Flooded Electrode

The air humidity influences the performance parameters of the air-zinc batteries. At high air humidity the electrode flooding is possible. On the other hand, at low air humidity a concentration of the electrolyte increases, the air electrodes get too dry. 

In a SOFC, there is no liquid electrolyte present that is susceptible to movement in the porous electrode structure, and electrode flooding is not a problem. Consequently, the three-phase interface that is necessary for efficient electrochemical reaction involves two solid phases (solid electrolyte/electrode) and a gas phase. A critical requirement of porous electrodes for SOFC is that they are sufficiently thin and porous to provide an extensive electrode/electrolyte interfacial region for electrochemical reaction. 

G. Y. Lin and T. V. Nguyen. Effect of thickness and hydrophobic polymer content of the gas diffusion layer on electrode flooding level in a PEMFC. Journal of the Electrochemical Society 152 (2005) A1942-A1948. 

W. He, G. Lin, and T. V. Nguyen. Diagnostic tool to detect electrode flooding in proton-exchange-membrane fuel cells. AIChE Journal 49 (2003) 3221-3228. 

Figure 8 also nicely describes two possible scenarios for electrode flooding. Defining the onset of electrode flooding by the dimensionless water concentration reaching unity (i.e., gas becomes saturated), Figure 8 shows that both anode and cathode will be flooded by liquid water condensed from the gas for thin membranes, while for thick membranes only the cathode is susceptible to flooding. 

We see that the main experimentally observed trends are reproduced within the percolation approach. At jo > 0.2 A cm-2 the optimal electrolyte content is 1.0 mg cm-2. At small current densities, electrodes with reduced electrolyte content can give slightly better performance. For the smallest electrolyte content of 0.1 mg cm-2, insufficient proton conductivity leads to electrode failure at jo 0.2 A cm-2. The deviation between experimental data and calculated curves at jo >0.6 A cm-2 is probably due to deficient water management in the experimentally studied cell, which leads to electrode flooding, a phenomenon that is not considered in the current model. 

Surface Electrode Diurnal Tide Surface Electrode Drained Nontidal Surface Electrode Flooded Nontidal... 

Avoidance of electrode flooding requires that water is transported from the electrodes out of the ceU. A critical component is the GDL, which is a multifunctional component. Its microstructure assures a fine distribution of the reactants over the electrodes. It is a spatially finely distributed current collector. Further, it... 

If more water is exhausted than produced, then humidification of the incoming anode gas becomes important (31). If there is too much humidification, however, the electrode floods, which causes problems with gas diffusion to the electrode. A temperature rise between the inlet and outlet of the flow field increases evaporation to maintain water content in the cell. There also have been attempts to control the water in the cell using external wicking connected to the membrane to either drain or supply water by capillary action. 

Using an anion exchange membrane instead of a liquid caustic alkali electrolyte in an alkaline fuel cell allows avoids problems of leakage, carbonation, precipitation of carbonate salts, and gas electrode flooding, increasing the volumetric energy density. It appears that the anion exchange membrane fuel cells (AEMFCs) have the potential to succeed in portable applieations [92,93]. 

Membrane. Perfluorosulfonic acid (PFSA) is the most commonly used membrane material [4], PFSA membranes are relatively strong and stable in both oxidative and reductive environments, since the structure of PFSA is based on a PTFE backbone. The conductivity of a well-humidified PFSA membrane can be as high as 0.2s cm. As is well known, fuel cell operation at elevated temperatures can increase the rates of reaction, reduce problems related to catalyst poisoning, reduce the use of expensive catalysts, and minimize problems due to electrode flooding. Unfortunately, a PFSA membrane must be kept hydrated to retain its proton conductivity. Moreover, a PFSA membrane is alcohol permeable if it is used in DAFCs. Because of the disadvantages of PFSA membranes, many alternatives have been proposed [106]. Five categories of membranes are classified (1) perfluorinated, (2) partially fluorinated, (3) non-fluorinated, (4) non-fluorinated composite, and (5) others. 

Oxygen starvation caused by air stoichiometry or electrode flooding can lead to cell reversal. When there is insufficient oxygen at the cathode to combine with the protons coming across the membrane, the oxygen reduction reaction (ORR)... 

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