**1.2.2 Solid oxide fuel cell (SOFC)**

The solid oxide fuel cell (SOFC) is the cell that operates at the highest temperatures (800- 1000 °C). It uses a solid electrolyte, which consists of a dense ceramic material with high ionic conductivity. In this cell, oxygen ion is transported through the electrolyte and, in the interface with the anode, it combines with hydrogen to create water and energy. The main advantages of the SOFC are that it produces electricity with high efficiency of 50-60% and does not require an external reformer to extract hydrogen from fuel due to its ability to internal reform. The waste heat can be recycled to produce additional electricity in the operation of cogeneration. The high temperature, which provides satisfactory characteristics

Fuel Cell: A Review and a New Approach

**1.4 Components of SOFC** 

ions from the electrolyte.

interface and the removal of byproducts.

**1.4.1 Anode** 

subjected.

of the anode are:

About YSZ Solid Oxide Electrolyte Deposition Direct on LSM Porous Substrate by Spray Pyrolysis 143

development of third generation SOFC (3G-SOFC) interconnect support type, allowing a reduction in the ceramic components thickness, accompanied by a reduction in operating temperature of the cell (800 °C) and the use of metallic interconnects. In this design, the electrolyte thickness has less than 20 µm and both, anode and cathode thickness, has about

50 µm (Wang, 2004). Figure 1 shows a schematic configuration of planar SOFCs.

Fig. 1. Representation of the configuration for the three-generations of planar SOFCs.

The anode of a fuel cell is the interface between the fuel and electrolyte. The main functions

Provide sites for electrochemical reactions of combustible gas catalytic oxidation with

Allow the diffusion of fuel gas for the reactive sites of the electrode/electrolyte

The anode material must possess, under the operating conditions of the fuel cell: good physical and chemical stability, chemical and structural compatibility with the electrolyte and interconnect, high ionic and electronic conductivity and catalytic activity for fuel oxidation (Ralph et al., 2001). The thermal stability is an important aspect to maintain the structural integrity throughout the temperature variations at which this component is

In general, the performance of the anode is defined by its electrical and electrochemical properties and therefore has a strong dependence on its microstructure. Thus, the control parameters, such as composition, size and distribution of particles and pores, are very important for optimizing the performance of the anode material of a solid oxide fuel cell.

Ceramic-metal composites, typically Ni-based, have been commonly used. Among them, the NiO-YSZ composite is the material of conventional fuel cells. Ni is also used because it has good electrical, mechanical and catalytic properties (Ralph et al., 2001). More recently, mixed conductors based on ceria (NiO-GDC) and transition metal perovskites (such as Fe, Mn, Cr and Ti) are being studied as potential candidates for anode materials for solid oxide fuel cells. However, to date, these materials do not present, in reducing atmospheres, values of electronic conductivity high enough for high performance fuel cell (Gong et al., 2010). The oxides of transition metals can have different oxidation states that can induce electron

Transport of generated electrons to the interconnect (external circuit).

in the cell as already mentioned, is also responsible for its major disadvantages, such as the problems of material selection, high heat detritions and the impossibility of using metallic materials, which cost much less than the ceramic materials currently used (Aruna & Rajam, 2008; Farooque & Maru, 2001; Srivastava et al., 1997 ).
