Effect of carbon fiber paper made from carbon felt with different yard weights on the performance of low temperature proton exchange membrane fuel cells

This study employed fuel cell gas diffusion layers (GDLs) consisting of carbon fiber paper made from carbon fiber felt with different yard weights in proton exchange membrane fuel cells (PEMFCs), and investigated the relationship between the yard weight of the carbon fiber paper and the fuel cell performance and thickness of the gasket. In this paper we discuss the relationship between carbon fiber felt with different yard weights and fuel cell performance and also explore the effect of carbon fiber paper thickness, air permeability, surface resistivity, and structural study. We focused on the material used for the gas diffusion layer in this study. Carbon fiber paper made in-house in this study contained 10 wt% (all percentages are by weight unless otherwise noted) phenolic resin. When the tested area was 25 cm², the test temperature was 40 °C, the gasket thickness was 0.06 mm, and the yard weight 70 g m⁻², fuel cell current density was 1968 mA cm⁻² at a load 0.3 V. When the gasket thickness was 0.36 mm and yard weight was 190 g m⁻², fuel current density was 1710 mA cm⁻² at a load of 0.3 V.     

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.     

Effect of conductive carbon material content and structure in carbon fiber paper made from carbon felt on the performance of a proton exchange membrane fuel cell

This study concerns the use of conductive carbon material with different content and structure to produce carbon fiber paper for use in proton exchange membrane fuel cells, and investigates how changes in the content and structure of the conductive carbon material influence fuel cell performance.In this study, phenolic resin is used as a conductive carbon material, and is subjected to heat treatment at temperatures of 700 °C, 1000 °C, and 1400 °C, which changes its structure. Before carbon fiber paper is prepared from carbon felt, the felt is treated with phenolic resin solutions with resin content of 5, 10, 15, 20, 25, and 30 wt%. During fuel cell testing, torsion of 40, 60, 80, 100, and 120 kgf-cm is applied. The study found that when the phenolic resin content is 15 wt%, the heat treatment temperature 1400 °C, the test area 25 cm², and the test temperature 65 °C, a fuel cell can achieve a current density of 2020 mA cm⁻² at 0.5 V and torque of 120 kgf-cm.     

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.     

High performance cathode based on carbon fiber felt for magnesium-air fuel cells

A series of carbon fiber felt/PTFE based gas diffusion layers (GDL) for Mg-air fuel cells were prepared by a simple method of immersing carbon fiber felt in PTFE suspension. Critical properties of the as-prepared GDL, including the surface morphology, electronic resistivity, porosity and gas permeability, have been characterized to investigate the effect of PTFE suspension concentration and PTFE content on the properties of the GDL. The micrographs indicated that the PTFE was homogenously dispersed on the carbon fiber felts and showed structure with a microporous layer. The as-prepared GDL exhibited good mechanical property, high electronic conductivity, sufficient water repellency and high gas permeability. Compared with the Mg-air fuel cell with a traditional carbon powder based cathode, the performance and the stability of Mg-air fuel cell with the carbon fiber felt based GDL are improved significantly.     

Carbon film coating on gas diffusion layer for proton exchange membrane fuel cells

This study discusses a novel process to increase the performance of proton exchange membrane fuel cells (PEMFC). In order to improve the electrical conductivity and reduce the surface indentation of the carbon fibers, we modified the carbon fibers with pitch-based carbon materials (mesophase pitch and coal tar pitch). Compared with the gas diffusion backing (GDB), GDB-A240 and GDB-MP have 32% and 33% higher current densities at 0.5 V, respectively. Self-made carbon paper with the addition of a micro-porous layer (MPL) (GDL-A240 and GDL-MP) show improved performance compared with GDB-A240 and GDB-MP. The current densities of GDL-A240 and GDL-MP at 0.5 V increased by 37% and 31% compared with GDL, respectively. This study combines these two effects (carbon film and MPL coating) to promote high current density in a PEMFC.     

Effects of porosity gradient in gas diffusion layers on performance of proton exchange membrane fuel cells

A three-dimensional, two-phase, non-isothermal model has been developed to explore the interaction between heat and water transport in proton exchange membrane fuel cells (PEMFCs). Water condensate produced from the electrochemical reaction may accumulate in the open pores of the gas diffusion layer (GDL) and retard the oxygen transport to the catalyst sites. This study predicts the enhancement of the water transport for linear porosity gradient in the cathode GDL of a PEMFC. An optimal porosity distribution was found based on a parametric study. Results show that a optimal linear porosity gradient with ?₁ = 0.7 and ?₂ = 0.3 for the parallel and z-serpentine channel design leads to a maximum increase in the limiting current density from 10,696 Am⁻² to 13,136 Am⁻² and 14,053 Am⁻² to 16,616 Am⁻² at 0.49 V, respectively. On the other hand, the oxygen usage also increases from 36% to 46% for the parallel channel design and from 55% to 67% for the z-serpentine channel design. The formation of a porosity gradient in the GDL enhances the capillary diffusivity, increases the electrical conductivity, and hence, benefits the oxygen transport throughout the GDL. The present study provides a theoretical support for existing reports that a GDL with a gradient porosity improves cell performance.     

Investigation of sintered stainless steel fiber felt as gas diffusion layer in proton exchange membrane fuel cells

The feasibility of using sintered stainless steel fiber felt (SSSFF) as gas diffusion layer (GDL) in proton exchange membrane fuel cells (PEMFCs) is evaluated in this study. The SSSFF is coated with an amorphous carbon (a-C) film by closed field unbalanced magnetron sputter ion plating (CFUBMSIP) to enhance the corrosion resistance and reduce the contact resistance. The characteristics of treated SSSFF, including microscopic morphology, mechanical properties, electrical conductivity, electrochemical behavior and wettablity characterization, are systematically investigated and summarized according to the requirements of GDL in PEMFC. A membrane electrode assembly (MEA) with a-C coated SSSFF-15 GDL is fabricated and assembled with a-C coated stainless steel bipolar plates in a single cell. The initial peak power density of the single cell is 877.8 mW cm⁻² at a current density of 2324.9 mA cm⁻². Lifetime test of the single cell over 200 h indicates that the a-C coating protects the SSSFF-15 GDL from corrosion and decreases the performance degradation from 30.6% to 6.3%. The results show that the SSSFF GDL, enjoying higher compressive modulus and ductility, is a promising solution to improve fluid permeability of GDL under compression and PEMFC durability.     

Effect of gas diffusion layer modulus and land-groove geometry on membrane stresses in proton exchange membrane fuel cells

The electrical functionality of PEM fuel cells is facilitated by minimizing the contact resistances between different materials in the fuel cell, which is achieved via compressive clamping. The effect of the gas diffusion layer (GDL) modulus on the in-plane stress in the membrane after clamping is studied via numerical simulations, including both isotropic and anisotropic GDL properties. Furthermore, the effect of cell width and land-groove width ratio on the in-plane stress in the membrane subjected to a single hygro-thermal cycle is investigated for aligned and alternating gas channel geometries. The results from varying the GDL properties suggest that the in-plane stress in the membrane after clamping is due to a non-linear and coupled interaction of GDL and membrane deformation. The results of the geometric studies indicate that when the gas channels are aligned, the cell width and land-groove width ratio affect the in-plane stress distribution, but do not significantly affect the stress magnitudes. However, when the gas channels are alternating, the cell width and land-groove width ratio have significant effect on the membrane in-plane stresses. The effect of land-groove geometry is qualitatively verified by a series of experimental compression tests.     

Fabrication of a carbon nanofiber sheet as a micro-porous layer for proton exchange membrane fuel cells

A carbon nanofiber sheet (CNFS) has been prepared by electrospinning, stabilisation and subsequent carbonisation processes. Imaging with scanning electron microscope (SEM) indicates that the CNFS is formed by nonwoven nanofibers with diameters between 400 and 700 nm. The CNFS, with its three-dimensional pores, shows excellent electrical conductivity and hydrophobicity. In addition, it is found that the CNFS can be successfully applied as a micro-porous layer (MPL) in the cathode gas diffusion layer (GDL) of a proton exchange membrane fuel cell (PEMFC). The GDL with the CNFS as a MPL has higher gas permeability than a conventional GDL. Moreover, the resultant cathode GDL exhibits excellent fuel cell performance with a higher peak power density than that of a cathode GDL fabricated with a conventional MPL under the same test condition.     

Novel single-layer gas diffusion layer based on PTFE/carbon black composite for proton exchange membrane fuel cell

A series of poly(tetrafluoroethylene)/carbon black composite-based single-layer gas diffusion layers (PTFE/CB-GDLs) for proton exchange membrane fuel cell (PEMFC) was successfully prepared from carbon black and un-sintered PTFE, which included powder resin and colloidal dispersion, by a simple inexpensive method. The scanning electron micrographs of PTFE/CB-GDLs indicated that the PTFE resins were homogeneously dispersed in the carbon black matrix and showed a microporous layer (MPL)-like structure. The as-prepared PTFE/CB-GDLs exhibited good mechanical property, high gas permeability, and sufficient water repellency. The best current density obtained from the PEMFC with the single-layer PTFE/CB-GDL was 1.27 and 0.42 A cm⁻² for H₂/O₂ and H₂/air system, respectively.     

The effect of materials on proton exchange membrane fuel cell electrode performance

This paper describes the optimisation in the fabrication materials and techniques used in proton exchange membrane fuel cell (PEMFC) electrodes. The effect on the performance of membrane electrode assemblies (MEAs) from the solvents used in producing catalyst inks is reported. Comparison in MEA performances between various gas diffusion layers (GDLs) and the importance of microporous layers (MPLs) in gas diffusion electrodes (GDEs) are also shown. It was found that the best performances were achieved for GDEs using tetrahydrofuran (THF) as the solvent in the catalyst ink formulation and Sigracet 10BC as the GDL. The results also showed that our in-house painted GDEs were comparable to commercial ones (using Johnson Matthey HiSpec™ and E-TEK catalysts).     

Development of gas diffusion electrodes for low relative humidity proton exchange membrane fuel cells

A series of polyaniline nanofibers (PANFs) were synthesized and incorporated into gas diffusion electrodes (GDE) of proton exchange membrane fuel cells (PEMFC) to improve their performances at low relative humidity (RH) conditions. Three different placements to incorporate the PANFs in the anodes include (1) placing a PANFs layer between catalyst layer (CL) and membrane, (2) coating the CL with PANFs and catalyst mixed slurry, and (3) placing a PANFs layer between the CL and gas diffusion layer (GDL). Fuel cell performance data indicates that the last method is superior to the others and is adopted as incorporation method thereafter. Extensive studies on single cell performances have been conducted to compare the membrane electrode assemblies with and without the incorporation of PANFs in both anode and cathode. Polarization curves show the incorporation of H₂SO₄-doped PANFs is highly effective in improving the hydrophilic characteristic of the electrodes and thus can promote the PEMFC performance at low RH conditions. For example, with a lowering of reactant RH from 100 to 70%, the electrode with H₂SO₄-doped PANFs layer exhibits an increase in power density from 0.57 to 0.7 W cm⁻². On the other hand, a traditional carbon-supported platinum electrode exhibits a decline of performance from 0.73 to 0.55 W cm⁻².     

High performance proton exchange membrane fuel cell electrode assemblies

The conventional 5-layer membrane electrode assembly (MEA) consists of a proton exchange membrane (PEM) locating at its center, two layers of Pt-C-40 (Pt content 40 wt%) locating next on both surfaces of PEM, and two gas diffusion layers (GDL) locating next on the outer surfaces of Pt-C layers (structure-a MEA). In this paper, we report three modified MEAs consisting of Pt-C-40 (Pt content 40 wt%) and Pt-C-80 (Pt content 80 wt%) catalysts. These are: (1) 7-layer structure-b MEA with a thin Pt-C-80 layer locating between Pt-C-40 layer and PEM; (2) 7-layer structure-c MEA with a thin Pt-C-80 layer locating between Pt-C-40 layer and GDL; and (3) 5-layer structure-d MEA with Pt-C-40 and Pt-C-80 mixing homogeneously and locating between PEM and GDL. Under a fixed Pt loading, we find structure-b, -c, and -d MEAs with 20-40 wt% Pt contributed from Pt-C-80 have better fuel cell performance than structure-a MEA consisting only of Pt-C-40. The reasons for the better fuel cell performance of these modified MEAs are attributed to the better feasibility for O₂ gas to reach cathode Pt particles and lower proton transport resistance in catalyst layers of the modified MEAs than structure-a MEA.     

Hierarchy carbon paper for the gas diffusion layer of proton exchange membrane fuel cells

This communication described the fabrication of a hierarchy carbon paper, and its application to the gas diffusion layer (GDL) of proton exchange membrane (PEM) fuel cells. The carbon paper was fabricated by growing carbon nanotubes (CNTs) on carbon fibers via covalently assembling metal nanocatalysts. Surface morphology observation revealed a highly uniform distribution of hydrophobic materials within the carbon paper. The contact angle to water of this carbon paper was not only very large but also particularly even. Polarization measurements verified that the hierarchy carbon paper facilitated the self-humidifying of PEM fuel cells, which could be mainly attributed to its higher hydrophobic property as diagnosed by electrochemical impedance spectroscopy (EIS).     

Effect of water distribution in gas diffusion layer on proton exchange membrane fuel cell performance

Water management of proton exchange membrane fuel cells remains a prominent issue in research concerning fuel cells. In this study, the gas diffusion layer (GDL) of a fuel cell is partially treated with a hydrophobic agent, and the effect of GDL hydrophobicity on the water distribution in the fuel cell is examined. First, the effect of the position of the cathode GDL hydrophobic area relative to the channel on the fuel cell performance is investigated. Then, the water distribution in the fuel cell cathode GDL is observed using X-ray imaging. The experimental results indicate that when the hybrid GDL's hydrophobic area lies on the channel, water tends to accumulate under the rib, and the water content in the channel is low; this improves the fuel cell performance. When the hydrophobic area is under the rib, the water distribution is more uniform, but the performance deteriorates.     

Water permeation through gas diffusion layers of proton exchange membrane fuel cells

Water transport through gas diffusion layer of proton exchange membrane fuels cells is investigated experimentally. A filtration cell is designed and the permeation threshold and the apparent water permeability of several carbon papers are investigated. Similar carbon paper with different thicknesses and different Teflon loadings are tested to study the effects of geometrical and surface properties on the water transport. Permeation threshold increases with both GDL thickness and Teflon loading. In addition, a hysteresis effect exists in GDLs and the permeation threshold reduces as the samples are retested. Moreover, several compressed GDLs are tested and the results show that compression does not affect the breakthrough pressure significantly. The measured values of apparent permeability indicate that the majority of pores in GDLs are not filled with water and the reactant access to the catalyst layer is not hindered.     

Effects of a microporous layer on the performance degradation of proton exchange membrane fuel cells through repetitive freezing

The gas diffusion layer (GDL) covered with a microporous layer (MPL) is being widely used in proton exchange membrane fuel cells (PEMFCs). However, the effect of MPL on water transport is not so clear as yet; hence, many studies are still being carried out. In this study, the effect of MPL on the performance degradation of PEMFCs is investigated in repetitive freezing conditions. Two kinds of GDL differentiated by the existence of MPL are used in this experiment. Damage on the catalyst layer due to freezing takes place earlier when GDL with MPL is used. More water in the membrane and catalyst layer captured by MPL causes permanent damage on the catalyst layer faster. More detailed information about the degradation is obtained by electrochemical impedance spectroscopy (EIS). From the point of view that MPL reduces the ohmic resistance, it is effective until 40 freezing cycles, but has no more effect thereafter. On the other hand, from the point of view that MPL enhances mass transport, it delays the increase in the mass transport resistance.     

Recent progress of the gas diffusion layer in proton exchange membrane fuel cells: Material and structure designs of microporous layer

Proton exchange membrane fuel cells (PEMFCs) have become the most attractive power supply units for stationary and mobile applications. The operation, design characteristics, as well as performance of PEMFCs, are closely related to the multiphase transport of mass, heat, and electricity in the cell, a critical of which is the gas diffusion layer (GDL). It is very important to guarantee the transmission of water and gasses under high current density, and which is the weakness of PEMFCs at present. Microporous layer (MPL) is considered to be the key variable for mass transfer, so varieties of works focus on modification of MPL materials and its structure design. However, there is still a lack of special review to summarize and prospect the progress of MPL in recent years. This review article therefore focuses on the insights and comprehensive understanding of four critical issues of the MPL, the porosity, pore size distribution, wettability, structural design and the durability of MPL. At last, the conclusion and recommendations section summarized the future prospects and recommendations for possible research opportunities.