调制脉冲电沉积法制备质子交换膜燃料电池铂催化电极

通过调制脉冲电流在质子交换树脂(Nafion)粘接的无催化多孔碳电极(UCE)上电沉积Pt 催化剂, 对所沉积Pt 催化电极性能及负载量用循环伏安法(CV)、X 射线衍射仪(XRD)、透射电镜(TEM)及分光光度法进行了表征. 结果表明, 通过调制电沉积过程的脉冲参数, 能够实现质子交换膜燃料电池(PEMFC)电极Pt催化剂的直接电化学沉积, 能够调控电沉积Pt粒径, 并能有效地缓解电沉积过程中析氢对沉积金属催化剂铂的干扰, 所沉积的Pt 催化剂利用率较传统Nafion 粘接Pt/C催化电极要高. 脉冲导通时间ton 为300 μs、断通时间toff 为1200 μs, 脉冲峰值电流密度jp 为100 mA·cm-2 时, 电沉积120 s制得的电极的Pt 晶粒约5-8 nm, Pt 表面利用率为43.14%, 沉积Pt的电流效率为45%.     

Effect of cosintering of anode–electrolyte bilayer on the fabrication of anode-supported solid oxide fuel cells

A comparative study is carried out on the effect of cosintering temperature of anode–electrolyte bilayer on the fabrication and cell performance of anode-supported solid oxide fuel cells from commercially available tape casting materials. It was found that the sintering conditions have profound effects on the anode characteristic and cell performance. For low cosintering temperature as low as 1,250 °C, the electrolyte is unable to sinter fully and forms a porous structure which leads to a reduced open-circuit potential and poor cell performance especially under low current output. For further increasing cosintering temperature to 1,350 °C, the cell performance was lower under low current operation. However, the cell performance turns out to be better than that of high-temperature cosintering under high current output. Although at temperature as high as 1,500 °C the cell performs better than that of low temperature cosintering, the trend turn out to be reverse for high current operating due to less anode surface area resulting from overagglomeration of anode layer. An optimal cosintering temperature of 1,350–1,450 °C is recommended for commercially available anode–electrolyte bilayer of anode-supported solid oxide fuel cells.     

Does power ultrasound affect Nafion® dispersions?

The effect of low frequency power ultrasound on Nafion® ionomer used for fabricating proton exchange membrane fuel cell (PEMFC) and water electrolyzer (PEMWE) catalyst inks was investigated. In this study, a series of Nafion® dispersions having three concentrations (10, 5, and 2.5% w/v) were studied under various irradiation durations (t_us), at fixed ultrasonic frequency (f = 42 kHz) and ultrasonic power (P > 2 W), under either controlled or unregulated bulk solution temperature conditions using a laboratory ultrasonic cleaning bath. Viscosity (η), thermal degradation, and glass transition temperature (T_g) for all Nafion® dispersion samples was measured and compared to untreated Nafion® samples. In our conditions, it was found that power ultrasound lowered the viscosity of all tested Nafion® dispersion samples; whilst thermogravimetric and differential scanning calorimetry analyses showed that for all ultrasonically irradiated samples, a negligible overall polymer degradation and no obvious change in T_g was observed under controlled and unregulated bulk temperature conditions. It was found that it is possible that acoustic cavitation causes depolymerisation followed by a polymerisation initiation step during ultrasonication. By comparing the ultrasonically treated and high-shear mixed samples, it was also observed that acoustic and hydrodynamic cavitation played an important role in the reduction of dispersion viscosity.     

正交设计法优化PEMFC催化层的最佳配比

利用正交实验设计法优选PEMFC电极催化层制备的最佳条件.实验证实亲水电极(催化层中不含PTFE)性能优于疏水电极.在该工艺条件下,当Nafion的含量为1.4mg·cm-2,Pt含量为0.4mg·cm-2时,以常压的H2和空气分别作为燃料气和氧化剂,电池的最高功率可达到0.37W·cm-2.研究表明,提高Pt/C中的Pt含量将是提高催化剂性能的有效途径.     

Advanced nanostructure Ti0.7In0.3O2 support enhances electron transfer to Pt: Used as high performance catalyst for oxygen reduction reaction

ABSTRACT

The slow rate of the oxygen reduction reaction (ORR) and the instability of Pt based catalysts are two of the most important issues which must be solved in order to make proton exchange membrane fuel cells (PEMFCs) a reality. Here, we present a new approach by exploring robust non-carbon Ti_0.7In_0.3O₂ used as a novel functionalised co-catalytic support for Pt. This approach is based on the novel nanostructure Ti_0.7In_0.3O₂ support with “electronic transfer mechanism” from Ti_0.7In_0.3O₂ to Pt that can modify surface electronic structure of Pt, owing to a shift in the d-band centre of the surface Pt atoms. The 20 wt% Pt/Ti_0.7In_0.3O₂ catalyst shows high activity than that of that of the commercial 20 wt% Pt/C (E-TEK). Our data suggest this enhancement is a result of both the electronic structure change of Pt upon its synergistic interaction with Ti_0.7In_0.3O₂ and the inherent structural and chemical stability and the corrosion-resistance of the Ti_0.7In_0.3O₂ in acidic and oxidative environments.     

质子交换膜燃料电池动态特性仿真

建立了质子交换膜燃料电池数学模型,并进行了仿真实现,计算分析了质子交换膜燃料电池典型动态特性和温度对其工作状况的影响.结果表明PEMFC内气体传质速度是影响电压响应时间的决定因素,扩散层内液态水的积累需要较长的时间,数量级在102～103,温度升高会降低PEMFC的动态响应时间并提高电池的输出功率,温度超过80°C后会降低电池的输出性能.     

质子交换膜燃料电池的水平衡

水平衡是制约质子交换膜燃料电池（PEMFC）性能稳定的关键技术之一。本文针对以H2为燃料的PEMFC的水平衡,首先介绍了电池的工作原理及水迁移;通过实验,证明了电池失水、积水对电池性能及寿命的影响,说明了水平衡的重要性;从电池的组成结构及运行参数详细讨论了影响水平衡的主要因素;并对电池水平衡的管理方法作了讨论。     

Preparation of Nafion/PTFE/Zr(HPO4)2 composite membranes by direct impregnation method

The viscosities of as received 5.1 wt.% Nafion solutions (EW = 1100, Du Pont Co) blended with various concentrations of ZrOCl₂ were studied. We show the solution viscosity decreases as the wt. ratio of [ZrOCl₂]/[Nafion] is increased from 0.0 to 0.03, then the viscosity does not change significantly as the wt. ratio of [ZrOCl₂]/[Nafion] is increased from 0.03 to 0.16, and then the viscosity increases dramatically as the wt. ratio of [ZrOCl₂]/[Nafion] is increased above 0.16. Four Nafion solutions consisting of 5.1 wt.% Nafion and ZrOCl₂ with [ZrOCl₂]/[Nafion] wt. ratios of 0.019–0.24 were used with porous poly(tetrafluoroethylene) (PTFE) film to prepare zirconium hydrogenphosphate (ZrP) hybridized Nafion/PTFE (NF–ZrP) composite membranes by direct impregnating porous PTFE in Nafion/ZrOCl₂ solutions. The influence of [ZrOCl₂]/[Nafion] wt. ratio of Nafion/ZrOCl₂ solution on the membrane morphology of NF–ZrP and polyelectrolyte membrane fuel cell (PEMFC) performance at temperatures of 110–130 °C with relative humidity of 51.7–28.8% RH was investigated.     

Characterization of CO tolerance of PEMFC by ac impedance spectroscopy

The CO tolerance of a proton exchange membrane fuel cell (PEMFC) was investigated by ac impedance spectroscopy. The impedance of the fuel cell could be obtained by feeding oxygen into the cathode side and simulated gas into anode side. Furthermore, the anode impedance could be obtained by feeding hydrogen into the cathode side and simulated gas into anode side. The CO gas had a greater effect on the charge transfer reaction (high frequency arc) and hydrogen dissociative chemisorption (medium frequency arc) but little effect on the low frequency arc. Although the cathode impedance is a main part at high temperature, irrespective of CO concentration (≤100 ppm), the impedance of the full cell depends on anode impedance at low temperature and high CO concentration. It was found that CO gas has little effect on cathode impedance.     

Electrochemical and impedance spectroscopy studies in H2/O2 and methanol/O2 proton exchange membrane fuel cells

This works report results of the structural and the electrochemical characterization of membrane electrode assemblies (MEA) for proton exchange membrane fuel cells (PEMFC) under various cell conditions using different MEA production processes. Electrochemical impedance spectroscopy (EIS) was applied “on-line” (in situ) as a tool for diagnosis concerning the cell performance. MEA with a 25-cm² surface area were prepared using Pt/C and Pt–Ru/C commercial electrocatalysts from E-TEK and Pt–Ru/C electrocatalysts produced by the alcohol reduction process. The catalytic ink was applied directly onto the carbon cloth or, alternatively, onto the Nafion® membrane. Two carbon cloth thicknesses were tested as diffusion layers in the MEA: 0.346 mm (common) and 0.424 mm (ELAT). An increase of the electrocatalytic activity can be obtained by pH control in the alcohol reduction process, possibly due to the better particle dispersion and the smaller particle sizes observed. In addition, a slower current decay in the ohmic region was observed using the thinner carbon cloth. This can be related to a lower resistance of the gas flow through the cloth to the catalytic active layer. Different types of methanol feed were employed in the experiments: by humidification and by evaporation. The results showed that the choice of suitable methods for catalyst preparation as well as for MEA production enhance PEMFC performance.