Differences of behaviour in electrooxidation of 3,3′-dimethoxybenzidine and its N,N,N′,N′-tetraalkylated derivatives: a further example of potential inversion

The anodic oxidation of 3,3′-dimethoxybenzidine and its derivatives were studied by cyclic voltammetry, voltammetry at a rotating platinum electrode, chronopotentiometry and constant potential coulometry. The exhaustive oxidation of 3,3′-dimethoxybenzidine led at the potential of the first oxidation peak and second oxidation peak, respectively, to a stable cation radical salt (characterized by ESR spectroscopy) and to a quinone-diimine. Whereas, 3,3′-dimethoxy-N,N,N′,N′-tetramethylbenzidine afforded directly a dication salt owing to potential inversion 3,3′-dimethoxy-N,N,N′,N′-tetraethylbenzidine gave the corresponding soluble cation radical salt.     

Activity of gold towards methylamine electrooxidation

The kinetics of methylamine oxidation at a gold electrode in contact with an alkaline electrolyte solution was studied. The adsorptive behaviour of substrate molecules was determined by changes in the differential capacitance of the double layer at the electrode/solution interface. The electrooxidation of methylamine occurs only in the potential range of gold oxide layer formation. The general reaction pathways of methylamine oxidation on the gold electrode is proposed.     

Electrooxidation of formic acid on carbon supported PtxPd1−x (x = 0-1) nanocatalysts

In this work, carbon supported Pt_xPd_1−x (x = 0-1) nanocatalysts were investigated for formic acid oxidation. These catalysts were synthesized by a surfactant-stabilized method with 3-(N,N-dimethyldodecylammonio) propanesulfonate (SB12) as the stabilizer. They show better Pt/Pd dispersion and higher catalytic performance than the corresponding commercial catalysts. Furthermore, the electrocatalytic properties of Pt_xPd_1−x/C were found to depend strongly on the Pt/Pd deposition sequence and on the Pt/Pd atomic ratio. At a lower potential, formic acid oxidation current on co-deposited Pt_xPd_1−x/C catalysts increase with increasing Pd surface concentration. Nanoscale Pd/C is a promising formic acid oxidation catalyst candidate for the direct formic acid fuel cell.     

Treatment of phenol formaldehyde production wastewater by electrooxidation-electrofenton successive processes

ABSTRACT

Treatments of phenol formaldehyde producing wastewater (PFPW) by electrooxidation (EO) and electro-Fenton (EF) successive processes were carried out in a batch electrolytic reactor using graphite (Gr) and stainless steel (Ss) electrodes. After the completion of the EO process, the wastewater was further treated with EF process. The influence of operating variables such as current density, operating time, initial pH_i and H₂O₂ concentration was evaluated for removals of phenol, TOC and COD in PFPW. Gr/Gr, Gr/Ss or Ss/Ss and Ss/Gr electrode pair were used as anode and cathode. The best removal efficiency in the EO process was obtained with Gr/Gr (93%) as compared to Gr/Ss (82%), Ss/Ss (63%) and Ss/Gr (55%). The removal efficiencies for the EO process using Gr-Gr electrode pair were obtained as 93% for phenol, 61% for COD and 44% for TOC at initial pH_i 7,5 g/L of NaCl, 50 mA/cm² and 5 h. In the EF process, the removal efficiencies at pH_i 3,5 mA/cm² and 30 mM H₂O₂ and 45 min were 100% for phenol, 76% for COD and 59% for TOC. This study provided that the successive processes are an effective method for the removal of phenolic compounds from the wastewater.     

nPt (Hx−2nMoO3) as a promising catalyst for the oxidation of methanol. Synthesis and electrocatalytic properties

A new method for the synthesis of the catalyst systems Pt–Mo was suggested. nPt⁰(H_x−2nMoO₃)/GC electrodes were prepared by a redox reaction between the hydrogen-containing molybdenum bronzes and potassium tetrachloroplatinate (II) in acid solutions at open circuit potential. The electrodes were characterized by CVA, SEM, X-ray microanalysis, XRD, XPS and ICP-AES. Pt⁰conglomerates formation with nonuniform distribution over the molybdenum bronzes surface has been revealed. nPt⁰(H_x−2nMoO₃)/GC electrodes showed high catalytic activity (not inferior to Pt–Ru-catalyst) in the oxidation of carbon monoxide and methanol as compared with Pt/GC-electrodes. Catalytic effect is apparently achieved by effective oxidation of strongly chemisorbed species (CO_ads, HCO_ads), which occurs at boundaries platinum – molybdenum oxide. Therefore nPt⁰(H_x−2nMoO₃) can be considered as one of perspective catalysts for DMFC.     

Effects of acetone on electrooxidation of 2-propanol in alkaline medium on the Pd/Ni-foam electrode

Acetone is the main product of 2-propanol electrooxidation in both acid and alkaline electrolytes; it always co-exists with 2-propanol in the reaction solution due to its liquid nature. Whether acetone will affect the electrooxidation of 2-propanol has not been well documented, which is a key issue that needs to be addressed for the direct 2-propanol fuel cell. In this study, the influence of acetone on the electrooxidation of 2-propanol in alkaline medium is investigated, using state-of-the-art Pd electrode, by cyclic voltammetry and chronoamperometry. The electrode is prepared using a chemical replacement method, by dipping nickel foam into acidified PdCl₂ solution, and characterized by scanning electron microscopy. We found that the presence of acetone adversely affects electrooxidation performance of 2-propanol and substantially reduces the oxidation current of 2-propanol on Pd in alkaline medium. The acetone poisoning effect is interpreted by a competitive adsorption mechanism, in which acetone adsorbs onto Pd surface and occupies the active sites for 2-propanol electrooxidation, leading to a significant decrease in the number of these sites for 2-propanol electrooxidation. The results of this study point out that efficient electrocatalysts for 2-propanol electrooxidation in alkaline electrolytes must be non-adsorptive to acetone besides being highly active to 2-propanol oxidation.     

Investigation on Electrocatalytic Activity and Stability of Pt/C Catalyst Prepared by Facile Solvothermal Synthesis for Direct Methanol Fuel Cell

Pt nanoparticles supported on Vulcan XC‐72 carbon black have been synthesized by a facile solvothermal method. The obtained Pt/C catalysts are characterized by X‐ray diffraction (XRD), energy dispersive X‐ray analysis (EDAX), and transmission electron microscopy (TEM) analysis to identify Pt mean size and Pt content. The results of electrochemical measurements demonstrate that the Pt/C catalyst prepared at the reaction temperature of 140 °C and the reaction time of 2 h shows the biggest initial electrochemical area with an initial electrochemically active specific surface area (ESA) of 70.6 m²g_Pt⁻¹, the highest electrocatalytic stability with an ESA loss of 48.7% after 1,000 CV cycles, and the best electrocatalytic activity and stability toward methanol oxidation reaction (MOR) with a specific activity of 0.6 mA cm⁻² and a retention rate (the ratio of the final current density to the maximum current density) after 3,600 s of 42.8%. Moreover, the electrochemical performance of homemade Pt/C catalyst is superior to that of commercial Pt/C catalyst, suggesting that the solvothermal synthesis is a promising method for preparing Pt based catalyst.     

Carbon paste electrodes modified by Pt and Pt-Ni microparticles dispersed in polyindole film for electrocatalytic oxidation of methanol

Electrocatalytic activity of the Pt microparticles dispersed into polyindole (PIn) films obtained by electropolymerization on carbon paste electrodes (CPE) towards methanol oxidation in perchloric acid medium has been demonstrated and investigated using cyclic voltammetry, potentiodynamic polarization, chronoamperometry and impedance spectroscopic techniques. The results show that PIn films obtained on these electrodes serve as good host matrices for the dispersion of Pt microparticles and exhibit good catalytic activity towards the electrooxidation of methanol compared to bulk Pt and CPE modified with Pt. The morphology and composition of the modified and unmodified films were obtained using SEM and EDX techniques. The effect of scan rate, amount of Pt and concentration of methanol, on the activity of the electrode has been tested. The effect of alloying Pt with different amounts of Ni was studied and it was found that when the metals are deposited from a solution containing the metal salts in 1:1 ratio the activity towards methanol oxidation was significantly enhanced.     

Preparation and characterization of the dopamine film electrochemically deposited on a gold template and its applications for dopamine sensing in aqueous solution

A dopamine polymer film was electrogenerated on the bare gold template from a 5 × 10⁻³ M dopamine solution in phosphate buffer at pH 7 and next subjected to overoxidation in 0.1 M sodium hydroxide solution. The overoxidized dopamine polymer film obtained shows good permeability to cationic species and was used for quantitative determination of dopamine. A linear relationship between dopamine concentration and current response was obtained in the range of 1 × 10⁻⁶ M to 6 × 10⁻⁴ M with the detection limit 2 × 10⁻⁷ M. The results have shown that using the overoxidized dopamine film it is possible to perform electrochemical analysis of dopamine without interference of ascorbic and uric acids, which is the major limitation in dopamine determination. The modified electrode shows good selectivity, sensitivity, reproducibility and high stability.     

In situ FTIR spectroscopic studies of electrooxidation of ethanol on Pd electrode in alkaline media

Electrooxidation of ethanol on a polycrystalline Pd disk electrode in alkaline media was studied by in situ Fourier transform infrared (FTIR) reflection spectroscopy. The emphasis was put on the quantitative determination of intermediates and products involved in the oxidation. It has revealed that most of ethanol was incompletely oxidized to acetate. The selectivity for ethanol oxidation to CO₂ (existing as CO₃²⁻ in alkaline media) was determined as low as 2.5% in the potential region where Pd electrode exhibited considerable electrocatalytic activity (−0.60 to 0.0 V vs. SCE). Nevertheless, the ability of Pd for breaking C-C bond in ethanol is still slightly better than that of Pt under the same conditions. Besides, a very weak band of adsorbed intermediate, bridge-bonded CO (CO_B) was identified on the Pd electrode for the first time, suggesting that CO₂ and CO₃²⁻ species may also be generated through CO pathway (i.e., indirect pathway).