Al Electrode Modified by Au Atoms as a Novel Electrode for Electrocatalytic Oxidation of Thiosulfate

An aluminum electrode modified with gold atoms was introduced as a novel electrode. Gold atoms were deposited both chemically and electrochemically onto the aluminum electrode to make an aluminum/gold (Al/Au) modified electrode (ME). The experimental results showed that the Al/Au modified electrode prepared by chemical deposition, exhibits much more current than the electrochemical deposition method. The electrochemical behavior of the Al/Au modified electrode was studied by cyclic voltammometry. This modified electrode showed two pairs of peaks, a₁c₁ and a₂c₂, with surface‐confined characteristics in a 0.5 M phosphate buffer. The dependence of E_pa of the second peak (a₂c₂) on pH shows a Nernestian behavior with a slope of 55 mV per unit pH. The effect of different supporting electrolytes, solution's pH and different scan rates on electrochemical behavior of Al/Au modified electrode was studied. Au deposited electrochemically on a Pt electrode (Pt/Au) was also used as another modified electrode. A comparative study of electrochemical behavior of bare Al, Pt/Au and Al/Au modified electrodes showed that both Pt/Au and Al/Au electrodes have the ability of electrocatalytic oxidation of S₂O₃^2?, but the electrocatalytic oxidation on the latter was better than the former. The kinetics of the catalytic reaction was investigated by using cyclic voltammetry and chronoamperometry techniques. The average value of the rate constant for the catalytic reaction and the diffusion coefficient were evaluated by means of chronoamperometry technique.     

A new polyphenol modified electrode containing an anchored ruthenium complex and its use in electrocatalytic oxidation of organic substrates

This work describes the preparation of a new modified electrode containing a ruthenium complex (cis-aquadimethylbipyridyltriphenylphosphineruthenium II), bonded to a stable polyphenol film. This modified electrode promotes the fast electrocatalytic oxidation of safrol (5-allyl-benzo[1,3]dioxole) and isosafrol (5-propenyl-benzo[1,3]dioxole), giving two interesting products benzo[1,3]dioxole-5-carbaldehyde (piperonal) and 3-benzo[1,3]dioxol-5-yl-propenal respectively, with good yields. The electrode preparation can be carried out at a potential range which does not interfere on the anchored electroactive ruthenium complex, but it allows for the phenol oxidation to occur and therefore polymerize forming the polyphenol film. The catalytic character of this modified electrode is showed by its high turnover numbers. The procedure to isolate the products is very simple.     

Electrosorption of hydrogen into palladium-gold alloys

Hydrogen electrosorption into Pd-Au alloys has been studied in acidic solutions (1 M H₂SO₄) using cyclic voltammetry. Pd-Au electrodes with limited volume were prepared by electrochemical co-deposition. It was found that the maximum H/(Pd+Au) ratios decrease monotonically with increasing gold content and reach zero at ca. 70 at% Au. Similarly to the case of Pd limited volume electrodes, two peaks in the hydrogen region, corresponding to two types of sorbed hydrogen, are observed on voltammograms for Pd-rich alloys. The hydrogen capacity, H/(Pd+Au), measured electrochemically, depends on the sweep rate in the cyclic voltammetry experiments, which suggests that two different mechanisms for hydrogen desorption from the Pd-Au alloy are possible. After a strong decrease of Pd concentration at the electrode surface, caused by long cyclic polarization to sufficiently anodic potentials, the amount of absorbed hydrogen is still significant for alloys initially rich in Pd. The results obtained from CO adsorption experiments suggest that only Pd atoms are active in the hydrogen absorption/desorption process. Electronic Publication     

Recent development of non-faradaic potentiometry

Non-faradaic potentiometry has been plagued by a great many fundamental errors and a lack of conceptualization. Of greatest concern is the second Nernst equation hiatus. Potentiometry may be generally classified as faradaic and non-faradaic. The former deals with the redox reactions using the Nernst equation to explain the potential origin. The latter deals with the non-redox reactions using the Boltzmann and modified Boltzmann equations to explain the origin of electrode potential. Redox faradaic potentiometry has been well described in the textbooks. However, non-faradaic potentiometry has been almost completely neglected in the literature. Many well-known electrodes, such as the pH glass electrode, common reference electrodes, and ion selective electrodes (ISE) have been mistakenly interpreted as redox reactions or ion exchange reactions. New theories and experimental results show their mechanisms to be non-faradaic in nature. Furthermore, the reaction mechanisms for ISE have been confused in textbooks with redox reactions and the Nernst equation. The ISE potentials originating from adsorption of ions or charged particles based on surface charge density will be explained using the double and counterion triple layers concept. The new counterion triple layer concept may be applied to the potential development of sensors. The reason for a new concept, theory, or mechanism is to better explain the phenomena. Examples will be given of how our new concept explains the capacitor, counterion triple layer, surface adsorbed layers interactions, and the interface structure. We will also discuss the new sensor development based on the new adsorption concept. For the first time a new type of Ag/AgCl reference electrode for non-faradaic potentiometry will be presented, one without a liquid junction and with a Pt wire instead of a salt bridge. They will help open up a new horizon for electrochemical sensor research and may be used under unusual conditions, such as high temperature and high pressure, stirring, etc.     

A cobalt(II)-selective PVC membrane based on a Schiff base complex of N,N′-bis(salicylidene)-3,4-diaminotoluene

A new PVC membrane electrode for Co²⁺ based on N,N′-bis(salicylidene)-3,4-diaminotoluene, an excellent neutral carrier, has been fabricated using sodium tetraphenylborate (NaTPB) as an anionic excluder and dioctylphthalte (DOP) as a solvent mediator. The electrode exhibits a linear potential response in the concentration range of 7.9 × 10⁻⁸ to 1.0 × 10⁻¹ M with a slope of 30 ± 0.2 mV per decade. The detection limit of the proposed sensor is 5.0 × 10⁻⁸ M and it can be used over a period of 5 months. The proposed sensor revealed good selectivity over a wide variety of other cations including alkali, alkaline earth, heavy and transition metals and could be used in the pH range of 2.0-9.0. This electrode was successfully applied for the determination of Co²⁺in real samples and as an indicator electrode in potentiometric titration of cobalt ions.     

Development of an Amperometric Biosensor for β‐N‐Oxalyl‐L‐α,β‐Diaminopropionic Acid (β‐ODAP)

An amperometric method for the determination of the neurotoxic amino acid β‐N‐oxalyl‐L ‐α,β‐diaminopropionic acid (β‐ODAP) using a screen printed carbon electrode (SPCE) is reported. The electrode material was bulk‐modified with manganese dioxide and used as a detector in flow injection analysis (FIA). The enzyme glutamate oxidase (GlOx) was immobilized in a Nafion‐film on the electrode surface. The performance of the biosensor was optimized using glutamate as an analyte. Optimum parameters were found as: operational potential 440 mV (vs. Ag/AgCl), flow rate 0.2 mL min^?1, and carrier composition 0.1 mol L^?1 phosphate buffer (pH 7.75). The same conditions were used for the determination of β‐ODAP. The signal was linear within the concentration range 53–855 μmol L^?1 glutamate and 195–1950 μmol L^?1 β‐ODAP. Detection limits (as 3σ value) for both analytes were 9.12 and 111.0 μmol L^?1, respectively, with corresponding relative standard deviations of 3.3 and 4.5%. The biosensor retained more than 73% of its activity after 40 days of on‐line use.     

Electroanalytical Study of Prussian Blue Modified Glassy Carbon Paste Electrodes

Two types of glassy carbon (GC) powder (i.e., Sigradur K and Sigradur G) have been mixed with mineral oil to obtain glassy carbon paste electrodes (GCPE's). The electrochemical behavior of such electrodes at different percentages of glassy carbon has been evaluated with respect to the electrochemistry of ferricyanide as revealed with cyclic voltammetry and the best paste composition was chosen. GC was then modified with Prussian Blue (PB), mixed at different percentages with unmodified GC and with a fixed amount of mineral oil in order to obtain PB modified glassy carbon paste electrodes (PB‐GCPE's). PB‐GCPE's with different percentages of GC modified with PB (PB‐GC) were compared and the dependence on the amount of PB on their performances was evaluated by studying the parameters of cyclic voltammetry (i.e., current peak, ΔE_p, anodic and cathodic current ratio, charge density) and the amperometric response to H₂O₂. Data interpretation based on the GC surface area is presented. GCPE's with a selected amount of PB‐GC were then tested as H₂O₂ probes and all the analytical parameters together with the dependence on pH were evaluated. Some preliminary experiments with these electrodes assembled as glucose, lysine and lactate biosensors are also reported.     

Lower rim substituted tert-butylcalix[4]arenes. Part 8: Calix[4]arenes with dialkoxyphosphoryl functions. Synthesis and complexing properties

New compounds: 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis(3-diisopropoxyphosphorylpropoxy)calix[4]arene (1) and 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis(3-methoxyethoxyphosphorylpropoxy)calix[4]arene (2) were synthesized and their ionophoric properties in ion-selective membrane electrodes were studied in comparison with already described by us 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis(3-diethoxyphophorylpropoxy)calix[4]arene (3). Complexes of 1 with calcium(II), lanthanum(III), europium(III) and gadolinium(III) nitrates were prepared in direct reaction of the ligand and appropriate metal salts. They were characterized by spectral data (IR, UV/Vis, luminescence, NMR, ESI-MS) and elemental analysis. The similarity in complexing behavior of the (dialkoxyphosphoryl)propoxy-calix[4]arenes toward calcium and some lanthanides was observed.     

锂离子电池锡氧化物基负极材料的湿化学合成与电化学性质

采用新兴的湿化学方法合成了锡氧化物基粉末材料。用X-射线衍射、扫描电镜和电化学方法对材料的微观结构、形貌和电化学性能进行了详细的研究。结果表明，经400 ℃热处理4 h的锡氧化物基材料的颗粒大小均匀，平均粒径约为200 nm。这种材料的可逆充电容量超过570 mAh·g^-1，30次循环后平均每次循环的容量衰减只有0.15%。良好的电化学性能表明锡氧化物基材料有望作为新一代锂离子电池的负极材料。