO₄ solution and 2,6-pyridinediamine solution. Several techniques, including UV–vis absorption spectroscopy, scanning electron microscopy, cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy were employed to characterize the assembly process and performance of the biosensor. The results showed that this pPA–FCu nanostructure not only had excellent redox electrochemical activity, but also had good catalytic efficiency for hydrogen peroxide. Also the ZrO₂–CS–AuNPs had good film forming ability, high stability and good retention of bioactivity of the immobilized enzyme. The resulting biosensors showed a linear range from 7.80 × 10^?7 to 3.7 × 10^?3 mol L^?1, with a detection limit of 3.2 × 10^?7 mol L^?1 (S/N = 3) under optimized experimental conditions. The apparent Michaelis–Menten constant was determined to be 0.32 mM, showing good affinity. In addition, the biosensor which exhibits good analytical performance, acceptable stability and good selectivity, has potential for practical applications.     

A sensitivity-controlled hydrogen peroxide sensor based on self-assembled Prussian Blue modified electrode

In this communication, a hydrogen peroxide (H₂O₂) sensor based on self-assembled Prussian Blue (PB) modified electrode was reported. Thin film of PB was deposited on the electrode by self-assembly process including multiple sequential adsorption of ferric ions and hexacyanoferrate ions. The as-prepared PB modified electrode displayed sufficient stability for practical sensing application. At an applied potential of ?0.05 V vs. Ag/AgCl (sat. KCl), PB modified electrode with 30 layers exhibited a linear dependence on H₂O₂ concentration in the range of 1 × 10^?6–4 × 10^?4 M (r = 0.9998) with a sensitivity of 625 mA M^?1 cm^?2. It was found that the sensitivity of H₂O₂ sensors could be well controlled by adjusting the number of deposition cycles for PB preparation. This work demonstrates the feasibility of self-assembled PB modified electrode in sensing application, and provides an effective approach to control the sensitivity of PB-based amperometric biosensors.     

Enhancement of electrochemical and catalytic properties of MoS2 through ball-milling

MoS₂ nanosheets of one to few layer thickness present novel electronic and enhanced catalytic properties with respect to the bulk material. Here we show that a simple and highly scalable ball-milling procedure can lead to significant improvements of the electrochemical and catalytic properties of the bulk natural MoS₂. We characterized the material before and after the milling process by means of scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy in order to evaluate morphological and chemical features. We investigated the electrochemical properties by means of voltammetry techniques to monitor the electron transfer with [Fe(CN)₆]^{4 −/3 −} redox probe and the catalytic properties by monitoring the electrochemical hydrogen evolution reaction (HER). A significant overpotential lowering of about 210 mV is obtained for the HER by the ball-milled material when compared to bulk materials. This has a huge potential for the lowering of the energy consumption during hydrogen evolution. Ball-milling offers highly scalable dry method for large scale production of electrocatalyst with enhanced properties.     

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.     

One-step preparation of silver nanoparticle embedded amorphous carbon for nonenzymatic hydrogen peroxide sensing

Herein, we report a rapid and facile fabrication of Ag/C hybrid by anchoring Ag nanoparticles in amorphous carbon network for application in amperometric sensing of hydrogen peroxide. Ag/C hybrid was prepared by simply mixing silver nitrate aqueous solution with ethylene glycol and diphosphorus pentoxide in one step at room temperature. The embedding of Ag nanoparticles into the amorphous carbon support can greatly strengthen the stability of Ag nanoparticles, protecting them from oxidizing without loss of conductivity. The nanocomposite was investigated by transmission electron microscopy, energy dispersive X-ray analysis, X-ray diffraction technique, X-ray photoelectron spectroscopy and electrochemical measurements. The prepared Ag/C hybrid was fabricated onto the surface of glassy carbon electrode to investigate the sensing property towards hydrogen peroxide. The fabricated electrochemical sensor can determine hydrogen peroxide with a detection limit of 0.1 μM and up to 5.5 mM.     

Single microparticle applied in magnetic-switchable electrochemistry

In this work we demonstrated the micromanipulation of a single magnetic microparticle (Fe₃O₄) modified with Prussian blue (PB) for use in magnetic-switchable electrochemistry. A single Fe₃O₄-PB microparticle with 120 μm was isolated in an electrochemical microcell (20 μL), in which a fine control of PB electrochemical process on carbon electrode (Ø = 4.0 mm) was obtained. For cyclic voltammetry, redox processes attributed to PB/PW (Prussian blue/Prussian white) one electron redox couple were observed, however the capacitive currents were very high. On the other hand, by using differential pulse voltammetry, a maximum faradaic current for anodic peak of 200 nA cm^− 2 at 0.06 V was observed. Several and high stable chronoamperograms were obtained by “switch on” and “switch off” magnetic commutative states for a single microparticle, showing that the system developed here can be very promising for application in electrochemistry.     

A novel hydrogen peroxide sensor based on Ag nanoparticles electrodeposited on DNA-networks modified glassy carbon electrode

A novel strategy to fabricate hydrogen peroxide (H₂O₂) sensor was developed by electrodepositing Ag nanoparticles (NPs) on a glassy carbon electrode modified with three-dimensional DNA networks. The result of electrochemical experiments showed that such constructed sensor had a favorable catalytic ability to reduction of H₂O₂. The well catalytic activity of the sensor was ascribed to the DNA networks that facilitated the formation and homogenous distribution of small Ag NPs. The resulted sensor achieved 95% of the steady-state current within 2 s and had a 1.7 μM detection limit of H₂O₂.     

Electrografting of amino-TEMPO on graphene oxide and electrochemically reduced graphene oxide for electrocatalytic applications

4-Amino-2,2,6,6-tetramethyl-1-piperridine N-oxyl (4-amino-TEMPO), an electroactive nitroxide radical, was attached to the surface of graphene oxide (GO) and electrochemically reduced graphene oxide (ERGO) modified glassy carbon electrode by a simple, rapid and green electrografting method. The electroactive interfaces were analyzed by X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry (CV). The calculated surface coverage for 4-amino-TEMPO is up to 1.55 × 10^− 9 mol·cm^− 2. The modified electroactive interface exhibited excellent electrocatalytic activity towards the electro-oxidation of reduced glutathione (GSH) and hydrogen peroxide (H₂O₂).     

Impact of reforming catalyst on the anodic polarisation resistance in single-chamber SOFC fed by methane

This paper emphasises the electrochemical and catalytic properties of a Ni–10% GDC (10% gadolinium-doped ceria) cermet anode of a single-chamber solid oxide fuel cell (SC-SOFC). Innovative coupling of electrochemical impedance spectroscopy with gas chromatography measurements was carried out to characterise the anode material using an operando approach. The experiments were conducted in a symmetric anode/electrolyte/anode cell prepared by slurry coating resulting in 100 μm-thick anode layers. The electrochemical performance was assessed using a two-electrode arrangement between 400 °C and 650 °C, in a methane-rich atmosphere containing CH₄, O₂ and H₂O in a 14:2:6 volumetric ratio. The insertion of a Pt–CeO₂ based catalyst with high specific surface area inside the cermet layer was found to promote hydrogen production from the Water Gas Shift reaction and consequently to improve the electrochemical performances. Indeed, a promising polarisation resistance value of 12 Ω cm² was achieved at 600 °C with a catalytic loading of only 15 wt.%.     

Activity and stability of horseradish peroxidase in hydrophilic room temperature ionic liquid and its application in non-aqueous biosensing

The activity and stability of horseradish peroxidase (HRP) were investigated in a hydrophilic room temperature ionic liquid 1-butyl-3-methylimidazolium tetrafluroborate ([bmim][BF₄]) by electrochemical methods. Although no detectable activity exhibited in anhydrous [bmim][BF₄], HRP was active in the presence of a small amount of water (4.53%, v/v). And its activity can be improved by immobilization in agarose hydrogel. The immobilized HRP possesses excellent activity at 65 °C. It remained 80.2% of its initial activity after being immersed for 10.5 h in an aqueous mixture of [bmim][BF₄] with some hydrogen peroxide (H₂O₂) under room temperature, implying extremely high stability. Moreover, the immobilized HRP was found to be very sensitive and stable in H₂O-containing [bmim][BF₄] for the detection of H₂O₂, with a wide linear range of 6.10 × 10⁻⁷ to 1.32 × 10⁻⁴ mol l⁻¹ and low detection limit of 1.0 × 10⁻⁷ mol l⁻¹.     

Fast transfer hydrogenation using a highly active orthometalated heterocyclic carbene ruthenium catalyst

The free carbene 1,3,4-triphenyl-4,5-dihydro-1H-1,2,4-triazol-5-ylidene reacts with trans,cis-RuHCl(PPh₃)₂(ampy) (ampy = 2-(aminomethyl)pyridine) affording an orthometalated N-heterocyclic carbene complex characterized by an X-ray diffraction study. This compound in presence of NaOH shows very high catalytic activity for the transfer hydrogenation of several ketones to alcohols using 2-propanol as hydrogen source, affording TOF values up to 120,000 h⁻¹ (at 50% conversion).     

Direct electrochemistry and electrocatalysis of hemoglobin entrapped in composite matrix based on chitosan and CaCO3 nanoparticles

The direct electron transfer between hemoglobin (Hb) and the underlying glassy carbon electrode (GCE) can be readily achieved via a high biocompatible composite system based on biopolymer chitosan (CHT) and inorganic CaCO₃ nanoparticles (nano-CaCO₃). Cyclic voltammetry of Hb-CHT/nano-CaCO₃/GCE showed a pair of stable and quasi-reversible peaks for HbFe(III)/Fe(II) redox couple in pH 7.0 buffer. The electrochemical reaction of Hb immobilized in CHT/nano-CaCO₃ composite matrix exhibited a surface-controlled process accompanied by electron and proton transfer. The electron transfer rate constant was estimated to be 1.8 s⁻¹. This modified electrode showed a high thermal stability up to 60 °C. The apparent Michaelis–Menten constant was calculated to be 7.5 × 10⁻⁴ M, indicating a high catalytic activity of the immobilized Hb toward H₂O₂. The interaction between Hb and this nano-hybrid material was also investigated using FT-IR and UV–vis spectroscopy, indicating that Hb retained its native structure in this hybrid matrix.     

Promotion of PtIr and Pt catalytic activity towards ammonia electrooxidation through the modification of Zn

Zn is introduced into Pt and PtIr electrodes by applying potential cycles to their corresponding polycrystalline microdisc electrodes in a ZnCl₂-containing ionic liquid bath. Scanning-electron microscopy and energy-dispersive X-ray microanalysis studies show that nanostructured PtIrZn and PtZn layers created on the microdisc electrodes contain approximately 5 wt% Zn. Cyclic voltammetric studies reveal that PtZn and PtIrZn are significantly more active towards electrochemical ammonia oxidation in alkaline media than virgin Pt and PtIr electrodes. The PtIrZn electrode demonstrates a low onset potential of 0.30 V vs RHE and a high exchange current density of 4.3 × 10^− 8 A cm^− 2, which is favorably comparable to state-of-the-art electrocatalyts for the same reaction. The catalytic activity promotion by the Zn modification may be related to the inhibition of the hydrogen electrochemistry. PtIrZn appears therefore to be a very promising anode catalyst for direct ammonia fuel cells and ammonia electrolysis.     

Annealing temperature dependent catalytic water oxidation activity of iron oxyhydroxide thin films

Nanostructured iron oxyhydroxide(Fe OOH) thin films have been synthesized using an electrodeposition method on a nickel foam(NF) substrate and effect of air annealing temperature on the catalytic performance is studied. The as-deposited and annealed thin films were characterized by X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS), field emission scanning electron microscopy(FE-SEM) and linear sweep voltammetry(LSV) to determine their structural, morphological, compositional and electrochemical properties, respectively. The as-deposited nanostructured amorphous Fe OOH thin film is converted into a polycrystalline Fe_2O_3 with hematite crystal structure at a high temperature. The Fe OOH thin film acts as an efficient electrocatalyst for the oxygen evolution reaction(OER) in an alkaline 1 M KOH electrolyte. The film annealed at 200 °C shows high catalytic activity with an onset overpotential of 240 m V with a smaller Tafel slope of 48 m V/dec. Additionally, it needs an overpotential of 290 mV to the drive the current density of 10 m A/cm~2 and shows good stability in the 1 M KOH electrolyte solution.     

Highly efficient In–Sn alloy catalysts for electrochemical reduction of CO2 to formate

Gas diffusion electrodes (GDEs), including GDE-In_0.90Sn_0.10, GDE-In_0.47Sn_0.53 and GDE-In_0.22Sn_0.78, were prepared by electrodeposition of In–Sn alloys on carbon fiber paper, and then used to explore the electroreduction of CO₂ to formate in aqueous solution. Compared with commercial indium or Sn foil catalysts, the GDE-In_0.90Sn_0.10 electrode in particular is shown to have excellent catalytic performance towards electroreduction of CO₂ to formate, with a high Faradaic efficiency (~ 92%). More importantly, the catalytic activity of GDE-In_0.90Sn_0.10 remained reasonably stable over a 22-hour period of electrolysis, and a relatively high electrolytic current density (15 mA cm^− 2) was obtained in an aqueous medium, demonstrating its potential for electrochemical reduction of CO₂ to formate.     

An acidic cellulose–chitin hybrid gel as novel electrolyte for an electric double layer capacitor

A novel acidic cellulose–chitin hybrid gel electrolyte including binary ionic liquids (ILs) with an aqueous H₂SO₄ solution was prepared for an electric double layer capacitor (EDLC). Its electrochemical characteristics were investigated by galvanostatic charge–discharge measurements. The test cell with a hybrid gel electrolyte shows a specific capacitance of 162 F g^?1 at room temperature, which is higher than that for a cell with an H₂SO₄ electrolyte, 155 F g^?1. This hybrid gel electrolyte exhibits excellent high-rate discharge capability in a wide range of current densities as well as an aqueous H₂SO₄ solution. The discharge capacitance of the test cell can retain over 80% of its initial value in 100,000 cycles even at a high current density of 5000 mA g^?1.     

A simple cathodic process for carboxylating noble metals and generating new versatile electrode interfaces

The electrochemical reactivity of polarized metals such as platinum, palladium, and rhodium toward carbon dioxide in aprotic dimethylformamide (DMF) solutions of tetramethylammonium tetrafluoroborate (TMABF₄) is presented. The capacity of metals such as Pd and Pt to cathodically insert the electrolytes under superdry conditions (via the generation of organometallic intermediates analogous to Zintl metals) is combined with the concomitant carboxylation of those metals within a potential range from − 1 V to − 2.5 V vs. Ag/AgCl/KCl(sat). Under these conditions, dense surface carboxylation of these precious metals occurs, totally suppressing their catalytic activity. Thick layers of the carboxylated metals (platinum-CO₂^– and palladium-CO₂⁻) are chemically stable and may then be further functionalized for specific applications.     

Non-enzymatic detection of hydrogen peroxide using a functionalized three-dimensional graphene electrode

A novel three-dimensional (3D) electrochemical sensor was developed for highly sensitive detection of hydrogen peroxide (H₂O₂). Monolithic and macroporous graphene foam grown by chemical vapor deposition (CVD) served as the electrode scaffold. Using in-situ polymerized polydopamine as the linker, the 3D electrode was functionalized with thionine molecules which can efficiently mediate the reduction of H₂O₂ at close proximity to the electrode surface. Such stable non-enzymatic sensor is able to detect H₂O₂ with a wide linear range (0.4 to 660 μM), high sensitivity (169.7 μA mM^− 1), low detection limit (80 nM), and fast response (reaching 95% of the steady current within 3 s). Furthermore, this sensor was used for real-time detection of dynamic release of H₂O₂ from live cancer cells in response to a pro-inflammatory stimulant.     

Electrodeposited PbO2 thin film on Ti electrode for application in hybrid supercapacitor

PbO₂ thin films were prepared by pulse current technique on Ti substrate from Pb(NO₃)₂ plating solution. The hybrid supercapacitor was designed with PbO₂ thin film as positive electrode and activated carbon (AC) as negative electrode in the 5.3 M H₂SO₄ solution. Its electrochemical properties were determined by cyclic voltammetry (CV), charge–discharge test and electrochemical impedance spectroscopy (EIS). The results revealed that the PbO₂/AC hybrid supercapacitor exhibited large specific capacitance, high-power and stable cycle performance. In the potential range of 0.8–1.8 V, the hybrid supercapacitor can deliver a specific capacitance of 71.5 F g^?1 at a discharge current density of 200 mA g^?1(4 mA cm^?2) when the mass ratio of AC to PbO₂ was three, and after 4500 deep cycles, the specific capacitance remains at 64.4 F g^?1, or 32.2 Wh Kg^?1 in specific energy, and the capacity only fades 10% from its initial value.     

Structural and electrochemical properties of a porous nanostructured SnO2 film electrode for lithium-ion batteries

A B₂O₃-doped SnO₂ thin film was prepared by a novel experimental procedure combining the electrodeposition and the hydrothermal treatment, and its structure and electrochemical properties were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) analysis, energy dispersive X-ray (EDX) spectroscopy and galvanostatic charge–discharge tests. It was found that the as-prepared modified SnO₂ film shows a porous network structure with large specific surface area and high crystallinity. The results of electrochemical tests showed that the modified SnO₂ electrode presents the largest reversible capacity of 676 mAh g^?1 at the fourth cycle, close to the theoretical capacity of SnO₂ (790 mAh g^?1); and it still delivers a reversible Li storage capacity of 524 mAh g^?1 after 50 cycles. The reasons that the modified SnO₂ film electrode shows excellent electrochemical properties were also discussed.