Polymer Electrolyte Membrane Water Research Articles

Water Management Capacity of Metal Foam Flow Field for PEMFC under Flooding Situation.

Porous metal foam with complex opening geometry has been used as a flow field to enhance the distribution of reactant gas and the removal of water in polymer electrolyte membrane fuel cells. In this study, the water management capacity of a metal foam flow field is experimentally investigated by polarization curve tests and electrochemical impedance spectroscopy measurements. Additionally, the dynamic behavior of water at the cathode and anode under various flooding situations is examined. It is found that obvious flooding phenomena are observed after water addition both into the anode and cathode, which are alleviated during a constant-potential test at 0.6 V. Greater abilities of anti-flooding and mass transfer and higher current densities are found as the same amount of water is added at the anode. No diffusion loop is depicted in the impedance plots although a 58.3% flow volume is occupied by water. The maximum current density of 1.0 A cm-2 and the lowest Rct around 17 mΩ cm2 are obtained at the optimum state after 40 and 50 min of operation as 2.0 and 2.5 g of water are added, respectively. The porous metal pores store a certain amount of water to humidify the membrane and achieve an internal "self-humidification" function.

Convolutional neural network analysis of radiography images for rapid water quantification in PEM fuel cell

Polymer electrolyte membrane (PEM) fuel cells produce water as a byproduct, which, if not properly managed, will cause electrode “flooding” and consequently performance loss. Nonintrusive methods, such as neutron or X-ray radiography, have been employed to obtain in-situ water images in PEM fuel cell. This study presents one of the first studies developing a machine learning approach to analyze neutron radiography images using the convolutional neural network (CNN), a deep learning model, to quantify liquid water content in PEM fuel cell. The CNN model is trained using the labeled radiography images constructed from the contour legend, which contains the information of the water areal mass density. Image enhancement is carried out to generate additional data for CNN training. The properly-trained CNN model is subsequently applied to the radiography images to obtain the average water areal mass densities under various current densities, relative humidity (RH), and flow fields. The results show that the water content can be significantly reduced by using low RH inlet flow and the counter-flow configuration renders the fuel cell a higher water content than the co-flow one. In addition, the quad-serpentine flow field increases the water content in the current density range of 0.4–0.8 A/cm2 compared with the single-serpentine one. The CNN model takes less than 0.1 s to analyze an image and its results agree well with the literature data from the conventional image processing method with an accuracy of 91%. The CNN method is applicable to other radiography methods and is suitable for the online/rapid monitoring of liquid water in PEM fuel cell.

Impact of cross-linking of polymers on transport of salt and water in polyelectrolyte membranes: A mesoscopic simulation study.

Our recent atomistic simulation studies demonstrated that the transport properties of salt ions and water in non-crosslinked polymer electrolyte membrane exhibit an intriguing dependence on salt concentration that is opposite to that seen in electrolyte solutions. Here, we extend our study to probe the influence of the degree of cross-linking of the polymer on the transport properties of salt and water in polymer electrolyte membranes. Towards this objective, we use a coarse-grained model embedded within dissipative particle dynamics (DPD) mesoscale simulations, which allows us to access time scales necessary for studying crosslinked polymer systems. Our DPD simulations on non-crosslinked membranes reproduce results that are in qualitative agreement with our atomistic simulations. For the case of crosslinked membranes, our results demonstrate that the diffusion of salt ions and water is reduced significantly relative to crosslinked systems. However, the trends exhibited by the salt concentration dependence of diffusivities and the coordination of the cations with anions and with the polymer backbone remain qualitatively similar to those observed in non-crosslinked membranes.

Proton conductivity improvement of polymer electrolyte membrane using nano-scale explosion of water in the membrane

Proton conductivity of polymer electrolyte membrane (PEM) is greatly governed by the amount and distribution of water as well as morphology and alignment of hydrophilic channels forming the ion cluster network in the PEM. However, The water in PEM during hot-pressing above the glass-transition temperature of PEM and the boiling point of water has not been expected to influence the proton conductivity. Here we show that higher water amount of PEMs during the hot-pressing process results in better fuel cell performance due to shortcut-proton-pathways generated by the sudden water explosion on the nano-scale. Our results demonstrate a new post-PEM-processing method to enhance proton conductivity without additional tool/procedure, and provide some clues to the behavior of liquid molecules embedded on the nano-scale in polymers. This may open a new door to nano-scale explosion of water and/or other small liquid molecules for morphological change of pores/channels in polymer.

Nanoscale Transport Phenomena in PEM of PEFC by Large Scale Molecular Dynamics Simulations

In this paper, we analyzed the nanoscale transport phenomena in membrane electrode assembly (MEA) of polymer electrolyte fuel cell (PEFC) by large scale molecular dynamics (MD) simulations. Especially, (1) transport phenomena of proton and water in polymer electrolyte membrane (PEM), (2) oxygen permeability of ionomer in catalyst layer (CL), and (3) transport phenomena of water droplet in a nano pore were simulated, and the nanoscale transport characteristics were analyzed in detail. In the analysis of proton transfer in PEM, the simulation results were compared with some experimental results to evaluate the validity of our simulation. With regards to the oxygen permeability of ionomer, the dependence of water content on the permeability was estimated and the difference of characteristics between ionomer and bulk membrane was discussed. In the analysis of transport phenomena of a water droplet in a nano pore, we compared the results of our simulation with macroscopic governing equation.

S053021 ラマン分光法・密度汎関数法による固体高分子電解質膜内の水吸着状態解析([S05302]次世代電池のナノ・マイクロフルイディクス(2))

S053021 ラマン分光法・密度汎関数法による固体高分子電解質膜内の水吸着状態解析([S05302]次世代電池のナノ・マイクロフルイディクス(2))

Analysis of State of Water in Polymer Electrolyte Membrane by Raman Spectroscopy and DFT

Proton and water transport in polymer electrolyte membrane (PEM) are key transport properties for the improvement in PEMFCs performance under high current density operation which is desired in PEMFCs for automobiles. In this study, state of water in PEM is investigated by using confocal micro-Raman spectroscopy and density functional theory (DFT). The results showed that OH vibration peak shape indicated the state of water in the membrane. In particular, OH vibration peak around 3500cm-1 was strongly related to water transport through the membrane, while a peak around 3200cm-1 was assigned by formation of hydrogen-bonded water molecule network around sulfonic acid by DFT. DFT calculation also indicated that a hydronium ion around sulfonic acid contributes to the formation of water network.

Analysis of State of Water in Polymer Electrolyte Membrane by Raman Spectroscopy and DFT

not Available.

Absorption, Desorption, and Transport of Water in Polymer Electrolyte Membranes for Fuel Cells

The transport of water vapor through a Nafion membrane includes absorption of water at one membrane/gas diffusion layer interface, water transport in the membrane, and desorption of water at another interface. Based on the structure of the membrane, a model for the water transport through the membrane is presented. It was assumed that the mass-transfer coefficients for the absorption and desorption of water and the water diffusion coefficient were dependent on the volume fraction of water in the membrane. These parameters were determined from steady-state water transport flux through the membranes at different water activity gradients. The results show that the mass-transfer coefficient for the absorption of water (, ) is much lower than that for the desorption of water (, ). The parameters and describe the nonequilibrium water uptake of the membrane on operating conditions. Using these obtained parameters, the simulation results agree well with experimental data under many different conditions, including thickness of the membrane, water vapor/liquid water, temperature, and flow rate.

Water and Thermal Balance in PEM and Direct Methanol Fuel Cells

A key consideration for portable power systems is that they must operate simultaneously at water balance (no external water supply) and thermal balance (controlled temperature). Water and thermal management are intimately linked since evaporation is a potent source of cooling. This paper presents the basic design relationships that govern water and thermal balance in polymer electrolyte membrane (PEM) fuel cell stacks and systems. Hydrogen/air and direct methanol fuel cells are both addressed and compared. Operating conditions for simultaneous water and thermal balance can be specified based on the cell’s electrochemical performance and the operating environment. These conditions can be used to specify the overall size and complexity of the cooling equipment. The water balance properties can have strong effects on the size of the thermal management equipment required.