Activity and long-term stability of PEDOT as Pt catalyst support for the DMFC anode

The feasibility of using poly(3,4-ethylenedioxythiophene) (PEDOT) as Pt catalyst support for direct methanol fuel cell (DMFC) anodes was investigated. Measurements with freshly prepared Pt-PEDOT/C electrodes showed poor activity for methanol oxidation in a half-cell and a DMFC. A substantial enhancement in that activity was evident after either electrochemical over-oxidation of PEDOT or long-time storage of the Pt-PEDOT/C gas diffusion electrode (GDE) in air. Both procedures led to a reorganization and increase in porosity of the reaction layer, which obviously contributed to better methanol accessibility to Pt catalyst active centres. The effects of electrochemical activation and long-time storage in air on the morphology and elementary composition of the Pt-PEDOT layer were investigated by means of Hg porosimetry and SEM/EDAX. It was found that the increase in porosity was due to degradation of PEDOT characterized by a significant depletion of sulphur and oxygen in the conducting polymer matrix.     

The catalysts supported on metallized electrospun polyacrylonitrile fibrous mats for methanol oxidation

Polyacrylonitrile nanofibrous mats coated with continuous thin gold films (Au-PAN) have been fabricated by combining the electrospinning and electroless plating techniques. The Pt particles are electrodeposited on the Au-PAN fibers surface by multi-cycle CV method, and the Au-PAN decorated with Pt (Pt/Au-PAN) shows higher activity toward methanol electro-oxidation. The catalytic peak current for methanol oxidation on the optimum Pt/Au-PAN electrode can reach about 450 mA mg⁻¹ Pt which is much larger than the catalytic peak current for methanol oxidation (118.4 mA mg⁻¹ Pt) on the electrode prepared by loading commercial Pt/C on Au-PAN (Pt/C/Au-PAN). Further experiments reveal that the Pt/Au-PAN electrodes exhibit better stability and smaller charge transfer resistance than Pt/C/Au-PAN electrodes, which indicates that the Au-PAN may be developed as supporting material for catalyst. The microscopy images of the electrodes show that the Pt particles deposited on Au-PAN conglomerate into larger particles, and that the Pt/C catalyst loaded on the Au-PAN also exhibits conglomeration after stability test. The hydrogen adsorption-desorption experiments indicate that the electrochemical surface area of the Pt particles for the both kinds of electrodes has decreased after stability test.     

Electrocatalytic properties of Pt/carbon composite nanofibers

Pt/carbon composite nanofibers were prepared by electrodepositing Pt nanoparticles directly onto electrospun carbon nanofibers. The morphology and size of Pt nanoparticles were controlled by the electrodeposition time. The resulting Pt/carbon composite nanofibers were characterized by running cyclic voltammograms in 0.20 M H₂SO₄ and 5.0 mM K₄[Fe(CN)₆] + 0.10 M KCl solutions. The electrocatalytic activities of Pt/carbon composite nanofibers were measured by the oxidation of methanol. Results show that Pt/carbon composite nanofibers possess the properties of high active surface area and fast electron transfer rate, which lead to a good performance towards the electrocatalytic oxidation of methanol. It is also found that the Pt/carbon nanofiber electrode with a Pt loading of 0.170 mg cm⁻² has the highest activity.     

Mesoporous Pt–Ni catalyst and their electro catalytic activity towards methanol oxidation

Mesoporous Pt/Ni architecture has been prepared by template assisted electrochemical deposition of Pt–Ni over anodized aluminum oxide template followed by controlled de-alloying with nitric acid. Surface characteristics of the ordered bimetallic mesoporous Pt/Ni structure were systematically characterized through XRD, SEM, AFM and XPS analyses. It is designated by XPS analysis that presence of Ni significantly modifies surface characteristics and electronic states of Pt accompanied with a downshift in the d-band character of Pt. Mesoporous morphology is highly beneficial to offer readily accessible Pt catalytic sites for methanol oxidation reaction. The prepared bimetallic Pt/Ni was used as electro catalyst for DMFC. Comparison of electrocatalytic activity of bimetallic mesoporous Pt/Ni with bimetallic smooth Pt/Ni was interrogated using cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy analyses. Distinctly enhanced electrocatalytic activity with improved CO tolerance associated with bimetallic mesoporous Pt/Ni electrode towards methanol oxidation stems from a synergy existing between mesoporous structure with bi-metallic composition.     

Preparation of Pt/CeO2/HCSs anode electrocatalysts for direct methanol fuel cells

Hollow carbon spheres (HCSs) were prepared through a simple hydrothermal method using silica particles and glucose as the template and carbon precursor, respectively. HCSs used as supports for platinum catalysts deposited with cerium oxide (CeO₂) were prepared for application as anode catalysts in direct methanol fuel cells. The composition and structure of the samples were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The electrocatalytic properties of the as-prepared catalysts for methanol oxidation were investigated by cyclic voltammetry (CV). The Pt/CeO₂/HCSs catalyst heated at 550 °C for 1 h exhibited the best catalytic activity for methanol oxidation.     

Electro-reduction of oxygen and electro-oxidation of methanol at Pd monolayer-modified macroporous Pt electrode

With polystyrene latex spheres self-assembled on indium tin oxide-coated glass electrode as templates, highly ordered macroporous Pt was prepared by electrochemical deposition. Then, the macroporous Pt was modified by Pd monolayer involving the galvanic displacement of Cu monolayer formed by under-potential deposition on macroporous Pt. Electrocatalytic properties of the Pd-modified macroporous Pt electrode for oxygen reduction were investigated by cyclic voltammetry and chronoamperometry in O₂-saturated solution containing 0.1 M HClO₄. Methanol electro-oxidation on the Pd-modified macroporous Pt surfaces in 0.5 M H₂SO₄ containing 1 M CH₃OH was studied by cyclic voltammetry. The corresponding results showed that Pd-modified macroporous Pt electrode had negative catalytic activity for methanol oxidation in compared with macroporous Pt. However, Pd-modified macroporous Pt electrode had positive electrocatalytic activity to O₂ reduction.     

Pt/laponite clay-modified gold electrode for direct methanol fuel cells

This work employs a novel technique in which laponite clay-modified gold electrodes are used as the anode for direct methanol fuel cells. The platinum/laponite clay (Pt/Clay) films on indium tin oxide electrode were characterized by using scanning electron microscope and energy-dispersive X-ray spectroscopy. Various contents of laponite clay (0.1, 0.5, 1.0, and 2.0?wt%) with constant platinum (Pt) catalyst content on modified gold electrodes were studied as an anode catalyst for methanol oxidation. The catalyst poisoning was observed as a function of time. The 1.0?wt% Pt/Clay-modified gold electrode shows the highest activity for methanol oxidation, 27.73?% higher than Pt only modified gold electrode at 2.5?min. The peak current of 1?% Pt/Clay-modified gold electrode is 3.50?% higher than the peak current of Pt only modified gold electrode at 57.5?min. The higher content of Pt/Clay-modified gold electrode shows strong resistance to catalyst poisoning. The Pt/Clay-modified gold electrode is a new and promising electrode for a direct methanol fuel cell and can replace existing commercial catalysts.     

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.     

Porous Co/Co–Ni–Pt nanostructures prepared by galvanic replacement towards methanol electro-oxidation

The nanostructured Co/Co–Ni–Pt catalyst were synthesized by electrodeposition process and galvanic replacement reaction. The alloy prepared on a copper electrode (Cu/Co/Co–Ni–Zn) was dipped in platinum containing alkaline solution to produce a porous Cu/Co/Co–Ni–Pt catalyst. The catalyst was characterized by energy dispersive X-ray and scanning electron microscopy techniques and its electrocatalytic properties were evaluated using cyclic voltammetry, electrochemical impedance spectroscopy and chronoamperometry techniques. The results showed that the Co/Co–Ni–Pt coatings are porous, and composed of discrete Pt nanoparticles with the crystallite size of about 66 nm. It was shown from cyclic voltammograms in alkaline solutions that the oxidation current of methanol on the nanostructured Cu/Co/Co–Ni–Pt electrode was much higher than that on flat platinum. Electrochemical impedance spectra on the Co/Co–Ni–Pt electrode reveal that the charge transfer resistance decreases with the increase of anodic potentials. All results show that the Co/Co–Ni–Pt catalysts can be potential anode catalysts for the direct methanol fuel cell.     

Electroreduction of dioxygen (ORR) in alkaline medium on Ag/C and Pt/C nanostructured catalysts—effect of the presence of methanol

Ag/C catalysts with different loading were prepared using a colloidal route to obtain well dispersed catalysts on carbon, with a particle size close to 15 nm. An amount of 20 wt.% Ag on carbon was found to be the best loading in terms of current density and mass activity. The 20 wt.% Ag/C catalyst was then studied and the kinetics towards ORR was determined and compared with that of a 20 wt.% Pt/C catalyst. The number of exchanged electrons for the ORR was found to be close to four with the rotating disk electrode (RDE) as well as with the rotating ring disc electrode (RRDE) techniques. From the RDE results, the Tafel slopes b, the diffusion limiting current density inside the catalytic film (j_l^film) and the exchange current density (j₀) were evaluated. The Tafel slopes b and diffusion limiting current densities inside the catalytic film (j_l^film) were found to be in the same order for both catalysts, whereas the exchange current density (j₀), which is a suitable estimation of the activity of the catalyst, was at least 10 times higher at the Pt/C catalyst than at the Ag/C catalyst. The behavior of both catalysts in methanol containing electrolyte was investigated and it was found that at a low methanol concentration, the Pt/C catalyst was quasi-tolerant to methanol. But, at a high methanol concentration, the ORR at a Pt/C was affected. However, the Pt/C catalyst showed in each case better activity towards ORR than the Ag/C catalyst, even if the latter one was less affected by the presence of methanol than the former one.     

Pt supported on highly graphitized lace-like carbon for methanol electrooxidation

A simple solvothermal method has been used to synthesize highly graphitized lace-like carbon (GLC) using ethanol as the carbon source and Mg as reducing agent. The GLC is characterized by transmission electron microscopy, X-ray diffraction, N₂ adsorption, Raman spectroscopy and electrochemical techniques. The GLC synthesized at optimized conditions shows interlaced structure with an average thickness of 3 nm. Platinum on GLC electrocatalysts were prepared for methanol oxidation in acidic media for the first time. They show extremely higher activity for methanol oxidation compared to Pt/C electrocatalyst for the same Pt loadings. GLCs act as structural units to form mesopores and channels in the catalyst layers, which lead to the increase of the electrochemical active surface area and improvement in the mass transport by reducing the liquid sealing effect.     

Improved kinetics of methanol oxidation on Pt/hollow carbon sphere catalysts

Hollow carbon spheres (HCSs) have been prepared by combining the hydrothermal method and intermittent microwave heating (IMH) technique. The preparation factors affecting the performance of the HCSs are studied. The results show that Pt nanoparticles supported on HCSs (Pt/HCS), which were heated for 3 min in a microwave oven, give the best performance for methanol oxidation. The higher electrochemical active surface area of the Pt/HCS catalysts results in higher catalytic activity for methanol oxidation compared to that of the commercial Pt/C catalyst at the same Pt loadings. Higher exchange current density and lower reaction activation free energy are observed on Pt/HCS catalysts, indicating improved kinetics. It is recognized that the hollow structure of the Pt/HCS with open microspores and nanochannels is responsible for this higher catalytic activity for methanol oxidation.     

Graphitized mesoporous carbon supported Pt-SnO2 nanoparticles as a catalyst for methanol oxidation

A mesostructured composite catalyst, Pt-SnO₂ supported on graphitized mesoporous carbon (GMC), has been prepared and its electrochemical activity for methanol oxidation has been investigated. The materials were characterized by XRD, FESEM, TEM, EDX spectrum and N₂ sorption techniques. Cyclic voltammetry, chronoamperometry and steady-state polarization tests were adopted to characterize the electro-catalytic activities of the materials for methanol oxidation. The results show that, the overall methanol electro-oxidation catalytic activity of the mesostructured composite catalyst, 20 wt.% PtSnO₂ (1:1, mass ratio)/GMC, is obviously higher than that of 20 wt.% PtSnO₂/C with commercial carbon black as support under the same loading amount of Pt-SnO₂ catalysts, and is also much higher than that of commercial catalyst 20 wt.% Pt/C at half Pt using amount.     

Platinum nanopaticles supported on stacked-cup carbon nanofibers as electrocatalysts for proton exchange membrane fuel cell

Inexpensive stacked-cup carbon nanofibers (SC-CNFs) supported Pt nanoparticles with a loading from 5 to 30 wt.% were prepared through a modified ethylene glycol method. XRD and TEM characterizations show that the average Pt particle sizes increase with increasing metal loading, and they can be controlled <5 nm with a uniform dispersion. A self-developed filtration process was employed to fabricate Pt/SC-CNFs film-based membrane electrode assembly (MEA), and the catalyst transfer efficiency can reach nearly 100% using a super-hydrophobic polycarbonate filter. The thickness of catalyst layer can be accurately controlled through altering Pt loadings of the catalyst and electrode, this is in good agreement with our theoretical calculation. For Pt/SC-CNFs-based-MEAs, Pt cathode loading was found more critical than Pt anode loading on proton exchange membrane fuel cell (PEMFC) performance. The Pt/SC-CNFs-based MEA with an optimized 50 wt.% Nafion content demonstrates higher PEMFC performance than the carbon black-based MEA with an optimized 30 wt.% Nafion content. SC-CNFs possess much larger length-to-diameter ratio than carbon black particles, it makes Pt/SC-CNFs more easily form continuously conductive networks in the Nafion matrix than carbon black. Therefore, the Pt/SC-CNFs-based MEA demonstrates higher Pt utilization than carbon black-based MEA, which implies possible reduction in Pt loading of MEA.     

Electrocatalytic oxidation of methanol on carbon paste electrode modified by nickel ions dispersed into poly (1,5-diaminonaphthalene) film

Poly (1,5-diaminonaphthalene) film was prepared by using the repeated potential cycling technique in an acidic solution at the surface of carbon paste electrode. Then transition metal ions of Ni(II) were incorporated to the polymer by immersion of the modified electrode in a 1.0 M nickel chloride solution. The electrochemical characterization of this modified electrode exhibits stable redox behavior of the Ni(III)/Ni(II) couple. Also, cyclic voltammetric experiments showed that methanol electrooxidized at the surface of this Ni(II) dispersed polymeric modified carbon paste electrode [Ni/P-1,5-DAN/MCPE]. The mechanism of methanol oxidation changes from diffusion control at low concentration to a catalytic reaction at higher methanol concentration. The effects of both scan rate and methanol concentration on the anodic peak height of the methanol oxidation were discussed.     

Graphene-supported platinum and platinum-ruthenium nanoparticles with high electrocatalytic activity for methanol and ethanol oxidation

In this study, Pt and Pt-Ru nanoparticles were synthesized on graphene sheets and their electrocatalytic activity for methanol and ethanol oxidation was investigated. Experimental results demonstrate that, in comparison to the widely-used Vulcan XC-72R carbon black catalyst supports, graphene-supported Pt and Pt-Ru nanoparticles demonstrate enhanced efficiency for both methanol and ethanol electro-oxidations with regard to diffusion efficiency, oxidation potential, forward oxidation peak current density, and the ratio of the forward peak current density to the reverse peak current density. For instance, the forward peak current density of methanol oxidation for graphene- and carbon black-supported Pt nanoparticles is 19.1 and 9.76 mA/cm², respectively; and the ratios are 6.52 and 1.39, respectively; the forward peak current density of ethanol oxidation for graphene- and carbon black-supported Pt nanoparticles is 16.2 and 13.8 mA/cm², respectively; and the ratios are 3.66 and 0.90, respectively. These findings favor the use of graphene sheets as catalyst supports for both direct methanol and ethanol fuel cells.     

Electrooxidation of methanol on NiMn alloy modified graphite electrode

Nickel and nickel-manganese alloy modified graphite electrodes (G/Ni and G/NiMn) prepared by galvanostatic deposition were examined for their redox process and electrocatalytic activities towards the oxidation of methanol in alkaline solutions. The methods of cyclic voltammetery (CV), chronoamperometry (CA) and impedance spectroscopy (EIS) were employed. In CV studies, in the presence of methanol NiMn alloy modified electrode shows a significantly higher response for methanol oxidation. The peak current of the oxidation of nickel hydroxide increase is followed by a decrease in the corresponding cathodic current in presence of methanol. The anodic peak currents show linear dependency upon the square root of scan rate. This behavior is the characteristic of a diffusion controlled process. Under the CA regime the reaction followed a Cottrellian behavior and the diffusion coefficient of methanol was found to be 4 × 10⁻⁶ cm² s⁻¹. A mechanism based on the electro-chemical generation of Ni³⁺ active sites and their subsequent consumptions by methanol have been discussed and the corresponding rate law under the control of charge transfer has been developed and kinetic parameters have been derived. The charge transfer resistance accessible both theoretically and through the EIS have been used as criteria for derivation of the rate constant.     

High utilization platinum deposition on single-walled carbon nanotubes as catalysts for direct methanol fuel cell

This research aims to enhance the activity of Pt catalysts, thus to lower the loading of Pt metal in fuel cell. Highly dispersed platinum supported on single-walled carbon nanotubes (SWNTs) as catalyst was prepared by ion exchange method. The homemade Pt/SWNTs underwent a repetition of ion exchange and reduction process in order to achieve an increase of the metal loading. For comparison, the similar loading of Pt catalyst supported on carbon nanotubes was prepared by borohydride reduction method. The catalysts were characterized by using energy dispersive analysis of X-ray (EDAX), transmission electron micrograph (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectrum (XPS). Compared with the Pt/SWNTs catalyst prepared by borohydride method, higher Pt utilization was achieved on the SWNTs by ion exchange method. Furthermore, in comparison to the E-TEK 20 wt.% Pt/C catalyst with the support of carbon black, the results from electrochemical measurement indicated that the Pt/SWNTs prepared by ion exchange method displayed a higher catalytic activity for methanol oxidation and higher Pt utilization, while no significant increasing in the catalytic activity of the Pt/SWNTs catalyst obtained by borohydride method.     

载Pt石墨烯中空微球催化剂的制备及其电催化性能

目前,直接甲醇燃料电池（DMFC）已成为世界各国探寻新型绿色动力源的首选。铂基催化剂虽然被公认为催化甲醇氧化最有效的催化剂,但离其商业化应用仍然存在较大差距。提高铂的利用率和电催化性能被公认为是解决DMFC商业化的关键问题。基于以上考虑,本文采用一种不需要使用表面活性剂的模板辅助法成功合成出了石墨烯中空球,并利用电沉积法负载Pt纳米颗粒。该载Pt石墨烯中空微球具有非常高的比表面积（226.4m2/g）和相互连通的结构。电化学测试结果表明,该载Pt石墨烯中空球的电化学活性表面积高达43.27m2/(g,Pt),峰值电流密度几乎是商业铂碳的两倍,且稳定性明显高于商业化铂碳。该载Pt石墨烯中空球对甲醇氧化展现出了极好的应用前景。     

Pt–Sn/C electrocatalysts for methanol oxidation synthesized by reduction with formic acid

Carbon supported Pt–Sn alloy catalysts were prepared by reduction of Pt and Sn precursors with formic acid, and their electrocatalytic activity for methanol oxidation was compared with commercial Pt/C and Pt₇₅Sn₂₅/C electrocatalysts. By X-ray diffraction analysis it was found that the Pt lattice parameter increases with the addition of Sn, indicative of alloy formation. It was confirmed that Sn exhibits cocatalytic activity for CO oxidation. The onset potential for the methanol oxidation reaction of the Pt–Sn electrode was approximately 0.1 V smaller than that on Pt both at room temperature and at 90 °C. The best performance in a direct methanol fuel cell was obtained using the Pt₇₅Sn₂₅/C alloy catalyst prepared by the formic acid method as the result of an optimal balance of Sn content, degree of alloying and metal particle size.