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Polymer Electrolyte Fuel Cell (PEFC) is desired to be operated over 90℃ during the period from 2020 to 2025 in Japan. The aim of this study is to clarify the impact of microporous layer (MPL) on the temperature profile of interface between polymer electrolyte membrane (PEM) and catalyst layer at the cathode (i.e., the reaction surface) in a single PEFC with an initial temperature of cell (Tini) from 80℃ to 100℃. An 1D multi-plate heat transfer model based on temperature data of separator measured using thermograph in power generation was developed to evaluate temperature of the reaction surface (Treact). This study investigated the effect of MPL, Tini, flow rate and relative humidity of supply gas on Treact distribution. As a result, it is found that the impact of flow rate of supply gas on Treact distribution is little irrespective of MPL, Tini and relative humidity of supply gas. When MPL is not coated, Treact – Tini is higher by 2℃ - 3℃ and relatively flat compared to MPL coating condition and Treact – Tini with MPL is increased by 1℃ from the inlet to outlet of cell irrespective of Tini and relative humidity of supply gas. In addition, it is revealed that Treact – Tini with MPL is the highest when the relative humidity of supply gas is 40 %RH at the anode and 40 %RH at the cathode, which is the lowest relative humidity condition in this study.

Effects of polymer structure on the electroosmosis in proton exchange membranes (PEMs) have been investigated using a reactive molecular dynamics simulation. An anharmonic two-state empirical valence bond (αTS-EVB) model has been used to describe efficiently excess proton transport via the Grotthuss hopping mechanism. The electroosmotic drag coefficients (i.e., the number of water molecules transferred through the membrane per proton) has been evaluated directly in PEMs consisting of various equivalent weights (EWs). The electroosmotic drag coefficients from the MD simulations are in good agreement with the available experimental values at studied levels of hydration. It is shown that for low water contents the connectivity of the water clusters decreases with increasing EW, leading to a decrease in the electroosmotic drag coefficients. The proton and water mobility is also found to decrease with increasing EW because of the structural changes in the water cluster domains. The present simulations provide quantitative information about the direct link between electroosmosis and nanoscopic water domain structure in different polymer structures

A fuel cell with a simple structure and operating at nearly ambient temperature and pressure is suitable for low cost small-sized generator sets ranging from several to tens Watts for home, outdoor and emergency use. This kind of fuel cell is called passive or self-breathing PEFC. Water management is very important and sometimes crucial for a long term stable operation in the passive type PEFC because control of gas temperature and humidity is inherently not easy for the PEFC. In this paper, various performance characteristics regarding the passive type PEFC were experimentally investigated using a rated 55 W fuel cell module with 20 cells laid out in plane. The properties, such as the output voltage of each cell, the temperature, pressure and humidity of hydrogen and air, were measured with time in the dead-end system and the recirculation system for hydrogen supply. The water balance in the fuel cell module was then calculated and the behavior of generated water, which should cause output power breakdown and voltage fluctuation in certain conditions, was also discussed. Results showed that a sudden power breakdown in a long time continuous operation with dead-end hydrogen supply system was caused by flooding in the anode and that this shortcoming was overcome by introducing a simple hydrogen recirculation system with valves and a water trap. Results also showed that 95% of produced water by the reaction was discharged from the cathode to the atmosphere in the form of vapor and that 5% trapped in the form of liquid in the hydrogen recirculation system.

A three dimensional, single-phase, isothermal study of a polymer electrolyte fuel cell (PEFC) was conducted to investigate the mechanism of convective flow effect on the performance of fuel cell. Convective flow was caused by inlet velocity and cross flow through the GDL. To clarify the mechanism of cross flow effect on the performance of PEFC, it was induced in the parallel flow field, whereas cross flow inherently appear in the serpentine flow fields. In addition, to isolate the contribution of cross flow on the performance, the simulation was executed with a low current density where oxygen transport resistance was stronger than proton/electron transport resistance. Gas channels with a smaller pitch length produced a more uniform current density than those with a larger pitch length. With increase of inlet velocity the performance increases for any values of pitch length. Cross flow through the GDL caused by the differential pressure between adjacent channels had significantly enhanced the local current density of a PEFC and simultaneously increased the degree of non-uniformity in the current density. The cross flow can increase the performance of fuel cell by reducing the oxygen transport resistance. Therefore, it is possible to overcome the oxygen transport limitation by inducing cross flow.

The performance of high purity hydrogen production from methanol for a compact steam reformer with a hydrogen purification membrane was investigated experimentally. A 77 wt.% Pd/23 wt.% Ag membrane with 25µm thickness and CuO/ZnO/ Al2O3 catalyst were used. Heating was performed by a Bunsen type burner using City Gas 13A. The methanol reforming and purification of H2 were investigated at different reference catalyst zone temperatures (589-689K), pressures at the retentate side (0.2-0.5MPa), steam to methanol(S/C) ratios (0.8-1.6) and reactant flow rates (1.7 ×10-4 to 4.4×10-4 mol/s). The results show that at high reference temperature, high pressure and certain points of the reactant flow rate, the maximum hydrogen permeation rate is obtained when the S/C ratio is around 1. The modified Sieverts’ equation which considers the decrease in H2 concentration at the membrane surface, was proposed. The experimental result was lower than the permeation rate estimated by the modified Sieverts’ equation, which is probably caused by the adsorption of non-H2 species during permeation. It is further demonstrated that the modified Sieverts’ equation is able to estimate a more reasonable hydrogen permeation rate in comparison to the estimation by the ordinary Sieverts’ equation. In addition, it is shown that the compact methanol steam reformer with a Pd/Ag membrane is able to produce high purity hydrogen with very low CO concentration, which fulfills the Polymer Electrolyte Fuel Cell (PEFC) requirement (

The structure of cathode catalyst layer (CCL) has strong relationship with the performance of polymer electrolyte fuel cells (PEFCs). We investigated the relationship between the catalyst layer structure and the cell performance experimentally. Multi-layered CCL is used to investigate the effect of the layer design on the cell performance. Membrane side of CCL works, as a reaction area, more actively than the gas diffusion layer (GDL) side at low relative humidity (RH) due to the lower proton conductivity. On the other hand, when the cathode gas has less oxygen partial pressure at high RH, GDL side is more active than membrane side owing to low diffusivity of oxygen. We suggest that the volumetric catalyst concentration of the CCL membrane side should be higher at low RH, however at high RH with lower oxygen partial pressure in cathode gas, the GDL side should have higher concentration. Simple theoretical model is employed to see the behavior of the reaction distribution in the catalyst layer.

To point out the dominant factor of mass, heat and electric charge transfer phenomena in a single cell of PEFC for the promotion of power generation performance, the impact of gas channel pitch on in-plane distribution of mass concentration and temperature on reaction surface is investigated by simulation and experiment. Two-dimensional model of single cell which has the different gas channel pitch is simulated by CFD software. In the experiment using the separators which have different gas channel pitches, the data of power generation and in-plane distribution of temperature measured by thermograph are acquired to verify the simulation result. As a result, the in-plane distribution of gas, water and temperature on the reaction surface becomes more even with decreasing gas channel pitch under the condition investigated in this study, resulting that the power generation performance is promoted. With decreasing gas channel pitch, the temperature in observation area is dropped and total voltage is elevated. To enhance the power generation performance of PEFC under the conditions investigated in this study, the flow rate of supply gas of stoichiometric ratio of 1.00 and the gas channel pitch of 0.5 mm can be proposed.

Micromachined titanium thin film current collector, Ti-CC, that is developed in our previous work is used to investigate the concentration overpotential due to the liquid water filling in the through-holes of Ti-CC. The effects of the Ti-CC porosity, volumetric flow rate and the channel/rib width on i-V characteristics are examined. Previously proposed model for the limiting current density can describe the trend in experimental data. Comparison with the results of visualization experiment confirms the feasibility of the newly developed model for i-V relation at each water coverage ratio of the Ti-CC. The results quantitatively show the importance of concentration overpotential due to the water droplet and suggest possible improvement of the cell performance with proper liquid water management.

Polymer electrolyte fuel cell (PEFC) has been developing as clean power generation technology. However, there are some subjects to spread PEFC among industries and homes in the world. The one of such subjects is drop in power generation performance and durability caused by heat and mass distribution in a single cell of PEFC. The purpose of this study is to point out the dominant factor of heat and mass transfer phenomena and clarify the reason for heat and mass distribution in a single cell. With the aid of observation window, the in-plane temperature distribution in single cell under power generation was measured by thermograph. The influence of operation conditions on temperature distribution was investigated. Moreover, to clarify the heat and mass transfer mechanism theoretically, the simulations to investigate the factor needed for the ideal reaction and evaluate the influence of separator structure on heat and mass distribution were carried out.