Effect of ceria on carbon supported platinum catalysts for methanol electrooxidation

Pt–CeO₂/C catalysts were synthesized by a one-step microwave polyol process and compared with Pt/C (E-TEK) catalyst in terms of the electrochemical activity for methanol oxidation using the cyclic voltammetry and chronoamperometry. The results demonstrated that Pt–CeO₂/C catalysts exhibited lower onset potential, higher current peak and better stability for methanol electrooxidation than Pt/C (E-TEK) catalyst. The effect of ceria on the catalytic activity was investigated by electrochemical measurements and the highest electrochemical activity was obtained at the molar ratio of Pt to Ce by 2:1. The preliminary mechanism of the enhanced electrocatalytic performance for methanol oxidation was discussed.     

Pt-Pd alloy nanoparticle-decorated carbon nanotubes: a durable and methanol tolerant oxygen reduction electrocatalyst

We describe the decoration of multiwalled carbon nanotubes (MCNTs) with Pt-Pd alloy nanoelectrocatalysts of three different compositions and their electrocatalytic performance toward the oxygen reduction reaction (ORR). The decoration of the MCNTs involves polymer-assisted impregnation of metal precursors [Formula: see text] and [Formula: see text] and the subsequent reduction of the impregnated precursors by a modified polyol route. The composition of the catalyst was controlled by tuning the molar ratio of the precursors during their impregnation. Electron probe microscopic analysis shows that the catalysts have compositions of Pt(46)Pd(54,) Pt(64)Pd(36) and Pt(28)Pd(72). The Pt(46)Pd(54) and Pt(64)Pd(36) catalysts have truncated octahedral and icosahedral shapes with a size ranging from 8 to 10?nm. On the other hand, the catalyst of Pt(28)Pd(72) composition has a spherical/quasispherical shape with a size distribution of 1-2?nm. The XPS measurement confirms the signature of metallic Pt and Pd. The Pt(46)Pd(54) catalyst has a pronounced electrocatalytic activity toward the ORR with a specific and mass activity of 378 [Formula: see text] and [Formula: see text], respectively at 0.8?V. Moreover, the Pt(46)Pd(54) nanoelectrocatalyst is highly durable and it retains its initial catalytic activity even after 1000 extensive cycles. Interestingly, this catalyst has a very high tolerance toward methanol and it does not favor the oxidation of methanol in the potential window of 0.1-1.4?V. The electrocatalytic activity of the alloy electrocatalyst is compared with commercially available Pt black and MCNT-supported spherical Pt nanoparticles. The catalytic activity of the Pt(46)Pd(54) nanoelectrocatalyst is higher than the other catalysts. The Pt(46)Pd(54) catalyst outperforms the electrocatalytic activity of all other catalysts.     

Microwave-assisted synthesis of high-loading, highly dispersed Pt/carbon aerogel catalyst for direct methanol fuel cell

A Pt supported on carbon aerogel catalyst has been synthesized by the microwave-assisted polyol process. The Pt supported on carbon aerogel catalyst was characterized by high resolution transmission electron microscopy and X-ray diffraction. The results show a uniform dispersion of spherical Pt nanoparticles 2·5–3·0 nm in diameter. Cyclic voltammetry and chronoamperometry were used to evaluate the electrocatalytic activity of the Pt/carbon aerogel catalyst for methanol oxidation at room temperature. The Pt/carbon aerogel catalyst shows higher electrochemical catalytic activity and stability for methanol oxidation than a commercial Pt/C catalyst of the same Pt loading.     

Preparation Ru,Bi monolayer modified Pt nanoparticles as the anode catalyst for methanol oxidation

Platinum nanoparticles were successfully electrodeposited on indium tin oxide (ITO) surface in the solution with hexachloroplatinic acid and copper ion by cyclic voltammogram method. The micrographs and structure of Pt nanoparticles were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The electrocatalytic properties of Pt nanoparticles/ITO or modified by Ru, Bi underpotential deposition (UPD) for methanol oxidation have been investigated by cyclic voltammetry (CV) and chronoamperometry (CA). High electroactivity and good long-term stability can be observed. These results indicate that Pt nanoparticles modified by UPD may have potential applications in designing noble metal catalysts of fuel cells with low loading and high activity at the atomic level.     

Electrocatalytic activity of Pt nanoparticles supported on novel functionalized reduced graphene oxide-chitosan for methanol electrooxidation

Here, graphene oxide (GO) was synthesized by a modified Hummers’ method and was functionalized with 1,1′-dimethyl-4,4′-bipyridinium dichloride (MV) accompanied by chitosan (CH) to prepare a novel MV-RGO-CH support. Pt/MV-RGO-CH catalyst was prepared by immobilization of the Pt nanoparticles on MV-RGO-CH support. The microstructure and morphology of the prepared catalyst was characterized by transmission electron microscopy and X-ray powder diffraction analysis. The electrocatalytic activity of Pt/MV-RGO-CH catalyst was investigated for methanol electrooxidation through cyclic voltammetry (CV), CO_ads stripping voltammetry, chronoamperometry, and electrochemical impedance spectroscopy (EIS) techniques. The effects of some experimental factors for methanol electrooxidation such as methanol concentration, scan rate and temperature were studied at the prepared catalyst. Durability of the catalyst was also investigated. Comparing the catalytic activity of the Pt/MV-RGO-CH nanocatalyst with Pt/CH and Pt/MV-RGO catalysts indicated that Pt/MV-RGO-CH has a very good catalytic activity for methanol electrooxidation.     

Highly dense and uniformly dispersed platinum nanoparticles on poly(acrylic acid) modified multi-walled carbon nanotubes for methanol oxidation

Poly(acrylic acid) modified multi-walled carbon nanotubes (PAA-MWNTs) were synthesized through in situ radical polymerization in acetone and the PAA-MWNTs were used as supporting material for platinum nanoparticles. Platinum nanoparticles were deposited on the surface of PAA-MWNTs with high loading and high dispersion through ethylene glycol reduction. The size of Pt nanoparticles on PAA-MWNTs can be tuned by the water content in the reaction system and the loading amount can be adjusted by the mass ratio of H₂PtCl₆ to PAA-MWNTs. The electrocatalytic properties of the Pt/PAA-MWNTs catalyst were evaluated by methanol oxidation. The results of cyclic voltammetry show that the Pt/PAA-MWNTs composite possesses high electrocatalytic activity, good long-term stability and storage property, which can be attributed to the small particle size and high dispersion of Pt nanoparticles as well as the nature of MWNTs.     

Effect of the nanosized TiO2 particles in Pd/C catalysts as cathode materials in direct methanol fuel cells

Pd-TiO2/C catalysts were prepared by impregnating titanium dioxide (TiO2) on carbon-supported Pd (Pd/C) for use as the catalyst for the oxygen reduction reaction (ORR) in direct methanol fuel cells (DMFCs). Transmission electron microscope (TEM), scanning electron microscope (SEM) and X-ray diffraction (XRD) analyses were carried to confirm the distribution, morphology and structure of Pd and TiO2 on the carbon support. In fuel cell test, we confirmed that the addition of TiO2 nanoparticles make the improved catalytic activity of oxygen reduction. The electrochemical characterization of the Pd-TiO2/C catalyst for the ORR was carried out by cyclic voltammetry (CV) in the voltage window of 0.04 V to 1.2 V with scan rate of 25 mV/s. With the increase in the crystallite size of TiO2, the peak potential for OH(ads) desorption on the surface of Pd particle shifted to higher potential. This implies that TiO2 might affect the adsorption and desorption of oxygen molecules on Pd catalyst. The performance of Pd-TiO2/C as a cathode material was found to be similar to or better performance than that of Pt/C.     

Electrochemical characterization of nano-sized Pd-based catalysts as cathode materials in direct methanol fuel cells

To improve the catalytic activity of palladium (Pd) as a cathode catalyst in direct methanol fuel cells (DMFCs), we prepared palladium-titanium oxide (Pd-TiO2) catalysts which the Pd and TiO2 nanoparticles were simultaneously impregnated on carbon. We selected Pd and TiO2 as catalytic materials because of their electrochemical stability in acid solution. The crystal structure and the loading amount of Pd and TiO2 on carbon were characterized by X-ray diffraction (XRD) and energy dispersive X-ray microanalysis (EDX). The electrochemical characterization of Pd-TiO2/C catalysts for the oxygen reduction reaction was carried out in half and single cell systems. The catalytic activities of the Pd-TiO2 catalysts were strongly influenced by the TiO2 content. In the single cell test, the Pd-TiO2 catalysts showed very comparable performance to the Pt catalyst.     

Electrocatalytic activity of PtAu/C catalysts for glycerol oxidation

The electrocatalytic oxidation of glycerol on PtAu/C catalysts has been investigated by cyclic voltammetry. PtAu bimetallic nanoparticles are prepared by chemical reduction. Carbon-supported PtAu catalysts are found to exhibit high electrocatalytic activity for the oxidation of glycerol in alkaline solution in terms of oxidation potential and current density as well as stability, and PtAu/C catalysts with different Pt:Au composition ratios show no much difference in catalytic activity. In acidic solution, PtAu/C catalysts exhibit similar to Pt/C catalysts in activity, but the advantage of the PtAu/C catalysts in terms of per unit mass of platinum is still obvious. The PtAu/C catalysts, in a wide Pt:Au ratio range, show a remarkable enhancement in the mass specific activity of platinum with decreasing platinum content in both alkaline and acidic solutions. This is of significance for reducing the usage of platinum and indicates that though platinum acts as main active sites, gold also plays an important role in the function of PtAu/C catalysts.     

羟基锡酸盐载铂复合催化剂Pt/(Co,Zn)Sn(OH)6的合成及其甲醇电催化氧化性能

以羟基锡酸盐CoSn（OH）₆和ZnSn（OH）₆纳米空心立方体为前体,采用抗坏血酸作为弱还原剂,经过超声过程分别合成了羟基锡酸钴载Pt/CoSn（OH）₆和羟基锡酸锌载Pt/ZnSn（OH）₆复合催化剂,并在甲醇氧化反应（MOR）中表现出良好的性能。Pt/CoSn（OH）₆和Pt/ZnSn（OH）₆催化剂的单位质量活性分别为1 095.6 mA/mg和699.5 mA/mg,高于C载Pt（Pt/C）的594.6 mA/mg。利用XRD、SEM、TEM、XPS和电化学测试对催化剂晶体结构和性能间的关系进行了探索。CO溶出实验结果表明,羟基锡酸盐载体有利于Pt表面CO的去除,载体与Pt间的强相互作用和载体表面的大量羟基基团增强了催化剂的催化活性和CO抗毒性。此外,Pt/（Co,Zn）Sn（OH）₆催化剂中单质Pt高的相对含量也有利于提高MOR活性。通过研究载铂羟基锡酸盐电催化氧化甲醇性能,能够揭示载体结构对催化性能的影响,有助于羟基锡酸盐载铂复合催化剂在直接甲醇燃料电池（DMFCs）领域的应用。     

Electrocatalysts for methanol oxidation based on platinum/carbon nanofibers nanocomposite

New carbon nanomaterials, i.e., carbon nanotubes and nanofibers, with special physico-chemical properties, are recently studied as support for methanol oxidation reaction electrocatalysts replacing the most widely used carbon black. Particularly, carbon fibrous structures with high surface area and available open edges are thought to be promising. Platelet type carbon nanofibers, which have the graphene layers oriented perpendicularly to the fiber axis, exhibit a high ratio of edge to basal atoms. Different types of carbon nanofibers (tubular and platelet) were grown by plasma enhanced chemical vapour deposition on carbon paper substrates. The process was controlled and optimised in term of growth pressure and temperature. Carbon nanofibers were characterised by high resolution scanning electron microscopy and X-ray photoelectron spectroscopy to assess the morphological properties. Then carbon nanofibers of both morphologies were used as substrates for Pt electrodeposition. High resolution scanning electron microscopy images showed that the Pt nanoparticles distribution was well controlled and the particles size went down to few nanometers. Pt/carbon nanofibers nanocomposites were tested as electrocatalysts for methanol oxidation reaction. Cyclic voltammetry in H2SO4 revealed a catalyst with a high surface area. Cyclic voltammetry in presence of methanol indicated a high electrochemical activity for methanol oxidation reaction and a good long time stability compared to a carbon black supported Pt catalyst.     

Electrodeposition of platinum nanoparticles onto carbon nanofibers for electrocatalytic oxidation of methanol

Pt/carbon composite nanofibers were prepared by electrodepositing Pt nanoparticles onto electrospun carbon nanofibers and were used as catalysts towards the oxidation of methanol. The morphology and size of Pt nanoparticles were controlled by selectively adjusting the electrodeposition potential and time. SEM and TEM results show that the composite nanofibers were successfully obtained and Pt particle diameters were between 10 and 55 nm. The electrocatalytic activity of the composite nanofibers expressed by current density per Pt particle mass was found to depend on the particle size, showing an increasing activity when the catalyst diameter decreased.     

介孔碳化钨负载铂催化剂对甲醇氧化的电催化性能

采用硬模板法制备了介孔碳化钨(m-WC), 进一步还原铂的前驱体(H2PtCl6)得到Pt/m-WC催化剂。采用X射线粉末衍射(XRD)、透射电子显微镜(TEM)和X射线光电子能谱(XPS)等测试手段对样品的物相、结构和形貌进行了表征。结果表明, 所制得的m-WC载体为单一的碳化钨相, 孔径为10~20 nm, Pt/m-WC催化剂中Pt的粒径约为3.4 nm, 主要以金属态形式存在, 相对比较均一的Pt纳米粒子均匀地分散在载体的表面和孔道中。电化学测试结果表明, 与普通WC载Pt催化剂(Pt/c-WC)相比, Pt/m-WC催化剂具有较大的电化学活性表面积, 对甲醇呈现出更高的电催化氧化活性和更好的稳定性。     

Nanocomposite for methanol oxidation: synthesis and characterization of cubic Pt nanoparticles on graphene sheets

Abstract

We present our recent results on Pt nanoparticles on graphene sheets (Pt-NPs/G), a nanocomposite prepared with microwave assistance in ionic liquid 2-hydroxyethanaminiumformate. Preparation of Pt-NPs/G was achieved without the addition of extra reductant such as hydrazine or ethylene glycol. The Pt nanoparticles on graphene have a cubic-like shape (about 60 wt% Pt loading, Pt-NPs/G) and the particle size is 6 ± 3 nm from transmission electron microscopy results. Electrochemical cyclic voltammetry studies in 0.5 M aqueous H₂SO₄ were performed using Pt-NPs/G and separately, for comparison, using a commercially available electrocatalyst (60 wt% Pt loading, Pt/C). The electrochemical surface ratio of Pt-NPs/G to Pt/C is 0.745. The results of a methanol oxidation reaction (MOR) in 0.5 M aqueous H₂SO₄ + 1.0 M methanol for the two samples are presented. The MOR results show that the ratios of the current density of oxidation (I_f) to the current density of reduction (I_b) are 3.49 (Pt-NPs/G) and 1.37 (Pt/C), respectively, with a preference by 2.55 times favoring Pt-NPs/G. That is, the tolerance CO poisoning of Pt-NPs/G is better than that of commercial Pt/C.     

Pt／C催化剂的制备及其对甲醇电催化氧化的研究

首次报道了以乙二胺四乙酸（EDTA）作为螯合剂,采用硼氢化钠还原氯铂酸制备Pt／C（Pt的质量分数为20％）纳米催化剂,TEM分析表明,通过改变反应的pH值可以获得分散度与粒径不同的Pt粒子,当pH=12．5时,Pt的分散度最高,平均粒径最小（3．2nm）。催化剂的退火处理研究表明,经270℃氮气氛围内退火后,其电催化活性有了显著提高。使用循环伏安法在甲醇的溶液中电催化氧化研究结果表明,在pH=12．5时制备的催化剂对甲醇的电催化氧化活性最高。     

Platinum-gold nanoclusters as catalyst for direct methanol fuel cells

Nanosized platinum-gold alloys clusters have been deposited on gas diffusion electrode by sputter deposition. The deposits were characterized by FE-SEM, TEM and XPS in order to verify the formation of alloy nanoparticles and to study the influence of deposition technique on the nanomorphology. The deposition by sputtering process allowed a uniform distribution of metal particles on porous surface of carbon supports. Typical island growth mode was observed with the formation of a dispersed metal nanoclusters (mean size about 5 nm). Cyclic voltammetry was used to determine the electrochemical active surface and the electrocatalytic performance of the PtAu electrocatalysts for methanol oxidation reaction. The data were re-calculated in the form of mass specific activity (MSA). The sputter-catalyzed electrodes showed higher performance and stability compared to commercial catalysts.     

Preparation of nanosized Pt-Au alloy catalyst and its activity in methanol oxidation

The alloy catalyst has been widely used because it will be able to improve the activity and selectivity of the single metal catalyst in a given chemical reaction. In this study, the preparation and characteristics of nanosized Pt and Au particles on alumina and their catalytic activity were described. Nanosized Pt-Au catalysts were prepared by impregnation (IMP) method and deposition (DP) method using alumina or ZnO/Al2O3 as support. The size of Pt and Au particles were observed by transmission electron microscopy (TEM), energy dispersive spectroscope (EDS), and X-ray diffraction (XRD). Catalytic activity for oxidation of methanol was measured using a flow reactor. It could be seen that the Pt particle size and dispersion in the alloy catalysts was rarely influenced by preparation methods and Au particles coated by deposition method were well dispersed. TEM images showed that Au particles were well dispersed in the Pt/Au/ZnO/Al2O3 catalyst of which Au particles was supported by deposition method. The catalytic activity for methanol are given in the order of Pt-Au[IMP]/ZnO/Al2O3 > Pt[IMP]/Au[DP]/ZnO/Al2O3 > Au[DP]/Pt[IMP]/ZnO/Al2O3 > Pt-Au[DP]/ZnO/Al2O3. Therefore, Au particle size was doing not play an important role in increasing the oxidation activity, but the Au particles may promote the methanol oxidation.     

Pt/C doped TiO2/SWNTs as catalyst for methanol oxidation

Platinum/carbon doped titanium dioxide/single-walled carbon nanotubes (Pt/C/TiO2/SWNTs) were successfully prepared by blending method. These composite catalysts were found to exhibit an anatase TiO2 structure with uniform Pt/C and the existence of SWNTs can be confirmed by transmission electron microscopy (TEM). The composite of Pt/C with TiO2/SWNTs could improve an enhancement in catalytic properties upon applying TiO2/SWNTs as catalyst support. The catalytic oxidation of methanol of Pt/C doped TiO2/SWNTs is found to be higher as compared to the undoped and Pt/C doped materials.     

Synthesis of ordered macroporous Pt/Ru nanocomposites for the electrooxidation of methanol

Highly catalytic PtRu catalysts with different molar ratios of Pt to Ru have been synthesized by using the inverted colloidal crystals template technique. Three-dimensional ordered Pt/Ru alloys with pore size of 320 nm could be conveniently obtained by electrochemical codeposition of metal precursors inside the voids of the template. The structural and chemical properties of the macroporous catalysts were studied by using SEM, XPS and XRD methods. The decomposition and oxidation of methanol on the macroporous catalyst surfaces with different Pt and Ru molar ratios (Pt100Ru0, Pt90Ru10, Pt80Ru20, Pt70Ru30 and Pt56Ru44) were systemically discussed. Potentiostatic experiments showed that the special structure characteristics (e.g., interconnected pore framework and the flexible curvature) lead to enhanced methanol oxidation efficiency on the macroporous materials as compared to the directly deposited catalyst. These results demonstrate that the three-dimensional ordered porous bimetallic catalysts are promising alternatives for developing high performance DMFC anodic catalysts, especially for the fabrication of microfuel cells.     

Preparation and characterization of PtRu nanoparticles supported on nitrogen-doped porous carbon for electrooxidation of methanol

N-doped porous carbon nanospheres (PCNs) were prepared by chemical activation of nonporous carbon nanospheres (CNs), which were obtained via carbonization of polypyrrole nanospheres (PNs). The catalysts, PtRu and Pt nanoparticles supported on PCNs and Vulcan XC-72 carbon black, were prepared by ethylene glycol chemical reduction. Transmission electron microscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy were employed to characterize samples. It was found that PCNs containing N function groups possess a large number of micropores. Uniform and well-dispersed Pt and PtRu particles with narrow particle size distribution were observed. The electrooxidation of liquid methanol on these catalysts was investigated at room temperature by cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy (EIS). The results showed that alloy catalyst (Pt(1)Ru(1)/PCN) possessed the highest catalytic activity and better CO tolerance than the other PtRu and Pt-only catalysts; PtRu nanoparticles supported on PCN showed a higher catalytic activity and more stable sustained current than on carbon black XC-72. Compared to commercial Alfa Aesar PtRu catalyst, Pt(1)Ru(1)/PCN reveals an enhanced and durable catalytic activity in methanol oxidation because of the high dispersion of small PtRu nanoparticles and the presence of N species of support PCNs.