ZrO<Subscript>2</Subscript>/DNA-derivated polyion hybrid complex membrane for the determination of hydrogen peroxide in milk

An efficient biosensing substrate based on ZrO₂/DNA-derivated polyion complex (PIC) membrane has been developed for the determination of hydrogen peroxide (H₂O₂) in this study. To fabricate such a PIC membrane, ZrO₂ nanoparticles were initially electrodeposited on the bare gold electrode (ZrO₂/Au), and deoxyribonucleic acid (DNA)-doped hemoglobin mixture was then assembled onto the ZrO₂/Au surface. The double-strand DNA provided a biocompatible microenvironment for the immobilization of biomolecules, greatly amplified the surface coverage of biomolecules on the electrode surface, and improved the sensitivity of the biosensor. The fabricated procedure of the proposed biosensor was characterized by cyclic voltammetry, electrochemical impedance spectroscopy, and atomic force microscopy. The performance and factors influencing the performance of the biosensor were also evaluated. Under optimal conditions, the developed biosensor exhibited a well-defined electrochemical behavior toward the reduction of H₂O₂ ranging from 1.1 μM to 2.3 mM with a detection limit of 0.5 μM (S/N = 3). The biosensor was applied to the determination of H₂O₂ in milk with satisfactory results. It is important to note that the PIC membrane provided an alternative substrate for the immobilization of other proteins.     

Hydrothermal synthesis of ultra-highly concentrated,well-stable Ag nanoparticles and their application for enzymeless hydrogen peroxide detection

In this article, we have reported on the synthesis of ultra-highly concentrated (5.88 M), well-stable Ag nanoparticles (AgNPs). The AgNPs were formed by hydrothermal heat treatment of an aqueous solution of poly [(2-ethyldimethylammonioethyl methacrylate ethyl sulfate)-co-(1-vinylpyrrolidone)] (PQ11), a kind of cationic polyeletrolyte, in the presence of AgNO₃ powder at 170 °C, without the additional step of introducing other reducing agents and protective agents. Transmission electron microscopy (TEM) observations reveal that the as-formed AgNPs mainly consist of small nanoparticles about 10 nm in diameter. Most importantly, it was found that such dispersion can form stable films on bare electrode surfaces and the AgNPs contained therein still exhibit notable catalytic performance for reduction of hydrogen peroxide (H₂O₂). This H₂O₂ sensor has a fast amperometric response time of less than 3 s. Its linear range is estimated to be from 0.1 to 60 mM (r = 0.993), and the detection limit is estimated to be 1.6 μM at a signal-to-noise ratio of 3.     

A Prussian blue-based amperometric sensor for the determination of hydrogen peroxide residues in milk

A highly selective, sensitive, fast, and stable amperometric sensor for the determination of hydrogen peroxide residues in aseptic milk is presented. To fabricate this amperometric sensor, a thin film of Prussian blue was first electrodeposited on a glassy carbon electrode and then a Nafion polymer layer was formed on the top. It was found that Nafion film greatly improves the anti-interference ability and the stability of the Prussian blue-modified electrode. Factors that influence the overall analytical performance of the sensor, such as the concentration of Nafion drop and pH value of the electrolyte, were examined. Results show that the prepared sensor possesses efficient electrocatalytic activity towards hydrogen peroxide with the detection limit as low as 0.2 μM and linear range from 0.8 μM to 0.12 mM. The developed sensor was applied to the determination of hydrogen peroxide in milk with satisfactory results.     

Electrocatalysis of oxygen reduction reaction on Nafion/platinum/gas diffusion layer electrode for PEM fuel cell

In this work a new membrane electrode based on Pt-coated Nafion membrane was fabricated. Chemical deposition process was used to coat platinum on Nafion 117 membrane and then Pt-coated Nafion membrane was hot pressed on gas diffusion layer (GDL) to make new membrane electrode. The electrochemical and chemical studies of the Pt-coated Nafions were investigated by electrochemical techniques, X-ray diffraction and scanning electron microscopy. The electrochemical results indicated that as the concentration of H₂PtCl₆ increased, the oxygen reduction reaction rate increased until the concentration was reached where the reduction reaction was limited by the problem of mass transport. The electrochemical results for oxygen reduction reaction showed that the new electrode which prepared by plating Nafion membrane with 0.06 M H₂PtCl₆ in electroless plating solution, has a higher performance than other electrodes. The XRD results showed that the average platinum particle size of the best sample was about 3 nm. The loading of platinum for this electrode was 0.153 mg cm⁻².     

Microwave-assisted rapid synthesis of Ag nanoparticles/graphene nanosheet composites and their application for hydrogen peroxide detection

Abstract  

Ag nanoparticles/graphene nanosheet (AgNPs/GN) composites have been rapidly prepared by a one-pot microwave-assisted reduction method, carried out by microwave irradiation of a N,N-dimethylformamide (DMF) solution of graphene oxide (GO) and AgNO₃. Several analytical techniques including UV–vis spectroscopy, FT-IR spectroscopy, Raman spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM) have been used to characterize the resulting AgNPs/GN composites. It suggests that such composites exhibit good catalytic activity toward reduction of hydrogen peroxide (H₂O₂), leading to a H₂O₂ sensor with a fast amperometric response time of less than 2 s. The linear detection range is estimated to be from 0.1 to 100 mM (r = 0.999), and the detection limit is estimated to be 0.5 μM at a signal-to-noise ratio of 3.     

Performance of palladium electrode for electrochemical hydrogen pump using strontium-zirconate-based proton conductors

An electrode design with no use of three-phase boundary was investigated using palladium electrode. The hydrogen evolution rate of the palladium electrode cell using SrZr_0.9Y_0.1O_3 − α electrolyte followed Faraday’s law up to 180 mA cm⁻², and the anode and cathode overpotentials were significantly lower than those of a platinum electrode cell, suggesting that the palladium electrode is effective to improve the performance of the hydrogen-pumping cell using SrZrO₃-based electrolyte. The rate-determining step (RDS) for electrode reaction was also investigated by changing the electrode morphology and hydrogen partial pressure, and it was suggested that the RDS of the anode is a reaction at electrode/electrolyte interface.     

On the enzymatic formation of platinum nanoparticles

A dimeric hydrogenase enzyme (44.5 and 39.4 kDa sub units) was isolated in a 39.5% yield from the fungus Fusarium oxysporum and purified 4.64-fold by ion exchange chromatography on Sephacryl S-200. Characterisation of the enzyme afforded pH and temperature optima of 7.5 and 38 °C, respectively, a half-life stability of 36 min and a V _max and K _m of 3.57 nmol min⁻¹ mL⁻¹ and 2.25 mM, respectively. This enzyme was inhibited (non-competitively) by hydrogen hexachloroplatinic acid (H₂PtCl₆) at 1 or 2 mM with a K _i value of 118 μM. Incubation of the platinum salt with the pure enzyme under an atmosphere of hydrogen and optimum enzyme conditions (pH 7.5, 38 °C) afforded <10% bioreduction after 8 h while at conditions suitable for platinum nanoparticle formation (pH 9, 65 °C) over 90% reduction took place after the same length of time. Cell-free extract from the fungal isolates produced nearly 90% bioreduction of the platinum salt under both pH and temperature conditions. The bioreduction of the platinum salt by a hydrogenase enzyme takes place by a passive process and not an active one as previously understood.     

An electrochemical sensing platform based on a new Cd(II)-containing ionic liquid for the determination of trichloroacetic acid and bromate

The present work reports on the synthesis, characterization and performance of a new metal-containing ionic liquid [(C₃H₇)₂-bim]₂[CdCl₄] (bim = benzimidazole) as an electrocatalyst for trichloroacetic acid (TCA) and bromate reduction. The structure of Cd(II)-containing ionic liquid (Cd-IL) was characterized by X-ray crystallography, IR spectroscopy, and elemental analysis. The molecular structure contains two independent cations of 1,3-dipropyl-benzimidazolium and one anion of CdCl₄²⁻. The cadmium atom has a tetrahedral geometry by coordinating to four chlorine atoms. The melting point of Cd-IL is 73 °C. Electrochemical properties of the Cd-IL have been investigated by preparing bulk-modified carbon paste electrode, and Cd-IL is used as a binder and an electrocatalyst. This modified electrode has good electrocatalytic activity toward reduction of TCA and bromate. The detection limit and the sensitivity are 0.01 μM and 102.72 μA μM⁻¹ for trichloroacetic acid detection and 0.003 μM and 496.15 μA μM⁻¹ for bromate detection. This work demonstrates that the Cd-IL may become a new kind of functional material in constructing chemicals and biosensors.     

Spectroscopic properties of 1.8 μm emission of thulium ions in germanate glass

A new type host of germanate glass (GeO₂− BaO−BaF₂−Ga₂O₃−La₂O₃) codoped with Tm₂O₃ has been investigated for application as laser material. It possesses a large emission cross section with the value of 9.3×10⁻²¹ cm² at 1.8 μm. Judd-Ofelt intensity parameters and radiative transition probability are calculated and analyzed by Judd-Ofelt theory and absorption spectra. The infrared emission spectra at 1.8 μm have been obtained by using a 794 nm laser diode as excitation resource. The emission intensity ratio of 1.8 (³F₄→³H₆) to 1.47 μm (³H₄→³F₄) increases, while the experimental lifetime of the Tm³⁺:³H₄ level decreases by increasing Tm₂O₃ concentration, which is attributed to the presence of a cross relaxation process. The most intensive emission at 1.8 μm is achieved from the germanate glass with the concentration of Tm₂O₃ reaches 1.0 wt%. The extended overlap integral method is used to calculate the microparameter of the energy transfer and the critical distance, which are derived to better understand the energy transfer process of thulium ions in the germanate glass responsible for emission at 1.8 μm.     

Electrochemical promotion of catalyst surfaces deposited on ionic and mixed conductors

The effect of non-Faradaic electrochemical modification of catalytic activity (NEMCA) or electrochemical promotion (EP) was investigated on Pt films deposited on Y₂O₃-stabilized-ZrO₂ (YSZ), an O²⁻ conductor, TiO₂, a mixed conductor, and Nafion 117 solid polymer electrolyte (SPE), a H⁺ conductor and also on Pd films deposited on YSZ and β″-Al₂O₃ a Na⁺ conductor. Four catalytic systems were investigated, i.e. C₂H₆ oxidation on Pt/YSZ, C₂H₄ oxidation on Pd/YSZ and Pd/β″-Al₂O₃, C₂H₄ oxidation on Pt/TiO₂ and H₂ oxidation on Pt/Nafion 117 in contact with 0.1 M aqueous KOH solution. In all cases pronounced and reversible non-Faradaic electrochemical modification of catalytic rates was observed with catalytic rate enhancement up to 2000% and Faradaic efficiency values up to 5000. All reactions investigated exhibit a pronounced electrophobic behaviour which is due to the weakening of chemisorptive oxygen bond at high catalyst potentials. Ethane oxidation, however, also exhibits electrophilic behaviour at low potentials due to weakened binding of carbonaceous species on the surface. The general features of the phenomenon are similar for all four cases presented here showing that the NEMCA effect is a general, electrochemically induced, promoting catalytic phenomenon not depending on the reaction and the type of supporting electrolyte. Paper presented at the 2nd Euroconference on Solid State Ionics, Funchal, Madeira, Portugal, Sept. 10–16, 1995     

Structuring of aluminum films by laser-induced local oxidation in water

A simple method for patterning of thin (15–650 nm) aluminum films on glass substrates by direct, low-power, laser-thermal oxidation in water under common laboratory conditions is demonstrated. Local heating of the metal film enhances the formation of aluminum oxide (hydrargillite, Al₂O₃–3H₂O) and provokes breakdown of the passivation layer followed by local corrosion at temperatures close to the boiling point of water. Moving the focus of an Ar-ion laser (λ=488 nm) over the aluminum film with a speed of several μm/s yields grooves flanked by hydrargillite. Upon through oxidation of the metal these structures act as electrically insulating domains. Depending on the film thickness, the minimum width of the line structures measures between 266 nm and 600 nm. The required laser irradiation power ranges from 1.7 mW to 30 mW. It is found that the photo-thermal oxidation process allows for writing of two-dimensional electrode patterns. Received: 16 July 2001 / Accepted: 23 July 2001 / Published online: 2 October 2001     

H2S Solid oxide fuel cell based on a modified Barium cerate perovskite proton conductor

Urea combustion method was adopted to prepare precursor powder, MCeO₃ doped with Zr (M is alkaline earth element, such as barium, strontium, and calcium). The precursor powder has typically perovskite structure after being calcined at 873 K. In 773 K∼1,273 K, BaCe_0.425Zr_0.475Y_0.1O₃ has the highest conductivity above 10⁻² S cm⁻¹ and good chemical stability, while the phase transition may exist in H₂S atmosphere for the proton conductors. In the single fuel cell composed of MoS₂-BaCe_0.425Zr_0.475Y_0.1O_3-σ-Ag with BaCe_0.425Zr_0.475Y_0.1O_3-σ as electrolyte, the best performance is obtained. The open circuit voltage of fuel cell is all about 0.72 V, the max power density, 1.55 mW cm⁻². The performance drop is attributed to ohmic loss resulting from the separation of electrolyte and electrode, and improvement is required to bring out new anode materials compatible to the proton conductor, BaCe_0.425Zr_0.475Y_0.1O_3-σ, as electrolyte.     

Studies on modified anode polymer hydrogen sensor

An improved polymer electrolyte membrane (PEM) fuel cell based amperometric hydrogen sensor that operates at room temperature has been developed. The electrolyte used in the sensor is PVA/H₃PO₄ blend, which is a proton conducting solid polymer electrolyte. A blend of palladium and platinum coated on the membrane is used as anode and platinum as cathode. The sensor functions as a fuel cell, H₂/Pd-Pt//PVA-H₃PO₄//Pt/O₂, and the short circuit current is found to be linearly related to the hydrogen concentration. The present study aims at investigating the dependence of sensor behaviour on the anode composition. Paper presented at the 2nd International Conference on Ionic Devices, Anna University, Chennai, India, Nov. 28–30, 2003.     

Hydroxyl radical consumption following photolysis of vapor-phase hydrogen peroxide at 266?nm: Implications for?photofragmentation laser-induced fluorescence measurements of?hydrogen peroxide

The decay of OH concentration following photolysis of room-temperature vapor-phase hydrogen peroxide is studied as a function of photolysis fluence at 266 nm in an open air environment. The rate of decay is found to increase with increasing photolysis fluence, i.e., with increasing number of photodissociated H₂O₂(g) molecules. Single-exponential functions approximate the OH concentration decay rather well, even for higher photolysis levels, and the decay time is shown to be inversely proportional to the H₂O₂(g) concentration. For fluences of about 450 mJ/cm² the difference between a single-exponential decay and measured data is becoming evident after approximately 150 μs. Calculations based on a chemical kinetics model agree well with experimental data also for times >150 μs. By combining the model with measurements, the actual photolysis levels used in experiments are estimated. The best fit between measured data and the model suggests that about 1.1% of the H₂O₂(g) molecules are dissociated with a photolysis fluence of ∼450 mJ/cm², in reasonable agreement with a Beer–Lambert based estimation. Excitation scans did not unfold any differences between OH spectra recorded at different photolysis fluences.     

Lithiated c-V<Subscript>2</Subscript>O<Subscript>5</Subscript> thin-film as positive electrode for rocking-chair solid-state lithium microbattery

We report for the first time the use of lithiated crystalline V₂O₅ thin films as positive electrode in all-solid-state microbatteries. Crystalline Li_xV₂O₅ films (x ≈ 0.8 and 1.5) are obtained by vacuum evaporation of metallic lithium deposited on sputtered c-V₂O₅. An all-solid-state lithium microbattery of Li_1.5V₂O₅/LiPON/Li exhibited a typical reversible capacity of 50 μAh/cm² in the potential range 3.8/2.15 V which exceeds by far the results known on all-solid-state lithium batteries using amorphous V₂O₅ films and lithiated amorphous Li_xV₂O₅ thin films as positive electrode. Hence, the present work opens the possibility of using high performance crystalline lithiated V₂O₅ thin films in rocking-chair solid-state microbatteries.     

Ni-MH battery based on plasticized alkaline solid polymer electrolytes

Solid-state nickel metal hydride cells were fabricated using plasticized alkaline solid polymer electrolytes (ASPE) prepared from polyvinyl alcohol (PVA), potassium hydroxide (KOH), alumina (α-Al₂O₃), and propylene carbonate (PC). The ASPE film with PVA/KOH/α-Al₂O₃/PC/H₂O weight ratio of 1.00:0.67:0.09:2.64:1.32 and conductivity of (6.6 ± 1.7) × 10⁻⁴ S cm⁻¹ was used in fabrication of the electrochemical cells. To investigate the electrochemical properties of the plasticized ASPE, cells with the configuration Mg₂Ni/plasticized ASPE/Ni(OH)₂ were fabricated. At the eighth cycle with a current drain of 0.1 mA and plateau voltage of ∼1.1 V, the discharge lasted for 14 h before the cell was considered to have failed. The failure mode of the cell was due to the formation of thin Mg(OH)₂ insulating layers.     

A novel anode-supported stable BaCe0.7Ta0.1Y0.2O3− δ membrane prepared by all-solid-state process for solid oxide fuel cells

BaCe_0.7Ta_0.1Y_0.2O_{3− δ} (BCTY) and BaCe_0.8Y_0.2O_{3− δ} (BCY) were synthesized by solid-state reaction method at 1,300 °C for 20 h. After being exposed in 3% CO₂ + 3% H₂O + 94% N₂ at 700 °C for 20 h, the BCTY exhibited adequate chemical stability against carbonations while BCY decomposed into BaCO₃ and CeO₂. The BCTY showed the similar thermal expansion behavior to BCY from room temperature to 1,000 °C in air. The BCTY displayed a conductivity of 0.007 S/cm at 700 °C in humid hydrogen, lower than that of BCY (0.009 S/cm). A fuel cell with 10-μm thick BCTY membrane prepared through an all-solid-state process exhibited 1.004 V for OCV, 330 mW/cm² for maximum output at 700 °C, respectively. Short-term test shows that the fuel cell performance does not degrade after 20 h.     

TG-MS analysis on thermal decomposable components in the SEI film on Cr2O3 powder anode in Li-ion batteries

The thermal decomposable species in the solid electrolyte interphase (SEI) film on Cr₂O₃ powder anode at different lithiated and delithiated states in the first cycle were analyzed by thermogravimetry and mass spectrometry (TG-MS) technique. The weight loss ratio in a fully lithiated Cr₂O₃ electrode during TG measurement at 50–500 °C is 8.9 wt%, which is decreased to 1.5 wt% for a fully delithiated Cr₂O₃ electrode. This indicates that the SEI film on Cr₂O₃ powder anode is decomposed electrochemically upon delithiation. The main gas products are CH₂=CH₂, CO₂, and CH₃-containing volatile species in thermal reaction. They are released step-by-step in four characteristic temperature regions, which were originated mainly from oligomer and polyethylene-oxide-like species, partly from ROCO₂Li. It is also observed that the amount of thermal decomposable components in the SEI film on the fully lithiated Cr₂O₃ powder electrode is much higher than that on graphite and hard carbon anodes, indicating different SEI features of transition metal oxide anodes.     

Nafion based amperometric hydrogen sensor

A Nafion based amperometric hydrogen sensor that operates at room temperature has been developed. The electrolyte used in the sensor is Nafion 117, which is a proton conducting solid polymer electrolyte. Palladium catalyst was used on the sensing side and platinum supported on carbon on the air side. The sensor functions as fuel cell, H₂/Pd//Nafion//Pt/O₂ and the short circuit current is measured. The short circuit current is found to be linear with respect to concentration of hydrogen on the sensing side. The sensor is able to detect the concentration of hydrogen in argon down to ppb level. Details of assembly of the sensor, response behavior and applications are discussed. Paper presented at the 2nd International Conference on Ionic Devices, Anna University, Chennai, India, Nov. 28–30, 2003.     

Current status of astronomical observations on possible cosmological variations of the proton-to-electron mass ratio μ=m<Subscript>p</Subscript>/m<Subscript>e</Subscript>

Astronomical constraints on a possible cosmologicalvariation of the proton-to-electron mass ratio μ=m_p/m_e are discussed. The analysis of H₂ lines observed in thespectra of distant quasars Q 0405-443 (z_em=3.02) andQ 0347-383 (z_em=3.22) is performed [1] using, partly, very precise values of H₂ frequencies from new laboratorymeasurements [2] and sensitivity coefficients from newaccurate calculations [2,3]. A possibleμ-variation of Δμ/ μ= (2.0±0.6)×10^-5over 12 Gyr is not excluded. However, the discussion of systematicerrors show that some may well be underestimated. Thus, the abovevalue should be treated as the most stringent limit the cosmologicalvariation of μ at z≈2.6 - 3.0 (12 Gyr ago).