Phosphoric add fuel cell

In applications for static purpose, phosphoric add fuel cells have been constructed on a large scale for mainly test purposes. They have shown commerdal level performance and stability. More advanced types of fuel cells like molten carbonate fuel cells and solid oxide fuel cells are also under development for this purpose but are %t to reach that level. 

Fig. 1 Operation principle of the various types of fuel cells PEMFC polymer electrolyte membrane fuel cell, AFC alkatine fuel cell, PAFC phosphoric add fuel cell, MCFC molten carbonate fuel cell, SOFC sohd oxide fuel cell...

The efficiencies of the different energy conversion systems are compared in Fig. 3 as a function of the size of power plants. Figure 3 shows that the efficiencies of two types of fuel cell systems (phosphoric add fuel cell, PAFC, see Sect. 8.1.3.1.3 and solid oxide fuel cell, SOFC, see Sect. 8.1.3.2.2) are higher than those of engines and conventional power plants of comparable size. 

Classical phosphoric add fuel cells use phosphoric add as the electrolyte, which is immobilized in a Teflon bonded silicon carbide matrix. Phosphoric acid fuel cells usually work at temperatures around 200 °C and are able to tolerate carbon monoxide levels of up to 2 vol.% [1]. Platinum/ruthenium as the anode catalyst may improve the performance in presence of carbon monoxide, similar to PEM fuel cells [33]. 

Two main advantages of the phosphoric add fuel cell include a cogeneration efficiency of nearly 85 % and its ability to use impure hydrogen as fuel. PAFCs can tolerate a carbon monoxide concentration of about 1.5 % which increases the number of fuel types that can be used. Disadvantages of PAFCs include their use of platinum as a catalyst (like most other fuel cells) and their large size and weight. PAFCs also generate low current and power comparable to other types of fuel cells [13]. 

Stonehart, P. (1984) Caibon substrates for phosphoric add fuel cell cathodes. Carbon, 22, 423. 

Japanese Industrial Standard (2003) Accelerated Life Test Methods for Phosphoric Add Fuel Cell. Japanese Industrial Standard JIS C 8802 2003. 

Stonehart, P. (1992) Development of alloy electrocatalysts for phosphoric add fuel cells (PAFC). Journal of Applied Electrochemistry 22, 995-1001. 

Because of this extreme sensitivity, attention shifted to an acidic system, the phosphoric acid fuel cell (PAFC), for other applications. Although it is tolerant to CO, the need for liquid water to be present to facilitate proton migration adds complexity to the system. It is now a relatively mature technology, having been developed extensively for stationary power usage, and 200 kW units (designed for co-generation) are currently for sale and have demonstrated 40,000 hours of operation. An 11 MW model has also been tested. 

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. 

Phosphoric acid fuel cell (PAFC) Phosphoric add 200-220 35-45% limited efficiency, corrosion problems Stand-alone CHP generation... 

Usually, the starting point of model derivation is either a physical description along the channel or across the membrane electrode assembly (MEA). For HT-PEFCs, the interaction of product water and electrolyte deserves special attention. Water is produced on the cathode side of the fuel cell and will either be released to the gas phase or become adsorbed in the electrolyte. As can be derived from electrochemical impedance spectroscopy (EIS) measurements [14], water production and removal are not equally fast Water uptake of the membrane is very fast because the water production takes place inside the electrolyte, whereas the transport of water vapor to the gas channels is difiusion limited. It takes several minutes before a stationary state is reached for a single cell. The electrolyte, which consists of phosphoric add, water, and the membrane polymer, changes composition as a function of temperature and water content [15-18]. As a consequence, the proton conductivity changes as a function of current density [14, 19, 20). 

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