A novel MEA architecture for improving the performance of a DMFC

Direct methanol fuel cell (DMFC) consisting of a double-catalytic layered membrane electrode assembly (MEA) provide higher performance than that with the traditional MEA. This novel structured MEA includes a hydrophilic inner catalyst layer and a traditional electrode with an outer catalyst layer, which was made using both catalyst coated membrane (CCM) and gas diffusion electrode (GDE) methods. The inner catalyst was PtRu black on anode and Pt black on cathode. The outer catalyst was carbon supported Pt–Ru/Pt on anode and cathode, respectively. Thus in the double-catalytic layered electrodes three gradients were formed: catalyst concentration gradient, hydrophilicity gradient and porosity gradient, resulting in good mass transfer, proton and electron conducting and low methanol crossover. The peak density of DMFC with such MEA was 19 mW cm⁻², operated at 2 M CH₃OH, 2 atm oxygen at room temperature, which was much higher than DMFC with traditional MEA.     

Preparation process for improving cathode electrode structure in direct methanol fuel cell

The cathode electrode structure of the direct methanol fuel cell (DMFC) was improved by a novel catalyst ink preparation method. Regulation of the solvent polarity in the cathode catalyst ink caused increases in the electrochemical active surface (EAS) for the oxygen reduction reaction (ORR) as well as decreases in the methanol crossover effect. In a two-step preparation, agglomerates consisting of catalyst and Nafion ionomers were decreased in size, and polar groups in the ionomers formed organized networks in the cathode catalyst layer. Despite Pt catalysts in the cathode being only 0.5 mg cm^? 2, the maximum power density of the improved membrane electrode assembly (MEA) was 120 mW cm^? 2, at 3 M methanol, which was much larger than that of traditional MEA (67 mW cm^? 2).     

Effect of the Cathode Catalyst Layer Thickness on the Performance in Direct Methanol Fuel Cells

Catalyst deposition control is one of the overlooked areas of fuel cell fabrication and research that can affect the overall performance and cost of the fuel cell to manufacture for mass production. The effect of the different individual catalyst layer thicknesses and loadings of the cathode compartment of a direct methanol fuel cell (DMFC) was investigated. The drawdown method was performed at thicknesses varying from 1 mil to 8 mils with platinum loadings ranging from 0.25 mg cm^?2 to 2.0 mg cm^?2. The membrane electrode assemblies (MEAs) with thicker individual layers (8 mil and 4 mil) performed better overall compared to the ones prepared with thinner individual layers (1 mil). The power density maxima for the different loading levels followed an exponential decrease of platinum utilization at the higher loading levels. The painted MEAs tended to display the similar performance characteristics as the drawdown MEA layers closest to the thickness at the respective loadings.     

Study on a novel manufacturing process of membrane electrode assemblies for solid polymer electrolyte water electrolysis

A novel manufacturing process for catalyst coated membrane (CCM) was utilized to fabricate the membrane electrode assemblies (MEA) for solid polymer electrolyte (SPE) water electrolysis. The properties and performance of the modified CCM were analyzed and evaluated by SEM, electrochemistry impedance spectroscopy (EIS) and I–V curves. The characterizations reveal that the sprayed Nafion layers are very effective for increasing the reaction interface between SPE and the electrode catalyst layer. The test experiments show that the SPE water electrolyzer with new MEA structure can lower about 0.1 V of water electrolysis voltage at atmosphere pressure and 2 A cm⁻².     

自呼吸直接甲醇燃料电池膜电极的优化(英文)

针对空气自呼吸式直接甲醇燃料电池甲醇易渗透和阴极易水淹的特点,通过对催化层催化剂载量、阴极微孔层、阳极微孔层和膜等因素进行调控,对膜电极结构和性能的进行了优化.结果表明,使用高载量催化剂能有效降低甲醇渗透,但载量过高会引起传质阻力.当阳极微孔层PTFE含量为30%(bymass)时,可以有效促进CO2的均一析出,从而降低甲醇浓度梯度,减小甲醇透过.综合考虑甲醇渗透和阴极自返水,经优化后所得MEA在室温时自呼吸工作条件下,比功率密度达到33mW·cm-2,最优甲醇工作浓度为4mol·L-1.     

A novel single electrode supported direct methanol fuel cell

In this paper a single electrode supported direct methanol fuel cell (DMFC) is fabricated and tested. The novel architecture combines the elimination of the polymer electrolyte membrane (PEM) and the integration of the anode and cathode into one component. The thin film fabrication involves a sequential deposition of an anode catalyst layer, a cellulose acetate electronic insulating layer and a cathode catalyst layer onto a single carbon fibre paper substrate. The single electrode supported DMFC has a total thickness of 3.88 × 10^?2 cm and showed a 104% improvement in volumetric specific power density over a two electrode DMFC configuration under passive conditions at ambient temperature and pressure (1 atm, 25 °C).     

降低直接甲醇燃料电池浓差极化的含磺化碳管阻水夹层的构建

采用直接接枝法, 将来自对氨基苯磺酸的苯磺酸官能团引入氧化多壁碳纳米管, 制得磺化多壁碳纳米管(SO₃-MCNT). 再以SO₃-MCNT为填料, 以Nafion离聚物为黏结剂, 利用超声喷涂在商业N212质子交换膜一侧构建了新的膜层, 获得了一种复合膜(SO₃-MCNT?N212). 使用SO₃-MCNT?N212制备燃料电池膜电极(MEA), 并用于直接甲醇燃料电池(DMFC)测试. 与使用普通N212膜的膜电极相比, 该膜电极的性能得到明显提升. 进一步分析表明, SO₃-MCNT膜层的引入降低了阳极向阴极的跨膜水迁移作用, 缓解了阴极的水淹, 从而降低了浓差极化, 提升了膜电极的性能.     

溶胶-凝胶流动相异型直接甲醇燃料电池性能研究

以掺杂石墨粉的中间相碳微球(MCMB/G)烧结管为阴极支撑体,采用浸涂工艺分别制备了扩散层和催化层并在其外表面包裹Nafion膜,制得管状异型阴极并组装成异型直接甲醇燃料电池;采用溶胶-凝胶法制备了适用于直接甲醇燃料电池的溶胶-凝胶流动相。研究了溶胶-凝胶流动相异型直接甲醇燃料电池的阻抗,考察了阴极支撑体壁厚、阴极扩散层载量、实验温度和溶胶黏度等对电池极化性能的影响。结果表明,异型电池阻抗比传统平板电池大,但活化后电池阻抗明显下降;较低的溶胶黏度和较高的工作温度有利于提高电池性能;支撑体壁厚为1.3 mm、扩散层载量为3.5 mg/cm2时的电极性能最优。     

Proton exchange membrane using partially sulfonated polystyrene-b-poly(dimethylsiloxane) for direct methanol fuel cell

A diblock copolymer ionomer containing a rubbery poly(dimethylsiloxane) block has been developed as a proton exchange membrane for direct methanol fuel cell (DMFC). The partially sulfonated polystyrene-b-poly(dimethylsiloxane) (sPS-b-PDMS) membrane with 38% sulfonation degree exhibited 3 times lower methanol permeability and 2.6 times higher membrane selectivity (proton conductivity/methanol permeability) compared to Nafion^® 115 at 25 °C. Coexistence of microphase domains and ionic clusters was confirmed from the morphological studies by small-angle X-ray scattering and tapping-mode atomic force microscopy. Gas chromatographic analysis revealed that water/methanol selectivity of sPS-b-PDMS was 20 times higher than that of Nafion^® 115. Such a high water/methanol selectivity can be attributed to the existence of PDMS microdomains minimizing methanol permeation through hydrophilic ion channels. sPS-b-PDMS membranes were fabricated into membrane electrode assembly (MEA), and air-breathing DMFC test for these MEAs showed a better performance compared to the MEA composed of Nafion^® 115.     

Novel synthesis of a highly active carbon-supported Ru85Se15 chalcogenide catalyst for the oxygen reduction reaction

A carbon-supported Ru₈₅Se₁₅ chalcogenide catalyst was synthesized via a microwave-assisted polyol process using RuCl₃ and Na₂SeO₃ as the Ru and Se precursors. The Ru₈₅Se₁₅ chalcogenide catalyst was characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM) and inductively-coupled plasma-atomic emission spectroscopy (ICP-AES). The XRD pattern for Ru₈₅Se₁₅/C clearly exhibited the characteristic reflections of metallic ruthenium. The TEM image indicated that the Ru₈₅Se₁₅ chalcogenide catalyst was well dispersed on the surface of the carbon support with a narrow particle size distribution. Rotating disk electrode (RDE) and single-cell measurements were carried out to evaluate the electrocatalytic activity of the Ru₈₅Se₁₅ chalcogenide catalyst. The oxygen reduction reaction (ORR) activity of the Ru₈₅Se₁₅/C catalyst was compared with the commercial Pt/C catalyst with the absence/presence of methanol. In the absence of methanol, the Ru₈₅Se₁₅/C catalyst showed a comparable ORR activity with the Pt/C catalyst. However, in the presence of methanol, the Ru₈₅Se₁₅/C catalyst showed a better ORR activity than the Pt/C catalyst. The performance of the membrane electrode assembly (MEA) prepared with Ru₈₅Se₁₅/C as the cathode catalyst in a single proton exchange membrane fuel cell (PEMFC) showed the maximum power density of 400 mW cm⁻² at the current density of 1300 mA cm⁻².     

A novel electrode architecture for passive direct methanol fuel cells

The supply of cathode reactants in a passive direct methanol fuel cell (DMFC) relies on naturally breathing oxygen from ambient air. The successful operation of this type of passive fuel cell requires the overall mass transfer resistance of oxygen through the layered fuel cell structure to be minimized such that the voltage loss due to the oxygen concentration polarization can be reduced. In this work, we propose a new membrane electrode assembly (MEA), in which the conventional cathode gas diffusion layer (GDL) is eliminated while utilizing a porous metal structure for transporting oxygen and collecting current. We show theoretically that the new MEA enables a higher mass transfer rate of oxygen and thus better performance. The measured polarization and constant-current discharging behavior showed that the passive DMFC with the new MEA yielded better and much more stable performance than did the cell having the conventional MEA. The EIS spectrum analysis further demonstrated that the improved performance with the new MEA was attributed to the enhanced transport of oxygen as a result of the reduced mass transfer resistance in the fuel cell system.     

Single wall carbon nanotube supports for portable direct methanol fuel cells

Single-wall and multiwall carbon nanotubes are employed as carbon supports in direct methanol fuel cells (DMFC). The morphology and electrochemical activity of single-wall and multiwall carbon nanotubes obtained from different sources have been examined to probe the influence of carbon support on the overall performance of DMFC. The improved activity of the Pt-Ru catalyst dispersed on carbon nanotubes toward methanol oxidation is reflected as a shift in the onset potential and a lower charge transfer resistance at the electrode/electrolyte interface. The evaluation of carbon supports in a passive air breathing DMFC indicates that the observed power density depends on the nature and source of carbon nanostructures. The intrinsic property of the nanotubes, dispersion of the electrocatalyst and the electrochemically active surface area collectively influence the performance of the membrane electrode assembly (MEA). As compared to the commercial carbon black support, single wall carbon nanotubes when employed as the support for anchoring the electrocatalyst particles in the anode and cathode sides of MEA exhibited a approximately 30% enhancement in the power density of a single stack DMFC operating at 70 degrees C.     

Pt dendrimer nanocomposites for oxygen reduction reaction in direct methanol fuel cells

Dendrimer-encapsulated Pt nanoparticles (G4OHPt) were prepared by chemical reduction at room temperature. The G4OHPt, with average diameters of ca. 2.7 nm, were characterized by X-ray diffraction, scanning electron microscopy, and thermogravimetric analysis. Electrocatalytic behavior for oxygen reduction reaction was investigated using a rotating disk electrode configuration in an acidic medium, with and without the presence of methanol (0.01, 0.1, and 1 M). Kinetic studies showed that electrodes based on Pt nanoparticles encapsulated inside the dendrimer display a higher selectivity for ORR in the presence of methanol than electrodes based on commercial Pt black catalysts. Also, the dendritic polymer confers a protective effect on the Pt in the presence of methanol, which allows its use as a cathode in a direct methanol fuel cell operating at different temperatures. Good performance was obtained at 90 °C and 2 bar of pressure with a low platinum loading on the electrode surface.     

Operando 3D Visualization of Migration and Degradation of a Platinum Cathode Catalyst in a Polymer Electrolyte Fuel Cell

The three‐dimensional (3D) distribution and oxidation state of a Pt cathode catalyst in a practical membrane electrode assembly (MEA) were visualized in a practical polymer electrolyte fuel cell (PEFC) under fuel‐cell operating conditions. Operando 3D computed‐tomography imaging with X‐ray absorption near edge structure (XANES) spectroscopy (CT‐XANES) clearly revealed the heterogeneous migration and degradation of Pt cathode catalyst in an MEA during accelerated degradation test (ADT) of PEFC. The degradative Pt migration proceeded over the entire cathode catalyst layer and spread to MEA depth direction into the Nafion membrane.     

Application of polysulfone (PSf)– and polyether ether ketone (PEEK)–tungstophosphoric acid (TPA) composite membranes for water electrolysis

The ion exchange membrane using polysulfone (PSf) and polyether ether ketone (PEEK) as a basic material was prepared to apply in the polymer electrolyte membrane electrolysis (PEME). The sulfonated block copolymer of PSf and poly(phenylene sulfide sulfone) (SPSf-co-PPSS) and the sulfonated PEEK (SPEEK) were blended with tungstophosphoric acid (TPA) to avoid water swelling at elevated temperatures led to decrease in mechanical strength. These prepared ion exchange membranes showed some interesting characteristics including physicochemical stabilities, mechanical and membrane properties.The prepared ion exchange membrane was utilized to prepare the membrane electrode assembly (MEA). MEA consisted of Pt/PEM/Pt was prepared by equilibrium and non-equilibrium impregnation–reduction (I–R) methods. The prepared MEA by non-equilibrium I–R method was used in the PEME unit cell. The cell voltages of the MEA using SPSf-co-PPSS/TPA and SPEEK/TPA membranes were 1.83 V and 1.90 V at 1 A/cm² and 80 °C, with platinum loadings of 1.12 and 1.01 mg/cm², respectively.     

Developing a membrane-electrode assembly with reduced Pt content for a hydrogen—air fuel cell based on a PtCoCr catalyst and F-950 membrane

Laboratory methods are developed for forming an active layer (AL) with a synthesized PtCoCr catalyst (20 wt % Pt) on the F-950 perfluorinated membrane. AL composition and the conditions for forming 3- and 5-layer membrane-electrode assemblies (MEA) are optimized. Reproducible, stable, and high-discharge characteristics are obtained for a hydrogen-air fuel cell (HAFC). At a current density of 0.5 A/cm², the voltage of an MEA with cathode based on a PtCoCr catalyst is 0.66–0.68 V, and the maximum power density is 500 mW/cm². Replacing the commercial HiSPEC 4000 catalyst (40 wt % Pt) with PtCoCr (20 wt % Pt) in the AL composition of the cathode makes it possible to reduce Pt consumption by a factor of two without decreasing MEA discharge characteristics. The parameters that characterize the catalytic activity of catalysts under model conditions and in the MEA cathode composition are shown to be correlated.     

PEMFC用亲水型薄层MEA的制备及其性能

本文提出一种新颖简易的方法制备PEMFC的亲水型薄层MEA,其阴、阳极催化层Pt担量分别为0. 4和 0. 2mg/cm2.实验发现,在亲水型MEA的表面上,有大量钟乳石状细微颗粒存在,从而使电极催化层的比表面积增大.在小电流密度区( <1A/cm2 ),亲水型MEA的极化性能差于Pt担量为 0. 7mg/cm2的疏水型常规MEA,但在大电流密度区( >2A/cm2 ),则前者的极化性能优化后者;亲水型MEA的最大输出比功率为1. 23W/cm2,高于疏水型电极的 1. 19W/cm2;在大电流密度区,亲水型MEA中的Pt电化学比活性也明显高于疏水型电极.     

DMFC寿命测试过程中膜电极的表面和结构研究(英文)

设计并组装单电池寿命测试系统,测试直接甲醇燃料电池(DMFC)的运行寿命,获得不同运行时间下单电池的极化和功率曲线.测试结束后,分别对运行过的膜电极(MEA)催化剂(铂黑和铂钌黑)和Nafion117(膜作XRD,HRTEM,FTIR及Raman等表征.考察在长期运行条件下电池寿命性能与膜电极中催化剂的颗粒大小、分布、形态、表面物种以及膜的结构之间的关系.寿命测试结果表明,单电池在不同运行阶段其性能变化也不同.运行前200 h,电池性能衰减较显著;运行200~704 h性能较稳定,运行1 002 h后电池性能恶化.波谱实验发现,单电池长期运行后,其膜电极的阴、阳极催化剂颗粒变大.电池寿命性能的衰退伴随膜电极微结构、表面组成、催化剂/膜界面结构的变化以及Nafion 117(膜的老化.     

Performance and instabilities of proton exchange membrane fuel cells

Performance of proton exchange fuel cells with different membrane and electrode assembly (MEA) is studied. It is shown that MEA fabricated with catalyst plasma pulverization technology has the maximum performance. Some instabilities in the cell performance, observed with time, are probably due to periodic cathode flooding. Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 5, pp. 525–534. The text was submitted by the authors in English.     

低铂膜电极结构优化途径

膜电极是质子交换膜燃料电池的核心组件,长期以来,在衣院士的指导下,我国高度重视膜电极技术的开发. 目前,燃料电池的研发和产业化进入了一个新的时代,对膜电极提出来更高的要求,特别是在降低铂载量方面,提出了0.125 mg·W^-1的挑战性指标. 本文从活化极化、欧姆极化和传质极化三个方面分析了低铂载量情况下电池性能下降的原因,提出应重点关注催化剂在燃料电池工作区间（0.6 V ~ 0.8 V)的催化活性,并讨论了用电荷传输阻抗作为催化剂活性指示符的合理性. 从优化潜力来说,传质极化优化>活化极化优化>欧姆极化优化. 催化层结构优化是实现低铂目标的关键,重点是解决离子聚合物（ionomer）传递质子和阻碍气体的矛盾.