Perovskite Anode Materials

Perovskites have also been widely investigated as potential SOFC anode materials. Among these materials, chromites and titanates are promising [21, 22], Interesting results have been obtained with lanthanum strontium titanates [23] and especially cerium-doped lanthanum strontium titanate [24] however, it is now thought that the cerium-doped anodes are in fact two phases consisting of a ceria-perovskite assemblage [24], 

To make the B-site coordination more flexible and hence to improve electro-catalytic performance, Mn and Ga were introduced to replace Ti in La4Srg Tii2038 z-based fuel electrodes. Mn supports p-type conduction in oxidizing conditions and has been previously shown to promote electroreduction under 

SOFC conditions [33]. Furthermore, Mn is known to accept lower coordination numbers in perovskites [34], especially for Mn , and thus it may facilitate oxide ion migration. Similarly, Ga is well known to adopt lower coordination than octahedral in perovskite-related oxides. The possibility of mixed ionic/ 

Another important double perovskite is Sr2MgMo06 5, which has recently been shown to offer good performance, with power densities of 0.84 W/cm in H2 and 0.44 W/cm in CH4 at 800°C, and good sulfur tolerance [58]. The molybdenum-containing double perovskite was initially prepared at 1200°C in flowing 5% H2 and then deposited on top of a lanthanum ceria buffer layer before testing [59]. 

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Huang Y, Liang G, Croft M, Lehtimaki M, Karppinen M, Goodenough JB (2009) Double-perovskite anode materials Sr2MMoOs (M = co, ni) for solid oxide fuel cells. Chem Mater 21 2319-2326... 

Good results are obtained with oxide-coated valve metals as anode materials. These electrically conducting ceramic coatings of p-conducting spinel-ferrite (e.g., cobalt, nickel and lithium ferrites) have very low consumption rates. Lithium ferrite has proved particularly effective because it possesses excellent adhesion on titanium and niobium [26]. In addition, doping the perovskite structure with monovalent lithium ions provides good electrical conductivity for anodic reactions. Anodes produced in this way are distributed under the trade name Lida [27]. The consumption rate in seawater is given as 10 g A ar and in fresh water is... 

Huang Y-H, Dass RI, Xing Z-L, and Goodenough JB. Double perovskites as anode materials for solid oxide fuel cells. Science 2006 312 254—256. 

Similarly to the case of direct-oxidation anode materials, sulfur-tolerant anode materials based on sulfides [6, 7] or double-perovskite oxides have special requirements for their processing into SOFC layers. For example, nickel sulfide-promoted molybdenum sulfide is tolerant to high sulfur levels [7], However, it has a low melting temperature [6] that has resulted in the development of cobalt sulfide as a stabilizer of the molybdenum sulfide catalyst [6], CoS-MoS2 admixed with Ag has an even higher performance in H2S-containing fuels than in pure H2 [6]. However, processing methods such as PS, infiltration, or sol-gel techniques that can process... 

As with doped ceria, low electronic conductivity is an issue with perovskite anodes as well. Some perovskites show very high electronic conductivities under oxidizing environments, but most of these materials are much less conductive under the reducing environments to which they will be exposed at the anode. For example, the conductivity of Lao.75-Sro.25Cro.5Mno.5O3, a promising material developed by Tao and Irvine, decreases by almost 2 orders of... 

The previous discussion has focused on the properties of perovskite materials rather than on their performance as anodes. The number of actual fuel-cell studies is more limited, but this literature has been reviewed recently by Irvine. Various perovskites have been investigated as potential SOFC anode materials however, these early efforts were hampered by low electrochemical activity toward methane oxidation,poor anode structure,or insufficient electrode conductivity. Most recently, Tao and Irvine demonstrated that an anode based on (Lao.75Sro.25)o.9Cro.5Mno.503 can provide reasonable power densities at 1173 K in 3% humidified CH4. Barnett and co-workers also reported stable power generation with methane and propane fuels on an anode based on LaCr03 however, they reported that the addition of Ni, in levels too small to affect the conductivity, was crucial in providing activity for the electrochemical oxidation reactions. 

CRIEPI research group points out that there are some possibilities Ti-based pyrochlores (chemical formula A2B2O7) and perovskites (chemical formula ABO,) are candidates as the anode materials because of their high corrosion resistance in the 50 weight% H2SO4 solution at 353K. Also, improvement techniques of electronic conductivity for the pyrochlores and perovskites have been developed. 

We reported the preparation and crystallographic characteristics of various perovskites as candidates of the anode materials in sulfur-based hybrid cycle for hydrogen production and proposed some techniques of electrical conductivity appearance for the perovskites. 

Finally, it should be noted that numerous perovskite-related materials with relatively low oxygen ionic conductivity at 700-1200 K have been excluded from consideration in this brief survey, but may have potential electrochemical applications in fuel cell anodes, current collectors, sensors, and catalytic reactors. Further information on these applications is available elsewhere 1-4, 11, 159, 217-219]. 

B. A. Boukamp. The amazing perovskite anode. Nature materials 2, (2003) 294-296. 

The perovskite oxides of the general compositions ABO3 and A2BO4 with excellent electrical conductivities and electrocatalysis were considered as possible materials for the apphcation as anode materials in direct methanol fuel cells (DMFCs). White and... 

Singh RN, Sharma T, Singh A, Anindita, Mishra D, Tiwari SK (2008) Perovskite-t5fpe La2 cSr cNi04 (0 <= x <= 1) as active anode materials for methanol oxidation in alkaline solutions. Electrochim Acta 53(5) 2322-2330... 

Tao SW, Irvine JTS (2004) Catalytic properties of the perovskite oxide Lao.75Sro.25Cro.5Feo.503 in relation to its potential as a solid oxide fuel cell anode material. Chem Mater 16 4116-4121... 

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. 

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