Each of the 5 types of fuel cells have their own specifications and methods of construction. To stay within the parameters of this discussion I will compare a single PEM and SOFC cell. They are similar in their square shape, this allows for optimum use of raw materials in manufacturing with little waste.
PEM cells are flimsy, similar to Saran Wrap in thickness and texture, with a touch of stiffness added by a thin layering of platinum. The manufacture of this type of cell requires food grade, clean room methods without any contamination. This involves massive amounts of capital to build and maintain facilities. The labour costs are quite high because there is limited amount of raw materials that can be bulk handled.It also requires the development and production of new industrial tooling for assembly.
SOFC cells are robust, similar to a Compact Disc in thickness and texture, with a touch of brittleness added by the ceramic structure. The manufacture of the ceramic solid oxide cell requires the same amount of quality control, logistic support, and teamwork. Capital investment to manufacture a ceramic cell is much lower because a simple retro-fit of an existing refractory, bulk purchasing, and handling raw materials by the ton instead of an ounce, lowers per unit costs. Also existing industrial tooling is available for assembly.
Another cost savings feature of a SOFC is that it is a self supporting structure and does not require expensive 'flow-field plates' in its construction. Rather the flow is through the 'porous ceramics' increasing the surface area available for the ions to exchange, this makes a SOFC half the size as a PEM with equal power efficiency. Until just recently the main problem has been the seals between the ceramic plates.
The construction and maintenance of a SOFC stack uses industry standard parts,tools,and specifications e.g.- automotive torque wrench sequence that can be easily understood globally. The PEM requires specialized tools and training, as well insurance,gas code, and a myriad of other regulatory approvals. These codes and regulations have been developed over the last century for the health and safety of our planet. The number one danger of Hydrogen use in a PEM is it has to be virtually pure making it impossible to add a 'stinky smell' like we do to natural gas, this by-passes a most important sensor the human brain.
Another important difference is a SOFC relies on Oxygen for ion exchange not Hydrogen like a PEM. The auto industry has done a lot of their engineering on a Oxygen based technology e.g. G.M. has numerous patents dating back to 1970's with Zirconia (imitation diamond) sensors. This enables a SOFC to inter-face with the automotive industry a lot quicker and for at least one tenth of a PEM cost.
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