Phosphoric acid fuel cells disadvantages

Several types of fuel cells have been developed and are classified according to the electrolytes used alkaline fuel cells, molten carbonate fuel cells, phosphoric acid fuel cells (PAFCs), PEMFCs, and solid oxide fuel cells (SOFCs). As shown in Figure 1.3, the optimum operation temperatures of these fuel cells are different, and each type has different advantages and disadvantages. 

Many different types of fuel-cell membranes are currently in use in, e.g., solid-oxide fuel cells (SOFCs), molten-carbonate fuel cells (MCFCs), alkaline fuel eells (AFCs), phosphoric-acid fuel cells (PAFCs), and polymer-electrolyte membrane fuel cells (PEMFCs). One of the most widely used polymers in PEMFCs is Nalion, which is basically a fluorinated teflon-like hydrophobic polymer backbone with sulfonated hydrophilic side chains." Nafion and related sulfonic-add based polymers have the disadvantage that the polymer-conductivity is based on the presence of water and, thus, the operating temperature is limited to a temperature range of 80-100 °C. This constraint makes the water (and temperature) management of the fuel cell critical for its performance. Many computational studies and reviews have recently been pubhshed," and new types of polymers are proposed at any time, e.g. sulfonated aromatic polyarylenes," to meet these drawbacks. 

Polybenzimidazole (PBI) (initially manufactured by Hoechst-Celanese, now PE ME A) is one of the few polymers under consideration for high-temperature operation. The application of PBI [206, 207] and the noncommercial AB-PBI [208] in fuel cells was introduced by Savinell and coworkers. For that, the membrane was immersed in concentrated phosphoric acid to reach the needed proton conductivity. Operation up to 200 °C is reported [209]. A disadvantage of this class of membranes is the acid leaching out during operation, particularly problematic for cells directly fed with liquid fuels. Additionally, the phosphoric acid may adsorb on the platinum surface. A review on membranes for fuel cells operating above 100 °C has been recently published [209]. 

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