Novel methanol electro-oxidation catalyst assisting with functional phthalocyanine supports

Novel electro-catalyst based on phthalocyanine stabilized Pt colloids has been developed for methanol electro-oxidation. Water soluble Cu²⁺ phthalocyanine functioned with sulfonic groups were selected as catalyst supports because of the relatively high catalytic activity of Pt catalyst and nearly the same catalytic selectivity complex with Cu-phthalocyanine, compared to others that chelated with Fe, Co and Ni ions. The as-resulting Pt-CuTsPc catalysts have average particle size of 2 nm and narrow size distribution. With the assistance of CuTsPc supports, the methanol electro-oxidation activity and poison tolerance of Pt catalyst have a significant increase. I_f/I_b ratio (anodic peak current density, forward to backward) of the Pt-CuTsPc/C catalysts also has obvious increase to 2.5, from value of 0.8 for pure Pt/C catalyst. The reaction Tafel slope of Pt-CuTsPc/C catalysts is 56.6 mV dec⁻¹, much smaller than that of the Pt/C catalyst. The transient current density on Pt-CuTsPc/C at 0.60 V is enhanced to 650% of that on the Pt/C catalyst while the enhancement factor R for comparison of steady-state current obtained on Pt-CuTsPc/C and Pt/C catalyst varies between 111% and 534% in the potential region of 0.3-0.75 V.     

镍铝类水滑石在乙酸介质下催化氧化苯甲醛合成苯甲酸

采用共沉淀法合成了晶相单一、结晶度高的镍铝类水滑石,表征了其物化性能,将其应用于乙酸作为溶剂时苯甲醛液相空气氧化合成苯甲酸的反应当中,详细考察了反应条件的影响.结果表明NiAl-HTcs在有乙酸存在的条件下可以很好地催化氧化苯甲醛.当反应温度为70℃、V(苯甲醛)V(乙酸)=13、催化剂用量为0.1 g时,反应1 h后,苯甲醛的转化率便可接近100%,苯甲酸的选择性为100%.     

Carbon monoxide electrooxidation on porous Pt–Ru electrodes in sulphuric acid

CO electrooxidation on a Pt–Ru/C catalyst was investigated in sulphuric acid electrolyte. The physico-chemical properties of the Pt–Ru/C catalyst were studied by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The influence of temperature, CO partial pressure and proton concentration on the electrochemical oxidation rate was investigated by steady-state galvanostatic polarization measurements. The apparent activation energy decreased from 70 to 30kJmol–1 as the overpotential increased from 0.5 to 0.9V vs NHE. The reaction order with respect to carbon monoxide increased, passing from 0.4 to 1, with the increase of the overpotential from 0.5 to 0.7V vs NHE; a reaction order close to –1 with respect to the protonic concentration was observed, irrespective of the potential. Tafel slopes of about 136mVdec–1 were determined for oxidation of CO and CO/N2 mixtures.     

Oxygen reduction on poly(4-vinylpyridine)-modified ordinary pyrolytic graphite electrodes with adsorbed cobalt tetra-sulphonated phthalocyanine in acid solutions

Poly(4-vinylpyridine) (PVP) has been used to modify ordinary pyrolytic graphite (OPG) electrodes with adsorbed cobalt tetra-sulphonated phthalocyanine (CoTsPc) in acid solutions. These modified electrodes were prepared in different manners and characterized by cyclic voltammetry. Their electrocatalytic activity for oxygen reduction and stability in 0.05M H₂SO₄ solutions was examined at room temperature. The OPG/CoTsPc/PVP modified electrodes were found to be more active for oxygen reduction in 0.05M H₂SO₄ solutions as compared to the electrode with adsorbed CoTsPc on OPG without PVP. The increase in activity is due to the formation of an adduct between PVP and CoTsPc. U.v.-visible and FTIR studies provide evidence for such adduct formation. Over a 10 h period the activity of the OPG/CoTsPc/PVP system was essentially constant while that of OPG/CoTsPc without polymer decreased by a substantial amount (about 37%). The PVP layer inhibits the diffusion of the CoTsPc and/or Co out of the complex into the solution phase. The stability of the OPG/CoTsPc/PVP system may also be due to low solubility of the adduct between PVP and CoTsPc in a 0.05M H₂SO₄ solution. Thicker films of PVP decreased the diffusion limiting oxygen reduction current. The effect of pH of the electrolyte solution on the activity of such PVP-modified electrodes for oxygen reduction has also been investigated.     

FTIR spectroelectrochemical investigation of the electrocatalytic oxidation of ascorbic acid at platinum electrodes in acid medium

The electrochemical oxidation of ascorbic acid (AA) at a platinum electrode has been studied in 0.1 M HClO₄. In situ infrared reflectance spectroscopy (SPAIRS and SNIFTIRS techniques) was used to investigate the reaction intermediates. The identification of the different electroreactive species and adsorbed intermediates allowed us to postulate a reaction mechanism for the transformation of AA into dehydroascorbic acid (DHA).     

Electrocatalytic oxidation of ethanol on Pt–Mo bimetallic electrodes in acid medium

Pt–Mo alloy electrocatalysts were prepared by an arc-melting furnace process to investigate the origin of their enhanced activity toward ethanol oxidation. Two Mo contents were chosen in zones of the binary phase diagram where they are supposed to form either a pure alloy mixture or a solid solution. Pt–Mo alloy catalysts were more active than Pt-alone. Gradual Mo dissolution at the electrode surface was observed after voltammetric and chronoamperometric measurements. The dissolved Mo contributed to the catalytic effect of the electrode as underpotentially deposited (upd) adatoms. This dissolution probably also leads to an increase in the electrode surface roughness. Low molybdenum content in the electrode material enhances the activity toward ethanol oxidation when compared to Pt-alone. Ethanol oxidation was also investigated by in situ infrared reflectance spectroscopy in order to determine the presence of adsorbed intermediates like CO species. Acetaldehyde, acetic acid and CO₂ were also found by spectroscopic experiments.     

Screen-printed carbon electrodes modified with cobalt phthalocyanine for selective sulfur detection in cosmetic products

Cobalt phthalocyanine (CoPc) films were deposited on the surface of a screen-printed carbon electrode using a simple drop coating method. The cyclic voltammogram of the resulting CoPc modified screen-printed electrode (CoPc/SPE) prepared under optimum conditions shows a well-behaved redox couple due to the (Co(I)/Co(II)) system. The CoPc/SPE surface demonstrates excellent electrochemical activity towards the oxidation of sulfur in a 0.01 mol·L(-1) NaOH. A linear calibration curve with the detection limit (D(L), S/N = 3) of 0.325 mg·L(-1) was achieved by CoPc/SPE coupled with flow injection analysis of the sulfur concentration ranging from 4 to 1120 mg·L(-1). The precision of the system response was evaluated (3.60% and 3.52% RSD for 12 repeated injections), in the range of 64 and 480 mg·L(-1) sulfur. The applicability of the method was successfully demonstrated in a real sample analysis of sulfur in anti-acne creams, and good recovery was obtained. The CoPc/SPE displayed several advantages in sulfur determination including easy fabrication, high stability, and low cost.     

Ionic transport in conducting polymers/nickel tetrasulfonated phthalocyanine modified electrodes

This work describes the study of the ionic transport in polyaniline (PANI) and polypyrrole (PPY) modified electrodes polymerized in presence of nickel tetrasulfonated phthalocyanine (NiTsPc). Elemental analysis and infrared spectroscopy were used to characterize the resulting composite films. The impact of the phthalocyanine incorporation was evaluated by electrochemical quartz crystal microbalance under potentiodynamic conditions. Results have shown that the presence of the negative charge (SO₃⁻ groups) modifies the nature of the ‘ionic exchange’ membranes, during the cycling. In the case of PANI/NiTsPc modified electrodes, the electroneutralization is mainly achieved by the participation of protons both in HCl and in camphorsulfonic acid (HCSA) electrolyte solutions. For PPY/NiTsPc composites, the cation contribution is dominant in the case of LiCl and NaCl solutions and the anion transport becomes important when CsCl and BaCl₂ solutions are used.     

A phenyl-sulfonic acid anchored carbon-supported platinum catalyst for polymer electrolyte fuel cell electrodes

A method, to anchor phenyl-sulfonic acid functional groups with the platinum catalyst supported onto a high surface-area carbon substrate, is reported. The use of the catalyst in the electrodes of a polymer electrolyte fuel cell (PEFC) helps enhancing its performance. Characterization of the catalyst by Fourier transform infra red (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and point-of-zero-charge (PZC) studies suggests that the improvement in performance of the PEFC is facilitated not only by enlarging the three-phase boundary in the catalyst layer but also by providing ionic-conduction paths as well as by imparting negative charge to platinum sites with concomitant oxidation of sulfur present in the carbon support. It is argued that the negatively charged platinum sites help repel water facilitating oxygen to access the catalyst sites. The PEFC with modified carbon-supported platinum catalyst electrodes exhibits 40% enhancement in its power density as compared to the one with unmodified carbon-supported platinum catalyst electrodes.     

The electrochemical properties of imidazol-linked iron phthalocyanine—carbon electrodes

Electrodes for the electrochemical reduction of oxygen have been studied galvanostatically. The electrodes were of the activated carbon-polymeric iron phthalocyanine (FePc) type, made hydrophobic with a Teflon treatment. A link between the FePc and the carbon was achieved by covalently binding imidazol to the carbon surface and then letting the FePc co-ordinate to the free nitrogen of the imidazol molecule. In this way an initial improvement of the stability of the electrode potential and the polarization data was achieved. It has furthermore been established that the potential responds more rapidly to changes, i.e. it is more reversible, than an analogous electrode based on carbon that has not been treated with imidazol.     

Preparation of iron phthalocyanine catalyzed carbon electrodes by chemical modification

A technique for chemically bonding and polymerizing organometallic chelate catalysts on a carbon substrate has been developed, with the objective of improving catalyst activity and stability for the reduction of oxygen in acidic electrolytes. Acetylene black carbon was chemically modified by bonding with polymerized iron tetrachlorophthalocyanine catalyst, followed by heat treatment. An electrode made with this catalyst showed significant improvement in activity and stability as compard with a similar unmodified catalytic electrode.     

Spectroelectrochemical study of trichloroacetic acid reduction at copper electrodes in an aqueous sodium sulfate medium

The electrochemical reduction of trichloroacetic acid (TCAA) in water has been analyzed through voltammetric studies with a copper rotating disc electrode supported by controlled-potential bulk electrolysis and electrochemical surface-enhanced Raman spectroscopy (SERS) experiments. The influences of the mass-transport conditions and concentration were studied. It has been pointed out that the electrochemical reduction of trichloroacetic acid takes place prior to the massive hydrogen evolution. Strong adsorption was observed on the electrode surface, and dichloroacetic acid (DCAA), monochloroacetic acid (MCAA), and chloride anions were detected as reduction products. The SERS experiments point to a secondary mechanism in which dissociative adsorption of the trichloroacetic acid gives rise to the adsorption of CO, and therefore, to the production of 1C molecules as by-products of the electrochemical reduction.     

Electrochemical studies with tin electrodes in citric acid solutions

The electrochemical behaviour of tin in 0.5 M citric acid solution (pH=1.8) was studied by means of the potentiodynamic method. TheE-I profiles show an anodic current peak associated with a dissolution of the metal and the formation of a passivating film, and two cathodic current peaks which are related to the reduction of soluble Sn(II) species and reduction of the film. During the potential sweep in the cathodic direction, an anodic current peak can be observed and is interpreted in terms of a reactivation process. The data suggest that the passivation of tin in this medium occurs by a dissolution-precipitation mechanism. Depending on the potential sweep rate, the process is controlled either by mass transport or by the solution resistance in the pores of the film.     

Electrochemical and mössbauer investigations of polymeric iron phthalocyanine oxygen electrodes

Polymeric iron phthalocyanine precipitated on activated carbon has been heated to temperatures in the range 200–500° C and the catalytic activity for the electrochemical reduction of oxygen has been investigated. The catalysts were tested in porous, hydrophobic electrodes.Mössbauer spectra have been obtained for the catalyst powders exposed to different heating temperatures.Heat treatment was found to give electrodes with a higher rate of deactivation for the electrochemical reduction. This was particularly the case for heat treatments at temperatures higher than 300°C. An increase in the intensity of a doublet in the Mössbauer spectra corresponding to oxidized iron was obtained for the heat treated samples.This increase of oxidized iron was found to be correlated to the increased rate of deactivation for the electrodes.     

Oxygen reduction on ultra thin carbon supported polymeric phthalocyanine electrodes in 6 N KOH

Oxygen reduction on carbon supported polymeric iron, manganese and mixed Fe/Sn and Fe/Cu phthalocyanines has been examined in 6 N KOH, using the Vogel Lundquist ultra-thin electrode technique. Activity of samples prepared by gas phase in situ methods is 2–3 times greater than that observed for phthalocyanines precipitated from solution. While a reduced performance of mixed polyphthalocyanines occurs on introduction of Cu, introduction of Sn causes no change in activity up to 50% Sn.Results are examined as a function of support material. Current densities on the untreated supports are higher than on the corresponding supported catalyst in the diffusion region. This effect is interpreted by a superficial distribution of the catalyst.     

Derivatization of SWCNTs with cobalt phthalocyanine residues and applications in screen printed electrodes for electrochemical detection of thiocholine

Single-walled carbon nanotubes (SWCNTs) derivatized with cobalt phthalocyanine (CoPh) were applied onto screen-printed graphite electrodes (SPEs) to be used for the low-potential electrochemical oxidation of thiocholine (TCh). Covalent attachment of CoPh to SWCNTs via stable sulfonamide bonds was confirmed by Raman/FT-IR spectroscopy and thermogravimetric analysis (TGA) coupled with FT-IR detection. The resulting modified SPE surfaces (CoPh-SWCNT-SPEs) were characterized by cyclic voltammetry and electrochemical impedance spectroscopy (EIS) with the redox probe [F₃(CN)₆]^3−/4−. Detection of TCh was accomplished using cyclic voltammetry and amperometry; a lower overpotential (100 mV vs. Ag/AgCl pseudoreference electrode) was obtained using CoPh-SWCNT-SPEs as compared to unmodified SPEs and SPEs modified with non-functionalized SWCNTs (SWCNT-SPEs). The linear range for TCh detection was 0.077–0.45 mM, with a sensitivity of 5.11 × 10⁻¹ μA mM⁻¹ and a limit of detection of 0.038 mM according to the 3 s/m definition.     

Mechanism of di(methyl)ether (DME) electrooxidation at platinum electrodes in acid medium

The electrooxidation of DME was studied at a bulk platinum electrode. It was shown that the DME adsorption was a slow step in the overall oxidation reaction. The DME adsorption is potential dependent in the hydrogen region of platinum and independent in the double layer region. From low potential scan rate voltammetry and DME stripping experiments, it was shown that the DME oxidation mechanism occurred via several reaction paths. At low potentials, DME oxidation leads to the existence of a positive current plateau. “In situ” Infrared Reflectance Spectroscopy experiments were carried out to identify the intermediate and reaction products of DME adsorption and oxidation at different potentials. CO_L (linearly bonded CO), CO_B (bridge bonded CO), adsorbed COOH species and CO₂ were detected. From these electrochemical and spectro-electrochemical results, it was proposed that some adsorbed DME was hydrolysed and directly oxidized to CO₂ or HCOOH species and some partially blocked platinum sites at the surface forming Pt–CHO and/or Pt–CO. Then, as soon as platinum becomes able to activate water, a bifunctionnal mechanism occurs to form either HCOOH or CO₂ again following two different reaction paths.     

Simultaneous electrochemical and mössbauer measurements on polymeric iron phthalocyanine oxygen electrodes

Mössbauer spectra have been obtained on porous, hydrophobic electrodes in situ when used as oxygen reduction electrodes in sulphuric acid electrolyte. The electrodes consisted of polymeric iron phthalocyanine precipitated on activated carbon. Mössbauer spectra were also obtained on the same kind of electrodes which had been used for different amounts of time. The polymeric iron phthalocyanine was prepared using iron enriched in ⁵⁷Fe to get resolvable spectra.The Ms?sbauer spectra are characterized by the increase of a signal corresponding to oxidized iron as the catalytic activity decreases. A correlation between the amount of iron dissolved into the electrolyte and the electrode potential is seen during the first 100 h of operation.It is suggested that Fe(II) is oxidized to Fe(III) which is dissolved into the electrolyte.     

Thin-film catalyst layers for polymer electrolyte fuel cell electrodes

New structures for the Pt/C catalyst layer of polymer electrolyte fuel cell electrodes have been developed that substantially increase the utilization efficiency of the catalyst. Fabricating the catalyst layers and gas diffusion backings separately makes it possible to formulate each structure with the properties that are most suitable for its function. In the case of the catalyst layer, the optimal properties are hydrophilicity, thinness, uniformity, and the proper ratio of ionomer and supported catalyst. The catalyst layers are cast from solution as thin films that utilize the ionomer itself as a binder. The thin films are hot pressed directly onto the ionomer membranes, and the hydrophobic gas diffusion backings are inserted when the cells are assembled. The performances of fuel cells based on the thin film catalyst layers are comparable with those of gas diffusion electrode designs that utilize several times as much platinum, thus the specific activities of the Pt catalysts in the new structures are significantly higher.