Phosphoric acid fuel cell components

Aragane J, Murahashi T, Odaka T. 1988. Change of Pt distribution in the active components of phosphoric acid fuel cell. J Electrochem Soc 135 844-850. 

Table 5-1 Evolution of Cell Component Technology for Phosphoric Acid Fuel Cells... 

Phosphoric acid fuel cells rely on expensive components and, like pems, use platinum catalysts to accelerate the chemical reactions at the electrodes. Finally, they have not achieved the level of sales needed to significantly reduce manufacturing costs. For these reasons, UTC Fuel Cells is phasing out production of phosphoric acid fuel cells in favor of pem fuel cell technology, which is likely to be significantly less expensive. 

An electrolyte is an essential component within fuel cells, used to facilitate the selective migration of ions between the electrodes. Fuel cells are typically classified according to the electrolytes used alkaline fuel cell (AFC), polymer electrolyte (or proton exchange membrane) fuel cell (PEMFC), phosphoric acid fuel cell (PAFC),... 

The phosphoric acid fuel cell (PAFC) has a quite similar construction and components as the PEMFC the electrolyte is liquid phosphoric acid in an inert matrix. The operation temperature of 200°C avoids formation of liquid water and improves CO tolerance of the electrocatalyst. For the catalyst properties, the same requirements are valid as for the PEMFC - nanoparticles with a high surface area and a good dispersion on the carbon carrier material are required. The application of PAFC typically is the combined heat and power supply in the 200-kW power range. 

Non-repeat components. The components described in the previous section are usually referred to as repeat components since every cell has those components with multiple cells present in a cell stack. Non-repeat components are those that are used only once in a cell stack. The main non-repeat components in a cell stack assembly are pressure plates, coolant inlet and outlet manifolds, reactant inlet and outlet manifolds, and manifold seals. Multiple cells placed between coolers are stacked between two stainless steel pressure plates and loaded axially to arotmd 60 psi with the help of tie rods that run the entire length of the cell stack. Reactant manifolds are then assembled onto the cell stack with manifold seals placed between the cell stack and the manifold. These reactant manifolds are made of stainless steel and coated with PTFE coating to prevent phosphoric acid attack of the manifolds. It is very essential to ensure that there are no pin holes in the PTFE coating for the same reason mentioned above. In phosphoric acid fuel cells, manifold seals made... 

HT-PEM fuel cells operate with phosphoric acid doped polymer membrane as electrolyte. The acid is physically adsorbed to the membrane. The phosphoric acid distribution within the fuel cell components, such as membrane, catalyst layers, microporous layer, gas diffusion layers, and bipolar plates, is known to be a critical parameter for performance and life time of this type of fuel cells [10]. There are no defined specifications about phosphoric acid uptake of the bipolar plate because its impact on the fuel cell performance strongly depends on several parameters and always has to be considered in a context of the overall fuel cell design. 

Eberhardt SH, Marone F, Stampanoni M et al (2014) Quantifying phosphoric acid in high-temperature polymer electrolyte fuel cell components by X-ray tomographic microscopy. J Synchrotron Radiat 21 1319-1326... 

Traces of unreacted silica (Si02) in the SiC will produce a fluffy white precipitate, about which little is known. Certainly it is known that when hot concentrated phosphoric acid is in contact with glass hardware, the rapid formation of a fluffy gelatinous white precipitate is seen. From an X-ray diffraction analysis of the precipitate from operating fuel-cells, it was determined that the principal component was Si3(P04)4, although metallographic and SEM/EDS analyses support the presence of the other silico-phosphate complexes in varying amounts. 

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