Enhancement of the electrooxidation of ethanol on Pt-Sn-P/C catalysts prepared by chemical deposition process

In this paper, five Pt3Sn1/C catalysts have been prepared using three different methods. It was found that phosphorus deposited on the surface of carbon with Pt and Sn when sodium hypophosphite was used as reducing agent by optimization of synthetic conditions such as pH in the synthetic solution and temperature. The deposition of phosphorus should be effective on the size reduction and markedly reduces PtSn nanoparticle size, and raise electrochemical active surface (EAS) area of catalyst and improve the catalytic performance. TEM images show PtSnP nanoparticles are highly dispersed on the carbon surface with average diameters of 2 nm. The optimum composition is Pt3Sn1P2/C (note PtSn/C-3) catalyst in my work. With this composition, it shows very high activity for the electrooxidation of ethanol and exhibit enhanced performance compared with other two Pt3Sn1/C catalysts that prepared using ethylene glycol reduction method (note PtSn/C-EG) and borohydride reduction method (note PtSn/-B). The maximum power densities of direct ethanol fuel cell (DEFC) were 61 mW cm(-2) that is 150 and 170% higher than that of the PtSn/C-EG and PtSn/C-B catalyst.

The role of Sn in Pt-Sn/CeO2 catalysts for the complete oxidation of ethanol

The structural features and catalytic properties of Pt-Sn/CeO2 catalysts prepared by modified polyol method were extensively investigated for the complete oxidation of ethanol. CO chemisorption, TPR, DTA and XPS measurements identically indicated that the electronic configuration of Pt by Sn as well as the formation of PtSn alloy were the key factors in determining the nature of the active sites, A strong Pt/Sn atomic ratio dependence of catalytic perfortmances was observed. which was explained in terms of the change., in the Surface structure of metal phases and the electronic Pt-Sn interaction. (c) 2005 Elsevier B.V. All rights reserved.

Structure and chemical composition of supported Pt-Sn electrocatalysts for ethanol oxidation

Carbon supported PtSn alloy and PtSnOx particles with nominal Pt:Sn ratios of 3:1 were prepared by a modified polyol method. High resolution transmission electron microscopy (HRTEM) and X-ray microchemical analysis were used to characterize the composition, size, distribution, and morphology of PtSn particles. The particles are predominantly single nanocrystals with diameters in the order of 2.0-3.0 nm. According to the XRD results, the lattice constant of Pt in the PtSn alloy is dilated due to Sn atoms penetrating into the Pt crystalline lattice. While for PtSnOx nanoparticles, the lattice constant of Pt only changed a little. HRTEM micrograph of PtSnOx clearly shows that the change of the spacing of Pt (111) plane is neglectable, meanwhile, SnO2 nanoparticles, characterized with the nominal 0.264 nm spacing of SnO2 (10 1) plane, were found in the vicinity of Pt particles. In contrast, the HRTEM micrograph of PtSn alloy shows that the spacing of Pt (111) plane extends to 0.234 nm from the original 0.226 nm. High resolution energy dispersive X-ray spectroscopy (HR-EDS) analyses show that all investigated particles in the two PtSn catalysts represent uniform Pt/Sn compositions very close to the nominal one. Cyclic voltammograms (CV) in sulfuric acid show that the hydrogen ad/desorption was inhibited on the surface of PtSn alloy compared to that on the surface of the PtSnOx catalyst. PtSnOx catalyst showed higher catalytic activity for ethanol electro-oxidation than PtSn alloy from the results of chronoamperometry (CA) analysis and the performance of direct ethanol fuel cells (DEFCs). It is deduced that the unchanged lattice parameter of Pt in the PtSnOx catalyst is favorable to ethanol adsorption and meanwhile, tin oxide in the vicinity of Pt nanoparticles could offer oxygen species conveniently to remove the CO-like species of ethanolic residues to free Pt active sites. (C) 2005 Elsevier Ltd. All rights reserved.

稀土墩子和稀土氧化物对甲醇在Pt催化剂上电催化氧化性能的影响

直接甲醇燃料电池( DMFC )具有甲醇来源丰富，价格低廉，在常温常压下是液体，易于携带储存；体积小，重量轻，结构简单，容易操作；维修方便，价格低等优点，近年来得到普遍的关注。然而，要达到DMFC的商品化还存在一些问题。其中一个是阳极催化剂的电催化活性低和易被甲醇氧化的中间产物，如CO毒化。对于甲醇阳极电催化剂人们进行了大量的研究，比较有效的都是Pt－过渡金属或金属氧化物复合催化剂，如Pt－Ru、 Pt－Sn、Pt佩Rh、Pt－Pd、Pt佩Re、Pt－Ru－Sn－W、Pt－WO。和Pt－TIO。等。本文研究了电解液中的稀土离子和与Pt形成复合催化剂的稀土氧化物对甲醇电催化氧化反应的促进作用，得到了如下的结果：1．电解液中的稀土Ho, Eu, Gd或Dy离子对甲醇在光滑Pt电极或DMFC中使用的Pt/C电极上的电催化氧化反应有促进作用，主要表现在的起始氧化电位负移和氧化电流增加。而电解液中加入其它种类的稀土离子对甲醇在光滑Pt电极或Pt/C电极上的电催化氧化反应有阻碍作用，如起始氧化电位正移，峰电流降低。Fu、H食Dy或Gd离子对一甲醇在Pt上的电催化氧化反应有促进作用的主要原因可能与这些稀土离子与甲醇生成配合物能力有关。2．不同Pt一稀土氧化物／C催化剂对甲醇电催化氧化反应有不同的影响。当稀土氧化物是Eu, Ho, Dy或Gd的氧化物时，甲醇在Pt一稀土氧化物／C催化剂上甲醇电催化氧化反应的极化性能和稳定性要优于在Pt/C催化剂上，而在其它的Pt-稀土氧化物／C催化剂上，甲醇电催化氧化的极化性能和稳定性要差于Pt/C电极。用不同方法制备的Pt一稀土氧化物／C催化剂对甲醇电催化氧化反应的促进作用取决于催化剂的制备方法。如先在活性碳上还原沉积Pt，再沉积上稀土氧化物所得的Pt－稀土氧化物／C催化剂的促进作用要优于先在稀土氧化物上还原沉积Pt，再一起沉积到活性碳上或先再活性碳上沉积稀土氧化物，再还原沉积上Pt的方法。另外，Pt和稀上氧化物的原子比为2：1时，pt－稀土氧化物／c催化剂对甲醇电催化氧化反应的催化活性最佳。稀土氧化物对pt／C催化剂对甲醇氧化反应的电催化性质的影响与稀土离子相似。但用稀土离子的方法比较简便，因此，相比之下，用稀土离子来促进甲醇在Pt上的电催化氧化反应方法较好。3．用Eu, Gd, Dy, Ho的氧化物制得的Pt-稀土氧化物／C复合催化剂对co的电催化氧化反应的催化活性要高于Pt/C催化剂。相对于的情况，在co在Eu, Gd, Dy,Ho的氧化物的Pt／稀土氧化物／C复合催化剂电极上的循环伏安图中，CO的氧化峰峰电位比在Pt/C电极的有不同程度的负移。吸．初步确定了电极和单体电池制备的较好的工艺参数和工作条件。在发明一种薄电极制备方法，确定最佳的电极催化层配方等的基础上，制得的单体电池，在25℃工作时，输出功率密度峰值达到28 mW/cm~2。

Pt-based anode catalysts for direct ethanol fuel cells

In the present work, several carbon supported PtSn and PtSnRu catalysts were prepared with different atomic ratios and tested in direct ethanol fuel cells (DEFC) operated at lower temperature (T=90 degreesC). XRD and TEM results indicate that all of these catalysts consist of uniform nano-sized particles of narrow distribution and the average particle sizes are always less than 3.0 nm. As the content of Sn increases, the Pt lattice parameter becomes longer. Single direct ethanol fuel cell tests were used to evaluate the performance of carbon supported PtSn catalysts for ethanol electro-oxidation. It was found that the addition of Sn can enhance the activity towards ethanol electro-oxidation. It is also found that a single DEFC of Pt/Sn atomic ratioless than or equal to2, "Pt1Sn1/C, Pt3Sn2/C, and Pt2Sn1/C" shows better performance than those with Pt3Sn1/C and Pt4Sn1/C. But even adopting the least active PtSn catalyst, Pt4Sn1/C, the DEFC also exhibits higher performance than that with the commercial Pt1Ru1/C, which is dominatingly used in PEMFC at present as anode catalyst for both methanol electro-oxidation and CO-tolerance. At 90 degreesC, the DEFC exhibits the best performance when Pt2Sn1/C is adopted as anode catalysts. This distinct difference in DEFC performance between the catalysts examined here is attributed to the so-called bifunctional mechanism and to the electronic interaction between Pt and Sn. It is thought that -OHads, Surface Pt active sites and the ohmic effect of PtSn/C catalyst determines the electro-oxidation activity of PtSn catalysts with different Pt/Sn ratios. (C) 2004 Elsevier B.V. All rights reserved.

Pt based anode catalysts for direct ethanol fuel cells

In the present work several Pt-based anode catalysts supported on carbon XC-72R were prepared with a novel method and characterized by means of XRD, TEM and XPS analysis. It was found that all these catalysts are consisted of uniform nanosized particles with sharp distribution and Pt lattice parameter decreases with the addition of Ru or Pd and increases with the addition of Sn or W. Cyclic voltammetry (CV) measurements and single direct ethanol fuel cell (DEFC) tests jointly showed that the presence of Sn, Ru and W enhances the activity of Pt towards ethanol electro-oxidation in the following order: Pt1Sn1/C > Pt1Ru1/C > Pt1W1/C > Pt1Pd1/C > Pt/C. Moreover, Pt1Ru1/C further modified by W and Mo showed improved ethanol electro-oxidation activity, but its DEFC performance was found to be inferior to that measured for Pt1Sn1/C. Under this respect, several PtSn/C catalysts with different Pt/Sn atomic ratio were also identically prepared and characterized and their direct ethanol fuel cell performances were evaluated. It was found that the single direct ethanol fuel cell having Pt1Sn1/C or Pt3Sn2/C or Pt2Sn1/C as anode catalyst showed better performances than those with Pt3Sn1/C or Pt4Sn1/C. It was also found that the latter two cells exhibited higher performances than the single cell using Pt1Ru1/C, which is exclusively used in PEMFC as anode catalyst for both methanol electro-oxidation and CO-tolerance. This distinct difference in DEFC performance between the catalysts examined here would be attributed to the so-called bifunctional mechanism and to the electronic interaction between Pt and additives. It is thought that an amount of -OHads, an amount of surface Pt active sites and the conductivity effect of PtSn/C catalysts would determine the activity of PtSn/C with different Pt/Sn ratios. At lower temperature values or at low current density regions where the electro-oxidation of ethanol is considered not so fast and its chemisorption is not the rate-determining step, the Pt3Sn2/C seems to be more suitable for the direct ethanol fuel cell. At 75 degreesC, the single ethanol fuel cell with Pt3Sn2/C as anode catalyst showed a comparable performance to that with Pt2Sn1/C, but at higher temperature of 90 degreesC, the latter presented much better performance. It is thought from a practical point of view that Pt2Sn1/C, supplying sufficient -OHads and having adequate active Pt sites and acceptable ohmic effect, could be the appropriate anode catalyst for DEFC. (C) 2003 Elsevier B.V. All rights reserved.