Pt/WO_3/C nanocomposite with parallel WO_3 nanorods as cathode catalyst for proton exchange membrane fuel cells

Pt/WO3/C nanocomposites with parallel WO3 nanorods were synthesized and applied as the cathode catalyst for proton exchange membrane fuel cells(PEMFCs). Electrochemical results and single cell tests show that an enhanced activity for the oxygen reduction reaction(ORR) is obtained for the Pt/WO3/C catalyst compared with Pt/C. The higher catalytic activity might be ascribed to the improved Pt dispersion with smaller particle sizes. The Pt/WO3/C catalyst also exhibits a good electrochemical stability under potential cycling. Thus, the Pt/WO3/C catalyst can be used as a potential PEMFC cathode catalyst.     

Pristine and graphitized-MWCNTs as durable cathode-catalyst supports for PEFCs

Long-term deterioration in the performance of PEFCs is attributed largely to reduction in active area of the platinum catalyst at cathode, usually caused by carbon-support corrosion. Multi-walled carbon-nanotubes (MWCNTs) as cathode-catalyst support are found to enhance long-term stability of platinum catalyst (Pt) in relation to non-graphitic carbon. In addition, highly graphitic MWCNTs (G-MWCNTs) are found to be electrochemically more stable than pristine MWCNTs. This is because graphitic-carbon-supported-Pt (Pt/MWCNTs) cathodes exhibit higher resistance to carbon corrosion in-relation to non-graphitic-carbon-supported-Pt (Pt/C) cathodes in PEFCs during accelerated stress-test (AST) as evidenced by chronoamperometry and carbon dioxide studies. The corresponding change in electrochemical surface area (ESA), cell performance, and charge-transfer resistance are monitored through cyclic voltammetry, cell polarization, and impedance measurements, respectively. The extent of crystallinity, namely amorphous or graphitic nature of the three supports, is examined by Raman spectroscopy. X-ray diffraction and transmission electron microscopy studies both prior and after AST suggest lesser deformation in catalyst layer and catalyst particles for Pt/G-MWCNTs and Pt/MWCNTs cathodes in relation to Pt/C cathodes, reflecting that graphitic carbon-support resists carbon corrosion and helps mitigating aggregation of Pt particles. It is also found that with increasing degree of graphitization, the electrochemical stability for MWCNTs increases due to the lesser surface defects.     

The Mass Transfer of Proton on Meniscus Nafion/Pt/HOPG Electrode

Proton-exchange membrane fuel cells (PEMFCs) recently have been studied extensively because of their high performance^[1-3]. Since a small contacting area between the platinum catalyst and polymer electrolyte in PEMFCs, the platinum utilization is very important for this kind of cells. In order to improve the platinum utilization, Nafion solution is often impregnated into the gas-diffusion electrodes of PEMFCs. We introduced a partially immersed Nafion-coated electrode, Nafion/Pt/HOPG(highly oriented pyrolytic graphite) as a model electrode in PEMFC, to examine the effects of Nafion coating on the mass transport of hydrogen and proton at the meniscus and supermeniscus formed on the electrodes.     

Activity of platinum-gold alloys for glucose electrooxidation in biofuel cells

Carbon supported Pt-Au catalysts with different bimetallic compositions were prepared by water in oil (w/o) microemulsion. Carbon Vulcan XC-72 was added during the synthesis of particles in order to obtain their good dispersion and a mean particle size distribution of 5.02 +/- 0.56 nm. Structural characterization was performed using XRD at wide angles (WAXS), which showed that Pt-Au particles exhibited alloy properties. Electrochemical characterization allowed to estimate the surface composition of Pt-Au alloys, which was close to that of the bulk material Pt(20)Au(80). This catalyst composition displayed the best catalytic activity in steady-state conditions in comparison with Pt(50)Au(50) or Pt and Au alone. Moreover, a Pt-Au/C catalyst with a metal loading of 40 wt % was immobilized onto a carbon porous tube as anode. A membrane-less biofuel cell was tested using laccase/ABTS biocathode in phosphate buffer (pH 5).     

PEMFC催化剂的研究：自制Pt/C电催化剂的性质

研究了一种用于质子交换膜燃料电池(PEMFC)的自制Pt/C电催化剂(标记为THYT-1)的物理化学和电化学性质.将THYT-1电催化剂与E-TEK公司的同类电催化剂的组成、形态及电催化性能进行了比较.单电池测试结果显示, THYT-1的电催化性能优于E-TEK电催化剂. CV测试结果表明CO在这两种电催化剂上的电氧化性能相近；TEM分析表明两种催化剂上Pt晶粒在炭载体上呈均匀分布，平均粒径均为2～3 nm； XPS和XRD测试结果表明两种催化剂中Pt主要以金属态存在.这些数据表明THYT-1催化剂的物理化学性质与E-TEK公司的相类似.     

Polyaniline/Platinum Composite Cathode Catalysts Towards Durable Polymer Electrolyte Membrane Fuel Cells

Polymer stabilization proved to be a promising approach to increase the catalytic performance of common platinum/carbon based cathode catalysts (Pt/C) used in polymer electrolyte membrane fuel cells (PEMFCs). Platinum and polyaniline composite catalysts (Pt/C/PANI) were prepared by combining chemical polymerization reactions with anion exchange reactions. Electrochemical ex-situ characterizations of the decorated Pt/C/PANI catalysts show high catalytic activity toward the oxygen reduction reaction (ORR) and, more importantly, a significant enhanced durability compared to the undecorated Pt/C catalyst. Transmission electron microscopy (TEM) investigations reveal structural benefits of Pt/C/PANI for ORR catalysis. All studies confirm high potential of Pt/C/PANI for practical fuel cell application.     

Degradation Investigation of Electrocatalyst in Proton Exchange Membrane Fuel Cell at a High Energy Efficiency

The development of high efficient stacks is critical for the wide spread application of proton exchange membrane fuel cells (PEMFCs) in transportation and stationary power plant. Currently, the favorable operation conditions of PEMFCs are with single cell voltage between 0.65 and 0.7 V, corresponding to energy efficiency lower than 57%. For the long term, PEMFCs need to be operated at higher voltage to increase the energy efficiency and thus promote the fuel economy for transportation and stationary applications. Herein, PEMFC single cell was investigated to demonstrate its capability to working with voltage and energy efficiency higher than 0.8 V and 65%, respectively. It was demonstrated that the PEMFC encountered a significant performance degradation after the 64 h operation. The cell voltage declined by more than 13% at the current density of 1000 mA cm⁻², due to the electrode de-activation. The high operation potential of the cathode leads to the corrosion of carbon support and then causes the detachment of Pt nanoparticles, resulting in significant Pt agglomeration. The catalytic surface area of cathode Pt is thus reduced for oxygen reduction and the cell performance decreased. Therefore, electrochemically stable Pt catalyst is highly desirable for efficient PEMFCs operated under cell voltage higher than 0.8 V.     

壳聚糖修饰炭黑负载Pt-Au催化剂对甲醇氧化的电催化性能

以炭黑及自制的壳聚糖-炭黑(CHI-C)复合材料为载体,采用溶胶负载法制备了Pt_m＾Au/C及Pt_m＾Au/CHI-C催化剂(＾ 代表Au、Pt为分步负载,m代表Pt/Au原子比),通过紫外-可见吸收光谱、X射线衍射、透射电镜及X射线光电子能谱对催化剂进行了表征。利用循环伏安法和计时电流法分别测定了Pt-Au催化剂对甲醇电催化氧化反应的活性和稳定性,考查了Pt/Au原子比及CHI改性对电催化活性和稳定性的影响。结果表明,Pt_1.0＾Au/C具有最高的催化活性,炭黑中加入少量CHI能提高Pt_1.0＾Au/C催化剂的稳定性。     

无机胶体法制备Pt/C催化剂及其性能表征

采用无机胶体法制备用于质子交换膜燃料电池(PEMFC)的Pt/C催化剂。研究了影响PtO₂胶体生成和稳定性的因素(溶液的pH值、浓度和温度条件等)以及不同还原剂浓度对Pt/C催化剂性能的影响。透射电子显微镜测试结果表明，采用经优化的工艺条件所制备的Pt/C催化剂平均粒径为3 nm，且分散性好、粒度均匀。X-射线衍射分析表明，催化剂中Pt(111)晶面的相对含量较高，有利于加速氧还原反应。单体PEMFC的电压/电流密度曲线测试表明，所制备的Pt/C催化剂具有良好的电化学性能。     

High-performance hydrogen fuel cell using nitrate reduction reaction on a non-precious catalyst

The H(2)-NO(3)(-) electrochemical cell using nitrate reduction on a non-precious cathode catalyst shows much improved efficiency despite ～75% reduction of Pt metal loading as compared to typical PEMFCs using typical ORR on precious catalysts.     

Pt纳米催化剂在质子交换膜燃料电池催化层中的尺寸效应研究

以XC-72碳黑为载体, H2[PtCl6]为前驱体, 采用浸渍还原法并结合后续高温处理, 制备出不同尺寸Pt颗粒(3～8 nm)的Pt/C催化剂. 在基于质子交换膜燃料电池(PEMFC)单电池的电化学电解池中, 对实际PEMFC催化层中燃料电池反应的Pt催化剂尺寸效应进行了研究. 结果表明, 在PEMFC催化层环境中, Pt/C纳米催化剂对氢氧化和氧还原反应均有显著的粒度尺寸效应. 随着Pt粒度减小, 氢氧化和氧还原反应的表面积活性均降低.     

S‐Doping of an Fe/N/C ORR Catalyst for Polymer Electrolyte Membrane Fuel Cells with High Power Density

Fe/N/C is a promising non‐Pt electrocatalyst for the oxygen reduction reaction (ORR), but its catalytic activity is considerably inferior to that of Pt in acidic medium, the environment of polymer electrolyte membrane fuel cells (PEMFCs). An improved Fe/N/C catalyst (denoted as Fe/N/C‐SCN) derived from Fe(SCN)₃, poly‐m‐phenylenediamine, and carbon black is presented. The advantage of using Fe(SCN)₃ as iron source is that the obtained catalyst has a high level of S doping and high surface area, and thus exhibits excellent ORR activity (23 A g^?1 at 0.80 V) in 0.1 M H₂SO₄ solution. When the Fe/N/C‐SCN was applied in a PEMFC as cathode catalyst, the maximal power density could exceed 1 W cm^?2.     

Study of degradation of membrane-electrode assemblies of hydrogen-oxygen (air) fuel cell under the conditions of life tests and voltage cycling

The degradation processes of HiSPEC 9100 (60% Pt/C) and 13100 (70% Pt/C) cathodic monoplatinum catalysts, which were tested under the model conditions and in the composition of membrane-electrode assemblies (MEA) of hydrogen-air and hydrogen-oxygen fuel cells, are studied. It is shown that, in all cases, the main reason for a decrease in the catalyst activity was a decrease in its surface area, which was caused by the coarsening of platinum nanoparticles, irreversible oxidation of a fraction of active centers, and the destruction of the catalyst due to the carbon support oxidation. The results of electrochemical measurements are supplemented with the structural investigations by the methods of transmission electron microscopy (TEM), X-ray diffraction analysis (XRD), and X-ray photoelectron spectroscopy (XPS). It is found that the degradation processes of MEA in the accelerated stress tests (AST) are similar to those in the long-term life tests. With respect to a decrease in the catalyst active surface area, the application of 2500 cycles in the voltage range of 0.6 to 1.2 V in the AST is equivalent to the life tests for 1010 h. During the fuel cell operation, the destruction of polymer electrolyte proceeds along with the catalyst degradation. This leads to a decrease in the ion-exchange capacity of the membrane and ionomer in the composition of cathode active layer.     

The problem of Ru dissolution from Pt–Ru catalysts during fuel cell operation: analysis and solutions

Platinum–ruthenium catalysts are widely used as anode materials in polymer electrolyte fuel cells (PEMFCs) operating with reformate gas and in direct methanol fuel cells (DMFCs). Ruthenium dissolution from the Pt–Ru anode catalyst at potentials higher than 0.5?V vs. DHE, followed by migration and deposition to the Pt cathode can give rise to a decrease of the activity of both anode and cathode catalysts and to a worsening of cell performance. A major challenge for a suitable application of Pt–Ru catalysts in PEMFC and DMFC is to improve their stability against Ru dissolution. The purpose of this paper is to provide a better knowledge of the problem of Ru dissolution from Pt–Ru catalysts and its effect on fuel cell performance. The different ways to resolve this problem are discussed.     

质子交换膜燃料电池Pt/C阴极氧还原动力学模拟

质子交换膜燃料电池的商业化应用迫切要求降低其Pt载量. 本文通过Pt/C氧还原电极的动力学模型计算,研究了Pt/C电极中的氧分布、生成电流以及满足实际应用的最小Pt载量. 结果表明：燃料电池Pt/C电极,阴极产生严重浓差极化的催化层厚度为40mm;功率密度达到1.4 W•cm^-2（2.1 A•cm^-2@0.67 V）的电池性能需要3mm左右的Pt/C阴极催化层,阴极Pt载量为0.122 mg•cm^-2,即可使膜电极的阴极铂用量低于0.087 g•kW^-1.     

Effect of water electrolysis catalysts on carbon corrosion in polymer electrolyte membrane fuel cells

A new approach to preventing electrochemical carbon corrosion in the cathode of polymer electrolyte membrane fuel cells (PEMFCs) was developed. The addition of 2 wt % IrO(2) (0.016 mg cm(-2)) to the catalyst layer of the cathode was demonstrated to reduce the electrochemical corrosion of carbon by 76% at 1.6 V(NHE) and 70 °C compared with a commercial Pt/C catalyst of the same Pt loading of 0.4 mg cm(-2) and under the same test conditions. The IrO(2) was shown to behave as a catalyst for water electrolysis, thereby removing water from the catalyst layer, which promoted electrochemical carbon corrosion.     

Mapping Platinum Species in Polymer Electrolyte Fuel Cells by Spatially Resolved XAFS Techniques

There is limited information on the mechanism for platinum oxidation and dissolution in Pt/C cathode catalyst layers of polymer electrolyte fuel cells (PEFCs) under the operating conditions though these issues should be uncovered for the development of next‐generation PEFCs. Pt species in Pt/C cathode catalyst layers are mapped by a XAFS (X‐ray absorption fine structure) method and by a quick‐XAFS(QXAFS) method. Information on the site‐preferential oxidation and leaching of Pt cathode nanoparticles around the cathode boundary and the micro‐crack in degraded PEFCs is provided, which is relevant to the origin and mechanism of PEFC degradation.     

Pd-based PdPt(19:1)/C electrocatalyst as an electrode in PEM fuel cell

A carbon supported Pd-based PdPt catalyst with a Pd:Pt atomic ratio of 19:1 was synthesized and applied to a polymer electrolyte membrane fuel cell (PEMFC). Three different types of single cells with the electrodes containing (PdPt/C:Pt/C), (Pt/C:PdPt/C) and (PdPt/C:PdPt/C) as their anode and cathode electrocatalysts were fabricated and the performance of them was compared. The single cell using PdPt/C as the anode electrocatalyst showed a high performance comparable to the cell with a commercial Pt/C electrocatalyst. This indicates that Pd-based electrocatalysts can be used as an anode electrocatalyst in PEMFC with very small amount of Pt (just about 5 at.%).     

脉冲微波辅助化学还原合成Pt/C 催化剂及其电催化氧还原性能

采用脉冲微波辅助化学还原法制备了质子交换膜燃料电池(PEMFC)用Pt/C 催化剂. 通过透射电镜(TEM)和X射线衍射(XRD)等分析技术对催化剂的微观结构和形貌进行了表征, 并利用循环伏安(CV)、线性扫描(LSV)和恒电位测量等方法评价了催化剂催化氧还原性能. 在此基础上制备了膜电极(MEA)并组装成单电池, 考察了制备的Pt/C 催化剂作为阴极催化剂材料的电催化性能. 结果表明, 脉冲微波辅助化学还原法是一种制备PEMFC催化剂的有效方法, 溶液pH值和微波功率对Pt 颗粒直径和分散有重要影响. TEM和XRD结果显示, 当溶液pH值为10 且微波功率为2 kW时, Pt 纳米粒子较均匀地分散在碳载体上, 粒径分布在1.3-2.4 nm之间, 平均粒径为1.8 nm. CV、LSV和恒电位测试结果表明, 该催化剂电化学比表面积(ESA)为55.6 m²·g^-1, 具有良好的催化氧还原反应活性和稳定性. 单电池测试结果表明, 在溶液pH值为10条件下, 微波功率为2 kW时制备的催化剂作阴极催化剂时, 单电池最高功率密度为2.26 W·cm^-2·mg^-1, 高于微波功率为1 kW时的最高功率密度(2.15 W·cm^-2·mg^-1)和Johnson Matthey催化剂的最高功率密度(1.89 W·cm^-2·mg^-1).     

The ethanol electrooxidation at Pt layers deposited on polycrystalline Au

The ethanol electro-oxidation reaction was evaluated using a polycrystalline Au substrate modified with two different amounts of Pt using the galvanic exchange methodology. FTIR results suggest that Pt deposits have a greater ability to break the C-C bond present in the ethanol molecule. However, under potentiostatic conditions both modified Au surfaces undergo faster deactivation in comparison with polycrystalline platinum as indicated by the chronoamperometric results. XPS results indicate the presence of two phases depending on the Pt content. These are: (i) Pt-Au alloy and (ii) segregated Pt. The structural and electronic properties of these phases were related to the differences observed in the catalytic activity.