DOI: 10.1002/chem.201200536 Self-Recovery of Pd Nanoparticles That Were Dispersed over La(Sr)Fe(Mn)O 3 for Intelligent Oxide Anodes of Solid-Oxide Fuel Cells Tae Ho Shin, [a] Yohei Okamoto, [a] Shintaro Ida, [a, b] and Tatsumi Ishihara* [a, b] Introduction Solid-oxide fuel cells (SOFCs) have recently attracted con- siderable attention as one of the most-advanced technolo- gies for environmentally friendly power-generation because of their high energy-conversion efficiency and fuel-flexibili- ty; thus, SOFCs are currently approaching commercial use. [1–3] However, the use of SOFCs has been limited owing to of several challenging issues, such as low anode reliability, that is, poor tolerance to oxidation, and deactivation by coking. Cermets that include Ni have been widely used as the anode in the early stages of SOFC-development, mainly because Ni-based materials show good electrochemical con- ductivity and catalytic activity for the oxidation of hydro- gen; however, carbon-deposition and -oxidation readily occur on Ni, thereby resulting in deactivation of the cell. To avoid the challenges that are associated with Ni metal, many efforts have been made to develop the application of oxides as an alternative anode for SOFCs. For example, Tao etal. reported that reasonably high power densities could be ach- ieved in La 0.75 Sr 0.25 Cr 0.5 Mn 0.5 O 3 perovskite oxide, [4–6] whilst Gorte and co-workers reported ceria-based ceramic anodes with small amounts of metal additives, such as Cu or Pd, and SrTiO 3 -based oxides have also been reported as reliable SOFC anodes. [7–9] Previously, we found that relatively good power and excellent redox-tolerance can be achieved by using an oxide-composite anode that was composed of CeACHTUNGTRENNUNG(Mn, Fe)O 2 –La(Sr)Fe(Mn)O 3 . [10, 11] Despite these reports on the use of oxides as alternative anodes for SOFCs, the development of active oxide anodes remains a rather diffi- cult subject and further improvement in anodic performance is yet to be achieved because of their insufficient electrical conductivity and surface activity. Even so, oxide anodes can be expected to overcome some of the limitations of other anode materials that are used for SOFCs. In particular, perovskite-type oxides have attracted con- siderable recent attention and have been widely investigated as potential anode materials in SOFCs. The perovskite- oxide formula can be written as ABO 3 , where A represents a large cation (typically a rare-earth metal with a coordina- tion number of 12) and B represents a small element with a coordination number of 6, such as Co, Mn, Fe, or Cr. Perov- skites with transition elements that exhibit multivalence under different conditions at these B sites can be a source of high electronic- or mixed conduction. Therefore, good ionic- and mixed conductivity can be achieved for several perov- skite oxides. Moreover, the partial substitution of these A and B sites with many other metals, which can create de- fects, also promotes the catalytic performance of the perov- skites. Recently, the addition of cost-effective amounts of Abstract: Self-recovery is one of the most-desirable properties for functional materials. Recently, oxide anodes have attracted significant attention as alter- native anode materials for solid-oxide fuel cells (SOFCs) that can overcome reoxidation, deactivation, and coke- deposition. However, the electrical conductivity and surface activity of the most-widely used oxide anodes remain unsatisfactory. Herein, we report the synthesis of an “intelligent oxide anode” that exhibits self-recovery from power-density degradation in the redox cycle by using a Pd-doped La(Sr)Fe- (Mn)O 3 cell as an oxide anode for the SOFCs. We investigated the anodic performance and oxidation-tolerance of the cell by using Pd-doped perov- skite as an anode and fairly high maxi- mum power densities of 0.5 and 0.1 W cm 2 were achieved at 1073 and 873 K, respectively, despite using a 0.3 mm-thick electrolyte. Long-term stability was also examined and the power density was recovered upon ex- posure of the anode to air. This recov- ery of the power density can be ex- plained by the formation of Pd nano- particles, which were self-recovered through reoxidation and reduction. In addition, the self-recovery of the anode by oxidation was confirmed by XRD and SEM and this process was effective for improving the durability of SOFC systems when they were exposed to severe operating conditions. Keywords: fuel cells · lanthanum · oxides · palladium · redox chemis- try [a] Dr. T. H. Shin, Y. Okamoto, Dr. S. Ida, Prof. Dr. T. Ishihara Department of Applied Chemistry Faculty of Engineering Kyushu University Motooka 744, Nishiku, Fukuoka 819-0395 (Japan) Fax: (+ 81) 92-802-2871 E-mail: ishihara@cstf.kyushu-u.ac.jp [b] Dr. S. Ida, Prof. Dr. T. Ishihara International Institute for Carbon-Neutral Energy Research (I2CNER) Kyushu University Motooka 744, Nishiku, Fukuoka 819-0395 (Japan) Chem. Eur. J. 2012, 18, 11695 – 11702  2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 11695 FULL PAPER