Palladium Electrodes Research Articles

Wafer-level decoration of carbon nanotubes in field-effect transistor geometry with preformed gold nanoparticles using a microfluidic approach

A scalable on-chip functionalization approach for single-walled carbon nanotubes (SWCNTs) between palladium electrodes in the geometry of a field-effect transistor with preformed metallic nanoparticles is reported. This method is wafer-level compatible and comprises two stage of flow chemistry: a side-wall functionalization of as-deposited SWCNTs with long-chained ethylene glycol units and a microfluidic deposition of the nanoparticles. The scalability of our approach is achieved by using a microfluidic tool in contact with the silicon wafer (diameter 150mm), operated on a controlled heating stage with a temperature range up to 160°C and at flow rates of up to 200μL/s. We verify an effective and controllable deposition of gold nanoparticles (diameters 8.4±2.2nm), retaining the electronic properties of the CNT field-effect transistors on the wafer.

Electrocatalytic Reduction of Nitrate on Tin-modified Palladium Electrodes

The electrocatalytic reduction of nitrate was investigated in acidic media on Sn-modified polycrystalline palladium and Sn-modified palladium film electrodes (deposited on gold) by means of voltammetry in combination with on-line electrochemical mass spectrometry and on-line ion chromatography. The catalytic activity for this reaction is strongly enhanced by modification with Sn as pure Pd is not found to have a measurable activity for the nitrate reduction. Dominant volatile products are found to be N2O and in a smaller amount N2, while NH2OH is found to be the dominant non-volatile product. Furthermore, the influence of hydrogen absorption in Pd is investigated by using a multilayer Pd film and a submonolayer Pd film on a polycrystalline Au electrode. By comparing the product distribution of these electrodes with the bulk Pd electrode the effect of hydrogen absorption is found to be of negligible importance for the nitrate reduction as the product distribution and formation as a function of potential are similar compared to the bulk Pd electrode.

The effect of electrode material on the electrochemical formation of porous copper surfaces using hydrogen bubble templating

The electrodeposition of copper onto copper, gold, palladium and glassy carbon (GC) electrodes via a hydrogen bubble templating method is reported. It is found that the composition of the underlying electrode material significantly influences the morphology of the copper electrodeposit. Highly ordered porous structures are achieved with Cu and Au electrodes, however on Pd this order is disrupted and a rough randomly oriented surface is formed whereas on GC a bubble templating effect is not observed. Chronopotentiograms recorded during the electrodeposition process allows bubble formation and detachment from the surface to be monitored where distinctly different potential versus time profiles are observed at the different electrodes. The porous Cu surfaces are characterised with scanning electron microscopy, X-ray diffraction and cyclic voltammetric measurements recorded under alkaline conditions. The latter demonstrates that there are active sites present on electrodeposited copper whose coverage and reactivity depend on the underlying electrode material. The most active Cu surface is achieved at a Pd substrate for both the hydrogen evolution reaction and the catalytic reduction of ferricyanide ions with thiosulphate ions. This demonstrates that the highly ordered porous structure on the micron scale which typifies the morphology that can be achieved with the hydrogen bubbling template method is not required in producing the most effective material.

Palladium metal electrode and its analytical application to precipitation and acid–base analysis in aqueous and non-aqueous media

Electrochemical characterization of palladium electrode has been reported. The investigated electrode showed a linear dynamic response for p-toluensulfonic acid and iodide ions in the concentrations range between 5 × 10−1 and 1 × 10−5 mol L−1 with a Nernstian slope of 55 mV for p-toluensulfonic acid and 63 mV per decade for iodide ions in water, as well as 53 mV for p-toluensulfonic acid and 51 mV per decade for iodide ions in dioxane. The response time of the electrodes was less than 10 s in the used solvents. Some potential analytical applications of the sensors have been pointed. Palladium electrode for the potentiometric titrations of acids (citric, barbituric, and p-toluensulfonic acid), bases (N,N’-diphenylguanidine, tributylamine, and 2,2'–bipyridine), halides, and some real samples in aqueous and non-aqueous solutions were studied. Тetrabutylammonium hydroxide, perchloric acid, and silver nitrate proved to be very suitable titrating agents for these titrations. The standard deviation of the determination of the investigated compounds was less than 0.9 % from those obtained with a glass electrode, i.e., silver electrode.

Simulation of an asymmetric contacted carbon nanotube for solar-energy harvesting

Nanostructured materials offer great prospects in helping solar-energy harvesting devices to achieve their envisioned performances. Carbon nanotubes (CNT)-based devices were among the first to be proposed for this task. These devices are based on CNT field-effect transistors and CNT diodes. In this paper, the photovoltaic behavior of a diode structure formed from an asymmetrically contacted intrinsic CNT with scandium and palladium electrodes as source and drain, respectively, is investigated. A semi-classical simulator, which combines a quantum solution, for transmission through the electrodes/CNT interfaces with the semi-classical drift-diffusion equation and continuity equation for charge transport in the CNT has been built. The obtained simulation outcomes are compared with the available published experimental results.

OS0707 化学反応に伴う電極変形が及ぼすIPMCアクチュエータへの影響

An ionic polymer-metal composite (IPMC) actuator, which consists of a thin perfluorinated ionomer membrane and electrodes plated on both surfaces, undergoes a large bending motion when a low electric field is applied across its thickness. IPMC actuators are lightweight and soft and can operate in solutions. They are thus promising for a wide range of applications including MEMS sensors, artificial muscles, biomimetic systems, and medical devices. IPMC actuator with palladium electrodes shows tremendous large bending deformation at the applied voltage of over 2.5 V. To investigate the mechanism of this large deformation, we fabricated the actuator which consists of a thin polyamide membrane and electrodes plated on both surfaces. Polyamide membrane is not an electrolyte membrane and, thus, the deformation mechanism should be different from that of IPMC actuator. The tip displacements of these actuators were evaluated by applying voltage between plated palladium electrodes in an electrolyte. Also, we conducted cyclic voltammetry (CV) to identify chemical reactions on platted palladium electrodes. As the result, the polyamide membrane with palladium electrodes also showed the bending deformation over 2.5 V. Cyclic voltammetry analyses showed that the electrolysis of water and hydrogen formation occurred at cathode and the oxidation of palladium occurred at anode. Palladium electrodes absorbed hydrogen and expanded its volume at cathode. Therefore, it is concluded that this volume expansion causes the bending moment of membrane and assists the bending deformation of IPMC actuator with palladium electrodes.

Designing a Simple Electronic Tongue for Fermentation Monitoring

A method for monitoring a biotechnological fermentation using cyclic voltammetry in combination with chemometrics, commonly termed electronic tongue, is proposed. A simple palladized palladium electrode showed excellent sensitivity to glucose concentrations ranging from 0 to 9 g/L in a yeast fermentation medium (pH 5.3, 0.07 M chloride). This electrode is also sensitive to ethanol, but not able to separate it from the glucose signal. To separately quantify mixtures of glucose and ethanol as the product of yeast fermentations at least one additional electrode with different sensitivities is needed. Platinized platinum shows the required features. Long term stability is still an obstacle for application.

Spectroscopic elucidation of reaction pathways of acetaldehyde on platinum and palladium in acidic media

The electrochemical behavior of acetaldehyde on palladium and platinum electrodes in acidic media was comparatively studied by means of differential electrochemical mass spectrometry (DEMS) and in situ Fourier transform infrared spectroscopy (FTIRS) combined with cyclic voltammetry. It was observed that acetaldehyde decomposition depends on the catalyst material, applied potential, and reactant concentration. Additionally, it was detected that acetaldehyde adsorbs and dissociates at potentials lower than 0.60 V vs RHE, producing methane and adsorbed CO on Pd; while C2-species, CHx and COad are formed on Pt. Besides carbon dioxide, acetic acid and adsorbed acetate were observed at E > 0.6 V, and their contribution increased with acetaldehyde concentration. Differences between Pt and Pd in potential dependence of the products and intermediates were established. Calibration of the mass spectrometer, together with the use of labeled acetaldehyde and IR spectra, allows establishment of the nature of adsorbed species and products for both Pt and Pd at different potentials, elucidating global reaction pathways for acetaldehyde on these two noble metals.

Combined ATR-Seiras and IRAS Study of Dissociation and Oxidation of Alcohols At Palladium Electrode in Alkaline Media

not Available.

Thermodynamic properties of compounds in the PdO-H2O system at 25°C

Literature thermodynamic data on species and particles existing in the heterogeneous PdO-H2O system were checked for consistency, and the equilibrium constants for dissolution of palladium oxide and hydroxide in water and for Pd2+ (aq) hydrolysis were recommended. Δ f G 298.15 ° obtained in this work for Pd2+(aq) sharply differs (no less than by 6 kJ/mol) from values that are reported in fundamental thermodynamic reference books and based on experimentally measured palladium electrode potential at 25°C. Detailed examination of literature data on the thermodynamic properties of compounds in the Cl-Pd(aq) system is required to account for revealed inconsistency.

WSe2 field effect transistors with enhanced ambipolar characteristics

One of the most relevant features that a semiconducting channel material can offer when used in a field-effect transistor (FET) layout is its capability to enable both electron transport in the conduction band and hole transport in the valence band. In this way, complementary metal-oxide-semiconductor type applications become feasible once similar electron and hole drive current densities are achieved, and the threshold voltages are properly adjusted. In this article, we demonstrate pronounced ambipolar device characteristics of multilayer WSe2 FETs using different contact electrodes. Our study reveals that nickel electrodes facilitate electron injection while palladium electrodes are more efficient for hole injection. We also show, as an interesting demonstration, that by using nickel as the source contact electrode and palladium as the drain contact electrode, ambipolar device characteristics with similar on-state performance for both the electron and the hole branch can be achieved in WSe2 FETs. Finally, we discuss a unique technique based on the asymmetry in the ambipolar device characteristics to extract the Schottky barrier heights for such metal to WSe2 contacts.

Methanol electro-oxidation on a porous nanostructured Ni/Pd-Ni electrode in alkaline media

A nanostructured Ni/Pd-Ni catalyst with high activity for methanol oxidation in alkaline solution was prepared by electrodeposition followed by galvanic replacement, that is, electrodeposition of Ni-Zn on a Ni coating with subsequent replacement of the Zn by Pd at the open circuit potential in a Pd-containing alkaline solution. The surface morphology and composition of the coatings were examined by energy dispersive X-ray spectroscopy and scanning electron microscopy. The Ni/Pd-Ni coatings were porous and were composed of discrete Pd nanoparticles of about 58 nm. The electrocatalytic activity of the Ni/Pd-Ni electrodes for the oxidation of methanol was examined by cyclic voltammetry and electrochemical impedance spectroscopy. The onset potentials for methanol oxidation on Ni/Pd-Ni were 0.077 V and 0.884 V, which were lower than those for flat Pd and smooth Ni electrodes, respectively. The anodic peak current densities of these electrodes were 4.33 and 8.34 times higher than those of flat Pd (58.4 mA/cm 2 vs 13.47 mA/cm 2 ) and smooth Ni (58.4 mA/cm 2 vs 7 mA/cm 2 ). The nanostructured Ni/Pd-Ni electrode is a promising catalyst for methanol oxidation in alkaline media for fuel cell application. The nanostructured Ni/Pd-Ni electrode shows significantly greater electro-catalytic activity towards methanol oxidation than flat palladium and smooth nickel electrodes. The high activity of Ni/Pd-Ni electrode can be attributed to its high surface area.

Reduction of nitrate on electrochemically pre-reduced tin-modified palladium electrodes

The electrochemical pretreatment of Sn-modified Pd electrodes at the negative potentials of ⩽−0.2V vs. Ag/AgCl (sat. KCl) enhanced their electrocatalytic properties for the reduction of nitrate. Namely, the nitrate reduction current increased by several times depending on the potentials for the nitrate reduction and the pretreatment, and the product selectivity for the formation of N2 increased from 29% for the as-prepared (untreated) electrodes to 51%. The STM, XPS and cyclic voltammetric measurements revealed that the following structural changes were induced by the pretreatment. (1) Spontaneously adsorbed divalent tin was reduced to zero-valent tin. (2) The hydrogen adsorption and absorption ability of Pd was almost lost while the surface Sn fraction decreased. (3) Primary particles of ca. 30nm observed on a Pd and an as-prepared Sn/Pd electrode were reconstructed to larger particles of 45nm. Based on these results on the structural change and the literature on d-band filling in binary metal systems, it was concluded that the surface Sn/Pd alloy was formed, and thereby the surface electronic structure was changed. This accelerated N–O bond cleavage and decreased the hydrogenation ability.

Palladium as electrode in DNA sequencing

We construct a molecular junction comprising two identical “reader” molecules that are each linked on one end to a DNA single base via hydrogen bonds and on the other end to a palladium electrode. The structure of the junction is thus palladium-reader-base-reader-palladium. The palladium-reader contacts occur via Pd-S bonds. We calculated the electronic structure and conductance of the molecular junctions. Compared with the performance of molecular junctions with gold or titanium nitride electrodes, the current-voltage characteristics of the molecular junctions with palladium electrodes show higher sensitivity to the identity of the bridging DNA base, allowing the DNA bases to be distinguished more easily. Therefore, palladium is a superior electrode for molecular electronics and DNA sequencing.

Hydrogen absorption by a palladium electrode from a protic ionic liquid at temperatures exceeding 100 °C

Hydrogen adsorption in a palladium electrode driven by the electrochemical reduction of protons from a protic ionic liquid is presented. The amounts of hydrogen absorbed and desorbed in thin Pd films is similar in both the diethylmethylammonium-trifluoromethanesulfonate ionic liquid and in an aqueous H2SO4 solution, reaching H/Pd atomic ratios of 0.7 to 0.8. The electrochemical quartz crystal microbalance technique showed decreased absorption and desorption rates due to the slower proton transfer between the protic ionic liquid and the electrode. The use of this thermally stable ionic liquid allowed absorbing and desorbing hydrogen at temperatures up to 125°C, increasing the rate of the reactions.

Mechanical and electrochemical properties of an IPMC actuator with palladium electrodes in acid and alkaline solutions

An ionic polymer–metal composite (IPMC) actuator, which consists of a thin perfluorinated ionomer membrane and electrodes plated on both surfaces, undergoes a large bending motion when a low electric field is applied across its thickness. IPMC actuators are lightweight and soft and can operate in solutions. They are thus promising for a wide range of applications including MEMS sensors, artificial muscles, biomimetic systems, and medical devices. The deformation behavior of IPMC actuators depends on the pH of the working solution. However, their basic mechanism is not well understood. Therefore, this study investigates the deformation mechanism of an IPMC actuator with palladium electrodes in various pH solutions. The tip displacements of IPMC actuators were measured under a step voltage in various pH solutions. Cyclic voltammetry (CV) and alternating-current (AC) impedance measurements were then performed to investigate the effects of pH on the electrochemical properties of IPMC actuators. The responses to a step voltage indicate that the deformation behavior of an IPMC actuator depends on the pH: a lower pH gives a larger maximum tip displacement and more pronounced relaxation. In CV measurements, a lower pH results in more active reduction on the palladium electrode. In AC impedance measurements, a lower pH leads to a greater charge transfer resistance and a smaller double layer capacitance in an acid solution. Based on these mechanical and electrochemical measurements, we conclude that the maximum tip displacement and relaxation are governed by reduction on the palladium electrode and that the residual tip displacement is related to the charge transfer resistance and the double layer capacitance. These results are helpful for the use and control of IPMC actuators.

Electrochemical hydrogen pumps using Ba doped LaYbO3 type proton conducting electrolyte

The electrochemical hydrogen pumping using Ba doped LaYbO3 oxide (La0.9Ba0.1YbO3−α, LBYb-91) was investigated in this work. It was found that LBYb-91 can conduct a large amount of protons as much as 100 mA cm−2 and the theoretical hydrogen evolution is actually occurred by the proton conduction. It was also found that LBYb-91 has high chemical stability against CO2 and H2O, and showed a comparable cell performance to SrZr0.9Y0.1O3−α (SZY-91) with porous palladium electrode. The present study demonstrated that LBYb-91 is a potential candidate electrolyte material for the electrochemical cell to separate hydrogen from the reformed natural gas.

The evaluation of sugar content and firmness of non-climacteric pears based on voltammetric electronic tongue

The sugar content and firmness of non-climacteric pear of different cultivars were studied by a voltammetric electronic tongue (VE-tongue). The VE-tongue self-developed in this study comprised six working electrodes (gold, silver, platinum, palladium, tungsten, and titanium electrode), an Ag/AgCl reference electrode, and a platinum auxiliary electrode. The multi-frequency large amplitude pulse voltammetry (MLAPV) was applied to the working electrodes as the scanning potential waveform,and it consisted of four frequency segments of 1Hz, 10Hz, 100Hz, and 1000Hz. In this study, five cultivars of pear from different geographical origins were tested by VE-tongue, and the firmness and sugar content of pears were tested by the traditional methods. The characteristic data (the maximum and minimum values) obtained by VE-tongue were compressed by principal component analysis (PCA), and the principal components (PCs) were taken as the input variables of principal component regression (PCR), partial least squares regression (PLSR), and least squared-support vector machines (LS-SVMs) to predict sugar content and firmness. All the models showed good results, and LS-SVM preformed best in the prediction.

Infrared Spectroelectrochemical Study of Dissociation and Oxidation of Methanol at a Palladium Electrode in Alkaline Solution

The dissociative adsorption and electrooxidation of CH(3)OH at a Pd electrode in alkaline solution are investigated by using in situ infrared spectroscopy with both internal and external reflection modes. The former (ATR-SEIRAS) has a higher sensitivity of detecting surface species, and the latter (IRAS) can easily detect dissolved species trapped in a thin-layer-structured electrolyte. Real-time ATR-SEIRAS measurement indicates that CH(3)OH dissociates to CO(ad) species at a Pd electrode accompanied by a "dip" at open circuit potential, whereas deuterium-replaced CH(3)OH doesn't, suggesting that the breaking of the C-H bond is the rate-limiting step for the dissociative adsorption of CH(3)OH. Potential-dependent ATR-SEIRAS and IRAS measurements indicate that CH(3)OH is electrooxidized to formate and/or (bi)carbonate, the relative concentrations of which depend on the potential applied. Specifically, at potentials negative of ca. -0.15 V (vs Ag/AgCl), formate is the predominant product and (bi)carbonate (or CO(2) in the thin-layer structure of IRAS) is more favorable at potentials from -0.15 to 0.10 V. Further oxidation of the CO(ad) intermediate species arising from CH(3)OH dissociation is involved in forming (bi)carbonate at potentials above -0.15 V. Although the partial transformation from interfacial formate to (bi)carbonate may be justified, no bridge-bonded formate species can be detected over the potential range under investigation.

Encapsulation of fluidic tubing and microelectrodes in microfluidic devices: integrating off-chip process and coupling conventional capillary electrophoresis with electrochemical detection

In this paper, an approach to fabricate epoxy or polystyrene microdevices with encapsulated tubing and electrodes is described. Key features of this approach include a fixed alignment between the fluidic tubing and electrodes, the ability to polish the device when desired, and the low dead volume nature of the fluidic interconnects. It is shown that a variety of tubing can be encapsulated with this approach, including fused silica capillary, polyetheretherketone (PEEK), and perfluoroalkoxy (PFA), with the resulting tubing/microchip interface not leading to significant band broadening or plug dilution. The applicability of the devices with embedded tubing is demonstrated by integrating several off-chip analytical methods to the microchip. This includes droplet transfer, droplet desegmentation, and microchip-based flow injection analysis. Off-chip generated droplets can be transferred to the microchip with minimal coalescence, while flow injection studies showed improved peak shape and sensitivity when compared to the use of fluidic interconnects with an appreciable dead volume. Importantly, it is shown that this low dead volume approach can be extended to also enable the integration of conventional capillary electrophoresis (CE) with electrochemical detection. This is accomplished by embedding fused silica capillary along with palladium (for grounding the electrophoresis voltage) and platinum (for detection) electrodes. With this approach, up to 128,000 theoretical plates for dopamine was possible. In all cases, the tubing and electrodes are housed in a rigid base; this results in extremely robust devices that will be of interest to researchers wanting to develop microchips for use by non-experts.