零度以下环境中DMFC性能及传输特性

在零度以下环境中，直接甲醇燃料电池（DMFC）膜电极内的水结冰，将堵塞多孔层孔隙，影响反应物传输和电池性能。本文研究了-5℃条件下主动式DMFC的低温运行特性以及甲醇浓度、氧气流速和放电电流密度等参数的影响。实验结果表明：主动式DMFC可在-5℃环境中成功启动并稳定运行；此时最佳甲醇浓度为4mol／L，高于常温及以上条...     

自呼吸式DMFC电堆构建与电池性能研究

本文报道了一种能驱动风扇工作的自呼吸式DMFC小型电堆,电堆主要南燃料储罐、膜电极(MEA)、集流体等组成.文中针对影响该电池性能的主要参数,如电堆的活化过程、甲醇浓度等因素进行了研究.同时,本文还对电堆的恒电流放电时的电流曲线特点以及阴极水的生成规律进行了初步考察和探讨.     

直流道PEMFC两相流数学模型

建立直流道质子交换膜燃料电池(PEMFC)三维非等温两相流数学模型,基于质子交换膜与气体之间的水分传递特征,综合考虑电渗、浓度扩散及电化学反应作用的影响,发展了膜电极水分传递的非平衡扩散模型.并自主开发程序代码对电池内复杂的多物理场耦合传递过程进行数值模拟,研究PEMFC电极内气态水、液态水分布、质子膜含水量分布和水迁移特性等,分析单电池内部的温度分布特征,并获得电池极化性能曲线.     

直接甲醇燃料电池

文章简要介绍了直接甲醇燃料电池(DMFC)的主要特点、工作原理、应用前景、技术状态及其商业化面临的挑战，开发能够提高甲醇氧化和氧还原动力学速率的低成本电催化剂，制备具有高质子电导率、低甲醇渗透率的电解质膜，实现高性能、长寿命的电极、膜电极制备技术以及系统集成技术的突破对DMFC商业化至关重要。     

DMFC两相流及其对传质影响的研究

采用自制的实验系统对液态进料直接甲醇燃料电池(DMFC)阳极交叉指状流道内的两相况功特性进行了可视化实验研究.自制的DMFC单电池带有透明窗口,采用镀金的不锈钢阴极极板和透明的聚碳酸脂阳极流场板,电解质为Nafion117膜.实验过程中燃料电池的进口总管和出口总管是水平的,进口流道和出口流道是竖直的.实验发现,出口流道中典型的两相流流型是泡状流、而出口总管中的典型流型是弹状流.进口流道中的气弹和气柱导致了阳极传质恶化.     

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.     

直接甲醇燃料电池气、液相流动数值模拟

本文建立了直接甲醇燃料电池(DMFC)的二维两相模型,并重点研究阳极的两相流动和质量传递.模型考虑甲醇串流现象,定量计算了在不同电流密度下甲醇串流量的大小及其对电池工作性能的影响;模型中提出求解气、液单相流速的方法,并分别研究气、液流速对物质传递和电池性能的影响.定量分析发现:由甲醇串流产生的寄生电势导致实际开路电压值远低于理论值;在大电流密度下扩散层和催化层内的气相体积分数非常大,阻碍了液相燃料向催化层扩散,成为制约电池性能的关键因素;扩散层和催化层内存在气、液两相的反向流动,且气、液相速度分别有利于排出生成气体并推动液体燃料到达催化层;减小多孔介质的扩散率将削弱对流,恶化电池性能.     

接触热阻对水冷辉光放电电极温度分布影响的数值模拟

为了研究接触热阻对陶瓷绝缘水冷辉光放电电极温度及其分布的影响，利用计算流体动力学软件ANSYSCFX，模拟了电极表面温度、温差随氮化铝陶瓷与两侧铜导体之间接触热阻的变化。模拟结果表明：随着接触热阻的增大，氮化铝陶瓷与铜接触界面的温度跳变幅度增大，辉光放电电极整体温度上升，并且辉光放电电极表面的最高温度和最大温差均随之呈现指数上升的变化趋势。     

自呼吸式碱性直接葡萄糖燃料电池研究

本文设计了基于无Pt电极的自呼吸式阴离子交换膜(AEM)直接葡萄糖燃料电池(DGFC),并对其性能进行了实验研究。结果表明,在室温下,自呼吸式AEM-DGFC的最大功率密度达到20.8 mW·cm~(-2),最大电流密度为156mA·cm~(-2),优于以葡萄糖为反应物的传统的微生物燃料电池和酸性直接葡萄糖燃料电池(PEM-DGFC)。实验还探究了葡萄糖浓度以及KOH浓度对于自呼吸式直接葡萄糖燃料电池性能的影响,葡萄糖浓度的升高一方面会降低传质极化,另一方面会阻碍OH~-的传输,增大电池的内阻。0.7 M浓度的葡萄糖使燃料电池性能达到最优最优。KOH浓度从2M升高到4M时,使得阳极的GOR速率加快,电池性能进一步提升。     

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。     

Surface-modified Nafion membrane by trioctylphosphine-stabilized palladium nanoparticles for DMFC applications

Trioctylphosphine (TOP)/Pd composites have been synthesized and used as a methanol-barrier material to modify the surface of Nafion 115. The TOP/Pd composites have been applied to the surface of Nafion instead of being incorporated into the Nafion matrix, to provide the best chance of maintaining the inherent proton conductivity of Nafion. The properties of the TOP/Pd-modified membrane, in terms of its conductivity and methanol permeability, as well as the performance of the membrane electrode assembly (MEA) in direct methanol fuel cell (DMFC), have been analyzed and compared with those of bare Nafion. The DMFC performance of the TOP/Pd-modified membrane is somewhat better than that of the bare Nafion one at methanol concentration of 2 M and significantly better at a high concentration of 5 M. The TOP/Pd-modified membrane is able to operate the DMFC using a high concentration of methanol, which can satisfy the requirement to reduce the reactant volumes for portable applications as well as to achieve high performance. In contrast to bare Nafion, the TOP/Pd-modified membrane with its well-adhering and crack-free modified surface shows effect on reducing the methanol loss.     

Direct methanol fuel cells : Methanol crossover and its influence on single DMFC performance

In the present investigation, the methanol crossover rate through Nafion®-115 membrane at different temperatures and different concentrations had been investigated in a fuel cell test apparatus by using gas chromatography analysis. The singledirect methanol fuel cell (DMFC) tests were carried out to investigate the effect of the concentration of methanol aqueous solutions and cell temperature on methanol crossover and consequently, on the open circuit voltage and the cell performance of DMFC. It can be found that the methanol crossover rate through Nafion® membrane increases as methanol concentration and temperature increase. It can also be found that methanol crossover presented a negative effect on the open circuit voltage and the single DMFC performance. Single DMFC test results showed that an improved cell performance was obtained as temperature increased although the methanol crossover rate increased with temperature increment.     

The effect of cell orientations and environmental conditions on the performance of a passive DMFC single cell

A single cell passive air-breathing liquid feed direct methanol fuel cell (DMFC) is designed and fabricated. Furthermore, the effects of cell orientation and environmental conditions such as temperature and relative humidity on the performance of such passive DMFC are tested experimentally. The obtained results indicate that both environmental temperature and relative humidity have significant effects on the performance of fabricated fuel cell. The experimental data contained within this work shows that under lower relative humidity and higher temperature, the passive air-breathing direct methanol fuel cell has higher power output and better performance. According to experimental results, flooding has a vital role on the cell performance in various relative humidity and temperatures. The results also show that cell orientation has a strong effect on the performance of passive DMFC. The best power output and performance were achieved under vertical orientation.     

High-throughput screening of fuel cell electrocatalysts

The drawbacks of our earlier report of preparing fuel cell catalyst arrays by borohydride reduction of inkjet prepared arrays of metal salts are discussed along with the need for inclusion of state-of-the-art metrics in all array screening. An alternative method for screening of hydrogen/air cathode catalysts, direct methanol fuel cell (DMFC) anode catalysts, and catalyst loading studies is provided. State-of-the-art Johnson Matthey catalysts were used in control experiments to demonstrate the utility of the array fuel cell for high throughput screening of fuel cell catalysts in the 3-4 mg/cm² range. This report lays out hard learned rules for high throughput screening and demonstrates that the array fuel cell can be used for very precise screening of libraries of membrane electrode assembly (MEA) components without the pitfalls discussed in the introduction.     

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．     

Fabrication of Aquivion-type membranes and optimization of their elastic and transport characteristics

The solution casting technology was applied to manufacture thin polymer films (~?20–30 μm) from the ionomer solution of perfluorinated polymer with short side chains (an analogue of the commercial polymer Aquivion®). The influence of annealing temperature on the mechanical properties (elastic limit), proton conductivity, and heat capacity was investigated. The elastic limit, glass transition temperature, and proton conductivity of the samples were found to reach their maximum values at the annealing temperature 170?±?5 °C. Comparative studies of membrane-electrode assemblies (MEA) using the commercial (Nafion NR212) and solution-casted membranes were carried out. MEA with optimized Aquivion-type membranes showed satisfactory values of fuel crossover and maximum output power. The results of the conducted studies show that the prepared Aquivion-type membranes are very promising for practical application in MEA.     

Thermochemical process in preparation of ZnO film by TFA-MOD method

The excess weight loss due to the evaporation of zinc compound is observed in the growth of ZnO film by trifluoroacetate metalorganic deposition (TFA-MOD) method. Higher temperature (>90 °C) aging and/or addition of monoethanolamine (MEA) are effective to prevent the evaporation of zinc compound and increase the yield of ZnO. The mechanism of preventing evaporation is that zinc trifluoroacetate is hydrolyzed into Zn₄O(CF₃COO)₆. A three-dimensional structure of Zn₄O(CF₃COO)₆ is proposed. It is shown that higher temperature aging does harm to the surface morphology of ZnO films. The addition of MEA reduces the required aging temperature thus improves the surface morphology.     

Preparation of durable nanocatalyzed MEA for PEM fuel cell applications

Novel nanocatalyzed membrane electrode assembly (MEA) with high performance and durability for polymer electrolyte membrane fuel cell application is prepared by modifying nonequilibrium impregnation–reduction method. The electrochemical and physical properties of nanocatalyzed MEA have been examined using various techniques such as cyclic voltammetry, impedance spectroscopy, scanning electron microscopy, and X-ray diffraction studies. The lifetime of the nanocatalyzed MEA is studied and compared with that of the conventional one. It is observed that the performance and durability of nanocatalyzed MEA are better than the conventional one. In addition, the influence of supported carbon corrosion in MEA durability has been studied.     

Design of novel SPEEK-based proton exchange membranes by self-assembly method for fuel cells

Fuel cell represents a new energy conversion device, which promises to provide clean source of power. Fuel cell [particularly proton exchange membrane fuel cell and direct methanol fuel cell (DMFC)] is a promising candidate for transportation and portable power source applications. In DMFC, there is a problem of methanol crossover. In order to reduce such a problem, there has been an intensive research activity in the modification of Nafion. In the present investigation, self-assembled membranes were fabricated with sulfonated polyether ether ketone as the core part of the membrane. Aminated polysulfone and sulfonated polysulfone were used as the layers in order to prevent the crossover of methanol. The assembled membranes were characterized by ion exchange capacity, water and methanol absorption, and durability. The methanol permeability and selectivity ratio proved a strong influence on DMFC application. Scanning electron microscopy proved smooth surface, which established strong cohesive force for the polymer chains. Among the synthesized self-assembled membranes, the membrane with two bilayers was the best in terms of power density in DMFC. The membrane electrode assembly with two bilayers showed higher performance (~61.05 mW/cm²) than sulfonated poly(ether ether ketone) and Nafion in DMFC.     

Ultrasonic radiation to enable improvement of direct methanol fuel cell

To improve DMFC (direct methanol fuel cell) performance, a new method using ultrasonic radiation is proposed and a novel DMFC structure is designed and fabricated in the present paper. Three ultrasonic transducers (piezoelectric transducer, PZT) are integrated in the flow field plate to form the ultrasonic field in the liquid fuel. Ultrasonic frequency, acoustic power, and methanol concentration have been considered as variables in the experiments. With the help of ultrasonic radiation, the maximum output power and limiting current of cell can be independently increased by 30.73% and 40.54%, respectively. The best performance of DMFC is obtained at the condition of ultrasonic radiation (30 kHz and 4 W) fed with 2 M methanol solution, because both its limiting current and output power reach their maximum value simultaneously (222 mA and 33.6 mW, respectively) under this condition. These results conclude that ultrasonic can be an alternative choice for improving the cell performance, and can facilitate a guideline for the optimization of DMFC.