Enhanced activity in ethanol oxidation of Pt<Subscript>3</Subscript>Sn electrocatalysts synthesized by microwave irradiation

High surface area carbon supported Pt and Pt₃Sn catalysts were synthesized by microwave irradiation and investigated in the ethanol electro-oxidation reaction. The catalysts were obtained using a modified polyol method in an ethylene glycol solution and were characterized in terms of structure, morphology and composition by employing XRD, STM and EDX techniques. The diffraction peaks of Pt₃Sn/C catalyst in XRD patterns are shifted to lower 2θ values with respect to the corresponding peaks at Pt/C catalyst as a consequence of alloy formation between Pt and Sn. Particle size analysis from STM and XRD shows that Pt and Pt₃Sn clusters are of a small diameter (∼2 nm) with a narrow size distribution. Pt₃Sn/C catalyst is highly active in ethanol oxidation with the onset potential shifted for ∼150 mV to more negative values and with ∼2 times higher currents in comparison to Pt/C.     

Carbon-supported IrSn catalysts for a direct ethanol fuel cell

Carbon-supported Ir₃Sn/C and Ir/C catalysts were simply prepared with NaBH₄ as a reducing agent under the protection of ethylene glycol at room temperature. TEM and X-ray diffraction (XRD) data showed that the catalysts with small particle size exhibited the typical characteristic of a crystalline Ir fcc structure. Their electro-catalytic activities in comparison with Pt/C and Pt₃Sn/C catalysts also prepared by the NaBH₄ reduction process were characterized by cyclic voltammetry (CV), linear sweep voltammetry (LSV) and chronoamperometry (CA) techniques. The results indicated that Ir-based catalysts showed superior electro-catalytic activity towards ethanol oxidation to Pt/C and Pt₃Sn/C catalysts, mainly at low potential region. During single-cell tests at 90 °C, better performances of Ir-based catalysts as anodes were obtained compared to that of Pt/C catalyst. The comparable overall performance of Ir₃Sn/C to Pt₃Sn/C makes it a promising alternative choice of anode catalyst for direct ethanol fuel cells.     

多元醇法合成的Pt2.6Sn1Ru0.4/C用作直接乙醇燃料电池高性能阳极催化剂

采用多元醇法制备了不同原子比例和载量的PtSnRu/C催化剂,利用透射电镜和X射线光电子能谱表征了所制备催化剂的物化性能,采用直接乙醇燃料电池（DEFC）单池性能测试了其电化学性能,并利用电化学原位光谱、气相色谱和中和滴定分析了乙醇电氧化过程和产物. DEFC单电池测试表明Pt_2.6Sn₁Ru_0.4/C催化剂具有较高的电池性能,其中,以60 wt% Pt_2.6Sn₁Ru_0.4/C催化剂为阳极的DEFC性能最高,90 ℃下最高功率密度为121 mW/cm². 电化学原位红外光谱和阳极产物分析表明乙酸、乙醛、乙酸乙酯和CO₂是乙醇电化学氧化产物,Pt_2.6Sn₁Ru_0.4/C催化剂上乙醇的氧化效率较高. 阳极乙醇氧化活化能和催化剂表面组成分析结果表明,表面组成的相互作用使Pt_2.6Sn₁Ru_0.4/C催化剂具有较低的乙醇氧化活化能和较高的乙醇氧化活性.     

CO and methanol oxidation at platinum-tin electrodes

Electrooxidation of dissolved CO and methanol at platinum-tin electrodes with different phase composition (a two-phase Sn/Pt-catalyst, Pt-Sn alloy, and Pt₃Sn intermetallic compound) is studied. All studied catalysts show higher catalytic activity in the CO oxidation at lower potentials (0.3–0.5 V against reversible hydrogen electrode (RHE)), as compared with platinum; no catalysis is observed at higher potentials (0.7 V); moreover, inhibiting is observed in some cases. The catalyst with the most strongly ordered structure (Pt₃Sn) demonstrated the highest catalytic activity; however, it appeared being less stable against oxidation at potentials more positive than 1.0 V. Catalytic effects were practically absent in the CO-adsorbate oxidation process. The sequence of catalyst activities in the methanol oxidation process differed from that in the CO oxidation; in particular, Pt3Sn appeared being the least active. The observed difference can be associated with the difference in the CO and methanol adsorption mechanisms. The effect of the carbonaceous support dispersion on the current-voltage curves is discussed.     

Effect of thermal treatment on phase composition and ethanol oxidation activity of a carbon supported Pt50Sn50 alloy catalyst

A carbon supported Pt–Sn electrocatalyst in the Pt/Sn atomic ratio 50:50 was prepared by the reduction of Pt and Sn precursors with formic acid and thermally treated at 200 °C (i.e., in the presence of solid tin) and 500 °C (in the presence of molten tin) in flowing hydrogen. In the absence of thermal treatment, X-ray diffraction (XRD) analysis showed a solid solution of Sn in the face centered cubic (fcc) Pt and SnO₂. After thermal treatment, the formation of a main phase of hexagonal PtSn (niggliite) and a secondary phase of cubic Pt₃Sn was observed in the Pt50Sn50 catalyst. The relative amount of the PtSn phase increased with increasing thermal treatment temperature. The presence of molten tin gave rise to the formation of some big particles during annealing at 500 °C. The activity for the ethanol oxidation reaction (EOR) of the as-prepared catalyst was higher than that of both thermally treated catalysts and Pt75Sn25/C and Pt50Ru50/C by E-TEK. The higher activity for the EOR of the as-prepared Pt–Sn catalysts was ascribed to the presence of a large amount of SnO₂. Dedicated to Teresa Iwasita’s 65th birthday.     

Pt-SnO2 / C催化剂对乙醇和吸附态CO的电催化氧化

由于乙醇最有可能成为直接甲醇燃料电池（DMFC）的替代燃料，因此近年来。对乙醇的电化学氧化及直接乙醇燃料电池的研究已引起人们的很大兴趣。甲醇毒性较大并且易透过Nafion膜进入阴极造成阴极的混合电位而影响DMFC的阴极性能．这是制约DMFC走向实用化的主要问题之一。因此人们在致力于研究直接甲醇燃料电池的同时．也寻求其它的小分子醇作为甲醇的替代燃料。乙醇是除甲醇以外最简单的醇．它来源广泛．无毒，是可再生和环保型能源．并且也有较高的能量密度和反应活性。但是乙醇在电极上的完全氧化因涉及到C-C键的断裂要比甲醇困难．阳极反应动力学过程也比较缓慢。到目前为止铂基催化剂仍然是乙醇氧化最好的催化剂．虽然也有使用非铂催化剂研究乙醇的电氧化，但催化活性远不如铂基催化剂高。     

Effect of Ru addition on the structural characteristics and the electrochemical activity for ethanol oxidation of carbon supported Pt–Sn alloy catalysts

Binary Pt–Sn/C (1:1) and ternary Pt–Sn–Ru/C (1:1:0.3 and 1:1:1) catalysts were synthesized by reduction of precursors with formic acid, and their activity for ethanol oxidation was compared with that of commercial Pt/C and Pt–Ru/C catalysts. Linear sweep voltammetry measurements at 40 and 90 °C showed that for potentials higher than 0.3 V vs. RHE, the Pt–Sn–Ru/C (1:1:0.3) catalyst presents the highest activity for ethanol electro-oxidation, while the electrochemical activity of the Pt–Sn–Ru/C (1:1:1) catalyst was lower than that of both the binary Pt–Sn/C and Pt–Ru/C catalysts. Tests in a single direct ethanol fuel cell confirmed the superior performance of the Pt–Sn–Ru/C (1:1:0.3) electrocatalyst. The positive effect of the Ru presence in the Pt–Sn–Ru/C (1:1:0.3) catalyst was ascribed to the interactions between Sn and Ru oxides.     

Enhanced electrochemical activity for ethanol oxidation on the carbon-supported Pt3Te nanocatalysts by addition of Ru

Ternary Pt–Te–Ru catalysts with different atomic ratios were synthesized by reducing the precursor with formic acid. The physical and electrochemical characterization of the Pt₃TeRu_0.25/C catalyst was performed by transmission electron microscopy (TEM), X-ray diffraction, energy-dispersive X-ray spectroscopy equipped with TEM (TEM-EDX), X-ray photoelectron spectrometer, ethanol oxidation, and CO stripping. In TEM images, the Pt₃TeRu_0.25/C nanoparticles with an average particle size of around 2.9 nm were well dispersed on the carbon support. The Pt₃TeRu_0.25/C catalyst was superior to the Pt₃Te/C catalyst in respect of catalytic activity, durability, and CO tolerance. The positive effect of the Ru presence in the Pt₃TeRu_0.25/C catalyst was ascribed to the interactions of Ru or Ru oxides.     

Revealing the Effect of Surface Composition on Multiwalled Carbon Nanotubes Supported Pt-Fe Alloy Electrocatalysts for Methanol Oxidation Performance

The designs of efficient and inexpensive Pt-based catalysts for methanol oxidation reaction (MOR) are essential to boost the commercialization of direct methanol fuel cells. Here, the highly catalytic performance PtFe alloys supported on multiwalled carbon nanotubes (MWCNTs) decorating nitrogen-doped carbon (NC) have been successfully prepared via co-engineering of the surface composition and electronic structure. The Pt₁Fe₃@NC/MWCNTs catalyst with moderate Fe³⁺ feeding content (0.86 mA/mg_Pt) exhibits 2.26-fold enhancement in MOR mass activity compared to pristine Pt/C catalyst (0.38 mA/mg_Pt). Furthermore, the CO oxidation initial potential of Pt₁Fe₃@NC/MWCNTs catalyst is lower relative to Pt/C catalyst (0.71 V and 0.80 V). Benefited from the optimal surface compositions, the anti-corrosion ability of MWCNT, strong electron interaction between PtFe alloys and MWCNTs and the N-doped carbon (NC) layer, the Pt₁Fe₃@NC/MWCNTs catalyst presents an improved MOR performance and anti-CO poisoning ability. This study would open up new perspective for designing efficient electrocatalysts for the DMFCs field.     

直接乙醇燃料电池PtSn/C电催化剂的合成表征和性能

采用多元醇法制备了n(Pt)/n(Sn)比为2:1,3:1,4:1的PtSn/C电催化剂.通过XRD,TEM、循环伏安和氢化学吸附技术对催化剂进行了表征.TEM和XRD结果表明,不同比例的PtSn/C金属粒子的平均粒径均小于4nm,且粒径分布较窄;该系列催化剂中Pt具有fcc结构;PtSn间的相互作用使Pt晶格参数增大.循环伏安和氢化学吸附实验结果表明,加入Sn可抑制Pt对氢的吸附,Pt3Sn/C对乙醇的氧化电流比Pt4Sn/C高约1倍.用不同n(Pt)/n(Sn)比的催化剂作为直接醇类燃料电池阳极电催化剂,在相同条件下,随着Sn含量的增加,单电池最大输出功率逐渐增大,当Sn含量继续增大时,单池性能反而下降.导致不同比例PtSn催化剂活性差别的原因可能是由于Sn与Pt间的合金化程度不同和催化剂粒子尺寸效应及Sn含量对电池阻抗等几方面因素所致.对40h寿命测试前后的阳极Pt3Sn/C催化剂的分析(EnergydispersiveX-rayanalysis,EDX)结果表明,PtSn含量在测试前后均有所降低,PtSn催化剂的寿命尚有待改善.     

Adsorption and oxidation of ethanol on colloid-based Pt/C, PtRu/C and Pt3Sn/C catalysts: in situ FTIR spectroscopy and on-line DEMS studies

The interaction of colloid-based, carbon supported Pt/C (40 wt%), PtRu/C (45 wt%) and Pt3Sn/C (24 wt%) catalysts with ethanol and their performance for ethanol electrooxidation were investigated in model studies by electrochemical, in situ infrared spectroscopy and on-line differential electrochemical mass spectrometry measurements. The combined application of in situ spectroscopic techniques on realistic catalysts and under realistic reaction (DEMS, IR) and transport conditions (DEMS) yields new insight on mechanistic details of the reaction on these catalysts under the above reaction and transport conditions. Based on these results, the addition of Sn or Ru, though beneficial for the overall activity for ethanol oxidation, does not enhance the activity for C-C bond breaking. Dissociative adsorption of ethanol to form CO2 is more facile on the Pt/C catalyst than on PtRu/C and Pt3Sn/C catalysts within the potential range of technical interests (<0.6 V), but Pt/C is rapidly blocked by an inhibiting CO adlayer. In all cases acetaldehyde and acetic acid are dominant products, CO2 formation contributes less than 2% to the total current. The higher ethanol oxidation current density on the Pt3Sn/C catalyst at these potentials results from higher yields of C2 products, not from an improved complete ethanol oxidation to CO2.     

Pt/C电极表面活化处理对乙醇电催化氧化的影响

0引言直接甲醇燃料电池(DMFC)由于其燃料来源丰富、价格低廉、甲醇携带和储存安全方便等独特的优越性而越来越受到重视[1]。但DMFC中常用的阳极Pt催化剂对甲醇氧化的低的电催化活性及易于被甲醇氧化的中间体,吸附态的CO(COad)毒化的问题一直是制约DMFC走向实用化的关键问题[2,3]。由于甲醇分子小,在质子交换膜上有较大的透过作用,并且甲醇具有较高的毒性,所以寻求甲醇的替代燃料也是一直以来被广泛关注的问题[4,5]。乙醇是最简单的链醇分子,相对于甲醇来说,乙醇有很多优点,乙醇基本上没有毒性,来源丰富,价格可与甲醇竞争,能量密度高…     

Promotion of PtRu/C anode catalysts for ethanol oxidation reaction by addition of Sn modifier

PtRu/C anode electrocatalysts modified by Sn were prepared for ethanol oxidation reaction (EOR). Their phase structures, surface species, surface compositions, and EOR activities were characterized by XRD, XPS, temperature-programmed reduction (TPR), and CV, respectively. It has been found that in the PtRu/Sn_xC and PtSn/C alloy catalysts, some Sn alloyed with Pt to form Pt–Sn phase existed as the metallic state, however, the excess Sn existed as the amorphous SnO or crystalline SnO₂. Surface analyses and electrochemical measurements suggest that the surface Ru and amorphous SnO instead of the crystalline SnO₂ are important species for the promotion of EOR. As a result, compared with PtSn/C, the I₀₆ was enhanced about 200% for the PtRu/C electrocatalyst with 10 wt% of Sn modification.     

Hydrogenation of Benzonitrile on Sn-Pt/SiO2 Catalysts Prepared by Introducing SnEt4 to Pt/SiO2: Role of Tin

Liquid phase hydrogenation of benzonitrile was studied over Sn-Pt/SiO₂ catalysts prepared by introducing tetraethyl tin onto the 3 wt.% Pt/SiO₂ catalyst. Tin content of the catalysts ranged from 0.05 to 0.63 wt.%, whereas Sn/Pt surface atomic ratios determined by chemisorption measurements were between 0.1 to 3.5. Dibenzylamine selectivity influenced to a small extent by the level of conversion and the Sn/Pt ratio wasca. 75 %. The addition of tin to Pt in the range of (Sn/Pt)_surface = 0.50–1.25 led to an increase in the turnover frequency (TOF) by a factor of 2. TOF showed a maximum at a surface atomic ratio of Sn/Pt = 1. The enhancement of catalyst activity upon the addition of tin is explained by the formation of Sn⁺-Pt ensemble sites on the surface of bimetallic nanoclusters. It is suggested that highly dispersed positively charged tin species, by polarizing the triple bond, enhance the reactivity of the -CN group. Calcination at 300°C followed by re-reduction of the catalysts resulted in a monotonic decrease of specific activity with increasing Sn/Pt ratio.     

Study of Pt and Rh based supported catalysts modified with tetrabutyltin for the selective hydrogenation of 4-methoxyacetophenone

Catalysts based on Pt and Rh modified with Sn(C₄H₉)₄ were studied in the hydrogenation of 4-methoxyacetophenone. The selectivity to 1-(4-methoxyphenyl)ethanol was close to 100% at Sn/(Pt,Rh) = 1.0, however the catalytic activity decreased drastically. With respect to the balance between activity and selectivity the catalyst PtSnOM (Sn/Pt=0.4) showed the best performance.     

Catalytic effects of metal submonolayers formed by faradaic adsorption on the anodic oxidation of ascorbic acid at a platinum electrode

The catalytic effects of metal ions on the anodic oxidation of ascorbic acid on a Pt electrode in 1 M HClO₄ were studied by linear sweep voltammetry. The anodic peak due to a two-electron oxidation of ascorbic acid shifts to the negative potential side on the addition of Bi³⁺. This indicates the accelerating effect of Bi³⁺ on the oxidation of ascorbic acid. The presence of other metal ions, such as Pb²⁺, Hg²⁺, Tl⁺, Ag⁺ and Sb³⁺, also exerts similar effects. These metal ions were adsorbed on a Pt electrode at underpotentials and the adsorbed metals (denoted as M_ad) still remain on the electrode surface until the electrode potential goes up to and beyond the peak potential of the oxidation of ascorbic acid. On the other hand, metal ions forming no adsorbed layer on Pt, such as Co²⁺, Zn²⁺, Fe³⁺ and Ni²⁺, exhibit no catalytic effect. These facts suggest that the presence of a M_ad on Pt is essential for the promotion of the anodic oxidation of ascorbic acid. However, there is a difference in the catalytic action among the M_ad, for example, Cu_ad, Cd_ad, In_ad, Sn_ad and Mo_ad display no catalytic action.The catalytic activity depends on the degree of surface coverage by the M_ad. The maximal effect of the M_ad is attained in the submonolayer region. The effects of metal ions were discussed on the basis that the M_ad plays its major role in the removal of the adsorbed ascorbic acid occupying active sites on the electrode surface, and provides effective sites for the activation of adjacent water molecules. Furthermore, from the ¹³C NMR spectra for the oxidation products, the adsorbed water on the M_ad appears to function by promoting the subsequent hydration steps, following the electron-transfer step of ascorbic acid.     

Silica‐Encapsulated Pt‐Sn Intermetallic Nanoparticles: A Robust Catalytic Platform for Parahydrogen‐Induced Polarization of Gases and Liquids

Recently, a facile method for the synthesis of size‐monodisperse Pt, Pt₃Sn, and PtSn intermetallic nanoparticles (iNPs) that are confined within a thermally robust mesoporous silica (mSiO₂) shell was introduced. These nanomaterials offer improved selectivity, activity, and stability for large‐scale catalytic applications. Here we present the first study of parahydrogen‐induced polarization NMR on these Pt‐Sn catalysts. A 3000‐fold increase in the pairwise selectivity, relative to the monometallic Pt, was observed using the PtSn@mSiO₂ catalyst. The results are explained by the elimination of the three‐fold Pt sites on the Pt(111) surface. Furthermore, Pt‐Sn iNPs are shown to be a robust catalytic platform for parahydrogen‐induced polarization for in vivo magnetic resonance imaging.     

Ultrasmall and uniform Pt3Au clusters strongly suppress Ostwald ripening for efficient ethanol oxidation

Clean and uniform Pt₃Au clusters decorated on graphene (Pt₃Au@PDDA-G) with an average size as small as 2.1 nm were successfully synthesized, offering higher catalytic activity and stability toward ethanol oxidation than that of Pt₃Au@G and commercial Pt/C, respectively. The catalytic enhancement mechanism of Pt₃Au@PDDA-G was proposed and discussed, and this work demonstrated that the uniformly distributed Pt₃Au clusters could strongly suppress Ostwald ripening to retain their original crystals size and morphology for highly catalytic properties.     

Carbon-supported binary Li-Sn catalyst for acetylene hydrochlorination

The study of a novel catalyst containing LiCl and SnCl₂ (LiSn/AC) for acetylene hydrochlorination has been reported in this paper. Furthermore, the performance of both high activity (98.3%) and selectivity (>98.0%) are achieved by LiSn/AC catalysts under the reaction temperature of 200 °C and C₂H₂ hourly space velocity of 30 h^?1. The structural characteristics of the Sn based catalysts were deeply researched via BET, XRD, TEM, TPR, C₂H₂-TPD, XPS and TG techniques. According to these characteristic results, we proposed that the presence of Sn²⁺ exhibited better activity and stability than that of Sn⁴⁺ in Sn based catalysts. Additionally, LiCl additives not only can restrain the oxidation of Sn²⁺ and the loss of Sn⁴⁺ in fresh Sn based catalysts but also make the Sn^δ+ (δ = 2,4) species dispersed well on the surface of support. Therefore, the adsorption capacity of C₂H₂ and HCl was enhanced in LiSn/AC, which exhibited the better catalytic performance than that of Sn based catalyst.     

Platinum-Tin/Tin Oxide/CNT Catalysts for High-Performance Electrocatalytic Ethanol Oxidation

Ethanol is a promising liquid clean energy source in the energy conversion field. However, the self-poisoning caused by the strongly adsorbed reaction intermediates (typically, CO) is a critical problem in ethanol oxidation reaction. To address this issue, we proposed a joint use of two strategies, alloying of Pt with other metals and building Pt/metal-oxide interfaces, to achieve high-performance electrocatalytic ethanol oxidation. For this, a well-designed synthetic route combining wet impregnation with a two-step thermal treatment process was established to construct PtSn/SnO_x interfaces on carbon nanotubes. Using this route, the alloying of Pt−Sn and formation of PtSn−SnO_x interfaces can simultaneously be achieved, and the coverage of SnO_x thin films on PtSn alloy nanoparticles can be facilely tuned by the strong interaction between Pt and SnO_x. The results revealed that the partial coverage of SnO_x species not only retained the active sites, but also enhanced the CO anti-poisoning ability of the catalyst. Consequently, the H−PtSn/SnO_x/CNT-2 catalyst with an optimized PtSn−SnO_x interface showed significantly improved performances toward the ethanol oxidation reaction (825 mA mg_Pt⁻¹). This study provides deep insights into the structure-performance relationship of PtSn/metal oxide composite catalysts, which would be helpful for the future design and fabrication of high-performance Pt-based ethanol oxidation reaction catalysts.