Sensitive and Rapid Flow Injection Amperometric Hydrazine Sensor using an Electrodeposited Gold Nanoparticle Graphite Pencil Electrode

A gold (Au) nanoparticle-modified graphite pencil electrode was prepared by an electrodeposition procedure for the sensitive and rapid flow injection amperometric determination of hydrazine (N₂H₄). The electrodeposited Au nanoparticles on the pretreated graphite pencil electrode surface were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction spectroscopy, and electrochemical impedance spectroscopy. Cyclic voltammograms showed that the Au nanoparticle-modified pretreated graphite pencil electrode exhibits excellent electrocatalytic activity toward oxidation of hydrazine because the highly irreversibly and broadly observed oxidation peak at +600?mV at the pretreated graphite pencil electrode shifted to ?167?mV at the Au nanoparticle pretreated graphite pencil electrode; in addition, a significant enhancement in the oxidation peak current was obtained. Thus, the flow-injection (FI) amperometric hydrazine sensor was constructed based on its electrocatalytic oxidation at the Au nanoparticle-modified pretreated graphite pencil electrode. The Au nanoparticle-modified pretreated graphite pencil electrode exhibits a linear calibration curve between the flow injection amperometric current and hydrazine concentration within the concentration range from 0.01 to 100?µM with a detection limit of 0.002?µM. The flow injection amperometric sensor has been successfully used for the determination of N₂H₄ in water samples with good accuracy and precision.     

Silicomolybdate doped polypyrrole film modified glassy carbon electrode for electrocatalytic reduction of Cr(VI)

Electrically conducting polypyrrole (PPy) film doped with silicomolybdate (SiMo₁₂ or SiMo₁₂) was synthesized by electrochemical polymerization. The synthesized film is capable of fast charge propagation during redox reactions in strong acid medium 0.2 M H₂SO₄ solution. Electrochemical quartz crystal microbalance was used to study the mechanism and amount of SiMo₁₂ doped in the PPy matrix. The modified electrode surface was characterized by using atomic force microscope technique, and it was found that the minimum and maximum globule size were estimated to be in the range of 50–200 nm. The thickness of film was measured to be approximately 30 ± 10 nm. The modified electrode shows electrocatalytic activity towards reduction of Cr(VI) and periodate. The rate constant and optimal film thickness were determined for electrocatalytic reduction of Cr(VI) by using rotating disc electrode experiment. Analytical characterization of the SiMo₁₂ doped PPy film modified electrode was demonstrated by flow injection analysis (FIA) technique and shows good stability for 16 continuous injections for Cr(VI) reduction with RSD of 1.6%.     

Stacked graphene nanofibers doped polypyrrole nanocomposites for electrochemical sensing

This publication shows a single-step electropolymerization which has been carried out by the incorporation of an anionic stacked graphene nanofiber (SGNF) dopant into a polypyrrole (PPy) film, at a disposable screen-printed electrode. The incorporation of the SGNFs into the polymer does not affect their electrochemical properties, shown through cyclic voltammetry by the earlier oxidation of guanine, when compared with that at the graphite doped PPy electrode. The SGNF/PPy composite shows a high selectivity when used in the oxidation of guanine and hydrogen peroxide, both of which are important biomarkers used for biosensing. Disposable screen-printed electrodes provide an inexpensive, sensitive and portable substitute to glassy carbon electrodes, while giving a reproducible surface; qualities essential for effective bionsensing. The production of this single-step disposable SGNF/PPy composite electrode allows for further applications in the detection of biomedically important compounds and DNA sensing.     

Sensitive Flow-Injection Electrochemical Determination of Hydrogen Peroxide at a Palladium Nanoparticle-Modified Pencil Graphite Electrode

A novel flow-injection amperometric method was proposed for the sensitive and enzymeless determination of hydrogen peroxide based on its electrocatalytic reduction at a palladium nanoparticle-modified pretreated pencil graphite electrode in a laboratory-constructed electrochemical flow cell. Cyclic voltammograms of the unmodified and modified electrodes were recorded in pH 7.0 phosphate buffer containing 0.10 M KCl at a scan rate of 50?mV s^?1 for the investigation of electrocatalytic reduction of hydrogen peroxide at the palladium nanoparticle-modified pretreated pencil graphite electrode. Cyclic voltammograms of the pretreated pencil graphite electrode revealed an irreversible oxidation peak and a weak reduction peak of hydrogen peroxide at +1100?mV and –450?mV vs. an Ag/AgCl/KCl saturated reference electrode. However, the reduction of hydrogen peroxide was observed at –100?mV with an increase in current in the cyclic voltammograms of the palladium nanoparticle-modified pretreated pencil graphite electrode compared to the unmodified electrode. These results indicate that the palladium nanoparticle-modified pretreated pencil graphite electrode exhibits efficient electrocatalytic activity for the reduction of hydrogen peroxide. A linear concentration range was obtained between .01 and 10.0?mM hydrogen peroxide with a detection limit of 3.0 µM from flow injection amperometric current–time curves recorded in pH 7.0 phosphate buffer at –100?mV and a 2.0?mL min^?1 flow rate. The novelty of this work relies on its use of a laboratory-constructed flow cell constructed for the pencil graphite electrode using these inexpensive, disposable, and electrochemically reactive modified electrodes for the amperometric determination of hydrogen peroxide in a flow injection analysis system.     

Microelectrode Combinations of Gold and Polypyrrole Enable Highly Stable Two-electrode Electrochemical Impedance Spectroscopy Measurements under Turbulent Flow Conditions

An electrochemical impedance spectroscopy (EIS) sensor design is proposed based on a standard interdigitated electrode layout in which the smaller working electrode consists of gold (Au) whereas the larger combined counter and reference electrode is coated with a porous layer of polypyrrole (PPy) doped with polystyrene sulfonate (PSS) (PPy : PSS). Each electrode material was first characterized by EIS in a standard 3-electrode setup with subsequent spectra fitting by a modified Randles equivalent circuit. The differences in the spectra obtained by the PPy : PSS coated electrodes can be explained by an increased electroactive surface area due to the porous polymer film. The changes in morphology of the film are discussed with respect to the evolution of the elements of the electric equivalent circuit. When applying the Au/PPy : PSS electrode combination to a standard 2-electrode arrangement, the enlarged highly electroactive surface area of the PPy : PSS coating lowers the interfacial impedance in a way that mainly the gold working electrode contributes to the overall system impedance. Therefore, obtaining reproducible EIS signals depends only on the electrode's open-circuit potential (OCP) and on additional adsorption events at the gold electrode/electrolyte interface. We present a protocol for microelectrode coating with PPy : PSS, which enables highly stable 2-electrode EIS experiments without the need of a reference electrode. This combination is believed to be very useful if an integration of sensing electrodes inside Micro Total Analysis Systems is aspired.     

Electrophoretic Deposition of a Reduced Graphene–Au Nanoparticle Composite Film as Counter Electrode for CdS Quantum Dot‐Sensitized Solar Cells

A reduced graphene (RG)‐Au nanoparticle composite film is successfully fabricated by electrophoretic deposition and used as counter electrode for quantum dot‐sensitized solar cells. The RG‐Au composite is prepared by one‐step microwave‐assisted reduction of chloroaurate in alkaline solution with graphite oxide dispersion. Under one sun illumination (AM 1.5 G, 100 mW cm^?2), the cell with a RG‐Au counter electrode shows an energy conversion efficiency of 1.36 %, which is higher than those of cells employing conventional Pt or Au counter electrodes, due to the superior combination of highly catalytic Au nanoparticles and the conductive graphene network structure.     

毛细管电泳-多壁碳纳米管/聚吡咯/磷钼酸修饰电极电化学检测饮用水中的溴酸根

用电化学聚合法制备多壁碳纳米管/聚吡咯/磷钼酸修饰电极,利用循环伏安法研究溴酸根在此修饰电极上的电化学行为.考察了实验参数对分离检测体系的影响,并在优化条件下,采用毛细管电泳-安培检测法对溴酸根进行检测.结果表明:溴酸根离子在1.0×10-6～5.0×10-3 mol/L范围内和峰面积呈良好的线性关系,检出限(S/N=...     

EQCM and Fluoroelectrochemical Studies on the Catalytic Oxidation of NADH at a Pencil 8B‐Scrawled Gold Electrode with High Detection Sensitivity

We report for the first time the effective catalytic electrooxidation of nicotinamide adenine dinucleotide (NADH) on the pencil 8B‐scrawled gold electrode of an electrochemical quartz crystal microbalance (EQCM). The EQCM allowed us to quantitatively evaluate the catalytic activity of the pencil‐scrawled Au electrode. With increasing the mass of modified pencil powders, the peak potential for NADH oxidation shifted negatively, with maximum shift of ?0.35 V at saturated pencil modification; the NADH‐oxidation peak current density (j_p) was also notably increased, and the j_p at saturated pencil modification was found to be larger than those at conventional pencil 8B and bare Au electrodes. Sensitive amperometric detection of NADH was achieved at the gold electrode with saturated pencil modification, with low detection potential (0.4 V versus SCE), low detection limit (0.08 μmol L^?1) and wide linear range (0.2–710 μmol L^?1). The fluoroelectrochemical measurements of NADH at bare and pencil‐modified gold electrodes were also conducted with satisfactory results. The convenient and low‐cost modification of pencil powders on the Au electrode may have presented a new functional surface of the EQCM, which is recommended for wider applications to bioelectrochemical studies, especially in view of the EQCM's capability of providing abundant in situ information in relevant processes.     

Detection of Thiols by o‐Quinone Nanocomposite Modified Electrodes

A chemically modified glassy carbon (GC) electrode was developed as an amperometric sensor for detection of biological thiols. The electrode was modified by inclusion of co‐enzyme pyrroloquinoline quinone (PQQ) and a co‐catalyst of oxidized single wall carbon nanotubes (Ox‐SWNT) into a gold polypyrrole (Au‐PPy) nanocomposite matrix. The electrode (PQQ/Ox‐SWNT/Au‐PPy/GC) was characterized using scanning electron microscopy and cyclic voltammetry. Optimal conditions for the PQQ/Ox‐SWNT/Au‐PPy/GC electrode were determined and then utilized for the amperometric detection of L‐cysteine, N‐acetyl‐L‐cysteine, L‐penicillamine and D, L‐glutathione. The electrochemical response for each thiol in pH 3.2 citrate phosphate buffer at +450 mV (vs. Ag/AgCl) was found to be linear with limit of detections (LOD, S/N=3) ranging from 0.50 µM for L‐penicillamine to 1.55 µM for D, L‐glutathione with sensitivities of 30.2 nA/µM and 3.6 nA/µM respectively. The electrode design is simple and easy to construct using a minimum amount of co‐enzyme and co‐catalyst, resulting in detection methods with very good stability and improved sensitivity for thiol detection.     

Enhanced Electrocatalytic Performance of Anthraquinonemonosulfonate‐Doped Polypyrrole Composite: Electroanalysis for the Specific Roles of Anthraquinone Derivative and Polypyrrole Layer on Oxygen Reduction Reaction

To analyze the specific roles of anthraquinone‐2‐sulfonate (AQS) and polypyrrole (PPy) layer on oxygen reduction reaction (ORR), the electrocatalytic reduction of oxygen was investigated on the AQS/PPy composite modified graphite electrode. Results show that the enhanced electrocatalytic performance is attributed to the excellent electrocatalytic activity of the immobilized AQS functional groups to mediate two‐electron reduction of O₂ to H₂O₂. The PPy layer may not participate in ORR, but it can further catalyze the two‐electron reduction of H₂O₂ to produce H₂O in the potential range more negative than that the two‐electron reduction of oxygen proceeds efficiently on the AQS sites.     

Electrochemical preparation of effective and low cost catalyst for electrooxidation of ethanol

A nanocatalyst coating was prepared at surface of a glassy carbon electrode by electropolymerization of pyrrole by cycling the electrode potential between ?0.8 and 0.8 V (vs. Ag/AgCl). Then, polypyrrole film was potentiostatically coated with platinum nanoparticles at constant potential of ?0.2 V (vs. Ag/AgCl). The resulting electrode was denoted as GCE/PPy/Pt. This modified electrode was characterized by IR, SEM, TEM and EDX. The electrocatalytic oxidation of ethanol at the GCE/PPy/Pt has been investigated using cyclic voltammetric and chronoamperometric methods. The effects of various parameters on electrocatalytic oxidation of the ethanol, such as the thickness of PPy film, the amount of platinum nanoparticles, ethanol concentration, potential scan rate and working potential limit in anodic direction, were investigated. The kinetic of the ethanol oxidation is discussed on the GCE/PPy/Pt. The stability and reproducibility of this modified electrode were also studied.     

In situ AFM study of electrochemical synthesis of polypyrrole/Au nanocomposite

In this work, in situ AFM measurements with simultaneously electrochemical characterization were developed to study the mechanisms of both polypyrrole (PPy) and PPy/Au composite deposition. The nanoscale information derived from the in situ AFM images associated with theoretical simulation from the measured current–time transient (i–t) reveals that Au nanoparticles with negatively charged carboxylic groups can be the nuclei by both adsorption on the electrode surface and doping on PPy for the polymerization, and thus has faster nucleation and growth rate than Py alone at the early polymerization stage. The PPy/Au deposition shows parallel nucleation processes of Au nanoparticle and Py, and an instantaneous 3D nucleation mode. The work not only provides fundamental insights for PPy/Au nanocomposite deposition process, but also optimization approaches to fabricate a superior PPy/Au film with favorable features for greater potential applications.     

Electrooxidation of hydroquinone on simply prepared Au-Pt bimetallic nanoparticles

A facile method was used to prepare gold-platinum (Au-Pt) catalysts by direct electrodeposition via cyclic voltammetry in an acidic medium. Various parameters that affect the properties of electrodeposited catalysts were investigated such as initial applied potential, scan rate and deposition time. Initial applied potential plays a more important role in the preparation of bimetallic nanoparticles (AuPtNPs) since the kinetics of electrodeposition is in competition with the rate of hydrogen evolution. The AuPtNPs electrodeposited on pencil graphite (PG) were used to study the electrooxidation of hydroquinone. Various parameters such as pH, scan rate, concentration of hydroquinone and temperature were studied in the electrooxidation process. Apparent activation energy (E _a) for the electrooxidation of hydroquinone, calculated from the Arrhenius plot, shows that AuPtNPs catalysts (electrodeposited on the PG) offer less activation energy (ca. 9.500 kJ mol^?1) than the bare PG (ca. 10.345 kJ mol^?1). The AuPtNPs/PG shows better catalytic performance than the PG electrode due to the greater surface area it provides, thus resulting in more active sites available for adsorption of hydroquinone molecules on the surface of the catalyst.     

铂-氢钨青铜电极的制备及对氢氧化的电催化

采用电化学还原法在表面改性的碳布上,通过改变催化剂沉积顺序及氢钨青铜沉积时间制备铂-氢钨青铜复合催化剂,所得电极作为质子交换膜燃料电池(PEMFC)阳极。利用X射线衍射(XRD)、热重分析(TG)、扫描电子显微镜(SEM)、循环伏安(CV)及单电池极化性能测试研究了催化剂的组成、沉积量、分散性及其对氢氧化的电催化活性。实验结果表明,氢钨青铜沉积时间及催化剂沉积顺序对电极催化性能有显著影响,当氢钨青铜沉积时间为10 min,先沉积氢钨青铜、后沉积铂所得Pt/HxWO3电极对氢氧化具有最佳的催化活性。适量的氢钨青铜才能与铂形成较好的协同催化效应。     

Electrochemically Prepared Three‐dimensional Porous Nitrogen‐doped Graphene Modified Electrode for Non‐enzymatic Detection of Hydrogen Peroxide

A facile and green electrochemical method for the fabrication of three‐dimensional porous nitrogen‐doped graphene (3DNG) modified electrode was reported. This method embraces two consecutive steps: First, 3D graphene/polypyrrole (ERGO/PPy) composite was prepared by electrochemical co‐deposition of graphene and polypyrrole on a gold foil. Subsequently, the ERGO/PPy composite modified gold electrode was annealed at high temperature. Thus 3DNG modified electrode was obtained. Scanning electron microscopy (SEM), X‐ray photoelectron spectroscopy (XPS) and Raman spectroscopy were used to characterize the structure and morphology of the electrode. The electrode exhibits excellent electroanalytical performance for the reduction of hydrogen peroxide (H₂O₂). By linear sweep voltammetric measurement, the cathodic peak current was linearly proportional to H₂O₂ concentration in the range from 0.6 μM to 2.1 mM with a sensitivity of 1.0 μA μM⁻¹ cm⁻². The detection limit was ascertained to be 0.3 μM. The anti‐interference ability, reproducibility and stability of the electrode were carried out and the electrode was applied to the detection of H₂O₂ in serum sample with recoveries from 98.4 % to 103.2 %.     

Facile deposition of cobalt oxide based electrocatalyst on low-cost and tin-free electrode for water splitting

Facile deposition of a water-splitting catalyst on low-cost electrode materials could be attractive for hydrogen production from water and solar energy conversion. Herein we describe fast electrodeposition of cobalt-based water oxidation catalyst(Co-WOC) on simple graphite electrode for water splitting. The deposition process is quite fast, which reaches a plateau in less than 75 min and the final current density is～1.8 mA/cm2under the applied potential of 1.31 V at pH = 7.0. The scanning electron microscopy(SEM) study shows the formation of nanometer-sized particles(10-100 nm) on the surface of the electrode after only 2 min and micrometer-sized particles(2-5 μm) after 90 min of electrolysis. X-ray photoelectron spectroscopy(XPS) data demonstrate the as-synthesized ex-situ catalyst mainly contains Co2+and Co3+species incorporating a substantial amount of phosphate anions. These experiments suggest that cost-efficient cobalt oxide materials on graphite exhibit alluring ability for water splitting, which might provide a novel method to fabricate low-cost devices for electrochemical energy storage.     

Electrocatalytic oxidation and flow-injection determination of ascorbic acid at a graphite electrode modified with a polyaniline film containing electrodeposited palladium

A method for forming a composite film on the surface of a graphite electrode is proposed. Conditions for detecting the maximum catalytic current under batch and flow conditions are determined. A procedure for the electrocatalytic determination of ascorbic acid at the graphite electrode modified with a polyaniline film containing palladium particles is proposed. The catalytic effect of this electrode manifests itself by a ～300-mV decrease in the peak potential of ascorbic acid oxidation and by a multiple increase in the peak current of ascorbic acid oxidation as compared to the unmodified electrode. The linear dependence of the electrocatalytic response of the composite electrode on the concentration of ascorbic acid is observed down to 1 × 10^?8 M and 2.5 nmol of ascorbic acid under batch and flow-injection analysis conditions, respectively.     

Morphological and electrochemical characterisation of graphite electrodes coated with SPANI and Ni-cyclam

The preparation of the composite graphite–sulphonated polyaniline (SPANI)–Ni-cyclam was investigated with the purpose of dispersing a catalyst in a conducting matrix that allows a better electronic transfer from the surface of the electrode towards the reaction site. The graphite is a material with a high porosity, big area and cheaper than other materials. The electrochemical and morphological characterisations show that the best conditions for obtaining SPANI over graphite were reached with an anodic limit of 1,000 mV in H₂SO₄. The deposit of the Ni-cyclam over graphite–SPANI in basic medium allows the formation of a spongy and open material, which permits better accessibility to the catalytic sites, showing good catalytic properties. These results illustrate that the importance relays on the morphology and dispersion of the catalyst and not on the amount of catalytic material present in the composite. The electrocatalytical properties Ni-cyclam over graphite–SPANI was studied for the methanol oxidation in basic medium.     

Catalyzed microelectrode mediated by polypyrrole/Nafion® composite film for microfabricated fuel cell applications

A novel Si-based micromachined electrode composed of polypyrrole (PPy)/Nafion^® film and electrochemically deposited Pt nanocatalysts was prepared for the microfabricated fuel cell applications. In addition to its high surface area to host nanocatalyst particles, the PPy/Nafion^® composite film offers good electron and proton conductivity and the fabrication of such films is largely compatible with the micromachining process. The resulted catalyzed microelectrodes exhibit high electrochemical active surface area and high catalyst utilization. The corresponding Si-based micro membrane–electrode-assembly demonstrates good cell polarization characteristics using the H₂/O₂ feed.     

Low Cost Hydrogen Peroxide Sensor from Manganese Oxides Modified Pencil Graphite Electrode

Electrodeposition of manganese oxides film onto the cheap pencil graphite electrode using potassium permanganate precursor provides the good alternative method of fabrication the low cost hydrogen peroxide sensor. Effect of deposition potential, deposition time and concentration of potassium permanganate were investigated. The modified electrode displayed electrocatalytic activity towards the oxidation of hydrogen peroxide in alkaline medium. Amperometric detection of hydrogen peroxide in ammonium buffer pH 9.0 is possible at the operation potential of +0.50V vs Ag/AgCl instead of over +0.80V vs Ag/AgCl with unmodified electrode. Linear concentration range between 0.50-138ppm of hydrogen peroxide was obtained with a detection limit of 0.28ppm.