Sealless tubular cell

Sealless tubular cells fabricated by the electrochemical vapor deposition (EVD) technique. The durability is excellent, whereas the fabrication cost is expected to be quite high. This cell can be regarded as the standard cell when the relation among durability, efficiency, and cost is considered. 

This entry is organized as follows In section Historical Aspects of Reliability, Durability and Cost Issues, historical aspects are first described to provide essential points of SOFC stack/system development. The technological features of the first-generation cells, namely, sealless tubular cells, will be described in comparison with the second- and the third-generation cells in critical technological issues these are materials selection of interconnect (oxide or metal), sealing scheme, redox issues of nickel cermets, metal support cells, trade-off relation between reliability and performance, and materials chemistry associated with lowering operation temperature. 

Fig. 18.1 Sealless tubular cell (a) cell configuration and (b) stack configuration (From [13, 14])...

Immediately after the success of sealless tubular cells, one important analysis was made to clarify the technological features by Argonne National Laboratory [15]. Their main conclusions are given as follows ... 

Status of the sealless tubular cells concerning cost, efficiency, and durability can be summarized as shown in Fig. 18.3a. 

After knowing the success of Westinghouse and technological assessments by ANL, many people started to develop various kinds of SOFC stacks to overcome demerits of the sealless tubular cells. Depending on their technological strategies, several different attempts have been made. These can be summarized as follows ... 

Improvement of sealless tubular cells. To improve the volume power density, flatten tube type or delta type designs have been investigated by Siemens... 

Fig. 18.8 Impurities in anodes for four SOFC stacks with different materials and designs. Impurities were determined with SIMS on the 24 h operation and on the longer (about 5,000 h) operations, (a) High-temperature segment-in-series cell by MHI, (b) intermediate flatten tubular cell by Kyocera, (c) high temperature sealless tubular cells by TOTO, and (d) intermediate temperature disk-type planar cells by Mitsubishi Materials corp...

As described in the introduction, SOFC stack development started with the breakthrough by Westinghouse the sealless tubular cells can be categorized as stable but expensive stacks. Since then, many efforts have been focused on reducing the fabrication cost in the first-generation cells. 

Immediately after the first breakthrough with sealless tubular cells, detailed analyses were made by Ackerman at the Argonne National Laboratory (ANL) to identify the merits and demerits of the sealless tubular cells [3]. The main disadvantages were pointed out as follows ... 

A configuration for electrically connecting tubular cells to form a stack is described in Section 8.1.2 under sealless tubular configuration (Figure 8-6). The cells are connected in a series-parallel array by nickel felt strips that are exposed to the reducing fuel gas. In this arrangement, the nickel felt strips and cell interconnections extend the length of the cell. 

Sealless Tubular Configuration The most developed solid oxide fuel cell is the Siemens Westinghouse tubular cell. This approach results in eliminating seal problems between adjacent cells. A schematic representation of the cross section of the present Siemens Westinghouse... 

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