Electrochemical study of 7α,12,20-O-trimethyl-conacytone in acetonitrile

An electrochemical study of the electroreduction in anhydrous acetonitrile of 7α,12,20-O-trimethyl-conacytone, an abietane quinoid diterpene derivative from the natural product 7α-O-methyl-conacytone, showed two reduction signals. At the first reduction step, fast chemical reactions involving the loss of the methoxyl group located at C-7 with simultaneous regeneration of the quinoid moiety were observed. This electrogenerated quinone is reduced again, at the same potential used with the former quinone, resulting in a two-electron peak. These results were obtained by cyclic voltammetry and double-step chronoamperometry experiments. The electrolysis under methylating conditions of 7α-O-methyl-conacytone, at potential values of the second electron transfer, generates as major products, methoxy-hydroquinone, where the methoxy group at C-7 is lost, which is in agreement with the proposed mechanism. Therefore, the second reduction signal was attributed to the reduction of semiquinone intermediates by a mechanism not elucidated.     

Enhanced performance of direct peroxide/peroxide fuel cell by using ultrafine Nickel Ferric Ferrocyanide nanoparticles as the cathode catalyst

Direct peroxide-peroxide fuel cell (DPPFC) employing with H₂O₂ both as the fuel and oxidant is an attractive fuel cell due to its no intermediates, easy handling, low toxicity and expense. However, the major gap of DPPFC is the cathode performance as a result of the slow reaction kinetics of H₂O₂ electro-reduction and thus the target issue is to design cathode catalysts with high performance and low cost. Herein, different with using noble metal of state-of-the-art, we have successfully synthesized ultra-fine NiFe ferrocyanide (NiFeHCF) nanoparticles (the mean particles size is 2.5 nm) through a co-precipitation method, which is used as the cathode catalyst towards H₂O₂ reduction in acidic medium. The current density of H₂O₂ reduction on the resultant NiFeHCF electrode after the 1800 s test period at ?0.1, 0 and 0.1 V are 121, 93 and 76 mA cm², respectively. Meanwhile, a single two-compartment DPPFC cell with NiFeHCF nanoparticles as the cathode and Ni/Ni foam as the anode is assembled and displayed a stable OCP of 1.09 V and a peak power density of 36 mW cm^?2 at 20 °C, which is much higher than that of a DPPFC employed with Pd nano-catalyst as cathode.     

Electrochemical reduction of tert-butyl chloride—Computational study

In this work kinetics of the electrochemical reduction of the tert-butyl chloride molecule are studied. The two-dimensional potential surface E(x, y) was obtained from the Hamiltonian model used earlier [1] to study quantum effects on the reaction rate of the same reaction. In series of molecular dynamics simulations two different models, isotropic (γ_x = γ_y) and anisotropic (γ_x > γ_y), of the friction parameters for the solvent (γ_x) and for the C-Cl bond (γ_y) were considered. An influence of several factors, such as an overpotential, a solvent friction coefficient and a temperature, on the rate constants k obtained with the two models are presented and compared to the results obtained for the non-adiabatic mechanism. It is shown, that the anisotropic model predicts generally much smaller rates when compared to those calculated with the isotropic model and also with the non-adiabatic model. On the curves k(γ_x) the turnover region is very well defined for relatively low frictions in the isotropic case, while for the anisotropic case it is shifted towards much higher γ_x values. In all simulations the saddle point avoidance phenomenon was observed and its extent for different models and reaction conditions is discussed. Transfer coefficients α obtained for adiabatic and non-adiabatic reaction mechanisms as a function of the overpotential and temperature are also presented.     

Platinum Nanoparticles Anchored on TiO2/C Nanowires as a High Performance Catalyst for Hydrogen Peroxide Eletroreduction

In this paper, we employed the as‐prepared TiO₂/C core/shell nanoarrays (TiO₂/C) obtained by a facile thermal evaporation method as a three‐dimensional (3D) architecture to support Pt nanoparticles through an optimized electrodeposition process. The morphology and structure of the as‐prepared electrode are characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Its catalytic performance towards H₂O₂ electroreduction in basic medium is evaluated by linear sweep voltammetry (LSV) and chronoamperometry (CV). Results revealed that the electrode exhibits significantly high catalytic activity. The current density reached –0.172 A cm⁻² in 1 mol dm⁻³ NaOH and 0.5 mol dm⁻³ H₂O₂ at –1.1 V (vs. Ag/AgCl). This high performance might be due to the 3D electrode architecture inheriting the high electronic conductivity from carbon shell and providing a short pathway for the ion diffusion, and the using of Pt owning an excellent catalytic activity.     

Effect of light on the electrocatalytic reduction of furfural on copper electrode in N,N-dimethylformamide

Electrocatalytic reduction of furfural (2-furan-carboxaldehyde) has been investigated on copper electrode in N,N-dimethylformamide. The onset of the electron transfer process starts at around −0.80 V (SCE). Linear correlation has been found between the cathodic current peak (j_P) and furfural concentration. The influence of the incidence of light on the charge transfer process is also discussed. Spectroscopic evidences obtained by NMR indicate that the main product of electrocatalytic reduction of furfural was furfuryl alcohol in the dark and under illumination.     

Electrochemistry of isopolytungstate mixtures

Solutions of isopolytungstates are of interest as the precursors for electrodeposited rechargeable tungsten oxides, and also in relation to hydrogen evolution catalysis. Understanding of isopolytungstate electrochemistry is complicated by numerous pH-dependent equilibria. This paper presents some data of dc polarography and UV absorption spectroscopy for solutions always containing several types of coexisting isopolytungstate species, in order to understand the individual electrochemical reactivity of certain isopolyanions.     

Effect of flow rate and acid molarity on redox potential modulation during electroreduction of milk and simulated milk aqueous mineral phase

Electroreduction of milk is an efficient process to decrease the ORP of milk. However, the changes induced in milk are reversible and fouling is formed at the membrane surface. Results obtained showed that ORP reduction was more important when a flow rate of 300 ml/min was used in comparison with a flow rate of 100 ml/min. Moreover, at the higher flow rate, less fouling was observed on the membrane surface than at 100 ml/min. However, it appeared from the calculation of mass equivalent migrated that parameters studied (flow rate and acid concentration) did not have a direct influence on the electroreduction process but on the system resistance. This study is the first to our knowledge to show that in storage conditions where the gaseous exchanges and especially the oxygen are limited, it is possible to maintain during seven days a negative ORP in electroreduced milk.     

In-situ synthesis of zirconium oxycarbide by electroreduction of ZrO2/C in molten salt

Homogenous ZrC_xO_y powders have been successfully synthesized by in-situ electro-reduction of solid ZrO₂–C composite precursors in molten CaCl₂. The effect of applied cell voltage and molar ratio of ZrO₂ to C on preparation of ZrC_xO_y were investigated. The reduction pathway of the composite electrode was studied based on the analysis of intermediate products using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that ZrO₂ is firstly converted to CaZrO₃. The resulting CaZrO₃ is then reduced to ZrC_xO_y. The ZrC_xO_y formation is dramatically influenced by electrolysis voltage and molar ratio of ZrO₂ to C: a higher cell voltage and lower molar ratio of the ZrO₂ to C are more preferable for the formation of ZrC_xO_y powder. Homogenous ZrC_xO_y powders with particle size of ~100 nm are synthesized by ZrO₂/C starting elemental powders in CaCl₂ molten salt at 1123 K for more than 3 h, when the cell voltage is 3.0 V and the molar ratio of the ZrO₂ to carbon starting materials is 1:1.0.     

燃料电池氧阴极催化剂的研究

以松木碳为载体,水合肼为还原剂,采用化学还原沉积法制备了Ｐｔ－Ｍｎ／Ｃ催化剂。通过涂敷和热压制得Ｐｔ－Ｍｎ／Ｃ－Ｎａｆｉｏｎ膜氧阴极。采用电流—电位极化和恒电流放电法研究了Ｐｔ－Ｍｎ／Ｃ－Ｎａｆｉｏｎ膜氧阴极的性能。与我们以前报导的Ｐｔ／Ｃ和Ｐｔ－Ｃｒ／Ｃ催化剂比较,Ｐｔ－Ｍｎ／Ｃ催化剂对氧的电还原显示出更高的活性。考察了Ｍｎ含量对电极性能的影响。另外,Ｐｔ－Ｍｎ／Ｃ催化剂经热处理后性能有较大的提高。ＸＲＤ分析的结果表明,热处理催化剂活性的提高看来主要是由晶格结构改变的结果引起的。     

Spectroelectrochemical study of perchloroethylene reduction at copper electrodes in neutral aqueous medium

The potential-dependent chemical reaction of perchloroethylene (PCE) on copper in neutral noncomplexing aqueous media is explored by means of surface-enhanced Raman spectroscopy (SERS), linear sweep voltammetry and preparative electrolysis at controlled potential. Voltammetric peaks associated with copper oxide reduction in Na₂SO₄ solution in the presence and the absence of Cl⁻ are correlated with simultaneously acquired SER spectra. Perchloroethylene undergoes a dechlorination process at potentials at E ≤ −0.3 V vs. Ag/AgCl/KCl (3 M), as shown by the emergence of an intense CuCl stretching band at 290 cm⁻¹ and a CH stretching band together with the presence of Cl⁻ in the catholyte. In the potential region between 0 and −0.9 V vs. Ag/AgCl/KCl (3 M) a broad band assigned to CC structures is observed in the triple-bond region (∼1900 cm⁻¹, FWHM = 180 cm⁻¹). In addition, dichloroethylene (DCE) is detected (but not trichloroethylene (TCE)) in this potential region during preparative electrolysis. At potentials lower than −1 V vs. Ag/AgCl/KCl (3 M) carbon residues are the main product, detected on the copper surface by SERS (and confirmed by XPS), whereas in solution higher levels of dichloroethylene and trichloroethylene are detected with a DCE/TCE ratio below 1.