Study of a porous membrane humidification method in polymer electrolyte fuel cells (original) (raw)
Related papers
Humidification studies on polymer electrolyte membrane fuel cell
Journal of Power Sources, 2001
Two methods of humidifying the anode gas, namely, external and membrane humidi®cation, for a polymer electrolyte membrane fuel (PEMFC) cell are explained. It is found that the water of solvation of protons decreases with increase in the current density and the electrode area. This is due to insuf®cient external humidi®cation. In a membrane-based humidi®cation, an optimum set of parameters, such as gas¯ow rate, area and type of the membrane, must be chosen to achieve effective humidi®cation. The present study examines the dependence of water pick-up by hydrogen on the temperature, area and thickness of the membrane in membrane humidi®cation. Since the performance of the fuel cell is dependent more on hydrogen humidi®cation than on oxygen humidi®cation, the scope of the work is restricted to the humidi®cation of hydrogen using Na®on 1 membrane. An examination is made on the dependence of water pick-up by hydrogen in membrane humidi®cation on the temperature, area and thickness of the membrane. The dependence of fuel cell performance on membrane humidi®cation and external humidi®cation in the anode gas is also considered. #
Performance of PEM Fuel Cells without External Humidification of the Reactant Gases
ECS Proceedings Volumes, 1995
Operation of polymer electrolyte fuel cells (PEMFC) without external humidification of the reactant gases is advantageous for the PEMFC system. This is, because this mode of operation eliminates the need of a gas-humidification subsystem which is a burden the fuel pell system with respect to weight, complexity, cost and parasitic power. We investigated the possible range of operating conditions for a PEMFC using dry H /a ir by applying a simple model and it was found, that dry air, passing at the cathode, may be fully internally humidified by the water produced by the electrochemical reaction at temperatures up to 70 *C. The water distribution in the cell operated on dry gases is dominated by the backdiffusion o f product water to the anode. The dominating water back diffusion allows for internally humidifying also the hydrogen and prevents drying out o f the anode. With optimized membrane-electrode-assemblies (MEA), self-humidified cells achieve similar performance as cells withs standard MEA's and humdified gases. The performance of single cells and small stacks is investigated.
Journal of Power Sources, 2011
Although water management at the cathode is known to be critical in miniature polymer electrolyte membrane fuel cells (mPEMFCs), this study shows that control of water transport towards the anode is a determining factor to increase air-breathing mPEMFC performances. An analytical 1D model is developed to capture the water transport and water content profile in the membrane. It shows that drying at the anode and flooding at the cathode can happen simultaneously, mainly due to dominant electro-osmotic drag at low cell temperatures. Experimental results demonstrate that injecting water at the anode, at a rate of 3 times the amount produced at the cathode, increases the cell performances at high current densities. By this method, the limiting current and maximum power densities have been raised by 100% and 30% respectively.
Journal of Power Sources, 2006
For portable applications, the, characteristics of passive air-breathing PEMFCs were investigated by examining effects of cathode open area and relative humidity on the cell performance. Among the single cells with cathode open area from 52 to 94%, the single cell with the open area of 77% exhibited the highest performance. The cell performance was improved with increasing RH of atmosphere from 20 to 100% in the low current region while lowered in high current region. Those results were related with the mass transport of oxygen from the atmosphere to the catalyst layer and the degree of membrane hydration determining the ionic conductivity of the membrane.
Relative humidity control in polymer electrolyte membrane fuel cells without extra humidification
Journal of Power Sources, 2008
The performance of polymer electrolyte membrane fuel cells is highly influenced by the water content in the membrane. To prevent the membrane from drying, several researchers have proposed extra humidification on the input reactants. But in some applications, the extra size and weight of the humidifier should be avoided. In this research a control technique, which maintains the relative humidity on saturated conditions, is implemented by adjusting the air stoichiometry; the effects of drying of membrane and flooding of electrodes are considered, as well. For initial analysis, a mathematical model reveals the relationship among variables that can be difficult to monitor in a real machine. Also prediction can be tested optimizing time and resources. For instance, the effects of temperature and humidity can be analyzed separately. For experimental validation, tests in a fault tolerant fuel cell are conducted.
Nafion® Tubing Humidification System for Polymer Electrolyte Membrane Fuel Cells
Energies
Humidity and temperature have an essential influence on PEM fuel cell system performance. The water content within the polymeric membrane is important for enhancing proton conduction and achieving high efficiency of the system. The combination of non-stationary operation requests and the variability of environment conditions poses an important challenge to maintaining optimal membrane hydration. This paper presents a humidification and thermal control system, to prevent the membrane from drying. The main characteristics of such a device are small size and weight, compactness and robustness, easy implementation on commercial fuel cell, and low power consumption. In particular, the NTHS method was studied in a theoretical approach, tested and optimized in a laboratory and finally applied to a PEMFC of 1 kW that supplied energy for the prototype vehicle IDRA at the Shell Eco-Marathon competition. Using a specific electronic board, which controls several variables and decides the optima...
Journal of Power Sources, 2013
Polymer electrolyte membrane fuel cells (PEFC) with a porous flow field have been proposed as an alternative to cells with gas flow channels. In this study, the basic characteristics of a PEFC with a porous flow field are identified experimentally. It is shown that stable operation is maintained under conditions at high current density and low stoichiometric ratios of the cathode air, but that operation with low relative humidity gases is difficult in the porous type cell. To clarify the detailed causes of these characteristics, internal phenomena are investigated using a cell specially made for cross-section observations of the cathode porous flow field and temperature distribution measurements on the anode gas diffusion layer (GDL) surface. The direct observations show that the porous type cell is superior in draining the condensed water from the GDL surface, and that hydrophilic properties of the porous material is important for better cell performance at high current densities. The temperature measurements indicate that increases in temperature near the reaction area tends to be larger in the porous type cell than in the channel type cell due to the lower heat removal capability of the porous material, resulting in the unstable operation at relatively low humidities.
An analytic model of membrane humidifier for proton exchange membrane fuel cell
Environmental Engineering Science, 2014
An essential requirement for an operating PEM fuel cell is providing proper water content in the membrane. To avoid water flooding an appropriate water balance is required. Here, an analytic model of a planar membrane humidifier for PEM fuel cell is proposed where the effect of dimensional parameters includes membrane thickness, membrane area and channel hydraulic diameter are investigated. A Non-linear governing equations system is developed and solved. At each stage, the outlet temperatures, the water and heat transfer rates, relative humidity and the dew point at dry side outlet are presented and discussed. The humidifier is evaluated based on the decrease in difference between the dew point at wet side inlet and dry side outlet which leads to humidifier better performance. The results show that an increase in membrane thickness results in a decrease in dew point at dry side outlet which indicates a weak humidifier performance. Vaster membrane area can enhance humidifier performa...