Enhanced methanol electro-oxidation activity of PtRu catalysts supported on heteroatom-doped carbon

A typical heteroatom (nitrogen)-doped carbon materials were successfully synthesized through the carbonization of a hybrid containing traditional carbon black covered by in situ polymerized polyaniline. The nitrogen content onto carbon can be adjusted up to 5.1 at.% by changing the coverage of polyaniline. The effects of nitrogen doping on the surface physical and electrochemical properties of carbon were studied using XPS, XRD and HRTEM, as well as CV and EIS techniques. With increasing nitrogen doping, the carbon structure became more compact, showing curvatures and dislocations in the graphene stacking. The nitrogen-doped carbon also exhibited a higher accessible surface area in electrochemical reactions, and a lower charge transfer resistance at the carbon/electrolyte interface. Moreover, to investigate the influence of nitrogen doping on the electrocatalytic activity of the PtRu/C catalyst, comparisons in CO stripping and methanol oxidation were carried out on PtRu catalysts supported by non-doped and nitrogen-doped carbon. Since the promotional roles of nitrogen doping, including the high electrochemically accessible surface area, the richness of the disordered nanostructures and defects, and the high electron density on N-doped carbon supports, contribute to the synthesis of well-dispersed PtRu particles with high Pt utilization and stronger metal-support interactions, an enhanced catalytic activity for methanol oxidation was obtained in the case of the PtRu/N-C catalyst in comparison with the traditional PtRu/C catalyst.     

Polyaniline/porous carbon electrodes by chemical polymerisation: Effect of carbon surface chemistry

Polyaniline/porous carbon composite electrodes were prepared by chemical polymerisation and characterized in terms of porosity and performance as electrochemical capacitors.To obtain the composite electrodes two methods were used. The first method consisted of mixing, directly, the activated carbon with chemically polymerised polyaniline. The second one consisted of mixing the activated carbon with aniline and subsequent chemical polymerisation. Additionally, the second process was carried out with the porous carbon previously thermally treated in N₂ up to 900 °C in order to remove surface oxygen groups.Changes in porosity with the polyaniline addition were analysed. It has been proved that the method used strongly affects the porous structure. Dealing with the electrochemical performance, polyaniline and carbon mechanically mixed seem to work independently, being the composite behaviour a combination of the corresponding performance of both materials separately. The composites prepared by the second method (polymerisation over carbon) reveal the key role of surface chemistry in polyaniline coating. Aniline reacts with the oxygen complexes and their positive effect in capacitance is not observed.The second method (polymerisation over carbon) using a thermally treated carbon seems to be the best one since a more porous (or thinner) polyaniline film is produced.     

Electrochemical behaviour of glassy carbon electrodes modified with aryl groups

The electrochemical modification of the glassy carbon (GC) electrode surface with biphenyl, 1-naphthyl, 2-naphthyl, 4-bromophenyl, 4-decylphenyl and 4-nitrophenyl groups was performed by the diazonium reduction method. The blocking behaviour of aryl films grafted by three different procedures was compared. Oxygen reduction was studied on these modified GC electrodes using the rotating disk electrode (RDE) method. The highest blocking efficiency for O₂ reduction was observed for 4-bromophenyl groups. The barrier properties of aryl-modified GC surfaces were also characterised using Fe(CN)₆³⁻ and dopamine redox probes. Electrochemical measurements were carried out in 0.1 M K₂SO₄ containing 1 mM K₃Fe(CN)₆ and in 0.1 M H₂SO₄ containing 1 mM dopamine using cyclic voltammetry (CV). The blocking action varied significantly depending on the surface modifier used and the solution based redox species studied.     

Ni-Cu合金电极上苯甲醇的选择性电氧化

通过恒电流电沉积法在不同条件下制备了一系列Ni-Cu合金电极,采用扫描电镜(SEM)表征了其表面形态,用循环伏安法(CV)研究了在碱性溶液中苯甲醇在不同工艺条件下制备的Ni-Cu合金电极上的电氧化行为.并进一步用电化学原位红外光谱(in situ FTIP)从分子水平研究了苯甲醇在Ni-Cu合金电极上的电氧化过程.结果...     

Microwave activation of electrochemical processes: High temperature phenol and triclosan electro-oxidation at carbon and diamond electrodes

The electrochemical oxidation of phenolic compounds in aqueous media is known to be affected by the formation of electro-polymerized organic layers which lead to partial or complete electrode blocking. In this study the effect of high intensity microwave radiation applied locally at the electrode surface is investigated for the oxidation of phenol and triclosan in alkaline solution at a 500 μm diameter glassy carbon or at a 500 μm × 500 μm boron-doped diamond electrode. The temperature at the electrode surface and mass transport enhancement are determined by calibration with the Fe(CN)₆^3−/4− redox system in aqueous 0.3 M NaOH and 0.2 NaCl (pH 12) solution. The calibration shows that strong thermal and mass transport effects occur at both glassy carbon and boron-doped diamond electrodes. The average electrode temperature reaches up to 390 K and mass transport enhancements of more than 20-fold are possible. For the phenol electro-oxidation at glassy carbon electrodes and at a concentration below 2 mM a multi-electron oxidation (ca. 4 electrons) occurs in the presence of microwave radiation. For the electro-oxidation of the more hydrophobic triclosan only the one-electron oxidation occurs. Although currents are enhanced in presence of microwave radiation, rapid blocking of the electrode surface in particular at high phenol concentrations still occurs.     

Enhanced electrodetection of ascorbic acid in Adansonia digitata fruit by use of surface modified electrodes

Surface modified electrodes have been used to study the seed of A. digitata. The results show the ascorbic acid redox peak is greatly enhanced and the oxidation/reduction peaks coincide with those of the corresponding chemical standard. It is also shown that ascorbic acid adsorbs onto the clay-modified electrode.     

Thiols deposition onto the surface of glassy carbon electrodes mediated by electrical potential

Electrochemical oxidation of thiols in acetonitrile and application of this process for modification of glassy carbon electrodes were studied. Addition of strong deprotonating agent, tetrabutylammonium hydroxide, was found to facilitate oxidation of thiols as well as their deposition onto the carbon surface. Thus, in the presence of 1 mM tetrabutylammonium hydroxide, glassy carbon electrode can be grafted with 1 mM 3-(nitrobenzyl)mercaptan at as low as +200 mV (vs. SCE). The modified electrodes were characterized by electrochemical methods and XPS confirming the stable binding of thiols which were absent on the surface of unmodified and control treated electrodes. Surprisingly, surface modification occurs independent of RS radicals formation and is explained by nucleophilic addition of deprotonated thiols to the surface of carbon electrode. The electrode potential plays an important role in this process presumably modulating electrophilic properties of the carbon surface.     

High surface area diamond-like carbon electrodes grown on vertically aligned carbon nanotubes

Electrochemically active diamond-like carbon (DLC) electrodes featuring high specific surface area have been prepared by plasma-enhanced chemical vapour deposition (CVD) onto densely packed forests of vertically aligned multiwall carbon nanotubes (VACNTs). The DLC:VACNT composite film exhibits a complex topography with web like features and ridges generated by partial coalescence of the DLC over the CNT arrays. DLC:VACNT electrodes exhibit low background responses over a large potential window, low uncompensated resistance, as well as low charge-transfer impedance in the presence of ferrocyanide as a redox probe. The interfacial capacitance associated with the DLC:VACNT electrode is in the range of 0.6 mF cm⁻², a value two orders of magnitude larger than in conventional flat carbon electrodes. DLC films grown onto single-crystal Si(1 0 0) under identical conditions resulted in essentially insulating layers. Conducting-atomic force microscopy studies reveal that the film electro-activity does not arise from specific topographic features in the highly corrugated film. The ensemble of experimental results suggests that the enhanced electrochemical responses are not connected to areas in which the CNT support is exposed to the electrolyte solution. This is remarkable behaviour considering that no dopants have been included during the DLC film growth.     

Catalytic electro-oxidation of hydrazine on phthalocyanines deposited on graphite electrodes

The catalytic properties phthalocyanines of Fe, Co, Ni and Cu for the electro-oxidation of hydrazine have been examined. The metal chelates were deposited on ordinary pyrolytic graphite electrodes and their redox properties were studied by cyclic voltammetry. The catalytic activity was found to decrease as follows: FePc > CoPc > CuPc ～ NiPc > graphite.The kinetics of the process with Fe-Pc and Co-Pc were examined. Tafel slopes of 40 mV for Fe-Pc, and of 60 m V for Co-Pc were obtained. The chemical order in N₂H₄ is 1 both complexes. The order in OH^? is 2 for Fe-Pc and 1 for Co-Pc. With Fe-Pc, the transfer of a second electron seems to be rate determining. With Co-Pc, a slow chemical step preceded by a fast one-electron transfer seems to operate.     

Enhanced visible light-induced photoelectrocatalytic degradation of phenol by carbon nanotube-doped TiO2 electrodes

We used a modified sol-gel method to prepare titanium dioxide and multi-walled carbon nanotube (CNT) composites that we subsequently deposited onto indium tin oxide (ITO) conductive glass plates. We characterized these CNT-doped TiO₂ (CNT-TiO₂) films using X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and diffuse reflectance UV-vis spectroscopy. The photoelectrocatalytic (PEC) activity of the composites was evaluated through their ability to mediate the degradation of phenol. XRD measurements indicated that the TiO₂ component existed solely in the anatase phase and that the crystallinity of the CNTs was low. XPS indicated that carbon atoms could substitute for both oxygen and titanium atoms in the TiO₂ lattice to form Ti-C and Ti-O-C structures, which were responsible for the extra photoabsorption and PEC activity under illumination with visible light, in addition to those provided by the CNTs and carbonaceous and Ti³⁺ species. An interphase interaction between TiO₂ and the CNTs elevated the photoabsorbance of the composites in the visible light region. A sample of TiO₂ doped with 10% CNTs and calcined at 400 °C exhibited the highest photocurrent and PEC efficiency. We systematically investigated the effects of several parameters of the PEC process, including the applied potential and pH, on the phenol conversion.     

Enhanced interactions between multi-walled carbon nanotubes and polystyrene induced by melt mixing

The effect of melt mixing on the interaction between multi-walled carbon nanotubes (MWNTs) and polystyrene (PS) matrix has been investigated. The interaction between pristine MWNTs and PS in solution was found to exist but not strong enough to allow MWNTs to be soluble in solvent. In contrast, this interaction between MWNTs and PS was significantly enhanced by melt mixing, which led to increased amount of PS-functionalized MWNT exhibiting good solubility in some solvents. The mechanism of melt mixing on this enhanced interaction was attributed to both chemical bonding and physical interaction during the melt mixing.     

Enhanced performance in dye-sensitized solar cells via carbon nanofibers-platinum composite counter electrodes

A composite counter electrode (CE) made of electrospun carbon nanofibers (ECNs) and platinum (Pt) nanoparticles has been demonstrated for the first time to improve the performance of dye-sensitized solar cells (DSCs). The new ECN-Pt composite CE exhibited a more efficient electro-catalytic performance with lower charge transfer resistance (R(ct)), larger surface area, and faster reaction rate than those of conventional Pt. It reduced the overall series resistance (R(se)), decreased dark saturation current density (J(0)) and increased shunt resistance (R(sh)) of the DSCs, thereby leading to a higher fill factor (FF) and larger open circuit voltage (V(oc)). The reduced electron transport resistance (R(s)) and faster charge transfer rate in the CE led to a smaller overall cell series resistance (R(se)) in the ECN-Pt composite based DSCs. The DSCs based on an ECN-Pt CE achieved a η of ～8%, which was improved over those of pure Pt or ECN based cells.     

Structural rearrangement of a polycrystalline iron surface induced by carbon precipitation

The morphology of carbon precipitated at a polycrystalline iron surface, and the associated metal structural changes, have been examined by in situ hot stage scanning electron microscopy. Carbon is dissolved in the metal by reaction with methane at T ~ 750°C, and is precipitated by cooling the specimen below the Fe-C eutectoid temperature. The preparation of a clean thermally stable surface is described, along with the structural changes occurring in the CH₄ atmosphere during carbon dissolution. Precipitation on cooling is accompanied by a significant reorganisation of the metal surface structure. Facetted regions with step heights in the 100–300 Å range are smoothed out, the surface becoming covered with a laminar carbon film. There is no evidence of enhanced activity at grain boundary intersections. Intermediate stages in the complete precipitation process have been identified. The rate of lateral growth of the precipitated carbon overlayer is found to be limited by surface diffusion. The effect of adsorbed sulphur and oxygen impurities has been examined by scanning Auger microanalysis. The separation of particulate material from the surface, in a size range up to ~ 1.6 μm dia., has been observed if the specimen is cycled repeatedly between dissolution and precipitation temperatures.     

Non-enzymatic hydrogen peroxide detection using gold nanoclusters-modified phosphorus incorporated tetrahedral amorphous carbon electrodes

Sensitive electrochemical electrodes for hydrogen peroxide (H₂O₂) detection were developed using gold nanoclusters (NCs) to modify phosphorus incorporated tetrahedral amorphous carbon films (ta-C:P/Au). Au oxide covered Au NCs were electrodeposited on ta-C:P surfaces, and the size of Au/AuO_x NCs ranged between 50 nm and 91 nm, depending on the deposition time. The ta-C:P/Au electrodes exhibited higher electrocatalytic activity towards H₂O₂ oxidation compared to ta-C:P electrodes. This is due to the three-dimensional island structure of Au/AuO_x NCs, which accelerates electron exchange between ta-C:P and H₂O₂ in phosphate buffered solution. We also found that ta-C:P/Au electrodes with Au/AuO_x NCs of a smaller size and moderate coverage exhibited larger current response to H₂O₂ oxidation. The results obtained from amperometric response curves indicated that the use of Au/AuO_x NCs as microelectrodes directly favored H₂O₂ oxidation through hemispherical diffusion. The linear detection range of H₂O₂ at the non-enzymatic ta-C:P/Au electrodes was identified to be between 0.2 μM and 1 mM with a detection limit of 80 nM under optimized conditions. These ta-C:P/Au electrodes have potential applications in H₂O₂ sensing due to their high sensitivity, fast response and long-term stability.     

Introduction of sulfur groups onto the surface of carbon blacks

Three methods were employed to introduce sulfur groups (thiol and thio ester groups) onto the surface of a carbon black. Positive results were obtained and controled by functional group analysis and radiochemistry.     

High catalytic activity of chemically activated gold electrodes towards electro-oxidation of methanol

Electro-oxidation of methanol has been investigated on activated, rough gold electrodes in alkaline solutions. The electrodes were activated by formation and decomposition of gold amalgam. The oxidation of methanol starts at potentials about 400 mV less positive as compared with smooth poly and single crystal gold electrodes and the oxidation current is much higher. For freshly prepared, activated gold electrodes the oxidation current is similar to that obtained on smooth platinum, however it diminishes with time. The formation of small crystallites, which could trap OH⁻ anions, seems to be the most important factor for this unusual catalytic activity. The dependence of the oxidation process on electrode topography is discussed.     

Ring-opening polymerization of 2-oxazolines initiated by chloromethyl groups introduced onto carbon black surface

Summary The ring-opening polymerization of 2-oxazolines (OXZs) was found to be initiated by chloromethyl groups introduced onto carbon black surface. The introduction of chloromethyl groups onto the surface was achieved by the reaction of carbon black with 3,3-bischloromethylbenzoyl peroxide in carbon tetrachloride. During the polymerization, poly-OXZs were grafted from carbon black based on the propagation of the polymers from the surface: percentage of grafting increased with an increase of conversion and reached 40–60%. The polymerization was accelerated by the addition of potassium iodide. Poly-OXZ-grafted carbon black produced stable colloidal dispersions in both hydrophobic and hydrophilic solvents.     

The oxygen film on platinum electrodes and the electro-oxidation of acetate ions

The recent literature is reviewed and a consistent mechanistic and mathematical model is presented which can account for the varied phenomena observed experimentally during both steady-state and unsteady-state electrolysis of aqueous acetate solutions at Pt electrodes. In particular the following competing reactions are considered:

1.

complete oxidation of acetate ions to carbon dioxide,     

Role of oxygen surface groups in catalysis of hydrogasification of carbon black by potassium carbonate

The reaction rates of a nonporous graphitic carbon lampblack with hydrogen gas at 865°C and 500 psi were measured following treatments such as degassing and/or oxidation with and without impregnation of K₂CO₃. The results lead to the conclusion that oxygen surface groups enhance the reactivity of the carbon by generating “nascent” active sites on decomposition into CO and CO₂. In the catalyzed case the basic and C=O carbonyl groups form active and stable surface complexes. The acidic groups, on the other hand, could not be well characterized and may form stable and inactive or unstable and active complexes depending on their nature.