直接甲醇燃料电池两相非等温模型

本文建立了直接甲醇燃料电池的两相、非等温模型.采用多孔介质中的经典多相流动模型来计算电池内与电化学反应相耦合的传质、传热问题;模型中考虑了水的汽化凝结过程和甲醇窜流对电池性能的影响.计算结果表明电池内温度分布不均匀,温度最高点出现在阴极催化层;阳极甲醇浓度分布不均匀是造成阳极催化层内局部反应速率不均匀分布的主要原因,而阴极催化层局部反应速率主要依赖于阴极过电势的分布;大的流场板开口比条件下电池整体均匀性较好,性能得到提高.     

直接甲醇燃料电池反应和组分传递的模型计算

本文建立了直接甲醇燃料电池的二维、单相数学模型来研究电池内各种场的分布情况.模型中考虑了与电化学反应相伴随的、与流体动力学相关的反应与物料传递的耦合过程以及甲醇串流对阴极反应的影响;对阳极和阴极催化层传质过程引入了团聚块模型进行修正.计算了电池内的反应组分浓度分布和局部电流分布以及催化层沿长度方向的局部过电势分布,分析丁催化层内反应的非均匀性.在此基础上考察了对电池流场板结构的改进方案:减小集流板肋条宽度以及在肋条过窄时引入金属泡沫代替电池流场板和扩散层对电池性能的影响,通过对比计算表明两种改进均可以使得催化层反应均匀化,使电池输出性能得到提高,后者效果更佳.     

PEM燃料电池内水分布和温度分布的数值模拟

本文建立了一个两相流、非等温、三维模型来研究PEM燃料电池内的传递过程,讨论了其内部水分布和温度分布特性。模拟结果表明水分布和温度分布都不均匀。沿着流动方向阳极侧水浓度逐渐降低,而阴极侧水浓度却不断升高,导致阴极容易形成液态水;在垂直流动方向上,脊下水的浓度和液态水饱和度都高于流道下;不同放电电压下阴极GDL中液态水分布趋势不同。沿流动方向温度逐渐降低,反应气体不足时降低梯度更大;脊下膜电极中温度低于流道下;垂直膜电极方向上最高温度在阴极催化层,放电电压越低,温度梯度越大;相同放电电压下质子交换膜越厚,各处的温度越低,温度梯度也越小。     

基于非铂无膜阴极直接甲酸燃料电池性能特性

本文通过采用天然管状材料制备了一种非铂无膜的空气自呼吸一体式阴极。该电极实现了传统电极中的支撑层、气体扩散层和催化层的功能,因而省去了质子交换膜并简化了燃料电池阴极的制备工艺。基于上述阴极和镀Pd石墨棒阳极,本文构建了无膜管状自呼吸式直接甲酸燃料电池。文中还对阳极液酸碱性、支持电解质浓度、甲酸根浓度和阳极液流速对电池性能的影响特性进行了研究,结果表明,当阳极液采用0.5 mol/L HCOONa+4.0 mol/L KOH,流速为756μL/min时,电池可获得最大功率密度0.73 mW/cm~3。     

基于高氢气利用率的质子交换膜燃料电池运行特性研究

为了提高氢气利用率本文对氢氧燃料电池在不同的阳极进口压力、阴极过量系数以及工作温度下进行阳极长时间闭口运行,考察阳极闭口对电池性能的影响。在每个操作条件运行期间阳极电池阀均未中途打开(单个操作条件最长运行时间26 h),氢气利用率达100%。结果表明:氢氧燃料电池除了在低阴极过量系数且高电流密度之外在其它各工况下阳极闭口能长时间稳定运行。膜电极分区域断面SEM测试表明出口处附近区域阳极和阴极催化层均有所减薄而其它区域膜电极催化层均没有受到影响。这表明电池出口附近碳腐蚀造成的催化层减薄与电池出口附近处水淹是有必然联系的。     

过硫酸钾为电子受体的微生物燃料电池性能特性

本文采用过硫酸钾作阴极电子受体,阳极室接种厌氧活性污泥,构建了"H"型微生物燃料电池(MFC),并对电池产电性能进行了实验研究.结果表明,附着在阳极电极表面的生物膜对MFC的产电起着关键性的作用,电池性能随着阴极侧电解质溶液pH值降低而提高,随着过硫酸钾浓度增大而提高.电池的开路电压及最高输出功率在以过硫酸钾做电子受体时都要显著高于常用的铁氰酸钾电子受体.     

直接甲醇燃料电池膜及阴极模拟

本文提出一个针对直接甲醇燃料电池膜及阴极的二维、多组分稳态数学模型．模型根据直接甲醇膜燃料电池膜及阴极运行工况特性,考虑质量、动量、组分守恒以及电池中的电化学过程而建立,并应用了计算流体动力学(CFD)技术．模拟结果表明传质对直接甲醇燃料电池的性能影响很大;本文还进行了直接甲醇燃料电池阴极水管理的初步探讨．     

PEM燃料电池中的两相传质及其影响

建立了一个新的二维、两相流模型来研究质子交换膜(PEM)燃料电池中的两相传质及其对质子膜阻抗和阴极性能的影响。模型不仅将催化剂层(CL)包含在电极中,还考虑了电池中相变及其对传质的影响。模型可同时使用在电池的阴极和阳极。主要模拟了电池阴极中两相传质、质子膜阻抗、阴极有效孔隙率和电流密度。模拟结果显示,提高加湿温度可以降低质子膜的阻抗,但过高的加湿温度会降低阴极气体扩散层(GDL)的有效孔隙率,降低阴极的性能。     

直接甲醇燃料电池热传递数值模拟

本文建立了二维两相非等温的直接甲醇燃料电池(DMFC)模型,综合考虑了DMFC中的电化学反应、热传递、组分传递和甲醇串流。计算了电池内的温度分布、不同电流密度下的膜电极内部最大温差和膜电极平均温度;在此基础上研究了环境和甲醇进口浓度对电池性能、膜电极内平均温度和最大温差的影响。结果表明:膜电极内阴极的温度高于阳极;甲醇进口浓度的上升导致膜电极内平均温度和最大温差上升;环境对电池性能的影响很小。     

PEM燃料电池内液态水和温度分布特性

水和热的管理对PEM燃料电池的性能具有决定性的作用.本文建立了一个两相流模型,对PEM燃料电池换质子交换膜和阴极中的水分和温度进行了模拟,分析了燃料电池阴极中液态水和质子交换膜中水分,以及阴极催化剂层和质子交换膜中温度的分布状态.模拟结果显示:升高加湿温度,电池阴极中的液态水和质子交换膜中的含水量显著增加;沿着气体流动方向,燃料电池内的温度降低,水分含量升高;从质子交换膜阳极侧到阴极催化剂层中,温度先升高,达到最大值后,渐渐降低.     

Effects of flow field design on water management and reactant distribution in PEMFC: a review

The performance of a proton exchange membrane fuel cell (PEMFC) stack is affected by many factors, including the operating conditions, flow field and manifold design, and membrane performance. To achieve the desired PEMFC performance, the reactant must be uniformly distributed and effectively diffused into the catalyst layer for the electrochemical reaction. Water management and reactant distribution in fuel cells are crucial because they affect the distribution and diffusion rate of the reactant. This paper reviews the important research results reported in recent years related to the effects of water and reactant distribution on the performance and life span of PEMFC stacks.     

Electrostatic spraying of membrane electrode for proton exchange membrane fuel cell

In order to improve the performance of proton exchange membrane fuel cell (PEMFC), the optimization of electrostatic spraying of membrane electrode was conducted. The influence of the spraying voltage on morphology, elemental composition of catalyst layer, and performance of the PEMFC were investigated. The results show that increasing spraying voltage could reduce agglomeration of the carbon-supported platinum particles, leading to more uniform pore distribution. High voltage did not accelerate oxidation of platinum catalyst. A high electrochemical active surface area of 26.18 m²/g_pt was obtained when the platinum-carbon catalyst layer was deposited in cone jet mode. With further increasing spraying voltage, the total ohmic resistance and catalytic activity were changed slightly, whereas the charge transfer resistance was increased. Using the optimized electrostatic spraying parameters (injection rate = 100 μL min⁻¹, spraying voltage = 8.5 kV, and working distance = 12 mm), a peak power density of 1.408 W cm⁻² was obtained with an output voltage of 0.451 V.     

Effect of gas diffusion layer and membrane properties in an annular proton exchange membrane fuel cell

A complete three-dimensional and single phase computational dynamics model for annular proton exchange membrane (PEM) fuel cell is used to investigate the effect of changing gas diffusion layer and membrane properties on the performances, current density and gas concentration. The proposed model is a full cell model, which includes all the parts of the PEM fuel cell, flow channels, gas diffusion electrodes, catalyst layers and the membrane. Coupled transport and electrochemical kinetics equations are solved in a single domain; therefore no interfacial boundary condition is required at the internal boundaries between cell components. This computational fluid dynamics code is used as the direct problem solver, which is used to simulate the two-dimensional mass, momentum and species transport phenomena as well as the electron- and proton-transfer process taking place in a PEMFC that cannot be investigated experimentally. The results show that by increasing the thickness and decreasing the porosity of GDL the performance of the cell enhances that it is different with planner PEM fuel cell. Also the results show that by decreasing the thickness of the membrane the performance of the cell increases.     

不同进气湿度PEMFC动态响应分析

质子交换膜燃料电池(PEMFC)工作参数的影响最终要体现在对电池内传质过程的影响上。实验得到了在不同进气加湿程度下电池性能在启动工况中的变化,基于非稳态数学模型计算了不同阴极入口湿度下电池在负载渐变工况下膜内含水量和电流密度的瞬态响应,并与相应的实验工况进行了对比。     

Role of Acid Treatment of the Carbon Support in the Growth of Atomic-Layer-Deposited Pt Nanoparticles for PEMFC Fabrication

Ultrathin films or particles of atomic layer deposition (ALD) on high surface can improve the activity and durability of catalyst fields, so depending on the surface state, the ALD growth mechanism on porous materials should be systematically investigated and optimized to improve their characteristics of catalysts. Herein, a Pt catalyst used in polymer electrode membrane fuel cell (PEMFC) applications is synthesized through fluidized-bed-reactor ALD on carbon black whose surface is modified through treatment with citric acid. The functional groups, analyzed through X-ray photoelectron spectroscopy (XPS), are found to be maximized after 60 min of acid treatment with stirring. Compared with bare carbon (untreated), the acid-treated carbon presents rich oxidized functional groups and abundant defects but lower surface areas and pore volumes. After ALD Pt deposition, highly dense, uniform, and well-dispersed Pt nanoparticles (NPs) are observed on the carbon black subjected to acid treatment, because of the favorable surface modifications for ALD growth resulting from the acid treatment. The ALD-Pt NPs on the acid-treated carbon exhibit larger electrochemical active surface areas, improved oxygen reduction reactions, and PEMFC performances, when compared with that of NPs on bare carbon with similar Pt weight loading.     

High-throughput screening of binary catalysts for oxygen electroreduction

A series of Pt based and non-Pt catalysts for proton exchange membrane fuel cell (PEMFC) and direct methanol fuel cell (DMFC) have been evaluated towards oxygen reduction, by high-throughput optical screening. Fluorescein was first used as pH indicator for detecting pH change of the electrolyte in the vicinity of cathode caused by oxygen reduction. Arrays of catalyst spot comprised of binary catalysts and pure Pt were prepared by using robotic micro-dispenser. The analysis of fluorescence images has showed that some of Pt based catalysts including PtBi, PtCu, PtSe, PtTe and PtIr, as well as RuFe, as a non-Pt catalyst, exhibited higher activities and methanol tolerance than pure Pt. Moreover, acceptable stability of these catalysts at high potential in acid environment suits them to the requirements of cathode catalyst in PEMFC or DMFC.     

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.     

PEMFC气体扩散层干燥过程孔隙网络模拟

本文采用三维孔隙网络模型从孔隙尺度上对质子交换膜燃料电池气体扩散层中水分蒸发的干燥过程进行了模拟,并考虑了阴极流道的影响.计算结果表明毛细力在气体扩散层的干燥过程中起主要作用,气相从阴极流道底部开始,以沿气体扩散层厚度方向侵入为先,直到到达气体扩散层底部,随后气相才向流道肩部水平延伸侵入.蒸发速率随气体扩散层中水饱和度...     

Effect of the settings of electrospray deposition method on the structure and performance of the fuel cell catalyst layer

Catalyst layers of proton exchange membrane fuel cells (PEMFC) are formed by electrospray deposition (ESD) method. The cathode catalyst layers are formed and characterized by varying the settings of the system, such as flow rate, applied voltage and the distance between the capillary and the substrate. The dryness of the aggregates during deposition is evaluated using the Damkhöler number (Da), and the structure of the catalyst layer is observed using SEM, which shows that the catalyst layer is porous when dry and non-porous when insufficiently dry. In the case of insufficient drying, the structure changed significantly depending on the position. Single cell tests show that the maximum power density varies from 105 to 253 mWcm⁻² depending on the settings, even with the same catalyst ink and the same amount of platinum. Electrochemical impedance spectroscopy shows that the charge transfer and mass transport resistances tend to decrease with increase in Da.     

Evaluation of carbon-supported copper phthalocyanine (CuPc/C) as a cathode catalyst for fuel cells using Nafion as an electrolyte

Carbon-supported copper phthalocyanine (CuPc/C) nanoclusters, as a novel suitable cathode catalyst in polymer electrolyte membrane fuel cells, have been synthesized via a combined solvent impregnation and milling procedure along with high-temperature treatment. For optimizing the electrocatalytic activity of the catalyst obtained, the electrode with varying Nafion ionomer contents in the catalyst layer was screened by cyclic voltammetry and linear sweep voltammetry employing a rotating disk electrode technique to investigate the effect of Nafion ionomer as for alkaline electrolyte. For comparative purposes, electrode with various contents of available anion-ionomer was also investigated. The results revealed that the content of Nafion ionomer can affect the oxygen reduction reaction activity of the CuPc/C catalyst and an optimal content of Nafion ionomer was around 3.5?×?10¹?μg?cm^?2, which corresponds well with the electrode prepared using available anion-ionomer. The electrode prepared using Nafion ionomer can produce a comparable performance to that of using available anion-ionomer, giving an onset potential at 0.1 V with a half-wave potential of ?0.03 V. Furthermore, Koutechy–Levich analysis showed that the value of electron transfer number is in the range of 3.40 to 3.74 when using electrode with varying Nafion ionomer contents from 2.5?×?10¹ to 1.6?×?10²?μg?cm^?2. The membrane electrode assembly fabricated with the CuPc/C cathode catalyst with a loading of 3.6 mg?cm^?2 and a Nafion membrane immersed in 3 M KOH for 48 h produced a power density of 3.8 mW?cm^?2 at room temperature.