High efficient electrocatalytic oxidation of methanol on Pt/polyindoles composite catalysts

Novel composite catalysts have been fabricated by the electrodeposition of Pt onto the glassy carbon electrode (GC) modified respectively with polyindole (PIn) and poly(5-methoxyindole) (PMI) and used for the electrooxidation of methanol in acid solution of 0.5 M H₂SO₄ containing 1.0 M methanol. As-formed composite catalysts are characterized by SEM, XRD and the electrochemical methods. The results of the catalytic activity for methanol oxidation show that the two composite catalysts exhibit higher catalytic activity and stronger poisoning-tolerance than Pt/polypyrrole/GC (Pt/PPy/GC) and Pt/GC. Electrochemical impedance spectroscopy indicates that the methanol electrooxidation on the composite catalysts at various potentials shows different impedance behaviors. At the same time, the charge-transfer resistance for electrooxidation of methanol on Pt/PIn/GC and Pt/PMI/GC is smaller than those on Pt/PPy/GC and Pt/GC. The present study shows a promising choice of Pt/PIn and Pt/PMI as composite catalysts for methanol electrooxidation.     

Methanol electrooxidation on Pt particles dispersed into PANI/SWNT composite films

Conducting polymer composite films comprised of polyaniline (PANI) and single wall carbon nanotubes (SWNT) was prepared by electrochemical codeposition during the electropolymerization in an aniline solution with suspending SWNT. The fabricated composite films are assessed with respect to their potential application as support materials in Pt electrocatalyst for electrochemical oxidation of methanol. The PANI/SWNT composite film incorporated with SWNT has a higher polymeric degree and lower defect density in PANI structure than PANI film. Furthermore, the incorporation of SWNT also leads to higher electrochemically accessible surface areas (S_a), electronic conductivity and easier charge-transfer at polymer/electrolyte interfaces, which make higher dispersion and utilization for deposited Pt. Therefore, the Pt particles electrodeposited on PANI/SWNT composite polymer film exhibits excellent catalytic activity and stability for the electrooxidation of methanol in comparison to Pt supported on PANI film, which reveals that the composite film is more promising for application in electrocatalyst as a support material.     

Electrocatalytic oxidation of methanol on mono and bimetallic composite films: Pt and Pt–M (M = Ru,Ir and Sn) nano-particles in poly(o-aminophenol)

Mono and bimetallic composite catalysts have been formed by a three-step process, whereby the surface of aluminum electrode was pretreated upon immersion into a Pd(NH₃)₄Cl₂ solution (p-Al), was subsequently coated with a thin poly(o-aminophenol) (PoAP) layer by potentiodynamic electropolymerization of o-aminophenol and Pt and Pt alloys nano-particles were finally dispersed into the PoAP film by electrochemical methods. The electrocatalytic properties of the platinum doped (Pt/PoAP/p-Al) and Pt alloys doped (Pt–M/PoAP/p-Al, M = Ru, Ir and Sn) electrodes towards the methanol oxidation were investigated by cyclic voltammetry and compared with the electrocatalytic properties of pristine Pt and Pt particles on pretreated Al (Pt/p-Al) electrodes. The enhancement of the electrocatalytic activity of the Pt nano-particles, when Ru, Ir and Sn, are co-deposited in the polymer is also studied in detail. The effects of various parameters on the electrooxidation of methanol as well as the long-term stability of doped electrodes have also been investigated.     

Exceptional ethylene glycol electrooxidation activity enabled by sub-16 nm dendritic Pt–Cu nanocrystals catalysts

The catalysts for the electrooxidation of liquid fuel in the anodic electrode has severely limited the practical large-scale commercial application of fuel cells, and hence needs to be optimized. Herein, we report a facile one-pot method to successfully synthesize the sub-16 nm dendritic Pt–Cu nanocrystals (PtCu NCs) catalysts under the assistance of ultrasonic. In virtue of such dendritic structure, the alloy and electronic effects between Pt and Cu, such binary PtCu nanodendrites exhibited extremely high electrocatalytic performances towards ethylene glycol (EG) electrooxidation with the mass activity of 4259.2 mA mg^?1, 4.5 times higher than that of the commercial Pt/C. Moreover, the Pt₁Cu₁ nanocatalysts can endure at least 500 cycles with less activity decay, demonstrating a new class of Pt-based electrocatalysts with enhanced performance for fuel cells and beyond.     

Electrocatalytic properties of carbon-supported Pt-Ru catalysts with the high alloying degree for formic acid electrooxidation

A series of carbon-supported bimetallic Pt-Ru catalysts with high alloying degree and different Pt/Ru atomic ratio have been prepared by a chemical reduction method in the H₂O/ethanol/tetrahydrofuran (THF) mixture solvent. The structural and electronic properties of catalysts are characterized using X-ray reflection (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM). The electrooxidation of formic acid on these Pt-Ru nanoparticles are investigated by using cyclic voltammetry, chronoamperometry and CO-stripping measurements. The results of electrochemical measurements illustrate that the alloying degree and Pt/Ru atomic ratio of Pt-Ru catalyst play an important role in the electrocatalytic activity of the Pt-Ru/C catalyst for formic acid electrooxidation due to the bifunctional mechanism and the electronic effect. Since formic acid is an intermediate in the methanol electrooxidation on Pt electrode in acidic electrolyte, the observation provides an additional fundamental understanding of the structure-activity relationship of Pt-Ru catalyst for methanol electrooxidation.     

Pt support of multidimensional active sites and radial channels formed by SnO2 flower-like crystals for methanol and ethanol oxidation

SnO₂ nanoflowers and nanorods have been synthesized by the hydrothermal method without using any capping agent. Both types of SnO₂ nanostructures are selected as a support of Pt catalyst for methanol and ethanol electrooxidation. The synthesized SnO₂ nanostructures and SnO₂ supported platinum (Pt/SnO₂) catalysts are characterized by X-ray diffraction, scanning electron microscope and high resolution transmission electron microscope. The electrocatalytic properties of the Pt/SnO₂ and Pt/C catalysts for methanol and ethanol oxidation have been investigated systematically by typical electrochemical methods. The influence of SnO₂ morphology on its electrocatalytic activity is comparatively investigated. The Pt/SnO₂ flower-shaped catalyst shows higher electrocatalytic activity and better long-term cycle stability compared with other electrocatalysts owing to the multidimensional active sites and radial channels of liquid diffusion.     

Electrooxidation of CO and methanol on well-characterized carbon supported PtxSn electrodes. Effect of crystal structure

The role of two intermetallic phases of PtSn, namely Pt₃Sn (fcc phase) and PtSn (hcp phase) for the electrooxidation of CO and methanol has been evaluated. Carbon supported Pt₃Sn and PtSn nanosized particles have been prepared by controlled surface reactions. The actual structure of the PtSn alloys has been evaluated and confirmed by means of XRD and HR-TEM studies which reveal the predominance of either the hcp or the fcc phase in each catalyst. The catalysts have been further characterized to identify the actual metal loading and Pt/Sn atomic ratio in order to eliminate particle size or metal loading effects on their electrocatalytic performance. The performance of the catalysts for the electrooxidation of CO and methanol has been evaluated by electrochemical techniques along with in situ techniques such as electrochemical coupled Infrared Reflection Absorption Spectroscopy (EC-IRAS) and differential electrochemical mass spectrometry (DEMS). Altogether, the results presented in this work reveal that Pt₃Sn fcc is more active than PtSn hcp for the electrooxidation of CO and methanol and that the contribution of the hcp phase in those electrocatalytic processes is negligible.     

A facile method to synthesize well-dispersed PtRuMoOx and PtRuWOx nanoparticles and their electrocatalytic activities for methanol oxidation

PtRuMoO_x and PtRuWO_x catalysts supported on multi-wall carbon nanotubes (MWCNTs) are prepared by ultrasonic-assisted chemical reduction method. XRD measurements indicate that Pt exists as face-centered cubic structure, Ru is alloyed with platinum, and the metal oxides exist as an amorphous structure. TEM pictures show that PtRuMoO_x and PtRuWO_x catalysts are well dispersed on the surface of MWCNTs with the particle size of about 3 nm and a narrow particle size distribution. The electrochemical properties of the catalysts for methanol electrooxidation are studied by cyclic voltammetry (CV), chronoamperometry (CA) and chronopotentiometry (CP). The onset potentials for methanol oxidation on PtRuMoO_x and PtRuWO_x are more negative than that of pure Pt catalyst, shifting negatively by about 0.20 V and have better electrocatalytic activities than PtRu/MWCNTs.     

The effect of Sn on platinum dispersion in Pt/graphene catalysts for the methanol oxidation reaction

Sn-modified platinum catalysts are presently one of the most active catalysts for the room temperature electrooxidation of ethanol at low potentials. In this study, Pt–Sn/graphene catalysts containing different ratios of Pt and Sn were prepared by the solution-phase reduction. Microstructural characterization shows that metallic Pt, Pt–Sn alloy and tin dioxide (SnO₂) nanoparticles are distributed on the graphene sheets in the synthetic process. In terms of the electrocatalytic properties, graphene-supported Pt–Sn catalysts exhibit much higher current densities with increasing Sn proportions. It's proved that the addition of Sn not only decreases catalyst particles growth and agglomeration, but also promotes methanol electrooxidation by geometric effects on expanding Pt's lattice spacing, causing a synergistic effect between Pt and Sn nanoparticles.     

Methanol electro-oxidation on Pt/C modified by polyaniline nanofibers for DMFC applications

In the present study, in order to achieve an inexpensive tolerable anode catalyst for direct methanol fuel cell applications, a composite of polyaniline nanofibers and Pt/C nano-particles, identified by PANI/Pt/C, was prepared by in-situ electropolymerization of aniline and trifluoromethane sulfonic acid on glassy carbon. The effect of synthesized PANI nanofibers in methanol electrooxidation reaction was compared by bare Pt/C by different electrochemical methods such as; cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronoamperometry. Scanning electron microscopy (SEM) was also employed to morphological study of the modified catalyst layer. The test results reveal that introduction of PANI nanofibers within catalyst layer improves the catalyst activity in methanol oxidation, hinders and prevents catalyst from more poisoning by intermediate products of methanol oxidation and improves the mechanical properties of the catalyst layer. SEM images also indicate that PANI nanofibers placed between platinum particles and anchor platinum particles and alleviate the Pt migration during methanol electrooxidation.     

Enhanced electrocatalytic performance for methanol oxidation on Pt–TiO2/ITO electrode under UV illumination

Pt is one of the most important electrode materials employed in direct methanol fuel cell, and many efforts have been directed to improving its electrocatalytic performance. In this work, Pt–TiO₂ nanocomposites are successfully prepared by a sol–gel method. As revealed by TEM, Pt nanoparticles with an average size of 2.6 nm are well uniformly dispersed on porous TiO₂. XRD structural characterization indicates that Pt possesses a face centered cubic crystal structure while TiO₂ is in the format of both rutile and anatase phases. The electrochemical performance of as-prepared nanocomposite electrode (Pt–TiO₂/ITO) is evaluated by studying the electrocatalytic oxidation of methanol in an alkaline medium with or without UV illumination. Comparative experiments evince that the electrochemical performance of Pt–TiO₂/ITO for methanol electrooxidation is markedly improved under UV illumination. Under UV illumination, moreover, the poisoning resistance of Pt–TiO₂/ITO for methanol electrooxidation is significantly improved, as supported by the results of time-coursed current measurements.     

Titanium carbide nanoparticles supported Pt catalysts for methanol electrooxidation in acidic media

Titanium carbide (TiC) nanoparticles supported Pt catalyst for methanol electrooxidation is investigated for the first time. The resultant TiC/Pt catalysts are prepared by using a simple electrodeposition to load Pt nanoparticles on TiC nanocomposite. The electrodes are characterized by scanning electron microscopy and cyclic voltammetry. It is found that the TiC/Pt catalysts help alleviate the CO poisoning effect for methanol electrooxidation with a higher ratio of the forward anodic peak current (I_f) to the reverse anodic peak current (I_b). The improvement in the catalytic performance is attributed to the fact that TiC ameliorates the tolerance to CO adsorption on Pt nanoparticles. One possible mechanism to improve the CO tolerance of Pt taking TiC as supporting material in methanol electrooxidation is also proposed. The results suggest that TiC could be practical supporting materials to prepare electrocatalysts that are suitable for the methanol electrooxidation applications.     

Polyaniline decorated MoO3 nanorods: Synthesis,characterization and promoting effect to Pt electrocatalyst

The promoting effect of metal oxides to Pt catalysts toward methanol oxidation reaction (MOR) has attracted widespread attention in recent years. In this communication, we report the promoting effect of MoO₃ to Pt catalyst by rationally designing and tuning the nanostructure of the catalysts. MoO₃ nanorods are firstly synthesized through hydrothermal method and used as the substrate for the deposition of polyaniline (PANI) layer. The PANI-MoO₃ composite nanostructures are then used as the support for Pt catalyst. Depending on the preparation method of Pt nanoparticles, the nanostructure can be PANI nanotube supported Pt (Pt/PANI) through etching MoO₃ nanorods with NaBH₄ and PANI-MoO₃ composite nanorods supported Pt (Pt/PANI-MoO₃). The catalytic properties of the two catalysts toward MOR are investigated. Results show that the current of methanol oxidation on Pt/PANI-MoO₃ catalyst is comparable to that on Pt/PANI, while the peak potential of MOR on the former is lowered by 180 mV as compared with the latter, suggesting a much higher catalytic activity of Pt/PANI-MoO₃. The presence of MoO₃ may be responsible for the improvement of the catalytic properties through the co-synergistic effects of PANI and MoO₃.     

Fabrication of a bimetallic Cu/Pt particle-modified carbon nanotube paste electrode and its use for the electrocatalytic oxidation of methanol

In this work, carbon nanotube paste electrode (CNTPE) was used as a substrate for deposition of bimetallic Cu/Pt particles. At first, a Cu film was prepared by electrochemical reduction of Cu ions onto the CNTPE in 0.1 M H₂SO₄ solution. Cu/Pt catalysts were prepared by partial galvanic replacement of Cu with Pt by simply immersion of the Cu-coated CNTPE in 2.0 mM H₂PtCl₆ solution. The nature and surface morphology of the bare CNTPE and fabricated Cu/Pt species were characterized by scanning electron microscopy and energy dispersive X-ray spectrometry. The Cu/Pt-modified CNTPE exhibits remarkable electrocatalytic activity towards methanol oxidation. It has been shown that carbon nanotubes improve the electrocatalytic activity of the catalysts towards oxidation. Then, the influence of various parameters such as Cu source concentration, electrodeposition time, replacement time, and methanol concentration on its oxidation as well as long-term stability of the modified electrode have been investigated by electrochemical methods.     

Effect of deposition potential on the structure and electrocatalytic behavior of Pt micro/nanoparticles

In fuel cells, Pt is often employed as an electrode material to facilitate electrochemical reaction processes, in which morphology plays an important role. In this work, three kinds of Pt flowers have been prepared on a glassy electrode substrate via a facile electrochemical deposition in a solution of H₃PO₄; by controlling work potentials at −0.1 V, −0.2 V and −0.3 V, cauliflower-like, needle-like and rose-like shapes of Pt micro/nanoparticles as confirmed by SEM and XRD are obtained, respectively. Taking methanol oxidation as a model reaction and using CO stripping voltammogram in an acid medium, the electrocatalytic performance of as-prepared three Pt flowers has been evaluated. The three Pt flowers show different electrocatalytic activities, and the needle-like Pt flowers present the highest catalytic activity for electrooxidation of methanol and CO.     

Effect of polyoxometalate amount deposited on Pt/C electrocatalysts for CO tolerant electrooxidation of H2 in polymer electrolyte fuel cells

Polyoxometalate-deposited Pt/C electrocatalysts are prepared by impregnation with various amounts of polyoxometalate (POM) anions (from 2 to 16.7 wt.% PMo₁₂O₄₀^3–) on the Pt/C catalyst. The prepared electrocatalysts show a high CO electrooxidation performance over a half-cell system for CO stripping voltammetry, and CO tolerant electrooxidation of H₂ is further demonstrated over a proton exchange membrane fuel cell by using CO-containing H₂ gas feeds (0, 10, 50, and 100 ppm CO in H₂). In the CO stripping voltammograms, the onset and peak potentials for the CO oxidation appear to decrease as the POM deposition is increased, indicating that the electrooxidation of CO undergoes more efficiently on the catalyst surface with the deposited POMs on the Pt/C catalysts. In the single fuel cell tests with the CO-containing H₂ gases, the higher current density is also generated with the larger amounts of deposited POMs on the Pt/C catalysts. Importantly, the charge transfer resistance R_p appears to decrease monotonically with the POM amounts, which was measured by electrochemical impedance spectroscopy. Physico-chemical characterizations with electrocatalytic analyses show that the deposited POMs hardly affect the active phase of Pt catalyst itself but can help the electrooxidation of H₂ by efficiently oxidizing CO to prevent the Pt catalyst from poisoning. Consequently, this POM-deposited Pt/C catalyst can serve as a promising CO tolerant anode catalyst for the polymer electrolyte fuel cells that are operated with hydrocarbons-reformed H₂ fuel gases.     

Electrochemical fabrication of novel platinum-poly(5-nitroindole) composite catalyst and its application for methanol oxidation in alkaline medium

A novel composite catalyst, Pt nanoparticles supported on poly(5-nitroindole) (Pt/PNI), has been successfully prepared by the electrochemical method and used for the electrooxidation of methanol in alkaline media. As-prepared Pt/PNI was characterized by SEM, EDX and electrochemical methods. The results of the catalytic activity for methanol oxidation showed that Pt/PNI had higher catalytic activity and stronger poisoning-tolerance than Pt/Pt, Pt/GC and the common Pt electrode. The effects of different parameters related to the methanol oxidation reaction kinetics, such as Pt loading, mass of PNI film, concentration of methanol and KOH, potential scan rate, have also been investigated. The present study showed a promising choice of Pt/PNI as composite catalyst for methanol electrooxidation in alkaline medium.     

Catalytic activity,stability and impedance behavior of PtRu/C,PtPd/C and PtSn/C bimetallic catalysts toward methanol and formic acid oxidation

PtRu, PtPd and PtSn with weight ratios of (2:1) on carbon black (Vulcan XC-72) supported bimetallic catalysts were prepared by using microwave method via chemically reduction of H₂PtCl₆·6H₂O, RuCl₃, PdCl₂ and SnCl₂·2H₂O precursors with ethylene glycol (EG). These prepared catalysts were systematically investigated and obtained results were compared with commercial Pt black, PtRu black catalysts and with each other. The catalysts were characterized with XRD, ICP-MS, EDS and TEM. The electrocatalytic activities, stability and impedance of the catalysts were investigated in sulfuric acid/methanol and sulfuric acid/formic acid mixtures using electrochemical measurements. The results showed that PtSn/C catalyst showed comparable activity and durability with commercial Pt/C catalyst toward methanol oxidation. The synthesized PtRu/C catalyst was found to completely oxidize methanol and it showed more catalytic activity than commercial PtRu catalyst. Bimetallic PtPd/C catalyst gave better activity than both commercial Pt black and synthesized Pt/C catalyst for oxidation of formic acid. Higher electrochemical active surface areas were obtained with supported bimetallic catalysts.     

High efficient electrocatalytic oxidation of formic acid at Pt dispersed on porous poly(o-methoxyaniline)

A Pt-based composite electrode material has been developed by dispersing Pt nanoparticles on a porous poly(o-methoxyaniline) (POMA) film, which was produced via electropolymerization on a glassy carbon (GC) electrode. As-formed Pt/POMA/GC electrode was characterized by SEM, EDX and electrochemical analysis. Furthermore, the composite electrode material was evaluated by its electrocatalytic performance for formic acid oxidation using cyclic voltammetry and chronoamperometry methods. Compared to Pt deposited on bare GC (Pt/GC), Pt/POMA/GC exhibits higher catalytic activity and stronger poisoning-tolerance ability towards formic acid electro-oxidation. The improved performance is attributed to the synergetic effect between Pt and POMA. Also, as demonstrated by CO stripping voltammograms, the interference of CO on Pt/POMA/GC is greatly weakened. These results suggest that the POMA film has great potential to serve as a promising support material for the electrocatalytic oxidation of formic acid.     

Polycarbazole as an efficient promoter for electrocatalytic oxidation of formic acid on Pt and Pt-Ru nanoparticles

Electrocatalytic activities of the monometallic Pt and bimetallic Pt-Ru nanoparticles dispersed onto polycarbazole (PCZ) films obtained by the electropolymerization on glassy carbon electrode (GC) (i.e., Pt/PCZ/GC, Pt-Ru/PCZ/GC) towards formic acid oxidation have been investigated using cyclic voltammetry and chronoamperometry methods. As-formed electrodes are characterized by SEM, EDX and electrochemical analysis. Relative to Pt and Pt-Ru deposited on the bare GC (i.e., Pt/GC and Pt-Ru/GC), Pt/PCZ/GC and Pt-Ru/PCZ/GC, respectively, exhibit higher catalytic activity and stronger poisoning-tolerance ability towards formic acid electrooxidation. The enhanced performance is proposed to come from the synergetic effect between metal nanoparticles (Pt, Pt-Ru) and PCZ. At the same time, the results of the stripping voltammograms of CO show that PCZ can weaken largely the adsorption strength of CO on catalysts and can make CO oxidation easier under lower potential, implying further that PCZ can be used as an efficient promoter for electrocatalytic oxidation of formic acid on Pt/PCZ and Pt-Ru/PCZ catalysts.