Droplet pinning by PEM fuel cell GDL surfaces

In this work, side view images of liquid–gas–solid interfaces are observed during the evaporation of liquid water droplets on various commercially available untreated gas diffusion layers (GDLs). The change in contact diameter as a function of evaporative volume loss is measured to quantify the unpinning rates of micro-sized droplets. This contact diameter pinning behaviour during evaporation is correlated to the material topography, which is quantified through profilometry measurements. The carbon fibre paper with the smallest average roughness (15 μm) exhibits the strongest degree of pinning (unpinning at a rate of 0.13 mm/μL). Higher average surface roughnesses for felt (30 μm) and cloth yarn (32 μm) result in higher unpinning rates, 0.21 mm/μL and 0.19 mm/μL, respectively. These results indicate that common GDL materials exhibit Cassie–Baxter wetting behaviour, and reduced GDL roughness promotes droplet pinning. The material-specific droplet contact diameter progression should be considered during GDL selection for polymer electrolyte membrane (PEM) fuel cells. This work provides insight into the effect of GDL material properties on gas channel water management, as water droplets are expected to experience similar pinning to that observed in this work within the cathode gas channels of a PEM fuel cell.     

氢能发电技术的研究（Ⅳ）——电极扩散层对离子膜燃料电池放电性能的影响

研究了电极扩散层对离子膜燃料电池放电性能的影响。结果表明：制备扩散层的基体材料对燃料电池放电性能有较大的影响。本实验所采用的碳纸、碳膜和碳纤维布3种基体材料中,碳纤维布是一种较为理想的基体材料,不同扩散层所组装的燃料电池最大放电功率密度有较大的差别,碳纤维布扩散层所组装的燃料电池最大放电能量分别是碳纸和碳膜扩散层所组装的燃料电池最大放电能量的2.16倍和6.94倍。不同扩散层对燃料电池最佳放电运行时的放电电压和放电电流密度也都有一定的影响,特别是对放电电流密度影响更为强烈,电极扩散层的疏水性是影响燃料电池稳定放电寿命的一个重要因素,因此在电极扩散层的制备和基材选择过程中,必须充分考虑这一因素的影响。     

Novel superhydrophobic microporous layers for enhanced performance and efficient water management in PEM fuel cells

Microporous layers (MPLs) obtained from inks containing three fluorinated polymers (perfluoroalcoxy, fluorinated ethylene propylene and a fluorinated polyurethane based on perfluoropolyether blocks) replacing conventional PTFE were prepared. Inks composition and rheological behaviour were fixed in order to apply the blade coating technique for MPL deposition. Superhydrophobic layers were obtained since contact angles higher than 150° were measured. The samples, tested in a single fuel cell at lab scale, at 60 °C and different relative humidity (RH 80/100 and 80/60, hydrogen/air) evidenced that new polymers are able to improve electrical performances reaching maximum power density values higher than those showed by conventional MPLs based fuel cells. Electrochemical impedance spectroscopy (EIS) was also carried out on the running cell using a Frequency Response Analyzer to assess the different dissipation phenomena and related losses.     

Optimal microporous layer for proton exchange membrane fuel cell

This study elucidates how fabrication processes (screen-printing and spraying) and constituent materials (carbon paper as backing, Acetylene Black (AB) carbon (42 nm), XC-72R carbon (30 nm) or BP2000 (15 nm) as carbon powders, and 10-50% fluorinated ethylene propylene (FEP) as hydrophobic substances) for microporous layers (MPLs) affect the performance of proton exchange membrane fuel cells. The screen-printing process produces MPLs with smaller surface fractures than does the spraying process. The effect of optimal FEP content on cell performance is noted. The presence of an optimal FEP content is due to the counterbalance between enhanced performance produced with increased gas permeability and decreased performance yielded with small contact area and electrical conductivity with excess FEP. The MPL with large carbon powders is preferred when oxygen supply is limited; otherwise, small carbon powders should be utilized. Optimal MPL design should address negative effects possibly associated with contact resistance, gas permeation resistance, and excess water resistance.     

A novel multi-porous and hydrophilic anode diffusion layer for DMFC

The effect of hydrophilic treatment within the anode diffusion layer for direct methanol fuel cell (DMFC) has been investigated. By nitrated treatment, the surface structure and wettability of diffusion layer can be tuned. The anode micro-porous surface of carbon paper with hydrophilic adhesive after nitrated treatment presents more multi-hole structures with about 30 μm large pores and about 5 μm small pores, which were significantly larger than commercial carbon cloth and carbon paper without nitrated treatment. FTIR and EDS show that the surface of micro-porous layer has more oxygenic groups and the contact angles test also indicates that it becomes more hydrophilic after nitrated treatment. It is indicated that the anode charge transfer resistance and internal resistance dramatically decrease after nitrated treatment on the EIS test. The performance of assembled cell is also evaluated of which the power density of cell using novel diffusion layer (260 mW/cm²) is significantly higher than cell using commercial diffusion layer. The results indicate that this novel multi-porous and hydrophilic anode diffusion layer is suitable to DMFC.     

Effect of hydrophobic gas diffusion layers on the performance of the polymer exchange membrane fuel cell

This study uses fuel cell gas diffusion layers (GDLs) fabricated in the laboratory from carbon fiber cloth with different concentrations of hydrophobic agents in proton exchange membrane fuel cells (PEMFCs), and investigates the relationship between the hydrophobic agent content of the carbon fiber cloth and fuel cell performance.The paper examines the effect of hydrophobic agent content on GDL thickness, contact angle, air permeability, and surface and through-plane resistivity. Carbon fiber cloth is impregnated with hydrophobic agent concentrations of 0, 3, 5, 10, 30, and 50 wt%, and the resulting GDLs are subjected to performance tests. When the test piece area is 25 cm², the test temperature 80 °C, the gasket thickness 0.36 mm, and the hydrophobic agent content 5 wt%, a fuel cell using the GDL has a current density of 1430 mA cm⁻² at 0.3 V.     

Enhancing performance of microbial fuel cells by using novel double-layer-capacitor-materials modified anodes

Super-capacitor (SC) activated-carbon (AC) carbon-nanotubes (CNTs) (SC-AC-CNTs) is a kind of AC-based composite material and it combines the advantages of carbon nanotubes and activated carbon, including a series of peculiar properties such as low charge transmission resistance, super large specific area and excellent power characteristic. In this study, SC-AC-CNTs are first used to modify the carbon cloth (CC) anodes of microbial fuel cells (MFCs) and compared with that of SC-AC and CC. The measurements show that the specific surface area is increased from 219.519 m² g^?1 to 283.643 m² g^?1 after modification. The new anode is assembled in a urine-powered MFC (UMFC) to test its effectiveness. It is found that the amount of microorganisms attached on the new anode is much larger than that on the blank anode in UMFC. The maximum power densities of the UMFC assembled with SC-AC-CNTs and SC-AC modified anodes are 899.52 mW m^?2 and 555.10 mW m^?2, which are 2.9 and 1.8 times of that of the blank UMFC, respectively. The tests also shows that the UMFC with SC-AC-CNTs-modified anode creates a much longer duration of 105 h at high-voltage plateau in a single cycle that is about 2–3 times of the other two groups. These findings demonstrate that these two double layer capacitor materials can effectively boost overall MFC performance.     

Experimental analysis of materials in proton exchange membrane electrolysis cells

An accelerated supply and demand of energy has resulted in an increased need for efficient energy storage options, where storing energy in hydrogen gas emerges as one of the most attractive. In this study, a singular proton exchange membrane (PEM) electrolysis cell was designed using adequately low-cost materials, and tested using polarisation curves, cyclic voltammetry and AC impedance. A comparative study of various micro porous layer (MPL) materials was performed in an effort to find suitable options which are able to steadily operate under anodic conditions. The best performance was achieved using carbon cloth, however this material was unstable. Untreated porous titanium and nickel displayed increased stability, though these materials require further development to match the initial performance of carbon cloth as an MPL material.     

Carbon cloth based on PAN carbon fiber practicability for PEMFC applications

Carbon fiber cloth based on PAN (polyacrylonitrile) material was woven and fabricated into the gas diffusion layer (GDL) for PEMFC applications. This paper describes the newly developed carbon cloth as GDL and proves its feasibility for PEMFC. Such carbon cloth based GDLs have performance equal to that of conventional carbon papers verified using the standard test instrument. The mechanical tests show that as a supporting base, carbon cloth is more practical than carbon paper because of its superior compressibility, elasticity, and flexibility performance, making it more appropriate for ongoing manufacturing and assembly processes. Furthermore, even though carbon paper is structurally flatter and smoother than carbon cloth, the discharge curves of both substrates coated with a MPL (micro-porous layer) showed similar current density (around 750 mA/cm²) at 0.6 V. This indicates that the developed carbon cloth with MPL has achieved the required performance and provides an alternative selection from carbon paper as GDL.     

Carbon materials modified by plasma treatment as electrodes for supercapacitors

The carbon material was modified by RF plasma with various reactive gases: O₂, Ar and CO₂. Physicochemical properties of the final carbon products were characterized using different techniques such as gas adsorption method and XPS. Plasma modified materials enriched in oxygen functionalities were investigated as electrodes for supercapacitors in acidic medium. The electrochemical measurements have been carried out using cyclic voltammetry, galvanostatic charge/discharge and impedance spectroscopy. The electrochemical measurements have confirmed that capacity characteristics are closely connected with a type of plasma exposition. Modification processes have an influence on the kind and amount of surface functional groups in the carbon matrix. The moderate increase of capacity of carbon materials modified by plasma has been observed using symmetric two-electrode systems. Whereas investigations made in three-electrode system proved that the suitable selection of plasma modification parameters allows to obtain promising negative and positive electrode materials for supercapacitor application.     

Effect of carbon fiber cloth with different structure on the performance of low temperature proton exchange membrane fuel cells

This study uses fuel cell gas diffusion layers (GDLs) fabricated in the laboratory from carbon fiber cloth with different structure in proton exchange membrane fuel cells (PEMFCs), and investigates the relationship between the structure of the carbon fiber cloth and fuel cell performance.The paper discusses the relationship between fuel cell performance and structure of the carbon fiber cloth, and also examines the effect of the carbon fiber cloth’s thickness, air permeability, surface resistivity, XRD and elemental analysis. Carbon fiber cloth is carbonized at rates of 190, 220, 250, 280, and 310 °C min⁻¹ respectively, and the resulting carbon fiber cloth is tested in cells. When the test piece area is 25 cm², the test temperature 40 °C, the gasket thickness 0.36 mm, and the carbonization rate 280 °C min⁻¹, a fuel cell using the carbon fiber cloth achieves a current density of 1968 mA cm⁻² and a maximum power density of 633 mW cm⁻² at 0.3 V.     

Marangoni convection flow and heat transfer characteristics of water–CNT nanofluid droplets

ABSTRACT

The heat transfer characteristics of liquid droplets are influenced by the hydrophobicity of the surfaces. Fluid properties and surface energy play important roles in heat transfer assessment. In the present study, the influence of the contact angle on the flow field developed inside a nanofluid droplet consisting of a mixture of water and carbon nanotubes (CNT) is investigated. Flow field and heat transfer characteristics are simulated numerically in line with the experimental conditions. It is found that the flow velocity predicted numerically is in good agreement with the experimental data. Nusselt and Bond numbers increase at large contact angles and Marangoni force dominates over buoyancy force.     

Microbial fuel cell performance of multiwall carbon nanotubes on carbon cloth as electrodes

Microbial fuel cell (MFC), which can produce electricity during treatment of wastewater, has become one of the emerging technologies in the field of environmental protection and energy recovery. Of all parts of MFC, the electrode materials play a crucial role in the electricity generation. In this study, we investigate the performance of carbon nanotube (CNT) modified carbon cloth electrodes in single-chamber MFC. The MFC is first inoculated with bacteria in wastewater and then its capability of using acetate sodium as fuel is examined. The results show that the MFC with CNT coated onto carbon cloth electrode improves the power density. In this study, the obtained maximum power density is 65 mW m⁻², the highest chemical oxygen demand (COD) removal efficiency is 95%, and the maximum Coulombic efficiency is 67%. Compared with other reported studies, the CNT/carbon cloth composite electrode has demonstrated high potential for the use of MFC.     

Numerical modeling and experimental study of the influence of GDL properties on performance in a PEMFC

This work is to study the effect of properties of gas diffusion layer (GDL) on performance in a polymer electrolyte membrane fuel cell (PEMFC) by both numerical simulation and experiments. The 1-dimension numerical simulation using the mixture-phase model is developed to calculate polarization curve. We are able to estimate optimum GDL properties for cell performance from numerical simulation results. Various GDLs which have different properties are prepared to verify accuracy of the simulation results. The contact angle and gas permeability of GDLs are controlled by polytetrafluoroethylene (PTFE) content in micro-porous layers (MPLs). MPL slurry is prepared by homogeneous blending of carbon powder, PTFE suspension, isopropyl alcohol and glycerol. Then the slurry is coated on gas diffusion mediums (GDMs) surface with controlled thickness by blade coating method. Non-woven carbon papers which have different thicknesses of 200 μm and 380 μm are used as GDMs. The prepared GDLs are measured by surface morphology, contact angle, gas permeability and through-plane electrical resistance. Moreover, the GDLs are tested in a 25 cm² single cell at 70 °C in humidified H₂/air condition. The contact angle of GDL increases with increasing PTFE content in MPL. However, the gas permeability and through-plane electrical conductivity decrease with increasing PTFE content and thickness of GDM. These changes in properties of GDL greatly influence the cell performance. As a result, the best performance is obtained by GDL consists of 200 μm thick non-woven carbon paper as GDM and MPL contained 20 wt.% PTFE content.     

基于广州市政垃圾渗滤液的MFC性能及阳极微生物分析

为了分离纯化可适应渗滤液极端环境的产电菌,以广州市白云区李坑和兴丰两处垃圾填埋场获取的渗滤液为底物运行微生物燃料电池（microbial fuel cell, MFC）,待稳定输出多个周期后剪取阳极碳布进行单菌落培养和电镜扫描。结果显示,各组渗滤液底物MFC均能成功启动。李坑四季样的MFC峰值电压分别为0.334、0.331、0.321、0.328 V;兴丰四季样的MFC峰值电压分别为0.512、0.54、0.523、0.536 V。对各组渗滤液底物微生物燃料电池的阳极进行菌株分离纯化并单菌落培养构建阳极微生物系统发育树,发现经过MFC驯化后的阳极菌株具有较高丰度和差异性;SEM扫描发现各组实验中菌株均吸附在阳极碳布上形成稳定的膜结构,根据产电呼吸的基本电子传递机制推测渗滤液底物MFC中的微生物通过与阳极直接接触来传递电子。     

Dynamic behavior of droplet transport on realistic gas diffusion layer with inertial effect via a unified lattice Boltzmann method

The dynamic behavior of liquid droplets on a reconstructed real gas diffusion layer (GDL) surface with the inertial effect produced by the three dimensional (3D) flow channel is investigated using an improved pseudopotential multiphase model within the unified lattice Boltzmann model (ULBM) framework, which can realize thermodynamic consistency and tunable surface tension. The microstructure of the GDL (Toray-090) including carbon fibers and polytetrafluoroethylene (PTFE) is reconstructed by a stochastic and mixed-wettability model. The critical force formulation for the Cassie-Wenzel transition of a droplet on GDL surface is derived. The effects of inertia and contact angles on the liquid droplet transport process on a reconstructed real GDL surface with a 3D flow channel are investigated. The results show the normalized center-of-mass coordinate X may enter the channel wall area or fluctuate around the initial position. With increased inertia applied on the droplet, the normalized center-of-mass coordinate Y grows faster and the normalized center-of-mass coordinate Z decreases. It is found by the ULBM for the first time that the liquid droplet is pushed back into the GDL by inertial effect. With the increase of inertia and the decrease of contact angle of GDL, both the droplet penetration depth in GDL and the droplet invasion fraction increase. The droplet invasion fraction in GDL is up to 30%.     

E-玻璃纤维/乙烯基酯树脂复合材料拉伸与模态特性分析

对小型风力机叶片铺层结构所用的E-玻璃纤维/乙烯基酯树脂复合材料进行拉伸试验与试验模态分析,对比分析不同种类纤维的拉伸强度、破坏形态与弹性模量等抗拉性能与模态特性,得出以下结论:根据拉伸强度、破坏形态与弹性模量得出单轴向0°层合板的抗拉性能更好;随着层数增加,单轴向0°纤维布对挥舞固有频率的影响最大,双轴向±45°纤维布对扭转固有频率的影响最大;层数与铺设角度对一阶挥舞、扭转振型影响较小;小型风力机风轮的转速较高,可铺设更多的单轴向0°纤维布,以改变其模态特性;为初步探究单层、多层板模态参数间的关联性,分析得出铺层顺序的变化对层合板固有频率的影响最大值为1.45 Hz,并为E-玻璃纤维/乙烯基酯树脂复合材料钢叶片的生产与研究提供基础理论依据。     

Modified carbon materials for high-rate EDLCs application

Porous carbon materials, such as activated carbon and activated carbon aerogel, were modified chemically by using a surfactant sodium oleate to improve their specific capacity for high-rate electrochemical double layer capacitors (EDLCs) application. Main impacting factors have been examined for surface modification of activated carbon. Specific capacity can be improved significantly by the surface modification. The enhancement in specific capacity is mainly attributable to improvement in wettability of carbon materials, resulting in a higher usable surface area and a smaller internal resistance. The effects from surface modification become more marked at higher discharge rates, and a much higher energy density can be achieved for the modified carbon materials. In addition, the modified carbon materials possess comparable cycle stability to the original carbon.     

Experimental studies of the effect of cathode diffusion layer properties on a passive direct methanol fuel cell power output

A great challenge in a passive direct methanol fuel cell (pDMFC) is how to reduce both methanol and water crossover, from the anode to the cathode side, without significant losses on its power output. Different approaches including improving the membrane and modifying the cell structure and materials have been proposed in the last years.In this work, an experimental study was carried out to evaluate the effect of the cathode diffusion layer (CDL) properties on the power output of a pDMFC. Towards a cost reduction, lower catalyst loadings were used on both anode and cathode electrodes. Since the main goal was the optimization of a pDMFC using the materials commercially available, different carbon-fibber materials were employed as CDL. The experimental results were analysed based on the polarization curves and electrochemical impedance spectroscopy measurements with innovative electric equivalent circuit allowing the identification of the different losses, including the activation resistance of the parasitic cathode methanol oxidation.A maximum power density of 3.0 mW/cm² was obtained using carbon cloth with a lower thickness as CDL and a methanol concentration of 5 M.     

A review of gas diffusion layer in PEM fuel cells: Materials and designs

The gas diffusion layer (GDL) plays a key role on reactant gas diffusion and water management in proton exchange membrane (PEM) fuel cells. This paper reviews recent developments of single- and dual-layer GDLs for PEM fuel cells and various materials and approaches used for development of novel GDL. A variety of carbon- and metal-based macroporous substrates are presented. Hydrophobic treatments using different fluorinated polymers are addressed. Engineering parameters which control the performance of microporous layer such as carbon treatment, wettability, thickness, and microstructure are also reviewed. In addition, future prospects for development of new GDL development are discussed.