Alternative anode materials

There are a number of informative reviews on anodes for SOFCs [1-5], providing details on processing, fabrication, characterization, and electrochemical behavior of anode materials, especially the nickel-yttria stabilized zirconia (Ni-YSZ) cermet anodes. There are also several reviews dedicated to specific topics such as oxide anode materials [6], carbon-tolerant anode materials [7-9], sulfur-tolerant anode materials [10], and the redox cycling behavior of Ni-YSZ cermet anodes [11], In this chapter, we do not attempt to offer a comprehensive survey of the literature on SOFC anode research instead, we focus primarily on some critical issues in the preparation and testing of SOFC anodes, including the processing-property relationships that are well accepted in the SOFC community as well as some apparently contradictory observations reported in the literature. We will also briefly review some recent advancement in the development of alternative anode materials for improved tolerance to sulfur poisoning and carbon deposition. 

In recent years, there have been numerous studies on alternate anode materials. The areas of interest include carbon-tolerant anode materials, sulfur-tolerant anode materials, and redox-stable anode materials. The idea is that by developing alternative anode materials and structure, the reforming and the desulfurization unit could be eliminated, which would reduce the system complexity and cost dramatically. In this section, the studies into these new, alternative anode materials will be briefly touched upon. Because the number of candidate materials studied is quite large, the amount of study on any individual candidate anode material is rather small, and not much work has been done to reproduce the results reported. Therefore, it is not possible to fully evaluate the real potentials of those new materials proposed by different groups of researchers. Therefore, the focus would be on the fundamental issues for these alternative materials, instead of on the processing and properties of a specific candidate material. 

The development of new, alternative anode materials has recently attracted considerable interest. Several new materials show improved tolerance to sulfur poisoning and carbon deposition. However, critical issues associated with each candidate material are yet to be overcome. The traditional Ni-YSZ cermet anode still offers the best performance when clean hydrogen is used as the fuel and will continue to play an important role in SOFCs. 

One of the main objective of SOFCs in the future is the use of gaseous mixtures of C0-H2-H20 produced by coal gasification plants or by steam reforming a hydrocarbon fuel, especially methane. Very little data is available about the direct oxidation of methane in SOFCs [96, 97], Steele et al. [97] have recently confirmed the poor electrocatalytic activity of Pt electrodes for the anodic oxidation of methane at 800 °C. Although nickel fulfills major requirements for anode materials when H2 and CO are employed as fuels, its use for the direct oxidation of methane encourages carbon deposition. To overcome this problem, alternative anode materials must be... 

Goodenough, J.B., Huang, Y.H. Alternative anode materials for solid oxide fuel cells. J. Power Sources 2007,173,1-10. 

Due to its high theoretical capacity and safe working potential, SnO was believed as an alternative anode material for high-energy-density Li-ion... 

Another interesting application of the lithium-ion battery concept has been applied to the Sn02/LiNio gCog 2O2 electrodic couple [92]. Convertible oxides, and tin oxide in particular, first proposed as alternative anode materials by the Japanese Fuji Photo Film Company [93, 94], are presently the object of considerable attention in the lithium-ion battery community [95-98]. When negatively polarised in a lithium cell, tin oxide first undergoes an irreversible reaction shown in Equation 7.10. 

Because of the highly aggressive conditions in the high-temperature, molten salt media, attempts to find alternative anode materials or cell chemistries have been unsuccessful and developments in anode technology have been limited to minimizing the carbon consumption toward the stoichiometric requirement. Indeed, carbons are one of the few materials to be stable to cryolite at the operating temperature and hence, for example, it is also employed as an internal lining to the steel cell bodies. 

Alternative Anode Materials-Oxide Anode and Hydrocarbon Fuels Future Directions... 

Goodenough JB (2003) Oxide-ion electrolytes. Annu Rev Mater Res 33 91-128 Goodenough JB, Huang Y (2007) Alternative anode materials fin solid oxide fuel cells. J Power Sources 173 1... 

General While Ni/YSZ cermet is the most preferred anode material for SOFCs operating with hydrogen-containing fuels, there are several efforts to find alternative materials for the SOFC anode. Many studies on oxide anodes have been made for perovskite-related oxides. LaCr03 [230-237], LaFeOs [238], LaTiOs [239], and SrTiOs [240-243] systems are considered as possible alternative anode materials. 

Vemoux P, Guillodo M, Fouhtier J, Hammou A (2000) Alternative anode material for gradual methane reforming in solid oxide fuel cells. Solid Slate Ionics 135 425-431... 

In recent reviews by Goodenough and Huang (2007) and Sun and Stimming (2007), advances in alternative anode materials for SOFCs are described. 

Like Ni-YSZ, when the YSZ matrix is replaced with doped-Ce02, the cermet of Ni-Ce02 is formed which is also used as a SOFC anode. Attempts have also been made to develop alternate anode materials such as Ni-Al203, and Ni-Ti02 in order to eliminate the thermal (TEC) expansion mismatching between YSZ electrolyte and traditional Ni-YSZ anode (Stover et al. 1999). The TEC of YSZ and Ni/YSZ... 

Pfanzelt M, Kubiak P, Fleischhammer M, Wohlfahrt-Mehrens M (2011) Ti02 rutile - an alternative anode material for safe lithium-ion batteries. J Power Sourc 196 6815-6821... 

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