Polymer electrolyte fuel cells water balance

Dawn M. Bernard , "Water-Balance Calculations for Solid-Polymer-Electrolyte Fuel Cells," Journal of Electrochemical Society, Vol. 137, No. 11, November 1990. 

H. Nakajima, T. Konomi, and T. Kitahara. Direct water balance analysis on a polymer electrolyte fuel cell (PEFC) Effects of hydrophobic treatment and microporous layer addition to the gas diffusion layer of a PEFC on its performance during a simulated start-up operation. Journal of Power Sources 171 (2007) 457-463. 

This review has highlighted the important effects that should be modeled. These include two-phase flow of liquid water and gas in the fuel-cell sandwich, a robust membrane model that accounts for the different membrane transport modes, nonisothermal effects, especially in the directions perpendicular to the sandwich, and multidimensional effects such as changing gas composition along the channel, among others. For any model, a balance must be struck between the complexity required to describe the physical reality and the additional costs of such complexity. In other words, while more complex models more accurately describe the physics of the transport processes, they are more computationally costly and may have so many unknown parameters that their results are not as meaningful. Hopefully, this review has shown and broken down for the reader the vast complexities of transport within polymer-electrolyte fuel cells and the various ways they have been and can be modeled. 

Ahmed, S., Kopasz, J., Kumar, R., and Krumpelt, M. Water balance in a polymer electrolyte fuel cell system. Journal of Power Sources, 2002, 112, 519. 

Bemardi DM. Water-Balance Calculations for SoUd-Polymer-Electrolyte Fuel Cells. J Electrochem Soc 1990 137 3344-50. 

Chan, K. and Eikerling, M. 2014. Water balance model for polymer electrolyte fuel cells with ultrathin catalyst layers. 16, 2106-2117. 

Schneider, I. A., Kuhn, H., Wokaun, A., and Scherer, G. G. 2005. Study of water balance in a polymer electrolyte fuel cell by locally resolved impedance spectroscopy. 

Bernard , D.M. Water-balance calculations for sohd-polymer-electrolyte fuel cells. Journal of the Electrochemical Society, 137(11), 3344,1990. 

At present, polymer electrolyte membrane fuel cells and power plants based on such fuel cells are produced on commercial scale by a number of companies in many countries. As a rule, the standard battery version of the 1990s is used in these batteries, though in certain cases different ways of eliminating water and regulating the water balance (water management) have been adopted. 

The membrane has two functions. First, it acts as the electrolyte that provides ionic conduction between the anode and the cathode but is an electronic insulator. Second, it serves as a separator for the two-reactant gases. Some sources claim that solid polymer membranes (e.g., sulfonated fluorocarbon acid polymer) used in PEMFC are simpler, more reliable, and easier to maintain than other membrane types. Since the only liquid is water, corrosion is minimal. Pressure balances are not critical. However, proper water management is crucial for efficient fuel cell performance [6]. The fuel cell must operate under conditions in which the by-product water does not evaporate faster than it is produced, because the membrane must be hydrated. Dehydration of the membrane reduces proton conductivity. On the other hand, excess of water can lead to flooding of the electrodes. 

Water Flux in Polymer Electrolyte Membranes Water flux in the solid electrolyte membrane of the PEFC must be understood to grasp the concept of a local water balance in the fuel cell. From Chapter 5, we know that the ionic conductivity of perfluorosulfonic acid-based solid polymer electrolytes is a strong function of water content. Within the electrolyte, there are four basic modes of transport, as schematically illustrated in Figure 6.21 ... 

The performance of a polymer electrolyte membrane (PEM) fuel cell is significantly affected by liquid water generated at the cathode catalyst layer (CCL) potentially causing water flooding of cathode while the ionic conductivity of PEM is directly proportional to its water content. Therefore, it is essential to maintain a delicate water balance, which requires a good understanding of the liquid water transport in the PEM fuel cells. 

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