Solid oxide fuel cell membrane reactors

Figure 5.5 Principles of dense ceramic membrane reactors (a) electrochemical pump membrane reactor (EP-MR) (b) solid oxide fuel cell membrane reactor (SOEC-MR) (c) mixed ionic-electronic conducting membrane reactor (MIEC-MR).

Stoukides M, (2000). Solid electrolyte membrane reactors current experience and future outlook. Catalysis Reviews Science Engineering, 42 1-70 Sun C, Stimming U, (2007). Recent anode advances in solid oxide fuel cells. Journal of Power Sources 171 247-260... 

Figure 8.7 Schematic diagrams showing two electrocatalytic membrane reactor configurations (a) eicctrochemicai oxygen pumping and (b) solid oxide fuel cell operation.

Decreasing operation temperature of solid oxide fuel cells (SOFCs) and electrocatalytic reactors down to 800-1100 K requires developments of novel materials for electrodes and catalytic layers, applied onto the surface of solid electrolyte or mixed conducting membranes, with a high performance at reduced temperatures. Highly-dispersed active oxide powders can be prepared and deposited using various techniques, such as spray pyrolysis, sol-gel method, co-precipitation, electron beam deposition etc. However, most of these methods are relatively expensive or based on the use of complex equipment. This makes it necessary to search for alternative synthesis and porous-layer processing routes, enabling to decrease the costs of electrochemical cells. Recently, one synthesis technique based on the use... 

Scandia-stabilized zirconia (ScSZ) possesses the highest oxygen-ion conductivity among all zirconia-based oxides, and therefore represents a promising solid electrolyte for applications in electrochemical devices such as solid oxide fuel cells (SO PCs) and catalytic membrane reactors (further details are available in Section 1.6.6.3). 

Fu, X.-Z., Luo, J.-L., Sanger, A.R., Xu, Z.-R. and Chuang, K.T. (2010) Fabrication of bi-layered proton conducting membrane for hydrocarbon solid oxide fuel cell reactors. Electrochimica Acta, 55,1145-1149. 

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). 

Another class of dense inorganic membranes that have been used in membrane reactor applications are solid oxide type membranes. These materials (solid oxide electrolytes) are also finding widespread application in the area of fuel cells and as electrochemical oxygen pumps and sensors. Due to their importance they have received significant attention and their catalytic and electrochemical applications have been widely reviewed [94-98]. Solid materials are known which conduct a variety of cationic/anionic species [14,98]. For the purposes of the application of such materials in catalytic membrane reactor applications, however, only and conducting materials are of direct relevance. 

As shown in Fig. 5 7(b) the solid polymer electrolyte cell comprises a membrane, fuel cell type, porous electrodes and three further components z carbon collector, a platinized titanium anode support and a cathode support made from carbon-fibre paper The collector is moulded in graphite with a fluorocarbon polymer binder A 25 pm thick platinized titanium foil is moulded to the anode side to prevent oxidation. The purpose of the collector is to bnsure even fluid distribution over the active electrode area, to act as the main structural component of the cell, to provide sealing of fluid ports and the reactor and to carry current from one cell to the next E>emineralized water is carried across the cell via a number of channels moulded into the collector These channels terminate in recessed manifold areas each of which is fed from six drilled ports. The anode support is a porous conducting sheet of platinized titanium having a thickness of approximately 250 pm. The purpose of the support is to distribute current and fluid uniformly over the active electrode area. It also prevents masking of those parts of the electrode area which would be covered by the... 

---