Water balance in a free-breathing polymer electrolyte membrane fuel cell (original) (raw)
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Water transport characteristics of polymer electrolyte membrane fuel cell
International Journal of Hydrogen Energy, 2004
This paper describes the performance of a polymer electrolyte membrane fuel cell (PEMFC) system without humidiÿcation of the reactants which consumes a lot of parasitic power, increases the weight of the PEMFC system and thus adds complexity. Such PEMFC systems are preferable for portable applications. The results indicate that dry gas operation depends on various factors like reactant ow ÿeld design, area of the electrode and equilibration time for the product water. The performance of the fuel cell can be improved by giving some equilibration time for the product water, produced by the electrochemical reactions, to get transported across the membrane to the anode side, thus increasing the conductivity of the membrane. The water transported through the membrane across the cell was investigated by measuring the amount of product water at the anode side which allows humidiÿcation for the anode gas and less condensed water in the uid ow channels of the cathode. ?
Investigation of water transport through membrane in a PEM fuel cell by water balance experiments
Journal of Power Sources, 2006
Water balance in a polymer electrolyte membrane fuel cell (PEMFC) was investigated by measurements of the net drag coefficient under various conditions. The effects of water balance in the PEMFC on the cell performance were also investigated at different operating conditions. Experimental results reveal that the net drag coefficient of water through the membrane depended on current density and humidification of feed gases. It was found that the net drag coefficient (net number of water molecules transported per proton) ranged from −0.02 to 0.93, and was dependent on the operating conditions, the current load and the level of humidification. It was also found that the humidity of both anode and cathode inlet gases had a significant effect on the fuel cell performance. The resistance of the working fuel cell showed that the membrane resistance increased as the feed gas relative humidity (RH) decreased. The diffusion of water across Nafion membranes was also investigated by experimental water flux measurements. The electro-osmotic drag coefficient was evaluated from the experimental results of water balance and diffusion water flux measurements. The value of electro-osmotic drag coefficient, ranging from 1.5 to 2.6 under various operating conditions, was in agreement with literature values. The electro-osmotic drag coefficient, the net flux of water through the membrane and the effective drag as a function of operating conditions will also provide validation data for the fuel cell modeling and simulation efforts. (Q. Yan). even be irreversibly damaged in extreme cases. Therefore, polymer membrane materials used in PEMFCs must be hydrated in order to maintain high proton conductivity, and at the same time, excess water must be removed to prevent flooding. Membrane hydration is affected by the water transport phenomena in the membrane itself, which in turn is affected by the condition of the inlet gases and the operating parameters of the fuel cell. Therefore, it is very important to maintain an optimal water balance during the operation of PEMFCs. The water balance must be maintained to ensure that optimal performance is achieved.
Water balance in a polymer electrolyte fuel cell system
Journal of Power Sources, 2002
Polymer electrolyte fuel cell (PEFC) systems operating on carbonaceous fuels require water for fuel processing. Such systems can find wider applications if they do not require a supply of water in addition to the supply of fuel, that is, if they can be self-sustaining based on the water produced at the fuel cell stack. This paper considers a generic PEFC system and identifies the parameters that affect, and the extent of their contribution to, the net water balance in the system. These parameters include the steam-to-carbon and the oxygen-to-carbon ratios in the fuel processor, the electrochemical fuel and oxygen utilizations in the fuel cell stack, the ambient pressure and temperature, and the composition of the fuel used. The analysis shows that the amount of water lost from the system as water vapor in the exhaust is very sensitive to the system pressure and ambient temperature, while the amount of water produced in the system is a function of the composition of the fuel. Fuels with a high H/C (hydrogen to carbon atomic ratio) allow the system to be operated as a net water producer under a wider range of operating conditions. # Steam-to-carbon ratio in the fuel processor. Oxygen-to-fuel ratio in the fuel processor. Fuel and oxidant utilizations in the fuel cell stack.
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.
Effects of Flow Characteristics in Polymer Electrolyte Membrane Fuel Cell
An experimental and numerical study of polymer electrolyte membrane fuel cell (PEMFC) is presented and compared with the experimental data to investigate the effects of pressure gradient, flow rate, humidification and supplied oxidant type for the practical application. The membrane and electrolyte assembly (MEA) materials are implemented by double-tied catalyst layers. A single-phase two-dimensional steady-state model is is implemented for the numerical analysis. Testing condition is fixed at 60sccm and 70°C in anode and cathode, respectively. It is found that the performance of PEMFC depend highly on the conditions as gas pressure, temperature, thickness, supplied oxidant type (Oxygen/Air) as well as humidification. The results show that the humidification effect enhances the performance more than 20% and the pure oxygen gas as fuel improves current density more than 25% compared to ambient air suppliance as oxidant.
Evaluation of planar free-breathing polymer electrolyte membrane fuel cell design
Journal of Power Sources, 2004
A planar cell design for free-breathing fuel cell is studied. The cathode side of the cell was directly open to ambient air in a way that oxygen needed by the fuel cell reaction was provided by diffusion through the cathode side gas diffusion backing, i.e. the cell had no cathode side flow channels. The aim of the study was to demonstrate the feasibility of the cell concept by experimentally evaluating its performance with polarisation and current transient measurements. The orientation of the cell did not significantly affect the performance of the cell and signs of flooding were not observed. The maximum power density achieved in the polarisation measurements was ∼124 mW cm −2 . The current transient measurements revealed that with a small base load the cell is capable of producing momentarily current densities up to 500 mA cm −2 . The maximum transient power density achieved was ∼194 mW cm −2 at transient current density of 450 mA cm −2 . According to the results it seems that this kind of cell design is feasible for small-scale applications, such as portable computers.
Water transport in polymer electrolyte membrane fuel cells
2011
Polymer electrolyte membrane fuel cell (PEMFC) has been recognized as a promising zero-emission power source for portable, mobile and stationary applications. To simultaneously ensure high membrane proton conductivity and sufficient reactant delivery to reaction sites, water management has become one of the most important issues for PEMFC commercialization, and proper water management requires good understanding of water transport in different components of PEMFC. In this paper, previous researches related to water transport in PEMFC are comprehensively reviewed. The state and transport mechanism of water in different components are elaborated in detail. Based on the literature review, it is found that experimental techniques have been developed to predict distributions of water, gas species, temperature and other parameters in PEMFC. However, difficulties still remain for simultaneous measurements of multiple parameters, and the cell and system design modifications required by measurements need to be minimized. Previous modeling work on water transport in PEMFC involves developing rule-based and first-principle-based models, and first-principle-based models involve multi-scale methods from atomistic to full cell levels. Different models have been adopted for different purposes and they all together can provide a comprehensive view of water transport in PEMFC. With the development of computational power, application of lower length scale methods to higher length scales for more accurate and comprehensive results is feasible in the future. Researches related to cold start (startup from subzero temperatures) and high temperature PEMFC (HT-PEMFC) (operating at the temperatures higher than 100 C) are also reviewed. Ice formation that hinders reactant delivery and damages cell materials is the major issue for PEMFC cold start, and enhancing water absorption by membrane electrolyte and external heating have been identified as the most effective ways to reduce ice formation and accelerate temperature increment. HT-PEMFC that can operate without liquid water formation and membrane hydration greatly simplifies water management strategy, and promising performance of HT-PEMFC has been demonstrated.
Journal of Power Sources, 2009
The effect of the operating conditions, e.g., load, temperature, relative humidity (RH), and the MEA's aging condition on the pH of the water drained out from the cathode and anode sides of a H2/air PEM fuel cell was studied. Also the effect of the pollutants’ existence in natural air on the measured pH and the performance of the fuel cell was investigated. pH values as low as 1 were measured for the water drained out from the cathode side under a low temperature–low RH condition. Increasing the load, temperature or RH value resulted in an increase of the measured pH except for the low temperature–low RH condition where increasing the load resulted in a decrease in the measured pH. On the other hand, the pH value of the water drained out from the anode side was around 4 under the same low temperature–low RH condition. Aging of the MEA at 90 °C and RH of 100% for at least 30 h resulted in low measured pH values for the water drained out from the cathode side. The polarization behaviors of the cathode under these different conditions were measured and correlated to the pH change and the performance of the MEA. Measuring the pH using a flow pH meter for the water droplets drained out from the cathode side can be used as an alarm for the onset of the chemical degradation of the Nafion membrane.
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. #