A detailed study of AueNi bimetal synthesized by the phase separation mechanism for the cathode of low-temperature solid oxide fuel cells Tao Yang * , Carlos Manuel Rodrigues de Almeida, Devaraj Ramasamy, Francisco Jos  e Almeida Loureiro TEMA-NRD, Mechanical Engineering Department, Aveiro Institute of Nanotechnology (AIN), University of Aveiro, 3810-193 Aveiro, Portugal highlights  Phase separation mechanism was utilized to save 25% of the noble metal Au.  A highly active property towards oxygen reduction reactions was achieved.  Size effect and surface energies differences were used to get nanosphere AuNi.  A delicate cut and elemental mapping confirmed the coreeshell structure of AuNi.  Morphological and compositional aspects of catalysts were thoroughly investigated. article info Article history: Received 2 June 2014 Received in revised form 25 June 2014 Accepted 27 June 2014 Available online 7 July 2014 Keywords: AueNi Phase separation Nanosphere XPS Cathode and SOFCs abstract A facile co-reduction and annealing synthesis route of nanospheric particles of AueNi bimetal with adjustable composition was developed. In a typical synthesis, a direct co-reduction of HAuCl 4 .4H 2 O and NiCl 2 in aqueous solution was performed with the assistance of reductive NaBH 4 and an anionic sur- factant sodium dodecyl sulfate (SDS) functioned as the structure-directing agent. Ultrasonic mixing was used at the same time to control the size of the particles. The morphology, microstructure and the state of the surface atoms were analyzed in detail. These nanospheres showed enhanced electrocatalytic ac- tivity towards oxygen reduction reaction than that of pure Au nanoparticles, demonstrated in the low temperature SOFC as cathode. The maximum power density generated is 810 mW cm 2 at 550  C. This is a promising route of taking advantages the Phase Separation Mechanism to greatly reduce the use of noble metals in the ORR field without sacrificing the electrocatalytic activity. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Solid oxide fuel cells (SOFCs) are one of the favorite power sources amongst various fuel cells due to the diversity of useable fuels such as H 2 , formic acid, methanol, ethanol, propyl alcohol, glucose and various hydrocarbons. However, the cost of rare metals or ceramic support, catalyst and the maintenance in high temper- ature have seriously handicapped their commercialized develop- ment. For decades, great efforts have been devoted to lowering the temperature of SOFCs to 550e800  C, [1e5] where the choice of materials can be expanded and the reliability of cell components will also be improved. In order to reduce the operational temper- ature without hampering/decreasing the power density, efficient catalysts must be used. Noble metals such as Au, Pd and Pt are the ideal option when only the catalytic activity is taken into account, but the cost is high. There are two ways to deal with this issue. The first one is to partially replace the noble metal in the cata- lysts, such as intermetallic compounds, metallic sulfides, metallic oxides, metallic carbides and organometallic compounds; [6e10] The effect of non-noble metal Co, Ni, Biunderlayers/surface impu- rities on the properties of noble metal overlayers has been suc- cessfully utilized towards oxygen reduction for a number of bimetallic systems in the authors former research [11e 13]. As is known, nickel represents a unique electrode metal (anodic and cathodic material) of extremely importance for experimental studies and practical industrial applications. * Corresponding author. Tel.: þ351 916969863; fax: þ351 234 370 953. E-mail addresses: yangtao@ua.pt, 21825550@qq.com (T. Yang). Contents lists available at ScienceDirect Journal of Power Sources journal homepage: www.elsevier.com/locate/jpowsour http://dx.doi.org/10.1016/j.jpowsour.2014.06.151 0378-7753/© 2014 Elsevier B.V. All rights reserved. Journal of Power Sources 269 (2014) 46e53