Solid oxide fuel cell type membrane

For the pure oxygen ion conducting membrane, the electrons released from the chemical reactions have to be transported to the oxygen-rich side via an external circuit so as to precede the reaction and the oxygen permeation, as shown in Fig. 7.5c. In this case, electrical power is co-generated along with the production of valuable chemicals. Therefore, the membrane reactor operating in this mode is also called a solid oxide fuel cell type membrane reactor (SOFC-MR). 

There are six different types of fuel cells (Table 1.6) (1) alkaline fuel cell (AFC), (2) direct methanol fuel cell (DMFC), (3) molten carbonate fuel cell (MCFC), (4) phosphoric acid fuel cell (PAFC), (5) proton exchange membrane fuel cell (PEMFC), and (6) the solid oxide fuel cell (SOFC). They all differ in applications, operating temperatures, cost, and efficiency. 

We discuss both the Proton Exchange Membrane as well as the Solid Oxide Fuel Cells in this chapter (PEMFC and SOFC). Both types are in full development, the PEMFC for mobile and stationary applications, and the SOFC for stationary applications as well as for auxiliary power generation for transport. 

Oxides exhibiting only high ion conductivity are mainly fluorite-related structures based on zirconia or ceria. Zirconia-based electrolytes are currently used in solid oxide fuel cells (SOFCs). The MIEC oxides are more attractive for separative membrane applications, and these oxides mainly belong to the following types fluorite-related oxides doped to improve their electron conduction, - ... 

Current research is centred on making compact cells of high efficiency. They are described in terms of the electrolyte that is used. The principle types are alkali fuel cells, described above, with aqueous KOH as electrolyte, MCFCs (molten carbonate fuel cells), with a molten alkali metal or alkaline earth carbonate electrolyte, PAFCs (phosphoric acid fuel cells), PEMs (proton exchange membranes), using a solid polymer electrolyte that conducts ions, and SOFCs, (solid oxide fuel cells), with solid electrolytes that allow oxide ion, 0 , transport The... 

There exist a variety of fuel cells. For practical reasons, fuel cells are classified by the type of electrolyte employed. The following names and abbreviations are frequently used in publications alkaline fuel cells (AFC), molten carbonate fuel cells (MCFC), phosphoric acid fuel cells (PAFC), solid oxide fuel cells (SOFC), and proton exchange membrane fuel cells (PEMFC). Among different types of fuel cells under development today, the PEMFC, also called polymer electrolyte membrane fuel cells (PEFC), is considered as a potential future power source due to its unique characteristics [1-3]. The PEMFC consists of an anode where hydrogen oxidation takes place, a cathode where oxygen reduction occurs, and an electrolyte membrane that permits the transfer of protons from anode to cathode. PEMFC operates at low temperature that allows rapid start-up. Furthermore, with the absence of corrosive cell constituents, the use of the exotic materials required in other fuel cell types is not required [4]. 

Fuel cells are typically classified according to the types of the electrolytes they use. There are alkaline fuel cells (operating temperature -60-200 °C), phosphoric acid fuel cells ( 120-210 °C), molten carbonate fuel cells ( 650 °C), solid oxide fuel cells (-600-1000 °C), and proton-exchange membrane (PEM) fuel cells (RT-90 °C). A direct methanol fuel cell (DMFC) can be considered as a special type of the PEM fuel cell that uses methanol (in either vapor or liquid form) rather than hydrogen as the fuel. This review article focuses exclusively on PEM fuel cells. 

Fuel cells do not use a solid material to store their charge. Instead, low-temperature proton exchange membrane fuel cells use gases such as hydrogen and liquid ethanol (the same form of alcohol found in vodka) or methanol as fuels. These materials are pumped over the surface of the fuel cells, and in the presence of noble-metal catalysts, the protons in these fuels are broken away from the fuel molecule and transported through the electrolyte membrane to form water and heat in the presence of air. The liberated electrons can, just as in the case of batteries, be used to drive an electric motor. Other types of fuel cells, such as molten carbonate fuel cells and solid oxide fuel cells, can use fuels such as carbon in the form of coal, soot, or old rubber tires and operate at 800 degrees Celsius with a very high efficiency. 

Lan and Tao [22] successfully applied a novel fuel cell type with an alkaline membrane to oxidize ammonia at room temperature. Compared to solid oxide fuel cells, the alkaline membrane fuel cell is less brittle and can be operated at low temperatures. As an advantage of alkaline membrane fuel cells over conventional alkaline fuel cells, no KOH-based electrolyte is needed. The researchers used two types of anodes first platinum and ruthenium deposited on carbon and sec-raid chromium-decorated nickel. The ammraiia sources were either ammraiia gas or a 35 wt% aqueous ammonia solution. 

There are various types of fuel cells that are under development. The most noticeable ones are polymer electrolyte membrane (PEM) fuel cells, phosphoric acid fuel cells (PAFC), molten carbonate fuel cells (MCFC), and solid oxide fuel cells (SOFC). PEM fuel cells are mainly being targeted toward transportation needs due to their ability to provide high power densities at reasonable operating temperatures ( 100°C). PAFCs and MCFCs are being developed primarily for stationary applications since their power densities are lower than PEM. SOFCs are currently being developed for both stationary applications and transportation applications but high-temperature material development is needed before they become commercially viable. 

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. 

---