Hydrophilic Microporous Layer Research Articles

Impact of gas diffusion layers (GDLs) on MEA performance in PEFCs

We examined the effect of the hydrophobic/hydrophilic nature of the microporous layer (MPL) on membrane–electrode assembly (MEA) performance. The MEA using a hydrophilic MPL showed much better performance in a wide range of pressure and humidity conditions than that using a hydrophobic MPL. In the MEA operation without humidification, the MEA using a hydrophobic MPL showed a rapid drop in cell voltage with a rise in temperature, whereas the MEA employing a hydrophilic MPL maintained fairly high cell voltage even at 95°C, suggesting that the hydrophilic MPL helps prevent drying out of the membrane under the dry condition.

Hydrophilic and hydrophobic double microporous layer coated gas diffusion layer for enhancing performance of polymer electrolyte fuel cells under no-humidification at the cathode

Gas diffusion layers (GDLs) coated with a hydrophobic microporous layer (MPL) have been commonly used to improve the water management properties of polymer electrolyte fuel cells (PEFCs). In the present study, a new hydrophilic and hydrophobic double MPL coated GDL was developed to achieve further enhancement of PEFC performance under no-humidification at the cathode. The hydrophobic MPL, which consists of carbon black and polytetrafluoroethylene (PTFE), was coated on the carbon paper substrate. The hydrophilic layer, which consists of carbon black and polyvinyl alcohol (PVA), was also coated on the hydrophobic MPL. The hydrophilic layer is effective for conserving humidity at the catalyst layer, while the hydrophobic intermediate layer between the hydrophilic layer and the substrate prevents the removal of water in the hydrophilic layer via dry air in the substrate. Both decrease in the hydrophilic layer thickness to 5 μm and appropriate enhancement of hydrophilicity by increasing the PVA content to 5 mass% are effective for enhancing PEFC performance. Reducing the maximum pore diameter of hydrophobic intermediate layer to 20 μm is also effective for enhancing PEFC performance. However, when the pore diameter of the hydrophobic layer becomes too small, concentration overpotential tends to increase, thereby lowering PEFC performance.

Hydrophilic and Hydrophobic Double MPL Coated GDL to Enhance PEFC Performance under Low and High Humidity Conditions

Gas diffusion layers (GDLs) coated with a hydrophobic microporous layer (MPL) have been commonly used to improve the water management properties of polymer electrolyte fuel cells (PEFCs). In the present study, a new hydrophilic and hydrophobic double MPL coated GDL was developed to achieve further enhancement of PEFC performance under both low and high humidity conditions. For the double MPL coated GDLs, the hydrophilic layers using either PVA (polyvinyl alcohol) or TiO2 were coated on the hydrophobic MPL coated GDL. Under low humidity, the double MPLs with the hydrophilic layers using both PVA and TiO2 are effective for conserving humidity at the catalyst layer, thereby enhancing PEFC performance. Under high humidity, because hydrophilicity of the hydrophilic layer using PVA is too high, PEFC performance is deteriorated due to flooding. However, the appropriate hydrophilic layer using TiO2 is effective for reducing flooding, thereby enhancing PEFC performance.

Development of a novel hydrophobic/hydrophilic double micro porous layer for use in a cathode gas diffusion layer in PEMFC

In this study, a gas diffusion layer (GDL) was modified to improve the water management ability of a proton exchange membrane fuel cell (PEMFC). We developed a novel hydrophobic/hydrophilic double micro porous layer (MPL) that was coated on a gas diffusion backing layer (GDBL). The water management properties, vapor and water permeability, of the GDL were measured and the performance of single cells was evaluated under two different humidification conditions, R.H. 100% and 50%. The modified GDL, which contained a hydrophilic MPL in the middle of the GDL and a hydrophobic MPL on the surface, performed better than the conventional GDL, which contained only a single hydrophobic MPL, regardless of humidity, where the performance of the single cell was significantly improved under the low humidification condition. The hydrophilic MPL, which was in the middle of the modified GDL, was shown to act as an internal humidifier due to its water absorption ability as assessed by measuring the vapor and water permeability of this layer.

Influence of Hydrophilic and Hydrophobic Double MPL Coated GDL on PEFC Performance without Cathode Humidification

Gas diffusion layers (GDLs) coated with a hydrophobic microporous layer (MPL) have been commonly used to improve the water management properties of polymer electrolyte fuel cells (PEFCs). In the present study, a new hydrophilic and hydrophobic double MPL coated GDL was developed to achieve further enhancement of PEFC performance without cathode humidification. A hydrophobic binder of polytetrafluoroethylene (PTFE) and a hydrophilic binder of polyvinyl alcohol (PVA) were used to coat the MPL on the carbon paper substrate. The hydrophilic layer is effective for conserving humidity at the catalyst layer, while the hydrophobic intermediate layer between the hydrophilic layer and the substrate prevents the removal of water in the hydrophilic layer via dry air in the substrate. Reducing the hydrophilic layer thickness to 5 μm was effective for enhancing PEFC performance. Appropriate enhancement of hydrophilicity by increasing the PVA content to 5 mass% was also effective for enhancing PEFC performance.

Effect of wettability of anode microporous layer on performance and operation duration of passive air-breathing direct methanol fuel cells

The influence of the wettability of the anode microporous layer (MPL) on both cell performance and operation duration of air-breathing direct methanol fuel cells (DMFCs) was investigated. The experimental results demonstrated that a passive DMFC with a hydrophilic MPL (DMFC-L) in the anode gas diffusion layer (GDL) showed performance superior to that with a hydrophobic MPL (DMFC-B), when the performance evaluation was conducted by applying a holding time of 45 s at each current density. DMFC-B showed good performance at medium and high current densities when a holding time of 150 s was used. The observation of water accumulation on the cathode of DMFC-L indicated that the decreased performance resulted mainly from blockage of the oxygen supply path. The constant-current discharging test showed that DMFC-B exhibited a lower performance at the beginning of discharge. However, it showed a lower rate of water accumulation on the cathode and thereby relatively stable operation. Operating the passive DMFCs at high water evaporation rate confirmed the important role of the wettability of anode GDLs for cathode oxygen transport.

Water and methanol crossover in direct methanol fuel cells—Effect of anode diffusion media

Various anode diffusion media have been experimentally studied to reduce water crossover in a direct methanol fuel cell (DMFC). A two-phase water transport model was also employed to theoretically study their effects on water transport and saturation level in a DMFC anode. It is found that wettability of the anode microporous layer (MPL) has a dramatic effect on water crossover or the water transport coefficient ( α) through the membrane. Under different current densities, the MEA with a hydrophobic anode MPL has consistently low α, several times smaller than those with a hydrophilic MPL or without an anode MPL. Methanol transport in the anode is found to be not influenced by a hydrophobic anode MPL but inhibited by a hydrophilic one. Constant-current discharge shows that the MEA with hydrophobic anode MPL displays much smaller voltage fluctuation than that with the hydrophilic one. A modeling study of anode water transport reveals that the liquid saturation in the anode is lowered significantly with the increase of anode MPL contact angle, which is thus identified as a key parameter to minimize water crossover in a DMFC.