PEMFC膜电极电催化层的制备和性能

膜电极催化层的组成和电催化剂的活性对质子交换膜燃料电池的性能有很大影响．采用浸渍还原法制备出了Pt平均粒径为3．1nm的Pt／C催化剂．催化剂中Pt的粒径和在碳黑载体（VulcanXC-72）表面的分散程度采用透射电镜（TEM）进行测试．用Pt／C催化剂、适量的Nation溶液和PrFE乳液制备出质子交换膜燃料电池（PEMFc）膜电极的催化剂层,并研究了该催化剂层中PTFE含量对其性能的影响．实验表明,PTFE强烈的疏水性可以迫使部分水分向阳极反扩散,催化层中加入适量的PTFE可以使膜电极具有一定的水管理能力,在去掉辅助增湿系统的条件下具有良好的极化性能．     

质子交换膜燃料电池膜电极的结构优化

膜电极(membrane electrode assembly,MEA)是质子交换膜燃料电池(proton exchange membrane fuel cell,PEMFC)的核心部件,为PEMFC提供了多相物质传递的微通道和电化学反应场所。为了实现燃料电池商业化目标,需要制备高功率密度、低Pt载量、耐久性好的MEA。在MEA中除了催化剂以外,各功能层结构、层与层之间的界面都对MEA的性能具有重要影响。传统方法(CCS法和CCM法)制备的MEA在结构上有很多缺陷,明显制约了Pt的利用率和系统传质能力。通过优化各功能层结构消除缺陷,将有利于进一步提升PEMFC综合性能。本文从传统MEA结构存在的问题出发,梳理了近年来关于催化层、质子交换膜和气体扩散层结构优化方面的文献,归纳总结了各先进结构的制备方法、构效关系以及优缺点,对未来高性能、低成本和长寿命的MEA的开发具有指导意义。     

质子交换膜燃料电池CCM的制备条件对其性能的影响

采用催化剂涂覆的膜(CCM)和碳纸扩散层组成质子交换膜燃料电池的膜电极.CCM采用直接喷涂的方法制备,研究了与直接喷涂技术相关的影响因素,包括催化层中Nafion的含量和分布、有机溶剂的种类、喷涂操作条件等.CCM的表面形貌和孔结构采用扫描电镜(SEM)方法表征,MEA的电化学特性通过单体PEMFC的I-V曲线进行评价.实验结果表明,在优化条件下制备的CCM膜电极的结构和性能有明显的改善.     

Synthesis and characterization of Nafion/TiO2 nanocomposite membrane for proton exchange membrane fuel cell

In this study, the syntheses and characterizations of Nafion/TiO2 membranes for a proton exchange membrane fuel cell (PEMFC) were investigated. Porous TiO2 powders were synthesized using the sol-gel method; with Nafion/TiO2 nanocomposite membranes prepared using the casting method. An X-ray diffraction analysis demonstrated that the synthesized TiO2 had an anatase structure. The specific surface areas of the TiO2 and Nafion/TiO2 nanocomposite membrane were found to be 115.97 and 33.91 m2/g using a nitrogen adsorption analyzer. The energy dispersive spectra analysis indicated that the TiO2 particles were uniformly distributed in the nanocomposite membrane. The membrane electrode assembly prepared from the Nafion/TiO2 nanocomposite membrane gave the best PEMFC performance compared to the Nafion/P-25 and Nafion membranes.     

Investigation of the connectivity of hydrophilic domains in Nafion using electrochemical pore-directed nanolithography

A method of determining the connectivity of ion-conducting hydrophilic channels within the Nafion polymer electrolyte membrane by way of pore-directed nanolithography has been developed. Electrochemical etching of a silicon surface is performed through a Nafion-membrane mask. The resulting silicon surface imaged by tapping-mode atomic force microscopy (TMAFM) provides a footprint of the hydrophilic channels at the Nafion-silicon interface. In a similar fashion, a TMAFM phase-contrast image of the top surface of the Nafion mask prior to etching reveals the spatial distribution of hydrophilic domains at the surface of the polymer membrane. Collectively, these images provide detailed information about the structure of the hydrophilic channels at the top and bottom surfaces of the Nafion membrane. Autocorrelation statistical analysis of these two sets of images shows that only 48% of hydrophilic channels beginning at the Nafion surface connect to the silicon-Nafion interface.     

Nafion/silane nanocomposite membranes for high temperature polymer electrolyte membrane fuel cell

The polymer electrolyte membrane fuel cell (PEMFC) has been studied actively for both potable and stationary applications because it can offer high power density and be used only hydrogen and oxygen as environment-friendly fuels. Nafion which is widely used has mechanical and chemical stabilities as well as high conductivity. However, there is a drawback that it can be useless at high temperatures (> or = 90 degrees C) because proton conducting mechanism cannot work above 100 degrees C due to dehydration of membrane. Therefore, PEMFC should be operated for long-term at high temperatures continuously. In this study, we developed nanocomposite membrane using stable properties of Nafion and phosphonic acid groups which made proton conducting mechanism without water. 3-Aminopropyl triethoxysilane (APTES) was used to replace sulfonic acid groups of Nafion and then its aminopropyl group was chemically modified to phosphonic acid groups. The nanocomposite membrane showed very high conductivity (approximately 0.02 S/cm at 110 degrees C, <30% RH).     

Nanoscale current imaging of the conducting channels in proton exchange membrane fuel cells

The electrochemically active area of a proton exchange membrane fuel cell (PEMFC) is investigated using conductive probe atomic force microscopy (CP-AFM). A platinum-coated AFM tip is used as a nanoscale cathode in an operating PEMFC. We present results that show highly inhomogeneous distributions of conductive surface domains at several length scales. At length scales on the order of the aqueous domains of the membrane, approximately 50 nm, we observe single channel electrochemistry. I-V curves for single conducting channels are obtained, which yield insight into the nature of conductive regions across the PEM. In addition, we demonstrate a new characterization technique, phase current correlation microscopy, which gives a direct measure of the electrochemical activity for each aqueous domain. This shows that a large number ( approximately 60%) of the aqueous domains present at the surface of an operating Nafion membrane are inactive. We attribute this to a combination of limited aqueous domain connectivity and catalyst accessibility.     

再铸Nafion膜的制备与应用

采用溶液－浇铸法用商业化Nafion膜的溶解液制备再铸Nafion膜，对再铸Nafion膜进行了氧气渗透系数测试和电池性能评价，并与厚度相近的商业化Nafion膜进行比较，同时对再铸Nafion膜组装的PEMFC进行了短期稳定性考查，实验结果表明：通过溶液－浇铸法制备的再铸Nafion 膜可以应用于质子交换膜燃料电池，再铸Nafion膜的氧气渗透系数和电池性能与商业化Nafion膜相近，再铸Nafion膜组装PEMFC在150h之内未见电池性能下降。     

膜电极结构对质子交换膜燃料电池性能的影响

膜电极(MEA)作为质子交换膜燃料电池(PEMFC)的核心组件之一，其结构和组成对电池的性能有着重要的影响。提高膜电极性能的一个重要的指导思想是在催化粒子的周围形成良好的质子、电子和气体通道。以此为主线，从电极制备工艺的发展历程，Nafion的使用与质子通道的改进、电子通道的改进、阴极催化等几个方面详细地总结和讨论了近年来MEA的研究状况，并在此基础上对MEA的进一步研究提出了若干建议。     

Optimization of nafion ionomer content using synthesized Pt/carbon nanofibers catalyst in polymer electrolyte membrane fuel cell

In this study, carbon nanofiber (CNF) was used as a support in which 47.5 wt% Pt/CNFs catalyst was prepared by a modified polyol method. The platinum particle size and dispersion on the CNFs are approximately 2-4 nm as determined by X-ray diffractometry and transmission electron microscopy. The specific surface area was approximated as 55.90 m2/g by BET analysis. Electrodes were prepared by the spray method and have a size of 5 cm2. A commercial catalyst (TKK, 46 wt% Pt/C) was used as the anode and the cathode was Pt/CNFs. Different amounts of Nafion ionomer (Aldrich, 5 wt% solution, in the range of 0-20 wt%) were coated on a membrane (Dupont, Nafion 212) with 0.4 mg/cm2 of Pt catalyst at the cathode side. The resulting polarization, ohmic and mass transfer resistances changed significantly based on the Nafion ionomer content. Optimum Nafion ionomer content in the 47.5 wt% Pt/CNFs was 5 wt%. The well-dispersed Nafion ionomer was observed on the catalyst surface area using SEM-EDAX analysis. A sufficient triple-phase boundary was formed by a small amount of Nation ionomer due to the BET surface area of the Pt/CNFs.     

聚四氟乙烯膜表面的苯胺聚合沉积亲水改性研究

采用苯胺(An)分散聚合原位成膜的方法对等离子体预处理的聚四氟乙烯(PTFE)多孔膜进行亲水化改性,实验通过SEM、接触角测量等表征了PTFE膜的结构和表面亲水性质.试验结果表明,FTFE膜表面是内部留有孔道的纤维交织结构,有较强的疏水性;等离子体处理使聚合峰值提前,后期聚合速率增大,有利于An在PTFE膜的表面聚合沉积.接触角测试表明PANI/PTFE复合膜比原始膜的亲水性有了较好的改观.     

燃料电池用全氟磺酸型复合质子交换膜的研究

本文评述了用于质子交换膜燃料电池的几种全氟磺酸型复合质子交换膜的研究情况。根据这几种膜的制备工艺 ,评价了它们的优、缺点 ,以及在燃料电池上的潜在使用能力和性能 ,预示了燃料电池用质子交换膜的发展方向     

Reversed-phase membrane inlet mass spectrometry applied to the real-time monitoring of low molecular weight alcohols in chloroform.

Reversed-phase membrane inlet mass spectrometry incorporating a hollow-fiber Nafion membrane has been evaluated for the determination of low molecular weight alcohols in chloroform. The hydrophilic Nafion membrane preferentially transports methanol and ethanol, allowing percentage concentrations of the alcohols to be determined in a chloroform matrix. A linear response was observed for ethanol over the working range 0.5-2.5%, with a limit of detection of 0.1%. The application of reversed-phase membrane inlet mass spectrometry using a Nafion membrane to the monitoring of a chloroform recovery process has been investigated using a residual gas analyzer. Evolving methanol and ethanol concentrations were determined in real time and compared favorably with off-line determinations by gas chromatography.     

New electrocatalysts for unitized regenerative fuel cell: Pt-Ir alloy deposited on the proton exchange membrane surface by impregnation-reduction method

In this paper, a modified technique to prepare Pt-Ir catalyst layer on the proton exchange membrane (PEM) surface using the impregnation-reduction (IR) method is proposed to improve the electrocatalytic activity as well as the life cycle of the bifunctional oxygen electrode (BOE). The resulted electrocatalysts were characterized by the Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), Electron Probe Micro-Analysis (EPMA), and Transmission Electron Microscope (TEM). The electrocatalytic properties of the Pt-Ir layer on PEM surface for the oxygen reduction and water oxidation reactions as well as the life cycle of MEA were investigated. Experimental results showed that the Ir particles were dispersed densely in the platinum layer through the modified IR technique. The atomic ratio of Pt over Ir elements was 9:1, and the resulted thickness of the obtained Pt-Ir catalyst layer was about 1.0 microm. The Pt-Ir catalyst layer was composed of Pt layer doped with Ir nano-particles comprising nano Pt-Ir alloy phase. The large surface area of Ir core with Pt shell particles and the presence of nano Pt-Ir alloy phase led to a higher electrocatalytic activity of BOE. Due to the good binding between the Nafion membrane and the Pt-Ir alloy catalyst, as well as the composite structure of the resulted Pt-Ir, the life cycle of Unitized Regenerative Fuel Cell (URFC) is improved through this novel BOE.     

燃料电池用新型质子交换膜的研究进展

质子交换膜燃料电池(PEMFC)以其高效、清洁、高能量密度和高功率密度等诸多优点正引起人们越来越多的关注和研究．目前,质子交换膜是制约PEMFC技术应用的一个主要问题．为此,开发性能良好、成本经济的新型质子交换膜是一项很有意义的工作、综述了近几年国内外在新型质子交换膜(包括全氟磺酸膜、部分含氟磺酸膜、非氟质子交换膜)方面的研究进展．     

Pt nanoparticle-reduced graphene oxide nanohybrid for proton exchange membrane fuel cells

A platinum nanoparticle-reduced graphene oxide (Pt-RGO) nanohybrid for proton exchange membrane fuel cell (PEMFC) application was successfully prepared. The Pt nanoparticles (Pt NPs) were deposited onto chemically converted graphene nanosheets via ethylene glycol (EG) reduction. According to the powder X-ray diffraction (XRD) pattern and transmission electron microscopy (TEM) analysis, the face-centered cubic Pt NPs (3-5 nm in diameter) were homogeneously dispersed on the RGO nanosheets. The electrochemically active surface area and PEMFC power density of the Pt-RGO nanohybrid were determined to be 33.26 m2/g and 480 mW/cm2 (maximum values), respectively, at 75 degrees C and at a relative humidity (RH) of 100% in a single-cell test experiment.     

Composite endplates with pre-curvature for PEMFC (polymer electrolyte membrane fuel cell)

A conventional PEMFC (polymer electrolyte membrane fuel cell) stack is composed of multiple stack composed of GDL (gas diffusion layer), MEA (membrane electrode assemblies), and bipolar plates sandwiched in between two thick metallic endplates tightened by bands or tie-bolts as to maintain proper contact pressure on its active area and gasket interface. The proper contact pressure distribution in a stack offers low contact resistance for high energy efficiency and fluid leakage prevention as well. For which, the endplates should have proper structural stiffness.     

Pt‐Based Nanocrystal for Electrocatalytic Oxygen Reduction

Currently, Pt‐based electrocatalysts are adopted in the practical proton exchange membrane fuel cell (PEMFC), which converts the energy stored in hydrogen and oxygen into electrical power. However, the broad implementation of the PEMFC, like replacing the internal combustion engine in the present automobile fleet, sets a requirement for less Pt loading compared to current devices. In principle, the requirement needs the Pt‐based catalyst to be more active and stable. Two main strategies, engineering of the electronic (d‐band) structure (including controlling surface facet, tuning surface composition, and engineering surface strain) and optimizing the reactant adsorption sites are discussed and categorized based on the fundamental working principle. In addition, general routes for improving the electrochemical surface area, which improves activity normalized by the unit mass of precious group metal/platinum group metal, and stability of the electrocatalyst are also discussed. Furthermore, the recent progress of full fuel cell tests of novel electrocatalysts is summarized. It is suggested that a better understanding of the reactant/intermediate adsorption, electron transfer, and desorption occurring at the electrolyte–electrode interface is necessary to fully comprehend these electrified surface reactions, and standardized membrane electrode assembly (MEA) testing protocols should be practiced, and data with full parameters detailed, for reliable evaluation of catalyst functions in devices.     

Progress in modified carbon support materials for Pt and Pt-alloy cathode catalysts in polymer electrolyte membrane fuel cells

H₂-fed polymer electrolyte membrane fuel cells (PEMFCs) are the most advanced fuel cell technology to date and continue to be of great interest as prospective energy sources in numerous applications, including for low/zero-emission electric vehicles, distributed power generators in homes, and small portable electronic devices. However, the commercialization of PEMFC technology has been greatly hindered by certain challenges, mainly the sluggish kinetics of the oxygen reduction reaction at the cathode and the high cost of Pt-based cathode catalysts, the latter presently accounting for over 55% of the total PEMFC cost. To overcome the limited stability of state-of-the-art Pt/C, Pt and Pt-alloy catalysts supported on modified carbon materials have garnered significant interest in recent years. It is therefore timely to compile a review that focuses on Pt and Pt-alloy catalysts supported on modified carbon materials, examining their current R&D status, applications, challenges, and future prospects. This review provides a systematic and comprehensive survey of current Pt and Pt-alloy PEMFC cathode catalysts in terms of materials selection and design, synthesis methods, and structural features, emphasizing how these various aspects relate to the catalysts’ physicochemical characterization and performance, and with the aim of shedding light on the future direction of PEMFC research.     

Fully Packaged Nonenzymatic Glucose Microsensors With Nanoporous Platinum Electrodes for Anti-Fouling

CMOS integrable nonenzymatic glucose microsensors with nanoporous platinum (Pt) working and counter electrode (WE/CE) were first fabricated, packaged, and characterized with biocompatible Nafion and hydrophilic polyurethane (HPU) membrane materials. Optimal packaging material and its processing condition for these nonenzymatic sensors were investigated. The optimally packaged glucose microsensor was evaluated in human blood plasma solution for checking its biocompatibility and commercial applicability. The fabricated microsensors with nanoporous Pt WE/CE had a sensitivity of 7.75 $mu$A mM $^{-1}$ cm $^{- 2}$. The packaged microsensor with Nafion membrane had better performance characteristics than packaged one with HPU. The packaged microsensor with 1:6 ratio of Nafion to ethanol exhibited a sensitivity of 0.83 $mu$ A mM$^{- 1}$ cm$^{-2}$ and stable current change in the human blood plasma solution, while the current response of nonpackaged microsensor was rapidly saturated because adsorption of various proteins and cells as expected. These data indicate that the packaged nonenzymatic microsensor with biocompatible Nafion membrane is promising and strongly applicable for in vitro and in vivo glucose monitoring systems.