SOFC cathodes Solid oxide fuel cells

Solid oxide fuel cell, SOFC anodes, 97 catalysis in, 98,410 cathodes, 96... 

This presentation reports some studies on the materials and catalysis for solid oxide fuel cell (SOFC) in the author s laboratory and tries to offer some thoughts on related problems. The basic materials of SOFC are cathode, electrolyte, and anode materials, which are composed to form the membrane-electrode assembly, which then forms the unit cell for test. The cathode material is most important in the sense that most polarization is within the cathode layer. The electrolyte membrane should be as thin as possible and also posses as high an oxygen-ion conductivity as possible. The anode material should be able to deal with the carbon deposition problem especially when methane is used as the fuel. 

In solid oxide fuel cells (SOFCs), the cathode is the material where pure oxygen or oxygen from air is reduced through the following electrochemical reaction [1]... 

A solid oxide fuel cell (SOFC) consists of two electrodes anode and cathode, with a ceramic electrolyte between that transfers oxygen ions. A SOFC typically operates at a temperature between 700 and 1000 °C. at which temperature the ceramic electrolyte begins to exhibit sufficient ionic conductivity. This high operating temperature also accelerates electrochemical reactions therefore, a SOFC does not require precious metal catalysts to promote the reactions. More abundant materials such as nickel have sufficient catalytic activity to be used as SOFC electrodes. In addition, the SOFC is more fuel-flexible than other types of fuel cells, and reforming of hydrocarbon fuels can be performed inside the cell. This allows use of conventional hydrocarbon fuels in a SOFC without an external reformer. 

Figure 1. Schematic showing the roles of anode, cathode, and electrolyte in a solid oxide fuel cell (SOFC).

SOFC can be manufactured in different geometrical configurations, i.e. planar, tubular or monolithic. Regardless of the geometrical configuration, a solid oxide fuel cell is always composed of two porous electrodes (anode and cathode), a dense electrolyte, an anodic and a cathodic gas channel and two current collectors. For the sake of simplicity the planar configuration is taken as reference, as shown in Figure 3.1. 

Adler S.B., Wilson J.R., Schwartz D.T. (2003) Nonlinear harmonic response of mixed-conducting SOFC cathodes. In Solid Oxide Fuel Cells VIII (SOFC-VIII), Electrochemical Society Proceedings, 2003-07, S.C. Singhal and M. Dokiya (Eds.), The Electrochemical Society, Pennington, NJ, pp. 516-524. 

A single-chamber solid oxide fuel cell (SC-SOFC), which operates using a mixture of fuel and oxidant gases, provides several advantages over the conventional double-chamber SOFC, such as simplified cell structure with no sealing required and direct use of hydrocarbon fuel [1, 2], The oxygen activity at the electrodes of the SC-SOFC is not fixed and one electrode (anode) has a higher electrocatalytic activity for the oxidation of the fuel than the other (cathode). Oxidation reactions of a hydrocarbon fuel can... 

Illustration of one of the fuel cells in a stack of solid oxide fuel cells (SOFCs) where hydrogen fuel contacts an anode and the oxidizer acts on the cathode s surface. 

The working principles behind a solid oxide fuel cell (SOFC) are schematically illustrated in Figure 8.7, where, similar to the other fuel cell types, the three key parts of an SOFC, a cathode, an anode, and an electrolyte, are shown. The electrolyte is, in a majority of cases, an oxygen-anion ceramic conductor, which is, as well, an electronic insulator [5]. In the SOFC the fuel can be methane (CH4). Subsequently, in this case the oxidation reaction in the anode is given by... 

Solid oxide fuel cells (SOFC), which use oxygen conducting ceramic membranes to electo-combust H2, at the anode, by 02 -anions provided by the cathodic reduction of ambient oxygen at high temperatures. 

Electronically-conducting (Ln,A)(M,M>)03, 5 (M = Cr, Mn), used for cathodes and interconnects of - solid oxide fuel cells (SOFCs). 

L.-W. Tai, M.M. Nasrallah and H.U. Anderson, Lai-xSrxCoi-yFeyOs-a, A potential cathode for intermediate temperature SOFC applications, in S.C. Singhal and H. Iwahara (Eds.), Proceedings of the 3rd International Symposium on Solid Oxide Fuel Cells. The Electrochemical Society, Pennington, NJ, 1994, pp. 241-251. 

Solid oxide fuel cell (SOFC) uses solid ceramic material, such as Y2O3 stabilized Zr02 (YSZ), as an electrolyte. As SOFC operates at high temperature (600-1000° C), a variety of fuels, e.g., hydrogen, methane, and carbon monoxide, can directly be utilized. The high temperature places severe constraints on material selection and results in difficult fabrication process. Co-ZrO (or Ni-ZrO) and SrO doped LaMn03 have often been used for anode and cathode materials, respectively. 

Several recent breakthroughs in the design of solid oxide fuel cell (SOFC) anodes and cathodes are described in the Chapter of H. Uchida and M. Watanabe. The authors, who have pioneered several of these developments, provide a lucid presentation describing how careful fundamental investigations of interfacial electrocatalytic anode and cathode phenomena lead to novel electrode compositions and microstructures and to significant practical advances of SOFC anode and cathode stabihty and enhanced electrocatalysis. 

---