Chemical and electrochemical synthesis of polyaniline/platinum composites

The synthesis of polyaniline/platinum composites (PANI/Pt) has been achieved using both chemical and electrochemical methods. The direct chemical synthesis of PANI/Pt proceeds through the oxidation of aniline by PtCl₆²⁻ in the absence of a secondary oxidant. SEM images of these samples indicate that the Pt particles are on the order of ∼1 μm for the chemically prepared composite. Electrochemical PANI/Pt synthesis is initiated by the uptake and reduction of PtCl₆²⁻ into an a priori electrochemically deposited PANI film. This method produces a uniform dispersion of Pt particles with smaller particles with diameters ranging between 200 nm and 1 μm. The results indicate that electrochemical methods may be more suitable for controlling particle dimension. Both materials show reduced proton doping relative to PANI without Pt, indicating the metal particles directly influence proton doping and the oxidation state of the polymer. The electrochemical data indicate that the conductivity in solution is sufficient such that the normal acid doping is attainable for PANI/Pt produced using either synthetic method.     

Electro-oxidation kinetics of adsorbed CO on platinum electrocatalysts

We describe the voltammetric measurement of the full oxidation of adsorbed CO on unsupported platinum electrocatalysts, with concomitant cyclic voltammetry of the hydrogen adsorption and desorption. The hydrogen region of platinum is used to parse the platinum surface into sites associated with weakly bound (WB) hydrogen and strongly bound (SB) hydrogen. By monitoring changes in the hydrogen region while following the two observed CO oxidation peaks, we are able to identify the WB sites as being the most active sites for CO_ads electro-oxidation. The full oxidation peak is fitted to a model based on a modified Butler-Volmer equation that includes the two families of sites. Excellent agreement with experimental results is obtained, and the resulting fits yield the kinetic parameters for the two families of sites. When combined with coulometry, these kinetic analyses also show the importance of linear- and bridged-CO_ads species in the electro-oxidation process. Limitations of the model and the role of CO_ads dynamics amongst the various surface sites are discussed.     

Electrooxidation of methanol on Pt microparticles dispersed on SnO2 thin films

In this work, we have prepared electrodes through the electrodeposition of platinum micro particles on SnO₂ thin films in order to verify the application of this system as a catalyst for the electrooxidation of methanol. The oxide films were prepared through the method of polymeric precursor decomposition and calcinated at 550 °C. The employed oxides have proved to be a good matrix for the dispersion of platinum particles since they present high roughness. The maximum electrooxidation current was attained for a platinum content of approximately 600 μg cm⁻². The chronoamperometric results showed that the current values obtained for the electrooxidation of methanol were up to 10 times higher than the current values obtained with platinized platinum under the same conditions. The possible mechanisms that lead to this enhancement were discussed.     

Electro-oxidation of methanol on copper in alkaline solution

The electro-oxidation of methanol on copper in alkaline solutions has been studied by the methods of cyclic voltammetry, quasi-steady state polarization and chronoamperometry. It has been found that in the course of an anodic potential sweep the electro-oxidation of methanol follows the formation of Cu^III and is catalysed by this species through a mediated electron transfer mechanism. The reaction also continues in the early stages of the reversed cycle until it is stopped by the prohibitively negative potentials. The process is diffusion controlled and the current-time responses follow Cottrellian behavior. The rate constants, turnover frequency, anodic transfer coefficient and the apparent activation energy of the electro-oxidation reaction are reported.     

Electro-oxidation of methanol on Pt-Rh alloys

Methanol adsorption and electro-oxidation on Pt-Rh alloys have been studied in aqueous 0.5 M H₂SO₄ for a broad range of alloy surface composition including the pure Pt and Rh metals. Adsorption results have been compared with equivalent data obtained for CO and CO₂ adsorption on these alloys. Current densities of continuous methanol oxidation on Pt, Rh and a Pt-Rh alloy with optimum surface molar fraction of Rh have been measured.Although on the pure Pt and Rh metals the methanol adsorption products exhibit similar energetic stability, as judged from the peak potential of electro-desorption, on the Pt-Rh alloys, there is a lowering of the stability. Similar behavior is observed for the CO and CO₂ adsorption products, however, the lowering for methanol is much less than for CO and CO₂. In the case of methanol, the maximum lowering is obtained for a surface molar fraction of Rh equal to ca. 0.65 and it is the same alloy surface composition that results in maximum lowering of the stability of the CO₂ adsorption products, but not of the CO adsorption products (optimal fraction of Rh equal ca. 0.10). Structural similarity of the methanol and the CO₂ adsorption products finds support in similar values of the electrons-per-site parameter obtained.Pt-Rh alloys show insufficient electrode potential improvement over Pt in continuous methanol electro-oxidation due to the susceptibility of Rh to strong poisoning by the methanol adsorption products, which switches off the bi-functional mechanism of methanol electro-oxidation on this alloy. The presence of Rh in the alloy with Pt additionally strongly lowers the methanol electro-oxidation turnover rate of the Pt component.     

Corrosion-protective performance of nano polyaniline/ferrite dispersed alkyd coatings

The application of nanotechnology in the corrosion protection of metals has recently gained momentum. A polymer nanocomposite coating can effectively combine the benefits of organic polymers, such as elasticity and water resistance, to that of advanced inorganic materials, such as hardness and permeability. Environmental impact can also be improved by utilizing nanostructure particulates in coatings and eliminating the requirement of toxic solvents. Nanocomposites have also proven to be an effective alternative to phosphate-chromate pretreatment of metallic substrate, which is hazardous due to the presence of toxic hexavalent chromium. This article reports some of the preliminary investigations on the corrosion-resistance performance of soya oil alkyd, containing polyaniline/ferrite nanocomposite. The corrosion-protective performance was evaluated in terms of physico-mechanical properties, corrosion rate, and SEM studies. The polyaniline/ferrite nanocomposite coatings were found to show a far superior corrosion-resistance performance compared to that of a pure PANI/alkyd system.     

Electro-oxidation of methanol and ethylene glycol on platinum in alkaline solution: Poisoning effects and product analysis

The electrochemical oxidation of ethylene glycol on platinum was investigated and compared with that of methanol in alkaline solution by using various electrochemical and analytical measurements. Ethylene glycol showed much less significant electrode poisoning than methanol at low potential (400 mV). This phenomenon was clarified by analyzing the products of ethylene glycol oxidation. In ethylene glycol oxidation, partial oxidation to glycolate was much faster than complete oxidation to CO₂. In addition, there were two paths for ethylene glycol oxidation: poisoning and non-poisoning paths. The poisoning path led to the production of C1 compounds and the non-poisoning path gave oxalate. The non-poisoning path prevented the formation of poisonous species on platinum.     

Ethanol electrooxidation on platinum particles dispersed on poly(neutral red) film

The conductive polymer poly(neutral red) polymerized on a graphite electrode (PNR/graphite) as a support material was used for catalytic oxidation of ethanol in acidic solution and investigated by electrochemical methods. Pt particles loaded on the surface of PNR/graphite electrode exhibited higher electrocatalytic activity for ethanol oxidation in comparison with Pt particles supported directly on graphite. With the equivalent loading mass of Pt catalyst, the special activity (S _A ) at peak a of the Pt/PNR/graphite electrode polymerized for 10 cycles in 5 × 10⁻⁴ M NR + 0.5 M H₂SO₄ solution is 3,478 A C⁻¹ and about 2.20 times higher than that of the Pt/graphite electrode (1,582 A C⁻¹). The results show that the electrochemical performance of Pt catalyst for ethanol oxidation is improved by the addition of PNR     

Structural assembly effects of Pt nanoparticle–carbon nanotube–polyaniline nanocomposites on the enhancement of biohydrogen fuel cell performance

In this work, we designed various polyaniline (PANI) nanocomposites with platinum (Pt) nanoparticle-decorated multi-walled carbon nanotubes (MWCNTs), employed them as anodic catalysts, and studied their structural assembly effects with regard to enhancing biohydrogen fuel cell performance. Of two proposed structures, the PANI/Pt/MWCNTs multilayer nanocomposites showed superior electrocatalytic activities in the hydrogen oxidation reaction and in fuel cell power density relative to the Pt/MWCNTs@PANI core–shell design. These enhancements were attributed to the active interface formed between the Pt nanoparticles and polyaniline nanofibers, where the higher electronic and ionic conductivities of the thin PANI nanofiber layers in contact with Pt active sites were better than with the PANI bound Pt/MWCNTs. We also investigated the change in the electronic state of the composites and the charge-transfer rate caused by varying the structural assembly. Finally, the role of each catalyst component was examined to understand its individual effect on fuel cell performance and to understand its structural assembly effect on enhanced power density.     

Highly dispersed MglnCe-mixed metal oxides catalyzed direct carbonylation of glycerol and CO2 into glycerol carbonate

Glycerol carbonate,an important glycerol value-added product,has been widely used as an active intermediate and inert solvent in the synthesis of cosmetics,detergents,chemical intermediates,poly-mers,and so on.The direct carbonylation from glycerol with CO2 is considered a promising route,but still tough work due to the thermodynamic stability and the kinetic inertness of CO2.In this work,highly-selective direct carbonylation of glycerol and CO2 into glycerol carbonate has been achieved over highly dispersed MglnCe-mixed metal oxides(MglnCe-MMO),which were prepared through the topological transformation derived from the MglnCe-layered double hydroxides(MglnCe-LDHs).By precisely modulating the surface basic-acidic properties and the oxygen vacancies,an efficient carbonylation of glycerol with CO2 has been achieved with a selectivity of up to＞99％to glycerol carbonate.Deep investigation into the synergistic catalysis of base-acid sites and oxygen vacancies has been clarified.     

Palladium electrodeposition on polyaniline films

The electrochemical nucleation and growth of palladium particles onto polyaniline (PAni) films have been investigated by chronoamperometry and topographic and phase-mode atomic force microscopy (AFM). The films were synthesized under different potentiodynamic conditions in order to obtain polymer layers with comparable electroactivity but distinctly different morphology/porosity. The analysis of the current transients obtained for the initial stages of the Pd deposition indicates a 3D nucleative formation regime. A detailed Pd electrodeposition study onto the polymer matrix, using different deposition times, suggests that a constant number of critical nuclei is formed in the superficial part of the polymer porous matrix in the time scale between ca. 5 and 15 s.     

Anticorrosion performance of polyaniline nanostructures on mild steel

Different one-dimensional nanostructured polyanilines were synthesized in sulfuric acid solutions by conventional polymerization, interfacial polymerization and direct mixed reaction, respectively. The products were characterized with SEM, UV–vis and FTIR and the anticorrosion performance of products on mild steel were studied using electrochemical measurement in 3.5% NaCl aqueous solution. Results showed that the polyaniline nanofibers synthesized by direct mixed reaction have uniform morphology with diameters of 60–100 nm and more excellent protective properties than conventional aggregated polyaniline. Comparative studies revealed that the nanostructure and morphology of polyaniline could influence its anticorrosion performance.     

Electrorheological fluids based on nano-fibrous polyaniline

Using a modified oxidative polymerization, the nano-fibrous polyaniline with 200 nm diameter and several micrometer lengths was synthesized on a large scale and then was applied as a new electrorheological (ER) fluid. Compared to conventional granular polyaniline ER fluid, the nano-fibrous polyaniline ER fluid exhibited distinctly improved suspended stability. Under electric fields, the nano-fibrous PANI ER fluid also exhibited larger ER effect. Its shear stresses are about 1.2-1.5 times as high as those of the granular PANI ER fluid. At the same time, the shear stress of nano-fibrous PANI ER fluid could maintain a stable level and even an increase for the wide shear rate regions from 0.1 s⁻¹ to 1000 s⁻¹ under various electric fields. In addition, the dynamic experiment showed that the shear modulus of nano-fibrous polyaniline ER fluid under electric field was higher than that of the granular polyaniline fluid, which also confirmed the larger ER effect.     

Alternative platinum electrocatalyst supporter with micro/nanostructured polyaniline for direct methanol fuel cell applications

In this study, a series of micro/nanostructured polyanilines were synthesized and their morphology-dependent electrochemical properties for acting as a catalyst supporter for direct methanol fuel cell (DMFC) applications were investigated. These micro/nanostructures include submicron spheres, hollow microspheres, nanotubes, and nanofibers. Among the four micro/nanostructures, polyaniline nanofibers (PANF) manifest their superiority in high electrochemical active surface. Accordingly, PANF is adopted as the catalyst supporter thereafter. To couple with the use of the alternative catalyst supporter, this study also investigates the effect of reductant type on morphology and electrocatalytic properties of the PANF-supported Pt particles through a chemical reduction reaction. TEM images indicate that formic acid as a reductant results in well-dispersed Pt particles on the PANF surface. On the other hand, aggregations of Pt are observable when NaBH₄ is selected as a reductant. Moreover, the methanol oxidation current density measured with the Pt/PANF electrode being prepared by using formic acid is double that by using NaBH₄. Compared with Pt/XC-72, the Pt/PANF electrode possesses higher electrocatalytic activity and exhibits double power density. Moreover, Pt/PANF is superior to Pt/XC-72 in the aspect of operation stability based on a continuous discharge for 5 h.     

Generation of carbon dioxide from glycerol: Evidences of massive production on polycrystalline platinum

In this work we investigate the glycerol electrooxidation reaction on polycrystalline platinum in acid media. Cyclic voltammetry shows the existence of multiple oxidation peaks, which are related with a complex electrooxidation mechanism. We follow the voltammetric response of Pt in the presence of glycerol by using FTIR in situ. Results show that during glycerol electrooxidation massive amounts of CO₂ are produced. The production of CO₂ begins at low potentials and depends on the previous formation of adsorbed CO. This pathway is accelerated at high potentials and seems to be the main responsible for the rising of the currents observed in the cyclic voltammogram for potentials up to 1.0 V. Moreover, there is a parallel pathway involving the production of a carboxylic acid (probably glyceric acid), but the relative magnitudes of CO₂ bands and acid bands makes clear that the production of CO₂ is the dominant feature of the spectra, suggesting that glycerol can be a suitable candidate for use in direct alcohol fuel cells.     

Coupling reaction and azeotropic distillation for the synthesis of glycerol carbonate from glycerol and dimethyl carbonate

A new process, coupling reaction and azeotropic distillation was proposed for the synthesis of glycerol carbonate (GC) from glycerol (G) and dimethyl carbonate (DMC). The bench scale experimental investigation was systematically conducted for this new process. With calcium oxide (CaO) as the solid catalyst, the high yield of glycerol carbonate can be obtained at a low molar ratio of dimethyl carbonate to glycerol with the method of coupling reaction and azetropic distillation. The effect of azeotropic agents on glycerol carbonate yield was explored, and indicated that benzene was the most effective azeotropic agent. The effects of the process parameters, tower height, amount of added benzene, final temperature of tower bottom and reflux ratio were investigated. Glycerol carbonate yield can be as high as 98% under the conditions at molar ratio of dimethyl carbonate to glycerol 1:1, final temperature of tower bottom 85 °C, 1.5 mass ratio of added benzene to that in the azeotrope with methanol theoretically produced and reflux ratio 4. By continuously removing methanol from reaction system with the method of coupling reaction and azeotropic distillation, the yield of glycerol carbonate can be retained at high level using the recycled catalyst.     

Preparation and electroactivity of polyaniline/poly(acrylic acid) film electrodes modified by platinum microparticles

The preparation and properties of poly(acrylic acid) (PAA)-doped polyaniline (PANI) film electrodes further modified by electrodeposition of platinum particles were investigated by cyclic voltammetry and in situ conductivity measurement. The PANI/PAA film exhibits a better electroactivity and higher stability, even in solutions of lower acidity, although its polymerization rate is decreased three-fold compared to that of PANI. The conductivity of the PANI/PAA film increases by a factor of two compared to that of PANI. The effects of the carboxylic acid groups of PAA in the PANI matrix on the performance of the film are discussed. The electrocatalytic activity of PANI/PAA/Pt for reduction of hydrogen and oxidation of MeOH is higher than that of PANI modified with Pt particles alone. Characterization of the electrodes by SEM shows the platinum modification procedure yields roughly spherical catalyst particles 0.51mum in diameter dispersed throughout the polyaniline.     

Fabrication of polyoxometallate-modified gold nanoparticles and their utilization as supports for dispersed platinum in electrocatalysis

The usefulness of Keggin-type anions (PMo₁₂O₄₀³⁻) as both reducing, capping and activating agents during synthesis of polyoxometallate-modified gold nanoparticles is demonstrated here. Fabrication of gold nanoparticles stabilized with monolayer-type films of inorganic polyoxometallates (e.g. phosphododecamolybdates), Au-PMo₁₂, was achieved by treating an aqueous solution of gold precursor (HAuCl₄) with a solution of the partially reduced heteropolyblue molybdate. The choice of temperature strongly affected morphology and size of the resulting Au nanoparticles. The presence of strongly adsorbed molybdate-agents on surfaces of gold nanoparticles was evident from the independent infrared (FTIR by reflectance) and voltammetric experiments. Interfacial polymolybdate anions on Au prevent the particle agglomeration and support formation of the stable colloidal Au-PMo₁₂ solutions. They are colored due to existence of the plasmonic effect. The Au-PMo₁₂ nanoparticles typically had 30–40 nm diameters, and they were used as supports or carriers for dispersed catalytic platinum nanoparticles (of ca. 7–8 nm diameters). Polyoxometallates (PMo₁₂O₄₀³⁻) existing on gold surfaces could also interact with neighboring platinum centers thus acting as “linking” agents facilitating dispersion of Pt nanoparticles. Further, the phosphomolybdate adsorbates (on Au supports) are also likely to activate Pt sites (e.g. by providing reactive hydroxy groups) towards more efficient electrocatalytic oxidation of ethanol both under voltammetric and chronoamperometric conditions.